Biochemistry of Amyloid b-Protein and Amyloid Deposits in...

Biochemistry of Amyloid b-Protein and AmyloidDeposits in Alzheimer Disease

Colin L. Masters1 and Dennis J. Selkoe2

1The Mental Health Research Institute, The University of Melbourne, Parkville 3010, Australia2Center for Neurologic Diseases, Harvard Medical School and Brigham and Women’s Hospital, Boston,Massachusetts 02115

Correspondence: [email protected]

Progressive cerebral deposition of the amyloid b-protein (Ab) in brain regions servingmemory and cognition is an invariant and defining feature of Alzheimer disease. A highlysimilar but less robust process accompanies brain aging in many nondemented humans,lower primates, and some other mammals. The discovery of Ab as the subunit ofthe amyloid fibrils in meningocerebral blood vessels and parenchymal plaques has ledto innumerable studies of its biochemistry and potential cytotoxic properties. Here wewill review the discovery of Ab, numerous aspects of its complex biochemistry, andcurrent attempts to understand how a range of Ab assemblies, including soluble oligomersand insoluble fibrils, may precipitate and promote neuronal and glial alterations thatunderlie the development of dementia. Although the role of Ab as a key molecularfactor in the etiology of Alzheimer disease remains controversial, clinical trials ofamyloid-lowering agents, reviewed elsewhere in this book, are poised to resolve the questionof its pathogenic primacy.

THE LASTING IMPACT OF THE DISCOVERYOF AMYLOID b-PROTEIN ON THEELUCIDATION OF ALZHEIMERDISEASE

With the benefit of hindsight, it is now clearthat the isolation and partial sequencing

of the meningovascular amyloid b-protein(Ab) by George Glenner and Caine Wong in1984 provided a turning point for modernresearch on the fundamental mechanism ofAlzheimer disease (AD). Ever since Alzheimerpeered through the microscope at the brain ofhis first patient and wrote prophetically “scat-tered through the entire cortex . . . one foundmiliary foci that were caused by the deposition

of a peculiar substance . . .,” neuropathologistshad sought the nature of the amyloid materialfound in the senile plaque. By the early 1980s,as compositional analyses of the neurofibrillarytangle were beginning (see Mandelkow andMandelkow 2011), a few investigators turnedtheir attention to the identity of the amyloidprotein in vascular and plaque deposits. Inthis chapter, we will review how our biochem-ical understanding of the amyloid depositsemerged and has advanced, and we will describemany features of the peptides that comprise thishallmark lesion of AD and certain moleculesassociated with them. The trafficking andproteolytic processing of amyloid precursorprotein (APP), including the generation of

Editors: Dennis J. Selkoe, Eckhard Mandelkow, and David M. Holtzman

Additional Perspectives on The Biology of Alzheimer Disease available at www.perspectivesinmedicine.org

Copyright # 2012 Cold Spring Harbor Laboratory Press; all rights reserved.

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Med doi: 10.1101/cshperspect.a0062621

ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org

on January 27, 2021 - Published by Cold Spring Harbor Laboratory Presshttp://perspectivesinmedicine.cshlp.org/Downloaded from

http://perspectivesinmedicine.cshlp.org/

Ab, and the proteolytic degradation of the pep-tide are covered in other chapters (see Haasset al. 2011; Saido and Leissring 2011, respec-tively) and will not be discussed here.

BIOCHEMISTRY OF Ab INMENINGOVASCULAR AMYLOID DEPOSITSAND AMYLOID PLAQUE CORES

Because George Glenner’s earlier research onthe circulating precursors of nonneuralamyloid deposits (e.g., AL amyloid) convincedhim that the amyloid in AD might well bederived from a serum precursor, he focusedhis attention on the amyloid in meningeal vesselwalls. By stripping the meninges from postmor-tem AD brains, Glenner and Wong enriched foramyloid-bearing microvessels and discardedthe cerebral tissue with its potentially “contam-inating” amyloid plaques and neurofibrillarytangles (Glenner and Wong 1984b). They usedthe chaotropic salt guanidine hydrochloride(at 6M) to solubilize and then chromatograph-ically enrich the amyloid subunit, which ran as a4.2 kDa band on SDS-PAGE. HPLC purificationof the protein and amino-terminal sequencingto residue 24 revealed a unique sequence (theirreport of a glutamine rather than glutamate atposition 11 was corrected in their subsequentsequencing of Down’s syndrome meningovas-cular Ab). In this initial report, Glenner andWong suggested that this novel peptide mightturn out to be derived from a serum precursorand that it could “provide a diagnostic test forAlzheimer’s disease and a means to understandits pathogenesis.” Whereas the first of thesethree predictions turned out not to be true,the second and third clearly did.

Shortly after this paper appeared, Glennerand Wong published a highly similar study(Glenner and Wong 1984a) which showedthat the meningovascular amyloid subunit inDown’s syndrome brains was the same “b-pro-tein,” as they had dubbed it. Glenner calledattention to this evidence of a key biochemicalrelationship between Down’s syndrome andAD, a concept he had touted as early as 1979in a prescient article in Medical Hypotheses(Glenner 1979). He stressed that Down’s

syndrome may be a “predictable model” forAD and further suggested that “the geneticdefect in Alzheimer’s disease is localized onchromosome 21.” Glenner reasoned that,because trisomy 21 led to Alzheimer-type Abaccumulation in vessels and plaques, familialAD itself might well involve a defect in theprecursor of the b-protein on this chromo-some. This prediction turned out to be truein part; the first gene implicated in a familialform of AD was indeed the b-amyloid pre-cursor protein. What Glenner apparently didnot recognize—or at least state at the time—was the heterogeneity of familial forms of ADas well as the notion that many cases maynot be genetically determined. Nevertheless,these two brief papers in Biochemical and Bio-physical Research Communications, althoughnot viewed as potentially seminal in the monthsafter their publication, turned out to provideboth the factual and conceptual underpinningsfor all subsequent research on b-amyloidosisin AD.

During the years 1983–1985, efforts inde-pendent of those of Glenner were made inseveral laboratories to isolate and sequence theamyloid in senile plaque cores (Fig. 1) fromAD brains. These efforts began before the iden-tification of the vascular Ab peptide by Glennerand Wong, but they were greatly facilitated by it.In 1983, Allsop, Landon, and Kidd reported amethod for isolating intact neuritic plaquecores from postmortem AD brain and foundthem to be insoluble in various denaturants(Allsop et al. 1983). They published an aminoacid composition which did not resemble anypreviously described amyloid protein. Theauthors described a variety of contaminantsin their final preparations, including bacteria,leading to concerns about the accuracy of thiscomposition, although subsequent methodsproduced core preparations of greater puritybut generally similar composition, signifyingthe relative insensitivity of the amino acidcomposition of partially purified proteins as abiochemical comparator.

In the laboratories of Masters and Beyr-euther, Roher, Selkoe, and Frangione, distinctbut partially related methods for purifying

C.L. Masters and D.J. Selkoe

2 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Med doi: 10.1101/cshperspect.a006262

ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



and solubilizing amyloid plaque cores frompostmortem AD brain were developed. Mastersand colleagues first reported the protein subunitof amyloid plaque cores, using a method whichused nonionic detergent extraction of brain,pepsin digestion, and sucrose density gradientfractionation (Masters et al. 1985). The resul-tant cores were found to be approximately90% pure by microscopy and were partiallysoluble in high concentrations (10%) of SDSand BME and fully soluble in approximately70% formic acid. By both HPLC and SDS/urea PAGE, the formic acid-solubilized coreprotein ran not only at �4.3 kDa but also at�8, 12, and 16 kDa, demonstrating the readyassociation of the monomer into SDS-stableoligomers. Masters and Beyreuther pointedout that the molecular mass, amino acid com-position and amino-terminal sequence of theprotein they isolated from cores were essentiallyidentical to those described for vascular Ab

by Glenner, although their analyses showedconsiderable amino-terminal “raggedness” inthe plaque-derived protein. They concludedthat the shared 4 kDa subunit indicated a com-mon origin for the plaque and vascular amy-loids in AD. Again, Ab peptides isolated fromAD and Down’s syndrome plaques were indis-tinguishable. The amino-terminal heterogene-ity reported by Masters and Beyreuther wasstriking, in that only 12% of the sequenced pro-tein began at Asp1, with 64% starting at Phe4and the remainder at downstream residues, per-haps deriving in part from their use of pepsindigestion during plaque purification. In Mas-ters’ report, Glenner’s 24-residue sequence wasextended to residue 28, although the identitiesof two of those additional four residues werelater revised.

Plaque core purifications and analysesperformed at that time in three other labor-atories provided largely consistent findings.

F

Figure 1. Three-dimensional reconstructed image by confocal microscopy of a neuritic (senile) plaque in thecortex of a patient dying with Alzheimer disease. Red labeling is by an antibody to amyloid b-protein whichreveals the extracellular amyloid; green labeling is with an antibody against p-Tau which reveals intimately asso-ciated dystrophic neurites. Note that this plaque core is not a solid mass of amyloid but is fragmented and porousand contains abnormal cell processes intercalated within it. (Image courtesy of Dr. Eliezer Masliah, University ofCalifornia, San Diego, CA.)

Biochemistry of Amyloid b-Protein and Amyloid Deposits in AD

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Med doi: 10.1101/cshperspect.a006262 3

ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



The various methods employed took advantageof the insolubility of the amyloid cores in deter-gents such as SDS and their relative resistance toquantitative digestion by proteases. In the stud-ies of Roher et al. (1986) and Gorevic et al.(1986), as in that of Masters et al. (1985), pep-tidases were used to diminish contaminants,but this approach raised the possibility of par-tial digestion of Ab itself and the creation ofsome of the observed amino-terminal heteroge-neity. In the study of Selkoe et al. (1986) the useof extensive SDS extraction of the cores, thensucrose gradient centrifugation, and then atwo-step fluorescence-activated particle sorting(FACS) led to SDS-insoluble plaque cores thatwere .90–95% pure by electron microscopy,enabling an estimate (via amino acid analysis)of the protein content of a single plaque core:60–130 pg. However, the attempts of Selkoeand colleagues to sequence this purified plaqueamyloid after its solubilization in formic acidor saturated guanidine thiocyanate showed ablocked amino terminus. In subsequent years,biochemical and immunocytochemical studiesfrom several laboratories made clear that theamino termini of plaque Ab peptides are heter-ogeneous and include derivatized and amino-terminally blocked species, e.g., pyroglutamateat residue 3. It is likely that the degree of amino-terminal heterogeneity and the precise terminiobtained in various biochemical analyses ofplaque cores depends in considerable part onthe biochemical nature and harshness of theextraction protocol. It has been shown thatparticular purification reagents can chemicallyalter Ab structure, for example, the oxidationof Met35 in the presence of formic acid. Othertypes of amino acid modifications of plaqueAb, such as racemization and isomerization ofits aspartates (e.g., D-aspartate and L- and D-iso-aspartates) or formylation of serines during for-mic acid solubilization, have been reported. Theformer changes may occur during the prolongedaging of the deposited amyloid proteins in vivo,whereas the latter is an artifact of an in vitromethod of solubilization.

One amino-terminal modification that hasreceived particular attention is the proteolyticremoval of residues 1 and 2 (Asp and Ala) and

the subsequent cyclizing of residue 3 (Glu) toa pyroglutamate (designated N-3pE). Firstdescribed in biochemical extracts of AD cortex(Mori et al. 1992), this truncated species wasfound to be detectable immunohistochemi-cally in many diffuse (i.e., mostly nonfibrillar)plaques in AD and DS cortex (Saido et al.1995). This truncation increases the aggregationkinetics of Ab (D’Arrigo et al. 2009; Sanderset al. 2009; Wirths et al. 2010) and also obviatesthe amino-terminal binding of those therapeu-tic antibodies which target Asp1 of Ab (Gard-berg et al. 2009). Recent work has shown thatglutaminyl cyclase, an enzyme in brain andother tissues which cyclizes exposed glutamates,can do so with high efficiency at Glu3 (Seifertet al. 2009) after removal of the first two residuesby aminopeptidases (Schlenzig et al. 2009; Sev-alle et al. 2009). The amount of AbpE3 in thebrains of APP transgenic mice can increasewith time, suggesting that the deposits beginwith full-length Ab1-x, some of which is firsttruncated by local aminopeptidase activityand then modified by glutaminyl cyclase(Wirths et al. 2010). Other changes in the aminoterminus, including pathogenic mutations atresidues 6 and 7 (Ono et al. 2010), may havemajor effects on oligomerization.

Taken together, the early biochemical anal-yses of the amyloid fibrils in meningeal vesselsand cerebral plaque cores established thatthe subunit in both cases was a highly hydro-phobic �4 kDa protein with a unique sequencethat had a strong tendency to self-aggregateinto stable dimers, trimers, and tetramers,higher oligomers and, ultimately, typical 8 nmamyloid fibrils. One interesting sidelight ofthese studies was the observation that the Abderived from plaque cores was generally moreinsoluble than that from vascular deposits. Forexample, 6 M guanidine hydrochloride couldeffectively solubilize the latter but not theformer, whereas the stronger chaotropic salt,guanidine thiocyanate, at saturated (6.8 M) con-centrations, could solubilize the cores (Selkoeet al. 1986). The use of concentrated formicacid by Masters and coworkers provided areagent that appeared to bring even the mostinsoluble amyloid fibers in AD brains into



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



solution, and it has subsequently been widelyused for this purpose. That it can do so indicatesthat, in general, cerebral Ab proteins whichassemble into amyloid fibrils undergo little orno covalent cross-linking.

Although the identity of the protein subunitof Alzheimer amyloid was thus well establishedby 1986, the carboxy-terminal sequence beyondresidue 28 and the molecular origin of this smallpeptide remained unclear. As detailed in Haasset al. (2011), it was the power of molecular bio-logical approaches that enabled the elucidationof its full length and how it actually arose fromproteolysis of a large precursor polypeptide(Kang et al. 1987).

