| Research Abstract |
Conformation and dynamics of [ィイD113ィエD1C]Ala or-Val labeled bacteriorhodopsin (bR) and its site-directed mutants or its fragments which were either biosynthetically or chemically prepared, respectively, were revealed based on their ィイD113ィエD1C NMR studies when they were buried within purple membrane or lipid bilayers. First, it was shown that most of the observed αィイD2IIィエD2 helices with references to those of polyalanine dissolved in hexafluoroisopropanol whose ィイD113ィエD1C NMR peaks were displaced downfield up to 1 ppm was ascribed to the presence of slow anisotropic fluctuation of helical segments within lipid bilayers as revealed by their ィイD113ィエD1C NMR measurements. It was shown that the manner of insertion of the later peptide to the lipid bilayer is not always the same as that of the intact bR. The achieved spectral resolution for these preparations turned out to be maximal (twelve resolved signals) for [3-ィイD113ィエD1C]Ala-bR, as compared with that of [1-ィイD113ィエD1C]-or [2-ィイD113ィエD1C]Ala-bR. In particular, ィイD113ィエD1C NMR signals of 〔2-ィイD113ィエD1C〕Ala-bR were completely suppressed, because the current effort toward peak- narrowing by either dipolar decoupling experiments or magic angle spinning turned out to be ineffective due to the presence of conformational fluctuations of these regions interfered with frequenciences of proton decoupling or magic angle spinning. Therefore, it is found that the interhelical loop regions located at the membrane surface undergo conformational fluctuations with correlation times of 10ィイD1-4ィエD1s instead of the static picture as anticipated. Further, it turned out that the present NMR approach is the most suitable means to clarify dynamic feature of the surface regions including the C-terminus α-helical segment protruded from the membrane surface.
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