Directed Mutagenesis of a Photosystem II Extrinsic Protein

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9727777 Yocum The ability of photosystem II (PSII) to oxidize water to O2 requires the redox activity of a tetranuclear Mn cluster that is regulated by the presence of a 26.5 kDa extrinsic protein called Manganese Stabilizing Protein, or MSP. The structure and function of this protein will be probed using bacterial overexpression to produce site-directed mutants. Characterization of existing mutants shows that a disulfide bridge is not required for activity, that mutations affecting the N- and C-termini of MSP alter its ability to assemble with PSII, and that temperature-sensitive mutations that alter secondary structure can be induced to rebind to PSII. Building on these results, new experiments on MSP will focus on: 1. Effect of N- and C- terminal mutations on PSII binding and activity reconstitution; 2. Elucidating the mechanism by which a charge reversal mutation, R151D fails to restore high turnover rates in PSII; 3. Creating new mutations in efforts to provide new details about the effect of binding to PSII on MSP structure and activity, to determine whether engineered Cys mutations can provide new sites for covalent modification of MSP, and to attempt to identify MSP domains that are sensitive to Mn oxidation states. The ability of photosynthesis to produce atmospheric oxygen requires Manganese Stabilizing Protein. This project's goal is to understand how the protein facilitates oxygen evolution. Amino acids in the protein will be changed using molecular biological techniques. How these changes affect oxygen production will then be analyzed by examining mutated proteins to determine if their structures have been altered, and by assessing their ability to restore oxygen evolution. By comparing data from a number of modified versions of this protein, a model can be constructed that relates properties of Manganese Stabilizing Protein to those of the oxygen-evolving reaction.