In the almost 30 years since the biochemicalcharacterization of AD amyloid depositscommenced, we have come to realize that thecomplexity of this relatively short peptide isdetermined in part by the microenvironmentin which it is generated and resides. Althoughsmall amounts can be produced in the endo-plasmic reticulum and other vesicular organ-elles in the secretory pathway, much of thepeptide appears to arise from APP that has traf-ficked to the cell surface and is then sequentiallyprocessed byb- and g-secretase (both are aspar-tyl proteases) in the mildly acidic environmentof recycling endosomes (Selkoe 1994; Kaetheret al. 2006; Cirrito et al. 2008; and see Haasset al. 2011). As mentioned above, the peptideisolated from fibrillar amyloid plaques showssubstantial heterogeneity at both its aminoand carboxyl termini. Its biochemical proper-ties vary significantly depending on its terminalresidues, particularly at the hydrophobic car-boxyl terminus. Although the field has focuseduntil recently on two peptide lengths, the mostabundantly produced species (Ab1–40) andthe far less abundant but more aggregationprone Ab1–42, this is a simplification, as thevariability of carboxy-terminal lengths createdby g-secretase extends at least from Ab36 toAb43 (Kang et al. 1987). This heterogeneityarises secondary to the initial 1-cleavage ofAPP by the presenilin/g-secretase complex atthe membrane/cytoplasmic interface, namelyat Leu49-Val50 (Weidemann et al. 2002), fol-lowed by processive intramembrane processing

by this protease in an amino-terminal direction(i.e., first 1, then z and then g cleavages) (Qi-Takahara et al. 2005; Takami et al. 2009; andsee Haass et al. 2011).

AMYLOID FIBRILS OF Ab: STUDIES OF THEIRSTRUCTURE AND PROPERTIES

The pathognomonic lesions of AD are the fibril-lar extracellular deposits of Ab in parenchymalplaques and vascular amyloid and the intra-neuronal neurofibrillary tangles, which alsohave the tinctorial properties of amyloid(Serrano-Pozo et al. 2011). How Ab, includingits buffer-soluble oligomeric forms, may inducethe formation of intracellular tangles of the tauprotein is discussed elsewhere (Mandelkow andMandelkow 2011; Mucke and Selkoe 2011).Here we will review the pathway which convertsthe Ab region from its largely a-helical confor-mation when APP is embedded in the lipidmembrane to its gradual aggregation into largepolymers (filaments) rich in cross-b sheetstructure in the extracellular space of the brain.The conversion of a-helix or random coilstretches within normally soluble proteins intoprincipallyb-sheet rich assemblies is a commontheme in several neurodegenerative diseases.Drawing on the analogous prion theory, it isalso possible for a b-sheet conformer to induceor “seed” an a-helical conformer (or someother metastable intermediate) to adopt b-sheet structure (Eisele et al. 2009, 2010). Whatstructural relationship such intermediates infibrilogenesis have to the soluble, diffusibleoligomers of Ab detected in AD brain remainsuncertain. Despite more than 50 years of struc-tural analysis, the atomic resolution of classicalamyloid fibrils remains incomplete. Althoughmany techniques have been applied (includingsolid-state nuclear magnetic resonance andcryo-electron microscopy), the basic noncrys-talline subunit in the Ab fibril has preventedprogress (Caspar 2009; Kajava et al. 2010).Moreover, most of the data available on thestructure of Ab and its fibrils come from studiesof synthetic Ab peptides, and it remains unclearwhether these accurately model the natural Abassemblies found in AD brain.



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



Theoretical Computational and MolecularDynamic Models of the Ab Amyloid Fibril

Although the monomeric subunit of fibrils isthought to consist of two b-strands connectedby a turn, the ambiguous nature of the aminoand carboxyl termini have precluded develop-ment of a detailed model (Olofsson et al.2009b; Paparcone and Buehler 2009; Ramoset al. 2009). The convoluted carboxy-terminalfolding seen in a constrained oligomeric struc-ture (Streltsov et al. 2011) provides a caveatthat the simple, U-shapeb-turn may be an over-simplification. Some variability in this turnregion has now been identified using moleculardynamic (MD) simulations of dimers com-pared to trimers/pentamers (Horn and Sticht2010) and a triangular subunit forming a three-fold hexamer (Zheng et al. 2010). Constrainingtheb-turn by linking Asp23 to Lys28 also resultsin a system with increased fibrillogenic propen-sity (Reddy et al. 2009a). Placing theb-turn on aconstraining physical interface also affectsassembly (Fu et al. 2009), and this could haveimplications for Ab assembly when some ofthe peptide is bound to cell membranes, as islikely in the brain. Assembly at low or neutralpH may have an effect on the registration ofthe subunits within the fibril (Negureanu andBaumketner 2009). Interpeptide hydrogenbonds may play a major role in fibril growth,based on MD modeling (Reddy et al. 2009b;Takeda and Klimov 2009b, 2010). Oxidationof Met35 and assembly in quiescent versus agi-tated conditions have also been modeled andfound to have effects on the hydrophobic surfacesexposed on the fibrils (Wu et al. 2010a).

Structural Studies of Synthetic Ab Fibrils

Low-resolution (8 A) cryo-electron microscopyof synthetic Ab40 and Ab42 reveals similar pro-tofilament structures, with approximately 2.5peptides per cross-b repeat per protofilament(Schmidt et al. 2009). The lack of an integralnumber per repeat suggests that the assemblymay have undefinable amino termini withina tetrameric structure (Caspar 2009). Otherlow-resolution (10 A) cryo-EM reconstructions

have suggested that the carboxyl terminus formsthe inside wall of a hollow core (Zhang et al.2009d). Two-dimensional infrared spectros-copy discloses intramolecular water moleculesaround residues 17/34 and 18/36 in a confor-mation with a presumptive b-turn at 23/28.Substitutions around Glu22 and Asp23, eitherartificial or mimicking the pathogenic “Arctic”or “Iowa” FAD mutations, produce majoreffects on rates of aggregation (Peralvarez-Marın et al. 2009; Tycko et al. 2009), perhapsthrough a mechanism that involves off-registryside chain interactions (Takeda and Klimov2009c).

DIFFUSIBLE OLIGOMERS OF Ab

If one considers the trajectory of biochemicalstudies of Ab, it is clear that the field has movedover the last dozen years from an initial empha-sis on the fibrillar state found in amyloidplaques and meningocerebral vessels to a rangeof smaller, oligomeric Ab assemblies that arerelatively soluble and diffusible and thus moreable to exert a toxic effect on the neuronalplasma membrane, including synapses. A richand confusing vocabulary has developed todescribe the oligomers of Ab as they assemblealong pathways which may or may not lead tothe classical 8 nm amyloid fibrils found inplaques and blood vessels (Table 1). The meth-ods of analysis often determine nomenclature:biochemical characterization of synthetic ornatural (cellular and brain) Ab peptides usingSDS-PAGE or size exclusion chromatographyhas led to descriptions of assemblies containinga few (e.g., 2–20) monomers, usually desig-nated soluble oligomers; other methods, partic-ularly those using morphological or biophysicalapproaches on synthetic Ab such as electronmicroscopy or atomic force microscopy, maydescribe linear protofilaments (often �4 nmin diameter) or spherical/globular particles,each of which has been interpreted as a precur-sor of amyloid fibrils. It is important to empha-size here that many of the synthetic Ab assemblyforms reported in the literature have been madein vitro using supraphysiological concentrationsof a single-length peptide (e.g., Ab1–40), and



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



the occurrence of closely similar or identicalspecies in AD brain tissue may not have beenexplicitly confirmed structurally (immuno-chemical cross-reaction would not be sufficientconfirmation). One caveat in this regard is thatnatural Ab oligomers isolated from AD braintissue or APP-expressing cell cultures are farmore potent in electrophysiological or cytotox-icity assays than are synthetic assembly mixturessuch as ADDLs (“Ab-derived diffusible li-gands”) (Lambert et al. 1998) or protofibrils(Harper et al. 1997; Walsh et al. 1997), whichrequire high nanomolar concentrations to in-duce biological effects, suggesting that they con-tain many “off-pathway” (unnatural) assemblyforms that do not interact with neuronal mem-branes the way natural oligomers do. Indeed,some such synthetic “oligomers” have notbeen proven to be truly soluble in aqueous buf-fers (i.e., not pelletable at 100,000 g in an ultra-centrifuge), which is the case for naturaloligomers (see, for further reviews of the com-plexity of Ab assembly forms, Haass and Selkoe2007; Walsh and Selkoe 2007; Di Carlo 2010;Sakono and Zako 2010).

Synthetic Ab as a Substrate for OligomerFormation

Ever since the sequence of Ab became known,the easiest approach to study assembly hasbeen to aggregate synthetic peptides at supra-physiological concentrations in vitro (Castanoet al. 1986; Gorevic et al. 1986; Kirschner et al.1987). Classical biochemical analyses of the syn-thetic aggregates have been supplemented with

newer biophysical methods such as scanningtunneling microscopy (Liu et al. 2009a; Maet al. 2009), atomic force microscopy (Wu etal. 2010b), quartz crystal microbalance (Ogiet al. 2009), hydrogen exchange mass spectrom-etry (Zhang et al. 2009a), electron capture dis-sociation Fourier-transform ion cyclotronresonance mass spectroscopy (Sargaeva et al.2009), single-molecule spectroscopy (Dinget al. 2009), fluorescence photobleaching andquenching (Reinke et al. 2009; Edwin et al.2010), click peptide technique (Taniguchiet al. 2009), and ion mobility coupled withmass spectrometry (Bernstein et al. 2009). Theexperimental conditions for assembling syn-thetic Ab monomers into oligomers vary enor-mously with regard to the roles of temperature,salts, detergents, lipids, metal ions, fatty acids,and other molecules (Sahoo et al. 2009; Yuet al. 2009; Ahmed et al. 2010; Ladiwala et al.2010; Ryan et al. 2010), and each such conditionprovides constraints on the techniques the canbe used to study the synthetic peptide. Stabiliza-tion of synthetic dimers by cross-linking oxi-dized tyrosine-10 residues (Ono et al. 2009) orintroduced cysteine residues (O’Nuallain et al.2010) also provides a way to study this smallestoligomer and its role in the dynamic equili-brium of Ab assembly.

Amino acid substitutions and modifica-tions can readily be introduced into syntheticpeptides. However, to what degree these syn-thetic changes adequately model the in vivo sit-uation is often disregarded by investigators. Forexample, the familial intra-Ab mutations thatoccur in dominant fashion at position 22 or

Table 1. Ab assemblies described in the literature

A rich vocabulary that depends on the source of the peptide, the method of analysis, and the laboratory involved

Ab oligomers of natural or synthetic origin, as visualized chromatographically and/or on denaturing proteingels: monomers (A4), dimers (A8), trimers, tetramers (A16), pentamers, hexamers, dodecamer/12-mer(Ab�56), lower/higher order oligomers [(Ab)n]

Other synthetic oligomeric Ab assemblies: amyloid-b-derived diffusible ligands (ADDLs); Abmicelles, annular(pore-like) structures, (pre-)globulomers (globular oligomers), growth-arrested colloid particles, metastableaggregates, nanopore-like structures, neuroparticles, paranuclei/nucleating seeds, on/off pathwayintermediate states, spherical aggregates, etc.

Synthetic Ab fibrillar assemblies: protofibrils, prefibrils, fibrillar oligomers, nanofibrils



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



23 (E22G, E22Q, E22K, and D23N) result in theaccrual in vivo of a mixture of mutant and wild-type peptides of heterogeneous lengths, but thisis often not modeled in vitro (Masuda et al.2009; Murray et al. 2009b; Brorsson et al.2010). Nevertheless, synthetic Ab studies ofthis critical region do provide some informa-tion on the effects of these mutations on theb-turn at 25/26 versus 22/23 and consequenteffects on oligomerization and toxicity in vitro.

Molecular Dynamic Approaches toUnderstanding Synthetic Ab Oligomers

Although some progress in obtaining atomicresolution of the amino terminus and carboxylterminus of synthetic Ab has been made, theoverall structure(s) of the oligomer(s) at differ-ent assembly points remains elusive. A plethoraof MD simulations and theoretical modelinghas emerged. Starting at the amino terminus,Takeda and Klimov (2009a) find that amino-terminal truncation has an effect on oligomer(dimer) formation. The metal-binding regionof Ab around residues 6–14 has not yet beenadequately addressed by MD studies (seebelow), and there are conflicting results onmodels obtained for the loop and b-strandsassociated with the residue 16–35 region (Che-baro et al. 2009; Miller et al. 2009; Murray et al.2009a; Hamley et al. 2010; Wei et al. 2010). Theoxidation state of Met35 has long been of inter-est (Haeffner et al. 2010); this residue in thehydrophobic carboxyl terminus may play arole in oligomerization driven by hydrophobicinteractions (Zhao et al. 2009). Although ithas long been suspected that the highly hydro-phobic carboxyl terminus of Ab42 is a principaldeterminant of aggregation, its biophysical rolein oligomerization has only recently begun to beaddressed using synthetic peptides (Murrayet al. 2009a; Li et al. 2010). The structure ofthe carboxyl terminus may involve novel meta-stable conformations (b-hairpin at 35–37), butthese remain to be confirmed by crystallo-graphic methods (Wu et al. 2009). Higher orderoligomers (pentameric/hexameric assemblies)have been studied by MD and show differenteffects between the central hydrophobic and

carboxy-terminal regions when Ab40 and Ab42

are compared (Urbanc et al. 2010). Syntheticoligomers are also being used in attempts to dis-cover small molecules which are able to targetthese specific assemblies (Davis and Berkowitz2009a; Davis et al. 2009; Feng et al. 2009; Liuet al. 2009a; Nerelius et al. 2009; Pitt et al.2009; Riviere et al. 2009; Smith et al. 2009;Sun et al. 2009; Yamin et al. 2009; Hawkeset al. 2010; Ladiwala et al. 2010).

Recombinant Ab Oligomers

Ab oligomers obtained using recombinanttechniques appear to be as challenging towork with as their synthetic counterparts(Picone et al. 2009; Walsh et al. 2009; Streltsovet al. 2011). Nevertheless, recombinant con-structs have provided a way to conformationallyconstrain oligomerized Ab assemblies and arebeginning to provide novel insights into lower-order oligomers (e.g., dimers and tetramers) atatomic resolution (see Fig. 2; Streltsov et al.2011). Recombinant Ab42, with its strong fibril-logenic propensity, is coming under study(Zhang et al. 2009c; Finder et al. 2010). As a bac-terially derived product, it is difficult to fullyexclude impurities and adventitious factorsthat might interact with and co-purify withthe recombinant peptide. Although purifiedsynthetic Ab peptides can also contain impur-ities (e.g., racemized or truncated peptides),the faster aggregating and more potent toxicproperties of the recombinant material raisethe question of the presence of pro-aggregatingseeds and are worthy of further investigation(Finder et al. 2010).

