Previously Bio308

Hypotheses for molecular basis of bipolar disorder•Suggest problem lies in protein targetingHow are proteins targeted and delivered?

3 Stages: Budding, targeting/docking and fusion

How does a vesicle ‘know’ what components it should contain?

How does it ‘know’ which membrane it should go to?

How does it fuse when it gets there?

Budding

Fig 17-58

http://biology-animations.blogspot.com/2009/10/clathrin-animation.html

Coat Components

http://userpage.chemie.fu-berlin.de/biochemie/aghaucke/clath.jpg

ClathrinCOPICOPII

Identity determined by whatthe vesicle contains and it’s coat.

Budding IIER vesicle budding

Drin, G, and B. Antonny (2005) News and Views: Helices sculpt membrane. Nature vol: 437

Amino Acid Key

Highly hydrophobic

+ charged - charged

Other

Hydroxylated

Sar1p N-terminal helix

Sar1p-GTP form exposes helix that anchors protein to ER surface by‘floating’ with hydrophobic a.a. interacting with membrane core

Budding III

Drin, G, and B. Antonny (2005) News and Views: Helices sculpt membrane. Nature vol: 437

ER vesicle budding

Floating many Sar1p in top leaflet makes it ‘bigger’ than the bottom one.

Results --> bulge that can more easily interact with coat proteins.

Fission ER vesicle budding….fission

Ring of parallel helices at neck might aid fission.‘New’ data for ER; had seen a protein (epsin) help deform PM for clathrin coated vesicles.

May suggest that using a helix to deform membrane is common mechanism for budding/fission

Targeting/Docking:

http://dir2.nichd.nih.gov/nichd/cbmb/sob/in_vivo_dyn.html

What happens after budding?

How do vesicles dock with specific target membrane?

The SNARE hypothesis

Fig 17-59

V-SNARE

T-SNARE

Role of p115Role of Rab proteins

retrograde

Synaptic vesicle fusion

VAMP

SyntaxinSNAP 25

Synaptotagmin

Rab3a

Endocytosis

Endocytosis can be used to control the amount of a certaintype of protein found at the surface

Pinocytosis ‘problem’rate of pinocytosis internalizes 100% of PM per hour

?(How can this be?)

Maybe protein delivered correctly but problem lies in levels of recycling

Types of pinocytic vesicles

Clathrin-coated

Caveolae

Types of endocytosisFluid phase– soluble components ‘got caught’ in vesicle

Receptor-mediated– selected to be in vesicle

Select how?•Ligands bind receptors•Receptors cluster

Why do the receptors cluster and make a vesicle?•Receptors have signaling sequences•Signaling regions interact with adaptins•Adaptins recruit coats budding occurs

Separate: Recycle (R ) Degrade (L)

Endocytosis– then what? Endosomal sorting

Remove andDegrade (R & L)

Transcytose

Distinguishing between types

Similarities and differences between vesicles?

TransportExocyticEndocytic

How could you tell them apart experimentally?

Neurotransmitters are stored in and secreted from vesicles.Neurotransmitter receptors are delivered to

dendrite in vesicles.

Could sorting and targeting problems be at the root of bipolar disorder?

If sorting and targeting are the problems would you predict alteration of something like

the NT receptor, or a SNAREor of a protein like NSF, SNAP25?

Molecular Roads and Infrastructure

Bipolar disorder•Is it the cellular equivalent of ‘dead letter box’?

•Are cytoskeletal ‘problems’ a likely cause for for this disorder?

What are the components of the cytoskeletonand what do they do?