Assembly and Function of the Photosystem II Manganese Stabilizing Protein

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Photosystem II catalyzes O2 evolution and provides electrons that are used for sugar synthesis in photosynthesis. The O2-evolving reaction is catalyzed by 4 Mn atoms and requires a key protein subunit, manganese stabilizing protein, that controls Mn binding and rapid O2 evolution. This research project will characterize how manganese stabilizing protein's structure allows it to perform its role in O2 evolution. One set of experiments will identify amino acid sequences at the N-terminus of the protein that are essential for photosystem II binding, and that may also be required for Mn stability and rapid O2 production. A second research objective will further characterize manganese stabilizing protein's "natively unfolded" behavior in solution. The protein's unusual thermostability will be exploited as a probe to extend the characterization of its unusual solution structure and determine the extent to which the single -S-S- bond can be shown to be necessary for the thermostability of manganese stabilizing protein. Related experiments will determine whether solution structure changes in some mutant types of manganese stabilizing protein can be demonstrated to correlate with their assembly into photosystem II, and whether the integrity of the enzyme's Mn cluster affects this process. A third research project will explore the role of a highly conserved amino acid, arginine, that appears to be essential for manganese stabilizing protein's ability to promote the catalytic activity of the Mn cluster. These experiments will be coupled with analyses of structure and function of manganese stabilizing protein to discover why other changes in this amino acid residue produce unusual changes in manganese stabilizing protein activity without apparent changes in the protein's solution structure.