Tissue- and Cell-Derived Natural Oligomers

The ultimate goal of studying the biochemistryof Ab is to understand its nature and biologicalproperties as it accumulates in the human brain.Early studies detected SDS-stable low-noligomers on western blots of AD brain extracts(e.g., Masters et al. 1985; Roher et al. 1993),although their biological activities were notstudied at that juncture. The major advance ofgenerating mouse lines transgenic for human



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



APP (Games et al. 1995; Hsiao et al. 1996) hasprovided dynamic information about whichspecies accrue most quickly (principally Abending at residue 42) and how they aggregateand deposit over time (e.g., Hamaguchi et al.2009; Philipson et al. 2009; Tomiyama et al.2010; and see LaFerla and Duff 2011). The insitu association of Ab oligomers with lipidmembranes (Liu et al. 2010b), including post-synaptic densities (Koffie et al. 2009), inAPP transgenic mouse brains helps us under-stand how these potentially toxic Ab speciesare compartmentalized. However, only asmall number of studies characterizing solubleoligomers per se in transgenic mouse brainshas been published (Kawarabayashi et al. 2001;Lesne et al. 2006; Shankar et al. 2009; Phamet al. 2010).

Turning now to studies of human braintissue, soluble (aqueously extractable and non-pelletable) forms of Ab in postmortem ADcortex, which include monomers and vari-ous oligomers, have become recognized asstronger quantitative correlates of degree of cog-nitive impairment shortly before death than are

amyloid plaques (see Fig. 3; McLean et al. 1999;Tomic et al. 2009; Woltjer et al. 2009; McDonaldet al. 2010). Soluble Ab oligomers extractedfrom the cortex of typical AD subjects havebeen shown to potently inhibit long-termpotentiation (LTP), enhance long-term depres-sion (LTD), and reduce dendritic spine densityin slices of normal rodent hippocampus (Shan-kar et al. 2008). The extracts of soluble oligo-mers also disrupted the memory of a learnedbehavior after intracerebroventricular injectionin normal rats. These effects could be princi-pally attributed to dimers, the major SDS-stableoligomer detected on western blots of ADcortex. Importantly, insoluble amyloid plaquecores from the same brains did not impairLTP unless they were first solubilized to releaseAb dimers and other oligomers, suggestingthat plaque cores per se have low bioactivitybut sequester Ab dimers that can be synapto-toxic if released (Shankar et al. 2008). Thereis also evidence that soluble Ab oligomersisolated from AD cortex can induce hyperphos-phorylation of tau protein at AD-relevant epi-topes, followed by progressive collapse of the

Figure 2. Model of potential interactions of Ab18-41 dimer with membrane lipid bilayers. The hydrophobicdimer–dimer interface of the Ab18-41 tetramer is intercalated into the membrane surface through non-electrostatic interactions, whereas hydrophilic aspects (blue) with metal-binding sites (black) are on the mem-brane surface. (From Streltsov et al. 2011; reprinted, with permission, from the author.)



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



microtubule cytoskeleton and neuritic dystro-phy (Jin et al. 2011).

Although these results suggest a synapto-toxic role for dimers, there are other solubleoligomers detectable in AD brain, includinga �56 kDa putative dodecamer (Lesne et al.2009). A similar species has been detected inthe brains of some APP transgenic mice andits level is shown to correlate with the occur-rence of behavioral deficits; isolation of this spe-cies from mouse brain and subsequent icvinjection into wild-type rats induced decreasedspatial memory performance (Lesne et al. 2006;LaFerla and Duff 2011). In vivo, it is likely thatthere exists an array of low- and medium-sizedoligomers, at least some of which appear to bein equilibrium with fibrils in plaques. The latternotion is supported by the occurrence of a halo

of dystrophic neurites immediately aroundfibrillar plaques, with the neuritic dystrophydiminishing as one moves farther from theplaque; this halo zone is also immunoreactivewith certain antibodies that selectively detectsmall oligomers of Ab (Meyer-Luehmann etal. 2008; Koffie et al. 2009).

Using immunoaffinity techniques, Noguchiet al. (2009) have isolated 10–15 nm sphericalAb assemblies (mass .100 kDa) from AD cor-tex. How these relate to the lower orderSDS-stable oligomers discussed above remainsto be determined. Other post-translationallymodified Ab species, such as partial aspartateisomerization (Tomidokoro et al. 2010) andcarboxy-terminal heterogeneity that includeslonger Ab43 peptides (Welander et al. 2009),are being uncovered by isolating Ab directlyfrom postmortem human brain. In addition,direct analysis of human brain Ab fibrils maydisclose structural differences not predictablefrom similar analyses of synthetic fibrils (Para-vastu et al. 2009).

Neuronally generated Ab monomers andperhaps various oligomers are presumed toequilibrate within the interstitial fluid of thebrain and to turn over in relation to the ratesof Ab production, clearance, and aggregationinto amyloid fibrils. From the interstitial com-partment or brain parenchyma, soluble Abmonomers and oligomers may enter into theCSF compartment (Englund et al. 2009;Fukumoto et al. 2010) and even the peripheralblood circulation (Roher et al. 2009; Xia et al.2009). Although much more work is requiredto establish the existence of blood-borne Aboligomers and confirm their cerebral origin,there is preliminary evidence that blood dimerlevels may correlate with clinical features ofAD (Villemagne et al. 2010; see also Blennowet al. 2011). Interestingly, such blood-bornedimers are associated with blood cellularmembranes (mainly white cells and platelets)and may increase as the natural history of ADadvances (Villemagne et al. 2010). In contrast,levels of Ab42 monomers in both the CSFand plasma are generally considered to fallas AD progresses (Lui et al. 2010a; Blennowet al. 2011).

Soluble Aβ

Insoluble Aβ

Synthetic Aβ

A

B

C

AD1 C AD2 AD3

AD4 C AD5 AD6

2 ng 5 ng 10 ng

Mr kDa

Mr kDa

Mr kDa

12

48

12

48

12

48

Figure 3. Representative western blots showing Abin frontal cortex of selected Alzheimer disease (AD)and control subjects. (A) Soluble Ab in 175,000 gsupernatants after a single extraction in phosphate-buffered saline. (B) Insoluble Ab extracted fromthe 175,000 g pellets. (C) To enable quantificationand between-gel comparisons, synthetic Ab40 stand-ard curves were run on each gel. The markersdesignate monomeric (4 kDa), dimeric (8 kDa),and trimeric (12 kDa) forms of Ab. (From McLeanet al. 1999; reprinted, with permission, from theauthor.)



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



THE INTERACTIONS OF Ab WITH OTHERMOLECULES: SERENDIPITOUSBYSTANDERS AND/OR INTIMATEPARTNERS IN PATHOGENESIS?

Early compositional analyses performed onisolated amyloid plaque cores suggested thatAb, although clearly the major component,was not the sole protein constituent. Moreover,nonproteinaceous components were also iden-tified to varying degrees in enriched—albeitnot fully purified—plaque core preparations.It has been difficult to determine on a biochem-ical basis alone which of these additionalconstituents are important and integral com-ponents of the amyloid plaques and whichmight become adventitiously associated withAb during plaque purification from homogen-ized brain tissue. When a non-Ab componentof plaques is identified and antibodies are raisedto it, these can be used to attempt to label amy-loid plaques in situ at both the light and electronmicroscopic levels. Positive results suggest thata particular protein is indeed associated withthe amyloid deposits, although not an integralcomponent of the amyloid fibrils because, likeother tissue amyloids, the fibrils should be com-posed solely of the specific subunit protein.Indeed, the ability to reconstitute amyloidfibrils with an ultrastructure closely resem-bling the fibrils seen in situ from synthetic Abpeptides alone has strongly suggested thatthe sole component of the amyloid filamentsin vivo is Ab. A careful proteomic analysis ofamyloid plaque cores isolated from postmor-tem AD cortex by laser capture microdissectionconcluded that the only protein constituentdetectable by mass spectrometry in the isolatedcores was Ab (Soderberg et al. 2006), support-ing the conclusion that the plaque amyloidfibrils are composed of just this protein type.It should be noted, however, that the fibrilsmay consist in part of heteropolymers ofslightly different Ab peptides, rather than justhomopolymers of a single peptide length (e.g.,Ab1–42).

Nevertheless, a variety of other moleculeshas been found to be loosely or more tightlyassociated with amyloid deposits during their

isolation and can sometimes be shown immu-nocytochemically in diffuse and/or compactedplaques in situ. Because the morphology ofsenile plaques indicates the presence of severaldistinct cellular elements that are intimatelyapposed, including dystrophic axons and den-drites (Fig. 1) and the processes of activatedmicroglia and reactive astrocytes, any of theseas well as local microvessels could potentiallybe sources of various non-Ab constituents ofthe plaques. In short, mature amyloid (neuritic)plaques are heterogeneous mixtures of pro-teinaceous and nonproteinaceous constituents,and the temporal sequence of accrual of theseelements onto the presumed initial Ab polymerhas been difficult to determine.

A recently completed interactome of APPdisclosed more than 200 different entities whichinteract with different domains of APP (128validated, 74 putative), including a significantproportion interacting with the Ab region(Perreau et al. 2010). One of the earliest to beidentified was the enzyme acetylcholinesterase(AChE; Friede 1965), perhaps paradoxicalbecause of its subsequent role as a therapeutictarget for AD and surprising in that the mecha-nistic basis for the co-location of AChE with theamyloid plaques remains uncertain (De Ferrariet al. 2001). Most of the identified molecularinteractors of Ab in the brain remain equallymysterious and often raise the question of by-stander versus functionally significant partner.

Metal Ions

Because of their ubiquitous presence in humantissues, the bioavailable metal ions, Cu, Zn, andFe, have been obvious choices for investigationof amyloid association. For decades, uncer-tainty has reigned over the quantitative elemen-tal analysis of whole brain homogenates—andof isolated plaques or tangles—in AD comparedto normal aged controls and other neurodegen-erative diseases. At the level of grey matterhomogenates, there is no agreement that anyparticular metal ion is specifically elevated orlowered in AD brain. Most techniques havedetected elevations in Cu, Zn, or Fe in ADamyloid plaques, either in situ or after their



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



purification (see, for example, Rajendran et al.2009), but such analytical approaches havenever been entirely convincing. The observa-tions that both APP and Ab have sequencesconsistent with metal-binding motifs and met-allo-complexing activities add a new dimensionto this line of enquiry (Faller 2009; Duce et al.2010). Measuring the affinities of metal–pro-tein interactions is challenging (Xiao andWedd 2010) but, as technologies have improved,the general rule has emerged that the metalaffinities increase as the proteins move towardtheir sites of final subcellular compartmentali-zation and utilization. Thus, certain other pro-teins act as chaperones to take the metal ionsinto compartments where their higher affinityend-user proteins reside. The synapse has pro-ven to be a subcellular site where ions such asZn2þ and Cu2þ are used to modulate the activ-ities of key excitatory NMDA/AMPA receptors.It is in the vicinity of this cellular compartmentthat Ab may interact with these divalent cationsin a fashion that can alter the peptide’s confor-mation. This metal-based mechanism, as wellas the overall level of local excitatory neurotrans-mission (Cirrito et al. 2005), could help providean explanation for the topographic selectivity ofAb aggregation and extracellular deposition inthe AD brain, as there is an intriguing overlapbetween those areas of the brain rich in gluta-matergic terminals, free vesicular zinc, and Abamyloid plaques in certain APP transgenicmice (Stoltenberg et al. 2007).

With an emerging understanding of thepathways leading to soluble oligomer or insolu-ble fibril production, therapeutic strategiesloosely termed as “anti-Ab aggregation” needto be refocused on the specific steps being tar-geted (Rodriguez-Rodriguez et al. 2009; Yadavand Sonker 2009; Dickens and Franz 2010), par-ticularly with regard to the concept of “thera-peutic chelation” of metal ions. The conceptof therapeutic chelation needs to be qualifiedby the relative affinities each metal ion has forits target protein. Thus, metal “chaperone” is apreferred concept when discussing the reversi-ble interactions divalent cations can have withAb, regardless of which oligomeric or fibrillarassembly is being considered.

Ab and Copper

The average KD of Cu2þ for Ab is about 10210M

(i.e., low nanomolar) for both soluble andfibrillar forms of the synthetic peptide in vitro(Rozga et al. 2010; Xiao and Wedd 2010). Thismeans that other metallo-chaperone proteinswith higher (i.e., high picomolar or greater)affinities will prevent Cu2þ binding to Ab.This criterion would include human serumalbumin (Perrone et al. 2009), suggesting thatAb in locations (e.g., CSF or blood) remotefrom parenchymal brain compartments suchas neurites and synapses should be unmetal-lated. Furthermore, therapeutic compoundsdesigned to act as metal-ion chaperones withlow picomolar affinities would be expected tocompete with Ab for Cu2þ binding only withinthe brain parenchyma.

Ab may have more than one Cu2þ-bindingsite (Behbehani and Mirzaie 2009; Jun et al.2009; Sarell et al. 2009). Depending on the stoi-chiometry, Cu2þ–Ab interactions can causesynthetic Ab to aggregate in vitro principallyvia an oligomer-forming pathway or a fibrillo-genic pathway (Brzyska et al. 2009; Mooreet al. 2009; Olofsson et al. 2009a; Tougu et al.2009; Haeffner et al. 2010). That is, at sub-equimolar Cu2þ:Ab ratios, amyloid fibrilsform; at supra-equimolar ratios, stable oligom-ers form first, then dityrosine cross-linkagesoccur (Smith et al. 2007). The principal Cu2þ-binding site is coordinated within the first 16residues and involves His6, His13, and His14,together with the first two residues (Asp1,Ala2) (Dorlet et al. 2009; Drew et al. 2009a,b;Hureau et al. 2009a,b). This coordination envi-ronment is pleiotropic (Drew et al. 2009b), add-ing to the complexity of the analysis (Drochioiuet al. 2009; Hureau et al. 2009a). As was pre-dicted when the Ab sequence became known,the protonation of the histidine residues,dependent on pH, should have a major effectin the Ab folding pathway: metallation and fold-ing of Ab in the endosome/lysosome pathwaywill probably be quite different from that inthe extracellular or peri-synaptic compartments.

Cu2þ as a redox-active entity can also in-duce oxidative modification to Ab, particularly



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



at Tyr10 with consequent dityrosine covalentcross-links (Drew et al. 2009a,b; Moore et al.2009; Jiang et al. 2010). Other residues, suchas Met35, may participate (Barman et al. 2009;Butterfield et al. 2010), but this is not proven(da Silva et al. 2009). Whether the metal-modified Ab is capable of pro- or anti-oxidantactivity is also uncertain (Baruch-Suchodolskyand Fischer 2009), but it is an important ques-tion that needs to be resolved in terms of under-standing the toxicity of Ab oligomers. Reducingintracellular Cu2þ bioavailability has an inhibi-tory effect on Ab oligomer formation (Crouchet al. 2009a).

