Elucidation of the self-repair mechanism of the light-driven water oxidation in photosystem II (PSII): Crystallization of the Mn-depleted PSII and its structural/functional analysis

Photosystem II (PSII) of oxygenic photosynthesis has the unique capability of utilizing visible light to oxidize water at the Mn4CaO5-cluster (the water oxidizing complex, WOC). Important progress in elucidating the molecular structure of the WOC has been achieved in the last ten years involving protein crystallography on the cyanobacterial PSII core complex (PSIIcc) and X-ray absorption spectroscopy, providing a solid basis for the analysis of the molecular mechanisms of water oxidation that are still poorly understood. Our first research aim in this proposal is to improve the quality of our crystals of monomeric and dimeric PSIIcc to at least 2.0 Å resolution. These structural data will be combined with different spectroscopic measurements on single PSIIcc crystals (EPR, EXAFS, XAS) for understanding the catalytic process itself. The second central topic in our project is the elucidation of the self-repair mechanism of the light-driven water oxidation in PSIIcc that may be essential also in artificial water oxidation catalysts. For this reason our interest is the crystallization of PSIIcc with an assembly intermediate of the WOC as well as Mn-depleted PSIIcc. These structural data will give insight into structural changes accompanying the repair cycle.