lengths, energies and time scales in photosynthesis. implications for artificial systems

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 drivenElectron transfer(Tunneling, Diffusion)

Proton pumpingChemical 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

QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.

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 LHCI

ILH1-RC

Protein

72% 86% 83% 73% 89% 86% 62%

(B)Chls

18% 14% 4% 23% 10% 14% 30%

Carotenoid

s10% - 13% 4% 1% - 8%

Total 28% 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]

PSI 12 μs (100%) +0.45 0

PSII 12 μs (18%) -0.27 18

Bacterial

25 ms (9%) +0.07 24

Purple Bacteria

PSIIPSI Heliobacteria

Green Sulfur Bacteria

Side view

ConclusionsThe 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

However...

Implications for the “artificial leaf”

6.1 Å

10.6 Å15.5 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

302520151050 Distance [Å]

40

30

20

10

0

Counts

302520151050 Distance [Å]

25

20

15

10

5

0

Counts

302520151050 Distance [Å]

20

15

10

5

0

Counts

50403020100 Distance [Å]

LHI-RC PSII

LHCI-PSIPSI

LH2LH1

FMO LHC2 PSII

PSI

Chlorophyll ProteinsPSI

•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

PSIBacterial FerredoxinComplex I

Complex II Fe2 Hydrogenase NiFe 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 ICCIS1

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

LH2LH1

FMO LHC2 PSII

PSI

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 2PS3H2

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 Institute

New 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