Ab and Zinc

In contrast to Cu2þ, Zn2þ is redox inactive andtherefore cannot be directly involved in any oxi-dative processes involving Ab. In common withCu2þ, Zn2þ has pleotropic binding sites on Ab(Damante et al. 2009; Talmard et al. 2009; Milleret al. 2010) which can serve to drive syntheticAb aggregation in vitro. The Zn2þ-induced for-mation of cytotoxic Ab oligomers in proximityto excitatory glutamatergic synapses is believedto be a mechanism contributing to synapticdegeneration in AD (Deshpande et al. 2009).Zn–Ab complexes also become more resistantto proteolytic degradation in in vitro experi-ments (Crouch et al. 2009b), potentially allow-ing metal-bound Ab fibrils to accumulate in theextracellular space.

Ab and Iron

Studies of Fe3þ/Fe2þ complexes with Ab indi-cate a potential pro-aggregating role for thisabundant metal (Jiang et al. 2009a; Urangaet al. 2010), especially if evidence that Ab hassignificantly higher affinity for Fe2þ than doestransferrin (Jiang et al. 2009a) is confirmed.

Ab INTERACTIONS WITH CELLMEMBRANES, LIPOPROTEINS, ANDMEMBRANE-ASSOCIATED PROTEINS

The proteolytic release of Ab from APP isbelieved to occur principally in an endo-somal/lysosomal compartment or from the

surface of the plasma membrane (see Haasset al. 2011). Given the amphiphilic nature ofAb, it is not surprising that many potentialinteractions can occur once it is a free peptide.These interactions can be driven by phase/interface effects, electrostatic (charge) interac-tions dependent on the pH of the microenvi-ronment, and hydrophobic interactions if thehydrophobic carboxy-terminal region is ableto re-associate with the lipid bilayer. These typesof bonding apply also to Ab interactions withthe lipoprotein particles formed with ApoE,ApoA, and ApoJ, as well as with other mem-brane-associated macromolecular complexesin the vicinity of synapses such as NMDA,AMPA, insulin, and nicotinic ACh receptors.All of these complex protein interactions aredependent in part on the conformation andstate of assembly of Ab itself. When sequentialfractions of postmortem AD brain homoge-nates are analyzed, the major pool of Ab liesin the detergent-insoluble (e.g., formic acid-or guanidine-extractable) fraction, presumablyrepresenting rather insoluble amyloid plaques,but a considerable amount is apparently looselyassociated with cellular membranes (e.g., thesodium carbonate-extractable fraction). Thediffusible, aqueously extractable fraction (e.g.,buffered saline extract) is generally less than1–2% of the total recoverable brain Ab. It isthe membrane-associated pool of brain Abwhich can be recovered in sodium carbonateor Triton that we will focus on now (see Reliniet al. 2009 for a recent review).

Phase/Interface Effects

Most in vitro studies of the a-helix to b-sheetconversion and aggregation of Ab peptides areconducted at concentrations 3–4 orders ofmagnitude greater than those found in vivo.Moreover, the special microenvironment inwhich Ab aggregation is believed to occur invivo is not always taken into account, e.g., therelatively high concentrations of metal ions inand around synapses. The interface betweenthe interstitial fluid phase and the surface ofthe plasma membrane is likely to be a criticalfactor in influencing the aggregation pathway



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



of Ab. A number of in vitro studies find this,showing interface clustering of Ab (Chi et al.2010) that slows the lag phase of fibril formation(Hellstrand et al. 2010) by providing an envi-ronment for a hydrophobic layer adjacent tothe membrane interface (Jiang et al. 2009b).Physical movement/agitation at the water–membrane interface may also promote fibrillo-genesis (Morinaga et al. 2010; Wu et al. 2010a).The nature of this interface may thereforestrongly affect the Ab folding pathway (Kayedet al. 2009). In contrast to the hydrophilic ecto-domains of various proteins proposed to func-tion as Ab receptors, membrane lipid surfacesseem a more biophysically plausible receptorfor the highly hydrophobic Ab oligomers.

Electrostatic/Charge Effects

The role of negatively charged phospholipidhead groups, sphingolipids, sialic acid, etc. inaffecting the binding and oligomerization ofAb is being increasingly examined (Kayedet al. 2009; Salay et al. 2009; Kotarek and Moss2010; Sureshbabu et al. 2010). Smaller (1–2 nm diameter) synthetic Ab oligomers have agreater tendency to bind such charged speciesthan do those of larger (4–5 nm) size (Cizaset al. 2010). Local membrane charge may alsoalter the b-turn of synthetic Ab peptides (Gri-maldi et al. 2010). Exposed phosphatidylserinehas been proposed as a mediator of Ab–mem-brane surface interactions (Simakova andArispe 2007). MD modeling (Davis and Berko-witz 2009a,b) suggests the induction of subtlechanges in conformation around the b-turn ofAb fold on its membrane binding, and in vitrostudies show the effect of pH and the protona-tion of His13 and/or His14 when the amphi-philic domain Ab11-22 is used for membranebinding studies (Ravault et al. 2009). Using L-and D-handed enantiomers of Ab42, Ciccotostoet al. (2011) have reported that synthetic Abbinds directly to cell membranes in vivothrough phosphatidylserine and that this inter-action is stereospecific. The toxicity of Aboligomers may therefore be related in part tosome aspect of its specific electrostatic interac-tions with phosphatidylserine. Gangliosides

provide another charged interactor for Ab onthe cell surface (Nakazawa et al. 2009; Peterset al. 2009; Utsumi et al. 2009; Yagi-Utsumiet al. 2010), with potential effects on the foldingpattern of the peptide (Mao et al. 2010; Ogawaet al. 2011).

Hydrophobic Interactions of Ab

After the release of the Ab monomer from itspartially transmembrane location, a portion ofresultant Ab assemblies may bind and re-insertinto the hydrophobic lipid bilayer. There hasbeen a longstanding controversy in the field asto whether this re-insertion event leads to theformation of a complete transmembrane poreor whether membrane association and partialinsertion can disrupt the bilayer to such anextent that its structural integrity is compro-mised. MD simulations and in vitro artificiallipid membrane models of this insertional eventare plentiful (Friedman et al. 2009; Lemkul andBevan 2009; Miyashita et al. 2009; Qiu et al.2009; Song et al. 2009; Yang et al. 2009a,b; Mor-ita et al. 2010; Schauerte et al. 2010; Wang et al.2010), but rigorous evidence for a hydrophobicmembrane-traversing interaction in vivo is lack-ing. Using photobleaching Forster resonanceenergy transfer, there was a loss of signal fromthe hydrophobic carboxyl terminus of Ab as itinteracts with the plasma membrane of PC12cells, which may indicate its sequestrationwithin the lipid bilayer (Bateman and Chakra-bartty 2009). Addition of synthetic Ab42 oligo-mers to N2a and HT22 neuronal cell lines ledto significant cellular stiffening/rigidity (Lule-vich et al. 2010). Peripheral membrane associa-tion of Ab42 (but not Ab40) oligomers withlysosmes has also been suggested as evidenceof in vivo membrane insertion (Liu et al.2010b). Clearly, more evidence is required toprove actual transmembrane insertion of thepeptide in vivo.

Ab Interaction with Lipoproteins

Electrostatic or hydrophobic interactions of Abwith the various lipoprotein particles (ApoE,ApoA, ApoJ) are discussed elsewhere in this



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



volume (Holtzman et al. 2011). We note in vivoevidence of direct ApoE–Ab and ApoA1–Abinteractions (Bales et al. 2009; Paula-Limaet al. 2009), and that ApoE found in the brainis more heavily sialylated than that in theperipheral circulation (Kawasaki et al. 2009),potentially facilitating electrostatic interactionswith Ab (see above).

Ab Interactions with Selected MembranePolypeptides (e.g., NMDA and AChReceptors)

Growing evidence suggests the occurrence of atleast functional—if not physical—interactionsof Ab oligomers with NMDA or a7-nicotinicACh receptors or the cellular prion protein(Hu et al. 2009; Lauren et al. 2009; Li et al.2009; Liu et al. 2009b; Zhang et al. 2009b).However, much of this evidence comes fromstudies showing that antagonists or downstreamregulators of these and other cell-surface recep-tors (e.g., AMPA and insulin receptors) can mit-igate or fully prevent the effects of soluble Aboligomers on synaptic form and function (see,e.g., Shankar et al. 2007; Li et al. 2009). Suchstudies only indicate that the expression andnormal function of the receptor in question isnecessary for some of the downstream effectsof Ab on neurons to occur, not that these cell-surface polypeptides are the direct receptorsfor Ab in vivo. Instead, the binding of extracel-lular Ab oligomers—via their exposed hydro-phobic residues—to certain lipids in theplasma membrane could alter the biophysicalproperties of the bilayer and secondarily andsomewhat nonspecifically perturb the struc-tures (and thus the functions) of a variety ofmembrane-anchored neuronal receptor pro-teins. Moreover, as mentioned above, the highconcentrations of Zn2þ and Cu2þ found inand around NMDAR-containing post-synapticelements may be involved in the actions of Aboligomers at the membrane.

Other Ab Interactions

Over the past 30 years, many other proteinshave been described as being associated withAb extracellular deposits, using a variety of

immunohistochemical or biochemical approach-es. Among these, two broad categories of pro-teins stand out: extracellular matrix factorsand inflammatory/stress response factors. Thelatter include members of the complementcascade, cytokines, immunoglobulins, acutephase proteins, components of the inflammo-some, etc. The serine protease inhibitor, a1-antichymotrypsin, is an acute phase proteinthat may be tightly associated with amyloidplaque cores (Abraham et al. 1988). Biochemi-cal isolation approaches have also yielded co-purifying proteins of unknown pathogenicsignificance, e.g., a fragment (residues 60–95)of the neuronal protein, a-synuclein, namely,its NAC peptide (i.e., “non-amyloid compo-nent” of plaques). The fact that some corticalneurons in AD accumulate aggregates of a-sy-nuclein (Lewy bodies and neurites) provides apossible explanation for the co-purification ofthis protein fragment from homogenized ADcortex. Many other polypeptides of unknownmechanistic importance in the disease patho-genesis could be cited here. The fact that someamyloid-associated proteins differ in their pri-mary sequences and amounts between humanand mouse brain could help explain why APPtransgenic mice deposit plaques of humanAb but not always with the same local associa-tions and consequences (e.g., without signifi-cant neuronal loss).

CONCLUSIONS

Even the wealth of details and accompanyingreferences that we have discussed above cannotdo the subject of Ab biochemistry justice. SinceGlenner and Wong’s seminal paper in 1984,innumerable studies of this small, hydrophobic,and potentially lethal protein have been pub-lished. Indeed, several important aspects of itsbiology, including its mechanisms of formation(Haass et al. 2011) and clearance (Saido andLeissring 2011) and its measurement by brainimaging (Johnson et al. 2011) and in biologicalfluids (Blennow et al. 2011), are covered exten-sively in other parts of this volume. The geneticsof dominantly inherited AD and the pathobiol-ogy of the apolipoprotein 14 allele in AD have



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



combined to give Ab an apparent initiating rolein at least some forms of the AD syndrome.Because these familial forms are largely indis-tinguishable from “sporadic” late-onset AD,parsimony suggests that an imbalance betweenAb production and clearance—an Ab dysho-meostasis—is a driving force for many or allcases of AD as we define this eponymic syn-drome. And yet, precisely why Ab accumulatesand what upstream events can lead to this accu-mulation remains unknown for the majority ofcases of the disease. Perhaps only through theresults of clinical trials of agents that must beworking solely on Ab (e.g., highly specificanti-Ab antibodies) can we adequately test thetheory that Ab accumulation is a central patho-genic event in AD. For the sake of our patientsand their families, one can only hope that theanswer to this provocative question lies nottoo far in the future.

REFERENCES�Reference is also in this collection.

Abraham CR, Selkoe DJ, Potter H. 1988. Immunochemicalidentification of the serine protease inhibitor, a1-anti-chymotrypsin in the brain amyloid deposits of Alz-heimer’s disease. Cell 52: 487–501.

Ahmed M, Davis J, Aucoin D, Sato T, Ahuja S, Aimoto S,Elliott JI, Van Nostrand WE, Smith SO. 2010. Structuralconversion of neurotoxic amyloid-b1-42 oligomers tofibrils. Nat Struct Mol Biol 17: 561–567.

Allsop D, Landon M, Kidd M. 1983. The isolation andamino acid composition of senile plaque core protein.Brain Res 259: 348–352.

Bales KR, Liu F, Wu S, Lin SZ, Koger D, DeLong C, HansenJC, Sullivan PM, Paul SM. 2009. Human APOE isoform-dependent effects on brain b-amyloid levels in PDAPPtransgenic mice. J Neurosci 29: 6771–6779.

Barman A, Taves W, Prabhakar R. 2009. Insights into themechanism of methionine oxidation catalyzed by metal(Cu2þ, Zn2þ, and Fe3þ)-amyloid beta (Ab) peptide com-plexes: A computational study. J Comput Chem 30:1405–1413.

Baruch-Suchodolsky R, Fischer B. 2009. Ab40, either solubleor aggregated, is a remarkably potent antioxidant in cell-free oxidative systems. Biochemistry 48: 4354–4370.

Bateman DA, Chakrabartty A. 2009. Two distinct conforma-tions of Ab aggregates on the surface of living PC12 cells.Biophys J 96: 4260–4267.

Behbehani GR, Mirzaie M. 2009. A high performancemethod for thermodynamic study on the binding ofcopper ion and glycine with Alzheimer’s amyloid b pep-tide. J Therm Anal Calorim 96: 631–635.

Bernstein SL, Dupuis NF, Lazo ND, Wyttenbach T, CondronMM, Bitan G, Teplow DB, Shea J-E, Ruotolo BT, Robin-son CV, et al. 2009. Amyloid-b protein oligomerizationand the importance of tetramers and dodecamers inthe aetiology of Alzheimer’s disease. Nat Chem 1:326–331.

� Blennow K, Zetterberg H, Fagan AM. 2011. Fluid bio-markers in Alzheimer disease. Cold Spring Harb PerspectMed doi: 10.1101/cshperspect.a006221.

Brorsson AC, Bolognesi B, Tartaglia GG, Shammas SL, Fav-rin G, Watson I, Lomas DA, Chiti F, Vendruscolo M, Dob-son CM, et al. 2010. Intrinsic determinants of neurotoxicaggregate formation by the amyloid b peptide. Biophys J98: 1677–1684.

Brzyska M, Trzesniewska K, Wieckowska A, Szczepankie-wicz A, Elbaum D. 2009. Electrochemical and con-formational consequences of copper (Cu-I and Cu-II)binding to b-amyloid(1–40). Chembiochem 10: 1045–1055.

