Post on 18-Dec-2015
Lengths, Energies and Time Scales in
Photosynthesis.Implications for Artificial
Systems. Dror Noy
Plant Sciences Dept.Weizmann Institute of Science
Rehovot, Israel
How does Nature exploits fundamental physical
principles in the construction of biological
energy conversion systems?
How can we implement the Natural strategies in
man-made energy conversion systems?
Oxygenic PhotosynthesisThe best characterized
Natural energy conversion scheme
Carbon fixation
Photosystem II
Spatial Resolution: 2-3 ÅTemporal Resolution < 0.1 ps
Oxygenic PhotosynthesisThe best characterized
Natural energy conversion scheme
The fundamental processes
Light drivenLight drivenElectron transfer(Tunneling, Diffusion)
Proton pumping
Chemical transformation
2 x 2H+
2H+
NADP+ NADPHH+
2H+
We focus on the primary photosynthetic reactions because these are by-far the best characterized and probably the best understood biological energy conversion processes
We focus on the primary photosynthetic reactions because these are by-far the best characterized and probably the best understood biological energy conversion processes
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PSII PSI
A simpler view
Cartoon by Richard Walker, from “Energy Plants & Man” by David Walker
B6F
• Support the catalytic turnover rates
• Exceed the rates of inherent relaxation processes and back-reactions
• Energy and electron transfer rates between functional elements should be fast enough to:
• Each transfer rate has a distinctive dependence ondistance, and energy.
Time (Rates), Length, and
Energy Scales
Membrane Potential 0.1 - 0.01 s-1
Length and Energy Scales of Light Absorption
• Given an incoming photon flux, the absorption cross-sections defines a length scale
• The driving force of the redox reactions define an energy scale by limiting the number of useful photons
A typical organic chromophore can support up to 5 catalytic cycles/second
Pigment Composition of Photosynthtetic
EnzymesLH2 FMO PCP PSI PSII
LHCII
LH1-RC
Protein
72%
86% 83% 73% 89% 86% 62%
(B)Chls
18%
14% 4% 23% 10% 14% 30%
Carotenoid
s
10%
- 13% 4% 1% - 8%
Total28%
14% 17% 27% 11% 14% 38%
Different distance and energy dependence for electron and
energy transfer
Membrane Potential 0.1 - 0.01 s-1
Electron tunneling
EnergytransferElectron Transfer ∝ 10^(-0.6r-3.1⋅(ΔG+λ)2/λ)
Energy Transfer ∝ (ro/r)6
Implications for the “natural leaf”
τmax
(Amax
) ΔGo [V] rmax
[Å]
PSI12 μs
(100%)+0.45 0
PSII12 μs (18%)
-0.27 18
Bacterial
25 ms (9%)
+0.07 24
Purple Bacteria
PSII
PSI HeliobacteriaGreen Sulfur Bacteria
Side view
Conclusions
The basic physics of the transfer processes allow for a large degree of
tolerance
The basic physics of the transfer processes allow for a large degree of
tolerance
In photosystems, natural selection favors robust design with the
predominant parameter being control over cofactor distances
In photosystems, natural selection favors robust design with the
predominant parameter being control over cofactor distances
However...
Implications for the “artificial leaf”
6.1 Å
10.6 Å
15.5 Å
160 μs180 ns
360 ps
31 Å
ΔG = -0.35 eVλ = 0.7 eV
Energy transfer 10 ps
Distances must be controlled with sub nanometric accuracy
Concentration Quenching
70
60
50
40
30
20
10
0
Counts
302520151050Distance [Å]
40
30
20
10
0
Counts
302520151050Distance [Å]
25
20
15
10
5
0
Counts
302520151050Distance [Å]
20
15
10
5
0
Counts
50403020100Distance [Å]
LHI-RC PSII
LHCI-PSI
PSI
LH2LH2LH1LH1
FMOFMO LHC2LHC2 PSIIPSII
PSI
Chlorophyll ProteinsPSIPSI
•Rudimentary structures
•Iterative design
•High resolution structural information, only a bonus
Non-natural Systems
De Novo Designed Protein Building
Blocks for Energy and Electron
Transfer Relays
Hybrid Modular Design
De Novo Design of a Non-Natural Fold for
an Iron-Sulfur Protein
PSIPSIBacterial FerredoxinBacterial FerredoxinComplex IComplex I
Complex IIComplex II Fe2 HydrogenaseFe2 Hydrogenase NiFe HydrogenaseNiFe Hydrogenase
Iron-Sulfur Clusters Proteins
Incorporating an Iron-Sulfur Cluster Center into the
Hydrophobic Core of a Coiled Coil Protein
Grzyb et al. BBA-Bioenergetics 1797 (2010) pp. 406-413
CCIS1:Coiled Coil Iron Sulfur
Protein I
CCIS1
All C->S
Grzyb et al. BBA-Bioenergetics 1797 (2010) pp. 406-413
Ferredoxin Loop Interface to CCIS
CCIS1
CCIS-Fdx
De Novo Design of a Water Soluble
Analog of Transmembranal
Chlorophyll Proteins
LH2LH2LH1LH1
FMOFMO LHC2LHC2 PSIIPSII
PSIPSI
PSI
Chlorophyll Proteins
PSIIPSI
Multi-Chl Protein by Redesign of a Common
Natural MotifPSI
Converting a Transmembranal Motif into a Water-Soluble
Protein
Step 1: Identify External ResiduesStep 2: Build Connecting LoopStep 3: Replace Hydrophobic Residues with Hydrophylic Ones
Phytyl
HO
Water-Soluble BChls
H
Mg
Bacteriochlorophyll a
132-OH-Bacteriochlorophyll a
HO
Zn
132-OH-Bacteriopheophorbide a
132-OH-Zn-Bacteriochlorophyllide aZnBChlide
H
H
PS3H2:PhotoSystem 3 Helix
Protein 2Dimers
Monomers
PS3H2
PS3H2:PhotoSystem 3 Helix
Protein 2
PS3H2
PS3H2H62A
ConclusionsTwo examples of designing de novo protein cofactor complexes were presented:•An iron-sulfur cluster with a non-natural fold•A multi-Chl binding protein that is a water-soluble analog of a highly conserved transmembranal Chl-binding motifThese examples demonstrate: •The viability of protein de novo design for making novel functional proteins•The effectivity of the iterative design approach in identifying and correcting design flaws
Conclusions
Protein de novo design is a useful way of constructing the relays that will provide building blocks for energy conversion systems
By focusing on simple and robust energy and electron transfer relays we can achieve functional variability by “mixing and matching” a few unique catalytic centers
• Funding$Human Frontiers
Science Program Organization
$Weizmann InstituteNew Scientists Center
Acknowledgments
Les Dutton•Chris Moser
Israel Proteomics Center• Shira Albeck,Yoav Peleg,Tamar Unger
Wolfgang Lubitz• Maurice van Gastel
CollaborationAvigdor Scherz• Alex Brandis• Oksana Shlyk-Kerner
Zxab
Noy Group•Ilit Cohen-Ofri•Joanna Grzyb•Jebasingh Tennyson•Iris Margalit
Zxab
Lev Weiner, Daniella Goldfarb
Ron Koder
Vik Nanda
Noam Adir, Technion