Structural Basis for Electron Transfer Between the BacterialReaction Center and Cytochrome c2 in Rhodobacter Sphaeroide studied by Site Directed Mutagenesis

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9304782 Okamura Photosynthetic bacteria convert light energy into chemical energy by photo-induced electron transfer reactions in a pigment protein complex called the reaction center (RC). The initial charge separation within the RC is coupled to electron transfer across the membrane by electron transfer from a mobile electron carrier, cytochrome c2. Important features of the reaction between the RC and cytochrome c2 are the high rate of electron transfer and also the molecular recognition of electron transfer partners. The structural basis for these two properties will be investigated by studying the effects of mutating the following types of residues: (1) Charged residues on the RC and cytochrome will be modified to investigate electrostatic interactions between the two redox partners. Complementary charge changes on the RC (negative to positive charged residues) and cytochrome (negative to positive charged residues) will be made to map out the specific ion pairing interactions in the cytochrome RC complex. (2) Uncharged residues on the RC surface near the cytochrome binding site will be mutated to residues having different molecular sizes and hydrophobicity. The pattern of changes in binding and electron transfer observed will be used to map out the binding interaction and possible pathways for electron transfer. %%% Biological systems derive much of their energy from electron transfer between proteins in biological membranes. Two major questions of electron transfer that are currently not understood are: How do electron donor and acceptor proteins recognize and bind to each other? and what is the pathway for electron transfer though proteins? The answers to both of these questions will be studied for the reaction between the bacterial reaction center and cytochrome c2, from the photosynthetic bacterium Rb. sphaeroides. ***