Butterfield DA, Galvan V, Lange MB, Tang H, Sowell RA,Spilman P, Fombonne J, Gorostiza O, Zhang J, SultanaR, et al. 2010. In vivo oxidative stress in brain of Alz-heimer disease transgenic mice: Requirement for methio-nine 35 in amyloid b-peptide of APP. Free Radic Biol Med48: 136–144.

Caspar DL. 2009. Inconvenient facts about pathologicalamyloid fibrils. Proc Natl Acad Sci 106: 20555–20556.

Castano EM, Ghiso J, Prelli F, Gorevic PD, Migheli A, Fran-gione B. 1986. In vitro formation of amyloid fibrils fromtwo synthetic peptides of different lengths homologousto Alzheimer’s disease b-protein. Biochem Biophys ResCommun 141: 782–789.

Chebaro Y, Mousseau N, Derreumaux P. 2009. Structuresand thermodynamics of Alzheimer’s amyloid-bAb(16–35) monomer and dimer by replica exchangemolecular dynamics simulations: Implication for full-length Ab fibrillation. J Phys Chem B 113: 7668–7675.

Chi EY, Frey SL, Winans A, Lam KLH, Kjaer K, Majewski J,Lee KYC. 2010. Amyloid-b fibrillogenesis seeded byinterface-induced peptide misfolding and self-assembly.Biophys J 98: 2299–2308.

Ciccotosto GD, Tew DJ, Drew SC, Smith DG, Johanssen T,Lal V, Lau TL, Perez K, Curtain CC, Wade JD, et al.2011. Stereospecific interactions are necessary for Alz-heimer disease amyloid-b toxicity. Neurobiol Aging 32:235–248.

Cirrito JR, Yamada KA, Finn MB, Sloviter RS, Bales KR, MayPC, Schoepp DD, Paul SM, Mennerick S, Holtzman DM.2005. Synaptic activity regulates interstitial fluidamyloid-b levels in vivo. Neuron 48: 913–922.

Cirrito JR, Kang JE, Lee J, Stewart FR, Verges DK, SilverioLM, Bu G, Mennerick S, Holtzman DM. 2008. Endocyto-sis is required for synaptic activity-dependent release ofamyloid-beta in vivo. Neuron 58: 42–51.

Cizas P, Budvytyte R, Morkuniene R, Moldovan R, BroccioM, Losche M, Niaura G, Valincius G, Borutaite V. 2010.Size-dependent neurotoxicity of b-amyloid oligomers.Arch Biochem Biophy 496: 84–92.

Crouch PJ, Hung LW, Adlard PA, Cortes M, Lal V, Filiz G,Perez KA, Nurjono M, Caragounis A, Du T, et al.2009a. Increasing Cu bioavailability inhibits Ab oligo-



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



mers and tau phosphorylation. Proc Natl Acad Sci 106:381–386.

Crouch PJ, Tew DJ, Du T, Nguyen DN, Caragounis A, Filiz G,Blake RE, Trounce IA, Soon CPW, Laughton K, et al.2009b. Restored degradation of the Alzheimer’s amy-loid-b peptide by targeting amyloid formation. J Neuro-chem 108: 1198–1207.

D’Arrigo C, Tabaton M, Perico A. 2009. N-terminal trun-cated pyroglutamyl b amyloid peptide Abpy3–42 showsa faster aggregation kinetics than the full-length Ab1–42.Biopolymers 91: 861–873.

da Silva GFZ, Lykourinou VAngerhofer A, L-J Ming. 2009.Methionine does not reduce Cu(II)-b-amyloid!—Recti-fication of the roles of methionine-35 and reducingagents in metal-centered oxidation chemistry of Cu(II)-b-amyloid. Biochim Biophy Acta 1792: 49–55.

Damante CA, Osz K, Nagy Z, Pappalardo G, Grasso G,Impellizzeri G, Rizzarelli E, Sovago I. 2009. Metal loadingcapacity of Ab N-terminus: a combined potentiometricand spectroscopic study of zinc(II) complexes withAb(1–16), its short or mutated peptide fragments andits polyethylene glycol-ylated analogue. Inorg Chem 48:10405–10415.

Davis CH, Berkowitz ML. 2009a. Interaction betweenamyloid-b (1–42) peptide and phospholipid bilayers:A molecular dynamics study. Biophys J 96: 785–797.

Davis CH, Berkowitz ML. 2009b. Structure of the amyloid-b (1–42) monomer absorbed to model phospholipidbilayers: A molecular dynamics study. J Phys Chem B113: 14480–14486.

Davis TJ, Soto-Ortega DD, Kotarek JA, Gonzalez-VelasquezFJ, Sivakumar K, Wu LY, Wang Q, Moss MA. 2009. Com-parative study of inhibition at multiple stages of amyloid-b self-assembly provides mechanistic insight. Mol Phar-macol 76: 405–413.

De Ferrari GV, Canales MA, Shin I, Weiner LM, Silman I,Inestrosa NC. 2001. A structural motif of acetylcholines-terase that promotes amyloid b-peptide fibril formation.Biochemistry 40: 10447–10457.

Deshpande A, Kawai H, Metherate R, Glabe CG, Busciglio J.2009. A role for synaptic zinc in activity-dependent Aboligomer formation and accumulation at excitatory syn-apses. J Neurosci 29: 4004–4015.

Di Carlo M. 2010. Beta amyloid peptide: From differentaggregation forms to the activation of different biochem-ical pathways. Eur Biophys J Biophys Lett 39: 877–888.

Dickens MG, Franz KJ. 2010. A prochelator activated byhydrogen peroxide prevents metal-induced amyloid b

aggregation. Chembiochem 11: 59–62.

Ding H, Wong PT, Lee EL, Gafni A, Steel DG. 2009. Deter-mination of the oligomer size of amyloidogenic proteinb-amyloid(1–40) by single-molecule spectroscopy. Bio-phys J 97: 912–921.

Dorlet P, Gambarelli S, Faller P, Hureau C. 2009. Pulse EPRspectroscopy reveals the coordination sphere of cop-per(II) ions in the 1–16 amyloid-b peptide: A key roleof the first two N-terminus residues. Angew Chem IntEd Engl 48: 9273–9276.

Drew SC, Masters CL, Barnham KJ. 2009a. Alanine-2 car-bonyl is an oxygen ligand in Cu2þ coordination ofAlzheimer’s disease amyloid-b peptide—relevance to N-

terminally truncated forms. J Am Chem Soc 131:8760–8761.

Drew SC, Noble CJ, Masters CL, Hanson GR, Barnham KJ.2009b. Pleomorphic copper coordination by Alzheimer’sdisease amyloid-b peptide. J Am Chem Soc 131: 1195–1207.

Drochioiu G, Manea M, Dragusanu M, Murariu M, DraganES, Petre BA, Mezo G, Przybylski M. 2009. Interaction ofb-amyloid (1–40) peptide with pairs of metal ions: Anelectrospray ion trap mass spectrometric model study.Biophys Chem 144: 9–20.

Duce JA, Tsatsanis A, Cater MA, James SA, Robb E, WikheK, Leong SL, Perez K, Johanssen T, Greenough MA,et al. 2010. Iron-export ferroxidase activity of b-amyloidprecursor protein is inhibited by zinc in Alzheimer’s dis-ease. Cell 142: 857–867.

Edwin NJ, Hammer RP, McCarley RL, Russo PS. 2010.Reversibility of b-amyloid self-assembly: Effects of pHand added salts assessed by fluorescence photobleachingrecovery. Biomacromolecules 11: 341–347.

Eisele YS, Bolmont T, Heikenwalder M, Langer F, JacobsonLH, Yan ZX, Roth K, Aguzzi A, Staufenbiel M, WalkerLC, et al. 2009. Induction of cerebral b-amyloidosis:Intracerebral versus systemic Ab inoculation. Proc NatlAcad Sci 106: 12926–12931.

Eisele YS, Obermuller U, Heilbronner G, Baumann F, KaeserSA, Wolburg H, Walker LC, Staufenbiel M, HeikenwalderM, Jucker M. 2010. Peripherally applied Ab-containinginoculates induce cerebral b-amyloidosis. Science 330:980–982.

Englund H, Degerman Gunnarsson M, Brundin RM,Hedlund M, Kilander L, Lannfelt L, Pettersson FE.2009. Oligomerization partially explains the lowering ofAb42 in Alzheimer’s disease cerebrospinal fluid. Neuro-degener Dis 6: 139–147.

Faller P. 2009. Copper and zinc binding to amyloid-b: Coor-dination, dynamics, aggregation, reactivity and metal-ion transfer. Chembiochem 10: 2837–2845.

Feng Y, Wang XP, Yang SG, Wang YJ, Zhang X, Du XT, SunXX, Zhao M, Huang L, Liu RT. 2009. Resveratrol inhibitsbeta-amyloid oligomeric cytotoxicity but does notprevent oligomer formation. Neurotoxicology 30: 986–995.

Finder VH, Vodopivec I, Nitsch RM, Glockshuber R. 2010.The recombinant amyloid-b peptide Ab1-42 aggregatesfaster and is more neurotoxic than synthetic Ab1-42. JMol Biol 396: 9–18.

Friede RL. 1965. Enzyme histochemical studies of senileplaques. J Neuropathol Exp Neurol 24: 477–491.

Friedman R, Pellarin R, Caflisch A. 2009. Amyloid aggrega-tion on lipid bilayers and its impact on membranepermeability. J Mol Biol 387: 407–415.

Fu ZM, Luo Y, Derreumaux P, Wei GH. 2009. Inducedb-barrel formation of the Alzheimer’s Ab 25–35 oligo-mers on carbon nanotube surfaces: Implication foramyloid fibril inhibition. Biophys J 97: 1795–1803.

Fukumoto H, Tokuda T, Kasai T, Ishigami N, Hidaka H,Kondo M, Allsop D, Nakagawa M. 2010. High-mol-ecular-weight b-amyloid oligomers are elevated incerebrospinal fluid of Alzheimer patients. FASEB J 24:2716–2726.



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



Games D, Adams D, Alessandrini R, Barbour R, BertheletteP, Blackwell C, Carr T, Clemens J, Donaldson T, GillespieF, et al. 1995. Alzheimer-type neuropathology in trans-genic mice overexpressing V717F b-amyloid precursorprotein. Nature 373: 523–527.

Gardberg A, Dice L, Pridgen K, Ko J, Patterson P, Ou S,Wetzel R, Dealwis C. 2009. Structures of Ab-relatedpeptide-monoclonal antibody complexes. Biochemistry48: 5210–5217.

Glenner GG. 1979. Congophilic microangiopathy in thepathogenesis of Alzheimer’s syndrome (presenile de-mentia). Med Hypotheses 5: 1231–1236.

Glenner GG, Wong CW. 1984a. Alzheimer’s disease andDown’s syndrome: Sharing of a unique cerebrovascularamyloid fibril protein. Biochem Biophys Res Commun122: 1131–1135.

Glenner GG, Wong CW. 1984b. Alzheimer’s disease: Initialreport of the purification and characterization of a novelcerebrovascular amyloid protein. Biochem Biophys ResCommun 120: 885–890.

Gorevic P, Goni F, Pons-Estel B, Alvarez F, Peress R, Fran-gione B. 1986. Isolation and partial characterization ofneurofibrillary tangles and amyloid plaque cores in Al-zheimer’s disease: Immunohistological studies. J Neuro-pathol Exp Neurol 45: 647–664.

Grimaldi M, Scrima M, Esposito C, Vitiello G, Ramunno A,Limongelli V, D’Errico G, Novellino E, D’Ursi AM.2010. Membrane charge dependent states of theb-amyloid fragment Ab (16–35) with differentlycharged micelle aggregates. Biochim Biophys Acta 1798:660–671.

Haass C, Selkoe DJ. 2007. Soluble protein oligomers in neu-rodegeneration: Lessons from the Alzheimer’s amyloidb-peptide. Nat Rev Mol Cell Biol 8: 101–112.

� Haass C, Kaether C, Sisodia S, Thinakaran G. 2011. Traffick-ing and proteolytic processing of APP. Cold Spring HarbPerspect Med doi: 10.1101/cshperspect.a006270.

Haeffner F, Barnham KJ, Bush AI, Brinck T. 2010. Genera-tion of soluble oligomeric b-amyloid species via coppercatalyzed oxidation with implications for Alzheimer’sdisease: A DFT study. J Mol Model 16: 1103–1108.

Hamaguchi T, Ono K, Murase A, Yamada M. 2009. Phenoliccompounds prevent Alzheimer’s pathology through dif-ferent effects on the amyloid-b aggregation pathway.Am J Pathol 175: 2557–2565.

Hamley IW, Nutt DR, Brown GD, Miravet JF, Escuder B,Rodriguez-Llansola F. 2010. Influence of the solvent onthe self-assembly of a modified amyloid beta peptidefragment. II. NMR and computer simulation investiga-tion. J Phys Chem B 114: 940–951.

Harper JD, Wong SS, Lieber CM., Lansbury PT Jr. 1997.Observation of metastable Ab amyloid protofibrils byatomic force microscopy. Chem Biol 4: 119–125.

Hawkes CA, Deng LH, Shaw JE, Nitz M, McLaurin J. 2010.Small moleculeb-amyloid inhibitors that stabilize proto-fibrillar structures in vitro improve cognition and pathol-ogy in a mouse model of Alzheimer’s disease. Eur JNeurosci 31: 203–213.

Hellstrand E, Sparr E, Linse S. 2010. Retardation of Ab fibrilformation by phospholipid vesicles depends on mem-brane phase behavior. Biophys J 98: 2206–2214.

� Holtzman D, Herz J, Bu Guojun. 2011. Apolipoprotein Eand apolipoprotein E receptors: Normal biology androles in Alzheimer disease. Cold Spring Harb PerspectMed doi: 10.1101/cshperspect.a006312.

Horn AH, Sticht H. 2010. Amyloid-b42 oligomer structuresfrom fibrils: A systematic molecular dynamics study. JPhys Chem B 114: 2219–2226.

Hsiao K, Chapman P, Nilsen S, Ekman C, Harigaya Y, Youn-kin S, Yang F, Cole G. 1996. Correlative memory deficits,Ab elevation, and amyloid plaques in transgenic mice.Science 274: 99–102.

Hu NW, Klyubin I, Anwy R, Rowan MJ. 2009. GluN2Bsubunit-containing NMDA receptor antagonists preventAb-mediated synaptic plasticity disruption in vivo. ProcNatl Acad Sci 106: 20504–20509.

Hureau C, Balland V, Coppel Y, Solari PL, Fonda E, FallerP. 2009a. Importance of dynamical processes in the coor-dination chemistry and redox conversion of copperamyloid-b complexes. J Biol Inorg Chem 14: 995–1000.

