Pathways of electron and proton flow in a transmembrane, photon-driven quinone reductase/translocase supercomplex of proteins

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This proposed research is aimed at interactions between components of cellular processes, on a scale intermediate between cytoplasmic membrane fragments and the atoms comprising individual protein components of membrane-bound catalysts. We are studying the structure and function of domains of interaction within and between transmembrane protein complexes, with a focus on what we call the RC/LH1/PufX supercomplex. This photosynthetic pigment-protein supercomplex is composed of the reaction center (RC) complex, the light-harvesting 1 (LH1) complex, and the PufX protein key component. The primary goal is to elucidate pathways of electron and proton flow in the RC/LH1/PufX supercomplex, which functions as a photon- (light-) driven quinone reductase/translocase in a model organism, the bacterium Rhodobacter sphaeroides. Other goals are to determine how the supercomplex assembles and translocates quinones, and the biogenesis of the RC-specific cofactor, bacteriopheophytin. We also wish to solve a high-resolution crystal structure of an RC/LH1/PufX supercomplex to provide 3-D insights into the location and function of the PufX protein, and to facilitate the design and interpretation of site-directed mutagenesis experiments to test functional hypotheses arising from the structural data. This research is important to advance fundamental knowledge of the catalysis of protein-catalyzed electrochemical reactions, especially in relation to applications using biological material to generate electricity. Thus this research is of interest not only to scientists, but also the general public who could benefit from applications to harvest solar energy. It is anticipated that this research will advance the understanding of the assembly and interaction of membrane protein supercomplexes in general, with the additional potential of providing a foundation for the engineering of photovoltaic devices based on biological systems. Improved photovoltaic devices would benefit Canada by allowing increased use of a clean, essentially limitless energy source.