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Increasing the Exchange Time-Scale That Can Be Probed by CPMG Relaxation Dispersion NMR

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journal contribution
posted on 15.12.2011, 00:00 authored by Pramodh Vallurupalli, Guillaume Bouvignies, Lewis E. Kay
Carr–Purcell–Meiboom–Gill relaxation dispersion NMR spectroscopy has emerged as a valuable tool to characterize conformational exchange between major and minor states in a large variety of biomolecules. The window of exchange that is amenable for study, corresponding to rates on the order of 2000 s–1 or less, is limiting, however. Here we show that a combined analysis of both amide 15N and 1HN CPMG profiles and major state exchange induced 15N chemical shift changes leads to significant increases in the exchange time scale for which accurate exchange parameters and chemical shift differences between the interconverting states can be obtained. The utility of the approach is illustrated with examples involving a pair of protein systems that are in the moderately fast exchange regime. In these cases the analysis of dispersion profiles alone is not sufficient to obtain robust measures of exchange parameters and chemical shift differences. Inclusion of major state exchange induced 15N chemical shift changes measured in (15N–1HN) HMQC and HSQC data sets in addition to the 15N and 1HN dispersion profiles in the analysis “breaks” the correlation in parameters, allowing accurate values to be obtained. The approach is straightforward to implement and makes use of HMQC/HSQC data sets that are recorded as a matter of routine to obtain chemical shifts of the excited state. It promises to increase the range of exchanging systems involving low populated, transiently formed excited states that can be studied by relaxation dispersion NMR.