Hureau C, Coppel Y, Dorlet P, Solari PL, Sayen S, GuillonE, Sabater L, Faller P. 2009b. Deprotonation of theAsp1-Ala2 peptide bond induces modification of thedynamic copper(II) environment in the amyloid-b pep-tide near physiological pH. Angew Chem Int Ed Engl 48:9522–9525.

Jiang D, Li X, Williams R, Patel S, Men L, Wang Y, Zhou F.2009a. Ternary complexes of iron, amyloid-b, and nitri-lotriacetic acid: Binding affinities, redox properties, andrelevance to iron-induced oxidative stress in Alzheimer’sdisease. Biochemistry 48: 7939–7947.

Jiang DL, Dinh KL, Ruthenburg TC, Zhang Y, Su L, Land DP,Zhou FM. 2009b. A kinetic model for b-amyloid adsorp-tion at the air/solution interface and its implication tothe b-amyloid aggregation process. J Phys Chem B 113:3160–3168.

Jiang DL, Li XJ, Liu L, Yagnik GB, Zhou FM. 2010. Reactionrates and mechanism of the ascorbic acid oxidation bymolecular oxygen facilitated by Cu(II)-containing amy-loid-b complexes and aggregates. J Phys Chem B 114:4896–4903.

Jin M, Shepardson N, Yang T, Walsh D, Selkoe D. 2011. Solu-ble amyloid b-protein dimers isolated from Alzheimercortex directly induce Tau hyperphosphorylation andneuritic degeneration. Proc Natl Acad Sci 108: 5819–5824.

� Johnson KA, Fox NC, Sperling RA, Klunk WE. 2011. Brainimaging in Alzheimer disease. Cold Spring Harb PerspectMed doi: 10.1101/cshperspect.a006213.

Jun S, Gillespie JR, Shin BK, Saxena S. 2009. The secondCu(II)-binding site in a proton-rich environment inter-feres with the aggregation of amyloid-b(1–40) into amy-loid fibrils. Biochemistry 48: 10724–10732.

Kaether C, Schmitt S, Willem M, Haass C. 2006. Amyloidprecursor protein and Notch intracellular domains aregenerated after transport of their precursors to the cellsurface. Traffic 7: 408–415.

Kajava AV, Baxa U, Steven AC. 2010. b arcades: Recurringmotifs in naturally occurring and disease-related amyloidfibrils. FASEB J 24: 1311–1319.

Kang J, Lemaire H-G, Unterbeck A, Salbaum JM, MastersCL, Grzeschik K-H, Multhaup G, Beyreuther K, Muller-Hill B. 1987. The precursor of Alzheimer’s disease



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



amyloid A4 protein resembles a cell-surface receptor.Nature 325: 733–736.

Kawarabayashi T, Younkin LH, Saido TC, Shoji M, Ashe KH,Younkin SG. 2001. Age-dependent changes in brain, CSF,and plasma amyloid b protein in the Tg2576 transgenicmouse model of Alzheimer’s disease. J Neurosci 21:372–381.

Kawasaki K, Ogiwara N, Sugano M, Okumura N, YamauchiK. 2009. Sialic acid moiety of apolipoprotein E and itsimpact on the formation of lipoprotein particles inhuman cerebrospinal fluid. Clin Chim Acta 402: 61–66.

Kayed R, Pensalfini A, Margol L, Sokolov Y, Sarsoza F, HeadE, Hall J, Glabe C. 2009. Annular protofibrils are astructurally and functionally distinct type of amyloidoligomer. J Biol Chem 284: 4230–4237.

Kirschner DA, Inouye H, Duffy LK, Sinclair A, Lind M,Selkoe DJ. 1987. Synthetic peptide homologous to b pro-tein from Alzheimer disease forms amyloid-like fibrils invitro. Proc Natl Acad Sci 84: 6953–6957.

Koffie RM, Meyer-Luehmann M, Hashimoto T, Adams KW,Mielke ML, Garcia-Alloza M, Micheva KD, Smith SJ,Kim ML, Lee VM, et al. 2009. Oligomeric amyloid b

associates with postsynaptic densities and correlateswith excitatory synapse loss near senile plaques. ProcNatl Acad Sci 106: 4012–4017.

Kotarek JA, Moss MA. 2010. Impact of phospholipid bilayersaturation on amyloid-b protein aggregation intermedi-ate growth: A quartz crystal microbalance analysis. AnalBiochem 399: 30–38.

Ladiwala AR, Lin JC, Bale SS, Marcelino-Cruz AM, Bhatta-charya M, Dordick JS, Tessier PM. 2010. Resveratrolselectively remodels soluble oligomers and fibrils ofamyloid Ab into off-pathway conformers. J Biol Chem285: 24228–24237.

� LaFerla F, Duff K. 2011. Animal models of Alzheimerdisease. Cold Spring Harb Perspect Med doi: 10.1101/cshperspect.a006320.

Lambert MP, Barlow AK, Chromy BA, Edwards C, Freed R,Iosatos M, Morgan TE, Rozovsky I, Trommer B, Viola KL,et al. 1998. Diffusible, nonfribrillar ligands derived fromAb1 – 42 are potent central nervous system neurotoxins.Proc Natl Acad Sci 95: 6448–6453.

Lauren J, Gimbel DA, Nygaard HB, Gilbert JW, StrittmatterSM. 2009. Cellular prion protein mediates impairment ofsynaptic plasticity by amyloid-b oligomers. Nature 457:1128–1132.

Lemkul JA Bevan DR. 2009. Perturbation of membranes bythe amyloid b-peptide—a molecular dynamics study.FEBS J 276: 3060–3075.

Lesne S, Koh MT, Kotilinek L, Kayed R, Glabe CG, Yang A,Gallagher M, Ashe KH. 2006. A specific amyloid-b pro-tein assembly in the brain impairs memory. Nature 440:352–357.

Lesne S, Sherman MA, Handoka MA, Schneider JA, BennettDA, Ashe KH. 2009. Distinct brain Ab oligomers areassociated with different stages of Alzheimer’s disease.Soc Neurosci (Abstr 62720).

Li S, Hong S, Shepardson NE, Walsh DM, Shankar GM, Sel-koe D. 2009. Soluble oligomers of amyloid b proteinfacilitate hippocampal long-term depression by disrupt-ing neuronal glutamate uptake. Neuron 62: 788–801.

Li H, Monien BH, Fradinger EA, Urbanc B, Bitan G. 2010.Biophysical characterization of Ab42 C-terminal frag-ments: Inhibitors of Ab42 neurotoxicity. Biochemistry49: 1259–1267.

Liu L, Zhang L, Mao X, Niu L, Yang Y, Wang C. 2009a.Chaperon-mediated single molecular approach towardmodulating Ab peptide aggregation. Nano Lett 9:4066–4072.

Liu Q, Huang Y, Xue FQ, Simard A, DeChon J, Li G, ZhangJL, Lucero L, Wang M, Sierks M, et al. 2009b. A novel nic-otinic acetylcholine receptor subtype in basal gorebraincholinergic neurons with high sensitivity to amyloid pep-tides. J Neurosci 29: 918–929.

Lui JK, Laws SM, Li QX, Villemagne VL, Ames D, Brown B,Bush AI, De Ruyck K, Dromey J, Ellis KA, et al. 2010a.Plasma amyloid-b as a biomarker in Alzheimer’s disease:The AIBL study of aging. J Alzheimers Dis 20: 1233–1242.

Liu RQ, Zhou QH, Ji SR, Zhou Q, Feng D, Wu Y, Sui SF.2010b. Membrane localization of b-amyloid 1–42 inlysosomes: A possible mechanism for lysosome labiliza-tion. J Biol Chem 285: 19986–19996.

Lulevich V, Zimmer CC, Hong HS, Jin LW, Liu GY. 2010.Single-cell mechanics provides a sensitive and quantita-tive means for probing amyloid-b peptide and neuronalcell interactions. Proc Natl Acad Sci 107: 13872–13877.

Ma XJ, Liu L, Mao XB, Niu L, Deng K, Wu WH, Li YM, YangYL, Wang C. 2009. Amyloid b (1–42) folding multiplic-ity and single-molecule binding behavior studied withSTM. J Mol Biol 388: 894–901.

� Mandelkow E-M, Mandelkow E. 2011. Biochemistry andcell biology of Tau protein in neurofibrillary degenera-tion. Cold Spring Harb Perspect Med doi: 10.1101/cshperspect.a006247.

Mao YL, Shang ZG, Imai Y, Hoshino T, Tero R, Tanaka M,Yamamoto N, Yanagisawa K, Urisu T. 2010. Surface-induced phase separation of a sphingomyelin/choles-terol/ganglioside GM1-planar bilayer on mica surfacesand microdomain molecular conformation that acceler-ates Ab oligomerization. Biochim Biophys Acta 1798:1090–1099.

Masters CL, Simms G, Weinman NA, Multhaup G, McDon-ald BL, Beyreuther K. 1985. Amyloid plaque core proteinin Alzheimer disease and Down syndrome. Proc NatlAcad Sci 82: 4245–4249.

Masuda Y, Uemura S, Ohashi R, Nakanishi A, Takegoshi K,Shimizu T, Shirasawa T, Irie K. 2009. Identification ofphysiological and toxic conformations in Ab 42 aggre-gates. Chembiochem 10: 287–295.

McDonald JM, Savva GM, Brayne C, Welzel AT, Forster G,Shankar GM, Selkoe DJ, Ince PG, Walsh DM, MedicalResearch Council Cognitive Function and Aging Study.2010. The presence of sodium dodecyl sulphate-stableAb dimers is strongly associated with Alzheimer-typedementia. Brain 133: 1328–1341.

McLean CA, Cherny RA, Fraser FW, Fuller SJ, Smith MJ,Beyreuther K, Bush AI, Masters CL. 1999. Soluble poolof Ab amyloid as a determinant of severity of neuro-degeneration in Alzheimer’s disease. Ann Neurol 46:860–866.

Meyer-Luehmann M, Spires-Jones TL, Prada C, Garcia-Alloza M, de Calignon A, Rozkalne A, Koenigsknecht-Talboo J, Holtzman DM, Bacskai BJ, Hyman BT. 2008.



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



Rapid appearance and local toxicity of amyloid-bplaques in a mouse model of Alzheimer’s disease. Nature451: 720–724.

Miller Y, Ma BY, Nussinov R. 2009. Polymorphism of Alz-heimer’s Ab(17–42) (p3) oligomers: The importanceof the turn location and its conformation. Biophys J 97:1168–1177.

Miller Y, Ma B, Nussinov R. 2010. Zinc ions promote Alz-heimer Ab aggregation via population shift of poly-morphic states. Proc Natl Acad Sci 107: 9490–9495.

Miyashita N, Straub JE, Thirumalai D. 2009. Structures ofb-amyloid peptide 1–40, 1–42, and 1–55—the 672–726 fragment of APP-in a membrane environment withimplications for interactions with gamma-secretase. JAm Chem Soc 131: 17843–17852.

Moore BD, Rangachari V, Tay WM, Milkovic NM, Rose-nberry TL. 2009. Biophysical analyses of syntheticamyloid-b(1–42) aggregates before and after covalentcross-linking. Implications for deducing the structureof endogenous amyloid-b oligomers. Biochemistry 48:11796–11806.

Mori H, Takio K, Ogawara M, Selkoe DJ. 1992. Mass spec-trometry of purified amyloid b protein in Alzheimer’sdisease. J Biol Chem 267: 17082–17086.

Morinaga A, Hasegawa K, Nomura R, Ookoshi T, Ozawa D,Goto Y, Yamada M, Naiki H. 2010. Critical role of inter-faces and agitation on the nucleation of Ab amyloidfibrils at low concentrations of Ab monomers. BiochimBiophy Acta 1804: 986–995.

Morita M, Vestergaard M, Hamada T, Takagi M. 2010. Real-time observation of model membrane dynamics inducedby Alzheimer’s amyloid beta. Biophys Chem 147: 81–86.

� Mucke L, Selkoe D. 2011. Neurotoxicity of amyloid b-pro-tein: Synaptic and network dysfunction. Cold SpringHarb Perspect Med doi: 10.1101/cshperspect.a006338.

Murray MM, Bernstein SL, Nyugen V, Condron MM,Teplow DB, Bowers MT. 2009a. Amyloid b protein:Ab40 inhibits Ab42 oligomerization. J Am Chem Soc131: 6316–6317.

Murray MM, Krone MG, Bernstein SL, Baumketner A, Con-dron MM, Lazo ND, Teplow DB, Wyttenbach T, Shea JE,Bowers MT. 2009b. Amyloid b-protein: Experiment andtheory on the 21–30 fragment. J Phys Chem B 113:6041–6046.

Nakazawa Y, Suzuki Y, Williamson MP, Saito H, Asakura T.2009. The interaction of amyloid Ab(1–40) with lipidbilayers and ganglioside as studied by 31P solid-stateNMR. Chem Phys Lipids 158: 54–60.

Negureanu L, Baumketner A. 2009. Microscopic factors thatcontrolb-sheet registry in amyloid fibrils formed by frag-ment 11–25 of amyloid b peptide: Insights from com-puter simulations. J Mol Biol 389: 921–937.

Nerelius C, Sandegren A, Sargsyan H, Raunak R, Leijon-marck H, Chatterjee U, Fisahn A, Imarisio S, LomasDA, Crowther DC, et al. 2009. a-Helix targeting reducesamyloid-b peptide toxicity. Proc Natl Acad Sci 106:9191–9196.

Noguchi A, Matsumura S, Dezawa M, Tada M, Yanazawa M,Ito A, Akioka M, Kikuchi S, Sato M, Ideno S, et al.2009. Isolation and characterization of patient-derived,toxic, high mass amyloid b-protein (Ab) assembly

from Alzheimer disease brains. J Biol Chem 284:32895–32905.

O’Nuallain B, Freir DB, Nicoll AJ, Risse E, Ferguson N,Herron CE, Collinge J, Walsh DM. 2010. Amyloid b-pro-tein dimers rapidly form stable synaptotoxic protofibrils.J Neurosci 30: 14411–14419.

Ogawa M, Tsukuda M, Yamaguchi T, Ikeda K, Okada T, YanoY, Hoshino M, Matsuzaki K. 2011. Ganglioside-mediatedaggregation of amyloid b-proteins (Ab): Comparisonbetween Ab-(1–42) and Ab-(1–40). J Neurochem 116:851–857.

