Cation pumping systems play important roles in many cellular processes such as cell growth, motility, and tumorigenesis. Despite their ubiquity and importance, the molecular mechanism for vectoral transport is not well understood. Bacteriorhodopsin provides a robust model system for cation transport. It is a membrane bound protein from Halobacterium salinarium that acts as a light-driven proton pump. From work done to date it is known that it comprises a bundle of seven alpha helices and a retinal chromophore bound by a Schiff base at Lys216. It is also know that the photocycle comprises at least five intermediates. The goal of this work is to define connectivities between functional groups involved in the transport pathway and to determine how these connectivities change during the photocycle. This will be accomplished by solid state NMR, using carbon and nitrogen detected two dimensional deuterium exchange. Starting with a set of model compounds, the details of the exchange spectra will be established. Then, the variations in the chromophore/residue connectivity will be investigated in the light adapted bacteriorhodopsin and the photo intermediates of the proton-motive photocycle.
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