Conformational dynamics of a seven transmembrane helical protein Anabaena Sensory Rhodopsin probed by solid-state NMR.
 

Conformational dynamics of a seven transmembrane helical protein Anabaena Sensory Rhodopsin probed by solid-state NMR.

Related Articles Conformational dynamics of a seven transmembrane helical protein Anabaena Sensory Rhodopsin probed by solid-state NMR.

J Am Chem Soc. 2014 Jan 27;

Authors: Good DB, Wang S, Ward ME, Struppe JO, Brown LS, Lewandowski JR, Ladizhansky V

Abstract
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 (SSNMR) site-specific measurements of the dipolar order parameters and (15)N rotating frame spin-lattice (R1?) relaxation rates in a seven transmembrane helical protein Anabaena Sensory Rhodopsin (ASR) reconstituted in lipids. The magnitudes of the observed order parameters and their fairly homogeneous distribution indicate that both the well-defined transmembrane regions and the mainly unstructured intramembrane loops and turns undergo restricted, submicrosecond time scale motions. In contrast, the transverse spin relaxation 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 for the exposed regions. 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-C and F-G loops. These relatively slow time scales could be attributed to collective anisotropic motions. We find that collective motions of molecular fragments such as helices or loops (e.g., well-structured B-C loop) can explain the measured dipolar order parameters and (15)N R1? rates. We used the 3D Gaussian Axial Fluctuations (3D GAF) model to estimate amplitudes, directions and time scales of overall motions for helices and the extracellular B-C and F-G 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 motional time scale for the seventh helix G upproaches 100 ns. Similar time scales of roughly 100-200 ns are estimated for less structured solvent-exposed B-C and F-G loops.


PMID: 24467417 [PubMed - as supplied by publisher]



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