Lengths Energies and Time Scales in Photosynthesis Implications

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 manmade energy conversion systems?

Oxygenic Photosynthesis The best characterized Natural energy conversion scheme Carbon fixation Photosystem II

Oxygenic Photosynthesis The best characterized Natural energy conversion scheme Temporal Resolution < 0. 1 ps Spatial Resolution: 2 -3 Å

The fundamental Chemical transformation processes Light driven Proton pumping Electron transfer (Tunneling, Diffusion) 2 H+ NADP+ H+ NADPH 2 H+ 2 x 2 H+ We focus on the primary photosynthetic reactions

A simpler view • Energy and electron transfer rates between functional elements should be fast enough to: • Support the catalytic turnover rates • Exceed the rates of inherent relaxation processes and back -reactions PSII B 6 F PSI • Each transfer rate has a distinctive dependence on distance, and energy. Cartoon by Richard Walker, from “Energy Plants & Man” by David Walker

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 crosssections 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 Enzymes LH 2 FMO PCP PSI LH 1 PSII LHCII RC Protein 72% 86% 83% 73% 89% 86% 62% (B)Chl 18% 14% 4% 23% 10% 14% 30% s Carote 10% 13% 4% 1% 8% noids Total 28% 14% 17% 27% 11% 14% 38%

Different distance and energy dependence for electron and energy transfer Electron tunneling Energy transfer Electron Transfer ∝ 10^(-0. 6 r-3. 1⋅(ΔG+λ)2/λ) Energy Transfer ∝ (ro/r)6 Membrane Potential 0. 1 - 0. 01 s-1

Implications for the “natural leaf” Side view PSI τmax(Amax) Green Sulfur Bacteria Heliobacteria PSII Purple Bacteria o ΔG [V] rmax [Å] PSI 12 μs (100%) +0. 45 0 PSII 12 μs (18%) -0. 27 18 Bacterial 25 ms (9%) +0. 07 24

Conclusions 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

However. . .

Implications for the “artificial leaf” ΔG = -0. 35 e. V λ = 0. 7 e. V 15. 5 Å 10. 6 Å 6. 1 Å 360 ps 180 ns 160 μs Energy transfer 10 ps 31 Å Distances must be controlled with sub nanometric accuracy

Concentration Quenching LHI-RC PSII PSI LHCIPSI

Chlorophyll Proteins LH 1 LH 2 PSI FMO LHC 2 PSII

Non-natural Systems • Rudimentary • Iterative • High structures design resolution structural information, only a bonus

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

Iron-Sulfur Clusters Proteins Complex I Bacterial Ferredoxin PSI Complex II Fe 2 Hydrogenase Ni. Fe Hydrogenase

Incorporating an Iron-Sulfur Cluster Center into the Hydrophobic Core of a Coiled Coil Protein Grzyb et al. BBA-Bioenergetics 1797 (2010) pp. 406 -

CCIS 1: Coiled Coil Iron Sulfur Protein I CCIS 1 All C->S Grzyb et al. BBA-Bioenergetics 1797 (2010) pp. 406 -

Ferredoxin Loop Interface to CCIS 1 CCIS-Fdx

De Novo Design of a Water Soluble Analog of Transmembranal Chlorophyll Proteins

Chlorophyll Proteins LH 1 LH 2 PSI FMO LHC 2 PSII

Multi-Chl Protein by Redesign of a Common Natural Motif PSII

Converting a Transmembranal Motif into a Water-Soluble Protein Step 1: Identify External Residues Step 2: Build Connecting Loop Step 3: Replace Hydrophobic Residues with Hydrophylic Ones

Water-Soluble BChls Bacteriochlorophyll a H Mg Zn H 132 -OHBacteriochlorophyll a 132 -OHBacteriopheophorbide a HO H Phytyl HO Zn. BChlide 132 -OH-Zn. Bacteriochlorophyllide a

PS 3 H 2: Photo. System 3 Helix Protein 2 Dimers Monomers PS 3 H 2

PS 3 H 2: Photo. System 3 Helix Protein 2 PS 3 H 2 H 62 A

Conclusions Two 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 Chlbinding motif These 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 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 Protein de novo design is a useful way of constructing the relays that will provide building blocks for energy conversion systems

Acknowledgments Noy Group • Ilit Cohen-Ofri • Joanna Grzyb • Jebasingh Tennyson • Iris Margalit Wolfgang Lubitz • Maurice van Gastel Vik Nanda Zx ab Ron Koder Collaboration Avigdor Scherz Zx • Alex Brandis ab • Oksana Shlyk-Kerner Noam Adir, Technion Lev Weiner, Daniella Goldfarb Israel Proteomics Center • Shira Albeck, Yoav Peleg, Tamar Unger Les Dutton • Chris Moser • Funding $Human Frontiers Science Program Organization