Evidence for slow motion in proteins by multiple refocusing of heteronuclear nitrogen/proton multiple quantum coherences in NMR |
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Authors: | Dittmer Jens Bodenhausen Geoffrey |
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Institution: | Institut de chimie moléculaire et biologique, Ecole polytechnique fédérale de Lausanne, 1015 Lausanne, Switzerland. |
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Abstract: | A novel NMR method characterizes slow motions in proteins by multiple refocusing of double- and zero-quantum coherences of amide protons and nitrogen-15 nuclei. If both nuclei experience changes in their isotropic chemical shifts because of internal motions on slow time scales (mus - ms), this leads to a difference in the relaxation rates of double- and zero-quantum coherences. This is due to CSM/CSM (chemical shift modulation) cross-correlation effects that are related to the well-known chemical exchange contribution Rex to the decay rate R2 = 1/T2 of nitrogen-15 nuclei. The CSM/CSM contributions can be distinguished from other mechanisms through their dependence on the repetition rate of a Carr-Purcell-Meiboom-Gill (CPMG) multiple refocusing sequence. In ubiquitin, motional processes can be identified that could hitherto not be observed by conventional CPMG nitrogen-15 NMR. |
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