Ogi H, Hatanaka K, Fukunishi Y, Nagai H, Hirao M, Nish-iyama M. 2009. Aggregation behavior of amyloid b1 – 42

peptide studied using 55 MHz wireless-electrodelessquartz crystal microbalance—article no. 07GF01. Jpn JAppl Phys 48: doi: 10.1143/JJAP.48.07GF01.

Olofsson A, Lindhagen-Persson M, Vestling M, Sauer-Eriksson AE, Ohman A. 2009a. Quenched hydrogen/deuterium exchange NMR characterization of amyloid-bpeptide aggregates formed in the presence of Cu2þ orZn2þ. FEBS J 276: 4051–4060.

Olofsson A, Sauer-Eriksson AE, Ohman A. 2009b. Amyloidfibril dynamics revealed by combined hydrogen/deute-rium exchange and nuclear magnetic resonance. AnalBiochem 385: 374–376.

Ono K, Condron MM, Teplow DB. 2009. Structure-neuro-toxicity relationships of amyloid b-protein oligomers.Proc Natl Acad Sci 106: 14745–14750.

Ono K, Condron MM, Teplow DB. 2010. Effects of the Eng-lish (H6R) and Tottori (D7N) familial Alzheimer diseasemutations on amyloid b-protein assembly and toxicity. JBiol Chem 285: 23186–23197.

Paparcone R, Buehler MJ. 2009. Microscale structural modelof Alzheimer Ab(1–40) amyloid fibril—article no.243904. Appl Phys Lett 94: 43904–43904.

Paravastu AK, Qahwash I, Leapman RD, Meredith SC, TyckoR. 2009. Seeded growth of b-amyloid fibrils from Alz-heimer’s brain-derived fibrils produces a distinct fibrilstructure. Proc Natl Acad Sci 106: 7443–7448.

Paula-Lima AC, Tricerri MA, Brito-Moreira J, Bomfim TR,Oliveira FF, Magdesian MH, Grinberg LT, Panizzutti R,Ferreira ST. 2009. Human apolipoprotein A-I bindsamyloid-b and prevents A b-induced neurotoxicity. IntJ Biochem Cell Biol 41: 1361–1370.

Peralvarez-Marın A, Mateos L, Zhang C, Singh S, Cedazo-Minguez A, Visa N, Morozova-Roche L, Graslund A,Barth A. 2009. Influence of residue 22 on the folding,aggregation profile, and toxicity of the Alzheimer’s amy-loid b peptide. Biophys J 97: 277–285.

Perreau VM, Orchard S, Adlard PA, Bellingham SA, CappaiR, Ciccotosto GD, Cowie TF, Crouch PJ, Duce JA, Evin G,et al. 2010. A domain level interaction network of amy-loid precursor protein and Ab of Alzheimer’s disease.Proteomics 10: 2377–2395.

Perrone L, Mothes E, Vignes M, Mockel A, Figueroa C,Miquel MC, Maddelein ML, Faller P. 2009. Copper trans-fer from Cu-Ab to human serum albumin inhibits aggre-gation, radical production and reduces Ab toxicity.Chembiochem 11: 110–118.

Peters I, Igbavboa U, Schutt T, Haidari S, Hartig U, RoselloX, Bottner S, Copanaki E, Deller T, Kogel D, et al. 2009.The interaction of beta-amyloid protein with cellular



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



membranes stimulates its own production. Biochim Bio-phys Acta 1788: 964–972.

Pham E, Crews L, Ubhi K, Hansen L, Adame A, Cartier A,Salmon D, Galasko D, Michael S, Savas JN, et al. 2010.Progressive accumulation of amyloid-b oligomers in Alz-heimer’s disease and in amyloid precursor protein trans-genic mice is accompanied by selective alterations insynaptic scaffold proteins. FEBS J 277: 3051–3067.

Philipson O, Hammarstrom P, Nilsson KPR, Portelius E,Olofsson T, Ingelsson M, Hyman BT, Blennow K, Lann-felt L, Kalimo H, et al. 2009. A highly insoluble state ofAb similar to that of Alzheimer’s disease brain is foundin Arctic APP transgenic mice. Neurobiol Aging 30:1393–1405.

Picone P, Carrotta R, Montana G, Nobile MR, Biagio PLS,Di Carlo M. 2009. Ab oligomers and fibrillar aggregatesinduce different apoptotic pathways in LAN5 neuroblas-toma cell cultures. Biophys J 96: 4200–4211.

Pitt J, Roth W, Lacor P, Smith AB, Blankenship M, Velasco P,De Felice F, Breslin P, Klein WL. 2009. Alzheimer’s-associated Ab oligomers show altered structure, immu-noreactivity and synaptotoxicity with low doses ofoleocanthal. Toxicol Appl Pharmacol 240: 189–197.

Qi-Takahara Y, Morishima-Kawashima M, Tanimura Y,Dolios G, Hirotani N, Horikoshi Y, Kametani F, MaedaM, Saido TC, Wang R, et al. 2005. Longer forms ofamyloid b protein: Implications for the mechanism ofintramembrane cleavage by g-secretase. J Neurosci 25:436–445.

Qiu L, Lewis A, Como J, Vaughn MW, Huang J, SomerharjuP, Virtanen J, Cheng KH. 2009. Cholesterol modulates theinteraction of b-amyloid peptide with lipid bilayers. Bio-phys J 96: 4299–4307.

Rajendran R, Minqin R, Ynsa MD, Casadesus G, Smith MA,Perry G, Halliwell B, Watt F. 2009. A novel approach to theidentification and quantitative elemental analysis of amy-loid deposits—insights into the pathology of Alzheimer’sdisease. Biochem Biophys Res Commun 382: 91–95.

Ramos I, Fabris D, Qi W, Fernandez EJ, Good TA. 2009.Kinetic study of b-amyloid residue accessibility usingreductive alkylation and mass spectrometry. BiotechnolBioeng 104: 181–192.

Ravault S, Flore C, Saurel O, Milon A, Brasseur R, Lins L.2009. Study of the specific lipid binding propertiesof Ab 11–22 fragment at endosomal pH. Langmuir 25:10948–10953.

Reddy G, Straub JE, Thirumalai D. 2009a. Influence of pre-formed Asp23-Lys28 salt bridge on the conformationalfluctuations of monomers and dimers of Ab peptideswith implications for rates of fibril formation. J PhysChem B 113: 1162–1172.

Reddy G, Straubb JE, Thirumalai D. 2009b. Dynamics oflocking of peptides onto growing amyloid fibrils. ProcNatl Acad Sci 106: 11948–11953.

Reinke AA, Seh HY, Gestwicki JE. 2009. A chemical screen-ing approach reveals that indole fluorescence is quenchedby pre-fibrillar but not fibrillar amyloid-b. Bioorg MedChem Lett 19: 4952–4957.

Relini A, Cavalleri O, Rolandi R, Gliozzi A. 2009. The two-fold aspect of the interplay of amyloidogenic proteinswith lipid membranes. Chem Phys Lipids 158: 1–9.

Riviere C, Delaunay JC, Immel F, Cullin C, Monti JP. 2009.The polyphenol piceid destabilizes preformed amyloidfibrils and oligomers in vitro: Hypothesis on possiblemolecular mechanisms. Neurochem Res 34: 1120–1128.

Rodrıguez-Rodrıguez C, Sanchez de Groot N, Rimola A,Alvarez-Larena A, Lloveras V, Vidal-Gancedo J, VenturaS, Vendrell J, Sodupe M, Gonzalez-Duarte P. 2009.Design, selection, and characterization of thioflavin-based intercalation compounds with metal chelatingproperties for application in Alzheimer’s disease. J AmChem Soc 131: 1436–1451.

Roher A, Wolfe D, Palutke M, KuKuruga D. 1986. Purifica-tion, ultrastructure, and chemical analyses of Alzheimerdisease amyloid plaque core protein. Proc Natl Acad Sci83: 2662–2666.

Roher AE, Lowenson JD, Clarke S, Wolkow C, Wang R, Cot-ter RJ, Reardon I, Zurcher-Neely HA, Heinrikson RL, BallMJ, et al. 1993. Structural alterations in the peptide back-bone of b-amyloid core protein may account for its dep-osition and stability in Alzheimer’s disease. J Biol Chem268: 3072–3083.

Roher AE, Esh CL, Kokjohn TA, Castano EM, Van VickleGD, Kalback WM, Patton RL, Luehrs DC, Daugs ID,Kuo YM, et al. 2009. Amyloid beta peptides in humanplasma and tissues and their significance for Alzheimer’sdisease. Alzheimers Dement 5: 18–29.

Ryan DA, Narrow WC, Federoff HJ, Bowers WJ. 2010. Animproved method for generating consistent solubleamyloid-beta oligomer preparations for in vitro neuro-toxicity studies. J Neurosci Methods 190: 171–179.

Rozga M, Kłoniecki M, Dadlez M, Bal W. 2010. A directdetermination of the dissociation constant for theCu(II) complex of amyloid b1–40 peptide. Chem ResToxicol 23: 336–340.

Sahoo B, Nag S, Sengupta P, Maiti S. 2009. On the stabilityof the soluble amyloid aggregates. Biophys J 97: 1454–1460.

� Saido T, Leissring MA. 2011. Proteolytic degradation ofamyloid b-protein. Cold Spring Harb Perspect Med doi:10.1101/cshperspect.a006379.

Saido TC, Iwatsubo T, Mann DMA, Shimada H, Ihara Y,Kawashima S. 1995. Dominant and differential deposi-tion of distinct b-amyloid peptide species, AbN3(p3), insenile plaques. Neuron 14: 457–466.

Sakono M, Zako T. 2010. Amyloid oligomers: Formationand toxicity of Ab oligomers. FEBS J 277: 1348–1358.

Salay LC, Qi W, Keshet B, Tamm LK, Fernandez EJ. 2009.Membrane interactions of a self-assembling modelpeptide that mimics the self-association, structure andtoxicity of Ab(1–40). Biochim Biophys Acta 1788:1714–1721.

Sanders HM, Lust R, Teller JK. 2009. Amyloid-beta peptideAb p3–42 affects early aggregation of full-length Ab1–42. Peptides 30: 849–854.

Sarell CJ, Syme CD, Rigby SEJ, Viles JH. 2009. Copper(II)binding to amyloid-b fibrils of Alzheimer’s diseasereveals a picomolar affinity: Stoichiometry and coordina-tion geometry are independent of Ab oligomeric form.Biochemistry 48: 4388–4402.

Sargaeva NP, Lin C, O’Connor PB. 2009. Identification ofaspartic and isoaspartic acid residues in amyloid b



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



peptides, including Ab1–42, using electron-ion reac-tions. Anal Chem 81: 9778–9786.

Schauerte JA, Wong PT, Wisser KC, Ding H, Steel DG, GafniA. 2010. Simultaneous single-molecule fluorescence andconductivity studies reveal distinct classes of Ab specieson lipid bilayers. Biochemistry 49: 3031–3039.

Schlenzig D, Manhart S, Cinar Y, Kleinschmidt M, Hause G,Willbold D, Funke SA, Schilling S, Demuth HU. 2009.Pyroglutamate formation influences solubility andamyloidogenicity of amyloid peptides. Biochemistry 48:7072–7078.

Schmidt M, Sachse C, Richter W, Xu C, Fandrich M,Grigorieff N. 2009. Comparison of Alzheimer Ab(1–40) and Ab(1–42) amyloid fibrils reveals similar protofi-lament structures. Proc Natl Acad Sci 106: 19813–19818.

Seifert F, Schulz K, Koch B, Manhart S, Demuth HU, Schil-ling S. 2009. Glutaminyl cyclases display significant cata-lytic proficiency for glutamyl substrates. Biochemistry 48:11831–11833.

Selkoe DJ. 1994. Cell biology of the amyloid b-proteinprecursor and the mechanism of Alzheimer’s disease.Ann Rev Cell Biol 10: 373–403.

Selkoe DJ, Abraham CR, Podlisny MB, Duffy LK. 1986. Iso-lation of low-molecular-weight proteins from amyloidplaque fibers in Alzheimer’s disease. J Neurochem 146:1820–1834.

� Serrano-Pozo A, Frosch MP, Masliah E, Hyman BT. 2011.Neuropathological alterations in Alzheimer disease.Cold Spring Harb Perspect Med doi: 10.1101/cshper-spect.a006189.

Sevalle J, Amoyel A, Robert P, Fournie-Zaluski MC, RoquesB, Checler F. 2009. Aminopeptidase A contributes to theN-terminal truncation of amyloid b-peptide. J Neuro-chem 109: 248–256.

Shankar GM, Bloodgood BL, Townsend M, Walsh DM,Selkoe DJ, Sabatini BL. 2007. Natural oligomers of theAlzheimer amyloid-b protein induce reversible synapseloss by modulating an NMDA-type glutamate recep-tor-dependent signaling pathway. J Neurosci 27: 2866–2875.

Shankar GM, Li S, Mehta TH, Garcia-Munoz A, ShepardsonNE, Smith I, Brett FM, Farrell MA, Rowan MJ, LemereCA, et al. 2008. Amyloid-b protein dimers isolateddirectly from Alzheimer’s brains impair synaptic plasti-city and memory. Nat Med 14: 837–842.

Shankar GM, Leissring MA, Adame A, Sun X, Spooner E,Masliah E, Selkoe DJ, Lemere CA, Walsh DM. 2009.Biochemical and immunohistochemical analysis of anAlzheimer’s disease mouse model reveals the presenceof multiple cerebral Ab assembly forms throughout life.Neurobiol Dis 36: 293–302.

Simakova O, Arispe NJ. 2007. The cell-selective neurotoxic-ity of the Alzheimer’s Ab peptide is determined by surfacephosphatidylserine and cytosolic ATP levels. Membranebinding is required for Ab toxicity. J Neurosci 27:13719–13729.

Smith DP, Ciccotosto GD, Tew DJ, Fodero-Tavoletti MT,Johanssen T, Masters CL, Barnham KJ, Cappai R.2007. Concentration dependent Cu2þ induced aggre-gation and dityrosine formation of the Alzheimer’sdisease amyloid-b peptide. Biochemistry 46: 2881–2891.

Smith NW, Annunziata O, Dzyuba SV. 2009. AmphotericinB interactions with soluble oligomers of amyloid Ab1–42 peptide. Bioorg Med Chem 17: 2366–2370.

Soderberg L, Bogdanovic N, Axelsson B, Winblad B, Nas-lund J, Tjernberg LO. 2006. Analysis of single Alzheimersolid plaque cores by laser capture microscopy and nano-electrospray/tandem mass spectrometry. Biochemistry45: 9849–9856.

Song HP, Ritz S, Knoll W, Sinner EK. 2009. Conformationand topology of amyloid b-protein adsorbed on a teth-ered artificial membrane probed by surface plasmonfield-enhanced fluorescence spectroscopy. J Struct Biol168: 117–124.

