Recent Advances in the Study of Bacteriorhodopsin Dynamic Structure Using High-Field Solid-State Nuclear Magnetic Resonance Spectroscopy

This chapter demonstrates that with sufficiently sensitive nuclear magnetic resonance (NMR) instrumentation it is now possible to study in some detail amino acid dynamics in this membrane protein. Such observations allow comparison of motions between proteins in membranes and in conventional three-dimensional crystals and facilitates direct observation of the effects of lipids and sterols on protein structure. The results also directly complement the static structural information currently being obtained on Halobacterium halobium using neutron beam methods. From the studies, it is found backbone (C^α) labeled amino acids in the purple membrane of H. haiobium exhibit rigid-lattice spectra, except for a possible small population of surface residues. In addition, the dynamics of most aliphatic and aromatic amino acids in the purple membrane is reported one of a rather rigid protein protein; in most instances the ²H NMR spectra of the protein are rather similar to those of the solid amino acid, at the same temperature, except for the Phe and Tyr residues that undergo twofold flipping. Because it appears that Phe residues at least are located toward the center of the protein, where H⁺ translocation may occur, it seems possible that these motions could be of importance in the energy transduction process.