NMR STUDIES OF BIOLOGICAL MEMBRANES

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Solid-state nuclear magnetic resonance spectroscopy and resonance Raman spectroscopy are to be used as non-perturbative means of studying the structures, dynamics and functional mechanisms of proteins and peptides involved in membrane transport. In particular, we plan to study the purple membrane fragments of the plasma membrane of the halobacterium halobium, which contains a single protein that executes light driven proton transport, and model membranes containing enniatin ionophores, which facilitate passive cation transport. Samples will be isotopically enriched at specific sites to enhance NMR signals of interest, suppress interfering NMR signals, and to induce informative shifts in the resonance Raman spectrum. In the case of the purple membrane, we hope to learn which groups are exposed to the aqueous environment in native and bleached samples, what the pK's of the ionizable residues are, which ionizable groups change their state of protonation during the photo reaction cycle, which groups are in direct interaction with the chromophore, and what types of moleculr motion occur in various regions of the protein. In the case of the enniatin ionophores, we hope to learn what the stoichiometries and structures of the metal ion complexes are and what types of molecular motion occur in the aliphatic and aromatic side chains. In addition to illuminating the properties of these particular systems, it is hoped that these biophysical studies will provide models for other membrane transport systems and integral membrane proteins in general. Information about such proteins is ultimately important to our understanding of normal and pathological cell regulation and function.