Stoltenberg M, Bush AI, Bach G, Smidt K, Larsen A, RungbyJ, Lund S, Doering P, Danscher G. 2007. Amyloid plaquesarise from zinc-enriched cortical layers in APP/PS1transgenic mice and are paradoxically enlarged with diet-ary zinc deficiency. Neuroscience 150: 357–369.

Streltsov VA, Varghese JN, Masters CL, Nuttall SD. 2011.Crystal structure of the amyloid-b p3 fragment providesa model for oligomer formation in Alzheimer’s disease. JNeurosci 31: 1419–1426.

Sun X, Wu WH, Liu Q, Chen MS, Yu YP, Ma Y, Zhao YF, LiYM. 2009. Hybrid peptides attenuate cytotoxicity ofb-amyloid by inhibiting its oligomerization: Implicationfrom solvent effects. Peptides 30: 1282–1287.

Sureshbabu N, Kirubagaran R, Thangarajah H, Malar EJP,Jayakumar R. 2010. Lipid-induced conformational tran-sition of amyloid b peptide fragments. J Mol Neurosci 41:368–382.

Takami M, Nagashima Y, Sano Y, Ishihara S, Morishima-Kawashima M, Funamoto S, Ihara Y. 2009. g-Secretase:Successive tripeptide and tetrapeptide release from thetransmembrane domain of b-carboxyl terminal frag-ment. J Neurosci 29: 13042–13052.

Takeda T, Klimov DK. 2009a. Probing the effect of amino-terminal truncation for Ab(1–40) peptides. J PhysChem B 113: 6692–6702.

Takeda T, Klimov DK. 2009b. Replica exchange simulationsof the thermodynamics of Ab fibril growth. Biophys J 96:442–452.

Takeda T, Klimov DK. 2009c. Side chain interactions canimpede amyloid fibril growth: Replica exchange simula-tions of Ab peptide mutant. J Phys Chem B 113:11848–11857.

Takeda T, Klimov DK. 2010. Computational backbonemutagenesis of Ab peptides: Probing the role of back-bone hydrogen bonds in aggregation. J Phys Chem B114: 4755–4762.

Talmard C, Yona RL, Faller P. 2009. Mechanism of zinc(II)-promoted amyloid formation: Zinc(II) binding facili-tates the transition from the partiallya-helical conformerto aggregates of amyloid-b protein(1–28). J Biol InorgChem 14: 449–455.

Taniguchi A, Sohma Y, Hirayama Y, Mukai H, Kimura T,Hayashi Y, Matsuzaki K, Kiso Y. 2009. “Click peptide”:pH-triggered in situ production and aggregation ofmonomer Ab 1–42. Chembiochem 10: 710–715.

Tomic JL, Pensalfini A, Head E, Glabe CG. 2009. Solublefibrillar oligomer levels are elevated in Alzheimer’sdisease brain and correlate with cognitive dysfunction.Neurobiol Dis 35: 352–358.



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



Tomidokoro Y, Rostagno A, Neubert TA, Lu Y, Rebeck GW,Frangione B, Greenberg SM, Ghiso J. 2010. Iowa variantof familial Alzheimer’s disease. Accumulation of post-translationally modified Ab D23N in parenchymal andcerebrovascular amyloid deposits. Am J Pathol 176:1841–1854.

Tomiyama T, Matsuyama S, Iso H, Umeda T, Takuma H,Ohnishi K, Ishibashi K, Teraoka R, Sakama N, YamashitaT, et al. 2010. A mouse model of amyloid b oligomers:Their contribution to synaptic alteration, abnormal tauphosphorylation, glial activation, and neuronal loss invivo. J Neurosci 30: 4845–4856.

Tougu V, Karafin A, Zovo K, Chung RS, Howells C, West AK,Palumaa P. 2009. Zn(II)- and Cu(II)-induced non-fibril-lar aggregates of amyloid-b (1–42) peptide are trans-formed to amyloid fibrils, both spontaneously andunder the influence of metal chelators. J Neurochem110: 1784–1795.

Tycko R, Sciarretta KL, Orgel J, Meredith SC. 2009. Evidencefor novel b-sheet structures in Iowa mutant b-amyloidfibrils. Biochemistry 48: 6072–6084.

Uranga RM, Giusto NM, Salvador GA. 2010. Effect of tran-sition metals in synaptic damage induced by amyloidbeta peptide. Neuroscience 170: 381–389..

Urbanc B, Betnel M, Cruz L, Bitan G, Teplow DB. 2010. Elu-cidation of amyloid b-protein oligomerization mecha-nisms: Discrete molecular dynamics study. J Am ChemSoc 132: 4266–4280.

Utsumi M, Yamaguchi Y, Sasakawa H, Yamamoto N, Yana-gisawa K, Kato K. 2009. Up-and-down topologicalmode of amyloid b-peptide lying on hydrophilic/hydro-phobic interface of ganglioside clusters. Glycoconj J 26:999–1006.

Villemagne VL, Perez KA, Pike KE, Kok WM, Rowe CC,White AR, Bourgeat P, Salvado O, Bedo J, Hutton CA,et al. 2010. Blood-borne amyloid-b dimer correlateswith clinical markers of Alzheimer’s disease. J Neurosci30: 6315–6322.

Walsh DM, Selkoe DJ. 2007. Ab oligomers—a decade of dis-covery. J Neurochem 101: 1172–1184.

Walsh DM, Lomakin A, Benedek GB, Maggio JE, CondronMM, Teplow DB. 1997. Amyloid b-protein fibrillogene-sis: Detection of a protofibrillar intermediate. J BiolChem 272: 22364–22374.

Walsh DM, Thulin E, Minogue AM, Gustavsson N, Pang E,Teplow DB, Linse S. 2009. A facile method for expressionand purification of the Alzheimer’s disease-associatedamyloid b-peptide. FEBS J 276: 1266–1281.

Wang QM, Zhao C, Zhao J, Wang JD, Yang JC, Yu X, Zhen J.2010. Comparative molecular dynamics study of Abadsorption on the self-assembled monolayers. Langmuir26: 3308–3316.

Wei GH, Jewett AI, Shea JE. 2010. Structural diversity ofdimers of the Alzheimer amyloid-b(25–35) peptideand polymorphism of the resulting fibrils. Phys ChemChem Phys 12: 3622–3629.

Weidemann A, Eggert S, Reinhard FB, Vogel M, Paliga K,Baier G, Masters CL, Beyreuther K, Evin G. 2002. A novel1-cleavage within the transmembrane domain of theAlzheimer amyloid precursor protein demonstrateshomology with Notch processing. Biochemistry 41:2825–2835.

Welander H, Franberg J, Graff C, Sundstrom E, Winblad B,Tjernberg LO. 2009. Ab 43 is more frequent than Ab 40 inamyloid plaque cores from Alzheimer disease brains. JNeurochem 110: 697–706.

Wirths O, Bethge T, Marcello A, Harmeier A, Jawhar S,Lucassen PJ, Multhaup G, Brody DL, Esparza T, IngelssonM, et al. 2010. Pyroglutamate Abeta pathology in APP/PS1KI mice, sporadic and familial Alzheimer’s diseasecases. J Neural Transm 117: 85–96.

Woltjer RL, Sonnen JA, Sokal I, Rung LG, Yang W, KjerulfJD, Klingert D, Johnson C, Rhew I, Tsuang D, et al.2009. Quantitation and mapping of cerebral detergent-insoluble proteins in the elderly. Brain Pathol 19:365–374.

Wu C, Murray MM, Bernstein SL, Condron MM, Bitan G,Shea JE, Bowers MT. 2009. The structure of Ab 42 C-terminal fragments probed by a combined experimentaland theoretical study. J Mol Biol 387: 492–501.

Wu C, Bowers MT, Shea JE. 2010a. Molecular structures ofquiescently grown and brain-derived polymorphic fibrilsof the Alzheimer amyloid Ab9 – 40 peptide: A comparisonto agitated fibrils. PLoS Comput Biol 6: e1000693. doi:10.1372/journal/pcbi.1000693.

Wu JW, Breydo L, Isas JM, Lee J, Kuznetsov YG, Langen R,Glabe C. 2010b. Fibrillar oligomers nucleate the oligo-merization of monomeric amyloid b but do not seedfibril formation. J Biol Chem 285: 6071–6079.

Xia WM, Yang T, Shankar G, Smith IM, Shen Y, Walsh DM,Selkoe DJ. 2009. A specific enzyme-linked immunosorb-ent assay for measuring b-amyloid protein oligomers inhuman plasma and brain tissue of patients with Alz-heimer disease. Arch Neurol 66: 190–199.

Xiao Z, Wedd AG. 2010. The challenges of determiningmetal-protein affinities. Nat Prod Rep 27: 768–789.

Yadav A, Sonker M. 2009. Perspectives in designing anti-aggregation agents as Alzheimer disease drugs. Euro JMed Chem 44: 3866–3873.

Yagi-Utsumi M, Kameda T, Yamaguchi Y, Kato K. 2010.NMR characterization of the interactions betweenlyso-GM1 aqueous micelles and amyloid-b. FEBS Lett584: 831–836.

Yamin G, Ruchala P, Teplow DB. 2009. A peptide hairpininhibitor of amyloid b-protein oligomerization andfibrillogenesis. Biochemistry 48: 11329–11331.

Yang C, Li JY, Li Y, Zhu XL. 2009a. The effect of solvents onthe conformations of Amyloid b-peptide (1–42) studiedby molecular dynamics simulation. J Mol Struct: THEO-CHEM 895: 1–8.

Yang C, Zhu XL, Li JY, Chen K. 2009b. Molecular dynamicssimulation study on conformational behavior of Ab(1–40) and Ab(1–42) in water and methanol. J Mol Struct:THEOCHEM 907: 51–56.

Yu LP, Edalji R, Harlan JE, Holzman TF, Lopez AP, Labkov-sky B, Hillen H, Barghorn S, Ebert U, Richardson PL,et al. 2009. Structural characterization of a solubleamyloid b-peptide oligomer. Biochemistry 48: 1870–1877.

Zhang A, Qi W, Good TA, Fernandez EJ. 2009a. Structuraldifferences between Ab(1–40) intermediate oligomersand fibrils elucidated by proteolytic fragmentation andhydrogen/deuterium exchange. Biophys J 96: 1091–1104.



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



Zhang JF, Hou L, Gao XP, Guo F, Jing W, Qi JS, Qiao JT. 2009b.Amyloid b-protein differentially affects NMDA receptor-and GABAA receptor-mediated currents in rat hippocam-pal CA1 neurons. Prog Natl Sci 19: 963–972.

Zhang L, Yu HX, Song CC, Lin XF, Chen B, Tan C, Cao GX,Wang ZW. 2009c. Expression, purification, and charac-terization of recombinant human b-amyloid42 peptidein Escherichia coli. Protein Expres Purif 64: 55–62.

Zhang R, Hu XY, Khant H, Ludtke SJ, Chiu W, SchmidMF, Frieden C, Lee JM. 2009d. Interprotofilament in-

teractions between Alzheimer’s Ab1 – 42 peptides in amy-loid fibrils revealed by cryoEM. Proc Natl Acad Sci 106:4653–4658.

Zhao JH, Liu HL, Liu YF, Lin HY, Fang HW, Ho Y, Tsai WB.2009. Molecular dynamics simulations to investigatethe aggregation behaviors of the Ab(17–42) oligomers.J Biomol Struct Dyn 26: 481–490.

Zheng J, Yu X, Wang J, Yang JC, Wang Q. 2010. Molecularmodeling of two distinct triangular oligomers in amyloidb-protein. J Phys Chem B 114: 463–470.



ww

w.p

ersp

ecti

vesi

nm

edic

ine.

org



published online February 21, 2012Cold Spring Harb Perspect Med Colin L. Masters and Dennis J. Selkoe Disease

-Protein and Amyloid Deposits in AlzheimerβBiochemistry of Amyloid

Subject Collection The Biology of Alzheimer Disease

Animal Models of Alzheimer DiseaseFrank M. LaFerla and Kim N. Green

Alzheimer Disease in 2020

Dennis J. SelkoeDavid M. Holtzman, Eckhard Mandelkow and

-Peptide Clearance in Alzheimer DiseaseβNeurovascular Dysfunction and Faulty Amyloid

ZlokovicAbhay P. Sagare, Robert D. Bell and Berislav V.

The Genetics of Alzheimer DiseaseRudolph E. Tanzi

-ProteinβTreatment Strategies Targeting Amyloid

PangalosDale Schenk, Guriqbal S. Basi and Menelas N.

Fluid Biomarkers in Alzheimer DiseaseKaj Blennow, Henrik Zetterberg and Anne M. Fagan

DiseaseLysosomal System in Alzheimer−Autophagic

Proteasome System and the−The Ubiquitin

Ralph NixonYasuo Ihara, Maho Morishima-Kawashima and

Epidemiology of Alzheimer DiseaseRichard Mayeux and Yaakov Stern

Network Dysfunction-Protein: Synaptic andβNeurotoxicity of Amyloid

Lennart Mucke and Dennis J. SelkoeNeurofibrillary DegenerationBiochemistry and Cell Biology of Tau Protein in

Eva-Maria Mandelkow and Eckhard Mandelkow-ProteinβProteolytic Degradation of Amyloid

Takaomi Saido and Malcolm A. Leissring Deposits in Alzheimer Disease-Protein and AmyloidβBiochemistry of Amyloid

Colin L. Masters and Dennis J. SelkoeBrain Imaging in Alzheimer Disease

al.Keith A. Johnson, Nick C. Fox, Reisa A. Sperling, et Disease

The Neuropsychological Profile of Alzheimer

SalmonSandra Weintraub, Alissa H. Wicklund and David P.

Pharmacologic Treatment for Alzheimer DiseaseSymptomatic and Nonamyloid/Tau Based

SchneiderPaul S. Aisen, Jeffrey Cummings and Lon S.

Normal Biology and Roles in Alzheimer DiseaseApolipoprotein E and Apolipoprotein E Receptors:

David M. Holtzman, Joachim Herz and Guojun Bu

http://perspectivesinmedicine.cshlp.org/cgi/collection/ For additional articles in this collection, see

Copyright © 2012 Cold Spring Harbor Laboratory Press; all rights reserved


http://perspectivesinmedicine.cshlp.org/cgi/collection/

http://perspectivesinmedicine.cshlp.org/cgi/collection/


Biochemistry of Amyloid b-Protein and Amyloid Deposits in...

Documents

Transcript of Biochemistry of Amyloid b-Protein and Amyloid Deposits in...