Nuclear Magnetic Resonance--new Methods And Molecular St

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We have extended the technology for studying macromolecular structure in solution by NMR spectroscopy under weakly aligning conditions. New developments focus on a procedure that permits direct incorporation of small angle X-ray scattering data into NMR structure determination. Although computationally expensive, use of a ?glob? approach, which treats certain peptide groups as fixed single point units, accelerates the method by several orders of magnitude over a full atom calculation. Application to gamma-S crystallin showed a considerably better fit to homologous X-ray structure upon incorporation of experimental SAXS data in the structure refinement. Use of SAXS data is proving particularly useful for the study of molecular complexes and for studying quaternary structure of complex systems under solution conditions. Study of the tetrameric potassium channel KcsA in detergent micelles indicates that NMR studies of relatively large (65 kDa) membrane proteins intrinsically is feasible by NMR, provided that the system remains stable at elevated temperature. NMR data indicate that the channel/detergent aggregate tumbles as an oblate spheroid, reflecting the presence of detergent molecules on the hydrophobic surface that normally spans the membrane. K+ binding is found not to be disturbed by the presence of detergent, and no evidence for elevated, large amplitude motions is found in the closed state of the so-called selectivity filter domain of the channel. Novel experiments have been developed that permit characterization of the position of highly labile protons such as 2' hydoxyl protons in RNA. These experiments reveal unambiguously that the 2'OH proton in A-form helical regions of RNA points towards the base, and does not alternate between the C3' and base regions, as reported earlier in the literature.