The dynamic structure, function and regulation of Photosystem II in photosynthesis

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The sun powers almost all life on earth via photosynthesis. Solar energy conversion is one of the few renewable ways to produce clean energy to meet the increasing demands of modern civilization. Our long term research objectives are twofold; understand the mechanisms of photosynthetic energy conversion at the molecular level and construct feasible artificial photosynthetic systems mimicking the most crucial steps. The natural photosystems responsible for light capture and energy conversion are complex assemblies of proteins holding pigments and cofactors together to create biological nano-scale solar energy converters. The proteins are more than mere scaffolding: they increase light capture by tuning the colours of the pigments, facilitate photochemistry by controlling the cofactors and are intimately involved in all photosystem reactions. Photosystem II (PSII) catalyses the most energetically important reaction on earth by using light energy to split water into the oxygen we breathe, and electrons and protons used to store energy in chemical form. We seek to understand how the protein components of PSII optimize the efficiency and regulation of light absorption and how they facilitate the water-splitting reaction. It is not easy to experimentally isolate individual parts of the protein involved in specific reactions. We use molecular dynamics computer simulations to help us "see" the protein. Our simulations allow us to follow the individual motions and interactions of over 300,000 atoms in PSII and are used with a wide array of experimental data to understand how PSII works at a molecular level. We are also developing an artificial photosynthetic system that incorporates a novel pigment into a robust water soluble iron storage protein, bacterioferritin. Our unique protein based system is photochemically active, emulates the first steps of the water-splitting reaction in PSII and has a high enough oxidizing potential to ultimately oxidize water. We propose to continue our development of the bacterioferritin photosystem with the ultimate goal of light driven water-splitting and incorporation into a viable energy storage system.