Structural Basis for Electron Transfer between the Bacterial Reaction Center and Cytochrome C2 in Rhodobacter Sphaeroides

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OkamuraMCB 9974568The aim of this research is to determine the molecular basis for the electron transfer reaction between cytochrome c2 and the bacterial reaction center (RC). These studies will build upon recent advances in the x-ray co-crystal structure of the cytochrome c2/RC complex that show the cytochrome to be docked on the RC through a hydrophobic contact region forming a direct electron transfer pathway between heme and bacteriochlorophyll cofactors. The questions to be addressed concern the structure of the complex between the RC and cytochrome c2 and the mechanism of interprotein electron transfer. Site directed mutations on both RC and cytochrome will be constructed and the effects of these mutations on binding and rates of electron transfer will be determined. The effects of the mutations on the binding of the cytochrome will be used to give information about the relative importance of electrostatic and hydrophobic contributions. The effects of mutations on the collision rate of electron transfer will give information about the conformational dynamics involved in the protein association and electron transfer. These studies will also be extended to the effects on the electron transfer process in chromatophore membranes in order to explore the relative effects of the cytochrome RC interaction in modulating the overall efficiency of photosynthetic electron transfer. The membranes of photosynthetic bacteria contain the molecular machinery that permits the efficient conversion of light energy into chemical energy. The energy conversion requires a light induced charge separation in a protein called the reaction center, followed by rapid electron transfer through a chain of electron carriers that are arranged to do chemical work by pumping protons across the membrane. This research is aimed at investigating the structural basis for electron transfer to the light activated reaction center mediated by cytochrome c2. The reaction between cytochrome c2 and the RC in photosynthetic bacteria displays both a specificity in binding and high rate of interprotein electron transfer that are necessary to maintain a fast electron transfer through the electron transfer chain. These studies of the binding and electron transfer reactions between cytochrome c2 and the bacterial RC should provide the basis for understanding the energy conversion process in photosynthesis.