Conformational Dynamics of a Seven Transmembrane Helical Protein Anabaena Sensory Rhodopsin Probed by Solid-State NMR

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• 作者：Daryl B. Good ; Shenlin Wang ; Meaghan E. Ward ; Jochem Struppe ; Leonid S. Brown ; Józef R. Lewandowski ; Vladimir Ladizhansky
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：February 19, 2014
• 年：2014
• 卷：136
• 期：7
• 页码：2833-2842
• 全文大小：599K
• ISSN：1520-5126

文摘

The ability to detect and characterize molecular motions represents one of the unique strengths of nuclear magnetic resonance (NMR) spectroscopy. In this study, we report solid-state NMR site-specific measurements of the dipolar order parameters and ¹⁵N rotating frame spin鈥搇attice (R_1蟻) relaxation rates in a seven transmembrane helical protein Anabaena Sensory Rhodopsin reconstituted in lipids. The magnitudes of the observed order parameters indicate that both the well-defined transmembrane regions and the less structured intramembrane loops undergo restricted submicrosecond time scale motions. In contrast, the R_1蟻 rates, which were measured under fast magic angle spinning conditions, vary by an order of magnitude between the TM and exposed regions and suggest the presence of intermediate time scale motions. Using a simple model, which assumes a single exponential autocorrelation function, we estimated the time scales of dominant stochastic motions to be on the order of low tens of nanoseconds for most residues within the TM helices and tens to hundreds of nanoseconds for the extracellular B鈥揅 and F鈥揋 loops. These relatively slow time scales could be attributed to collective anisotropic motions. We used the 3D Gaussian axial fluctuations model to estimate amplitudes, directions, and time scales of overall motions for helices and the extracellular B鈥揅 and F鈥揋 loops. Within this model, the TM helices A,B,C,D,E,F undergo rigid body motions on a time scale of tens of nanoseconds, while the time scale for the seventh helix G approaches 100 ns. Similar time scales of roughly 100鈥?00 ns are estimated for the B鈥揅 and F鈥揋 loops.