Abstract
Chemical exchange saturation transfer (CEST) experiments are becoming increasingly popular for investigating biomolecular exchange dynamics with rates on the order of approximately 50–500 s−1 and a rich toolkit of different methods has emerged over the past few years. Typically, experiments are based on the evolution of longitudinal magnetization, or in some cases two-spin order, during a fixed CEST relaxation delay, with the same class of magnetization prepared at the start and selected at end of the CEST period. Here we present a pair of TROSY-based pulse schemes for recording amide and methyl 1H CEST profiles where longitudinal magnetization at the start evolves to produce two-spin order that is then selected at the completion of the CEST element. This selection process subtracts out contributions from 1H–1H cross-relaxation on the fly that would otherwise complicate analysis of the data. It also obviates the need to record spin-state selective CEST profiles as an alternative to eliminating NOE effects, leading to significant improvements in sensitivity. The utility of the approach is demonstrated on a sample of a cavity mutant of T4 lysozyme that undergoes chemical exchange between conformations where the cavity is free and occupied.
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Acknowledgements
This work was supported by grants from the Canadian Institutes of Health Research (CIHR) and the Natural Sciences and Engineering Research Council of Canada. T.Y. acknowledges post-doctoral support from the CIHR. L.E.K. holds a Canada Research Chair in Biochemistry. Valuable discussions with Dr. Ashok Sekhar are acknowledged.
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Yuwen, T., Kay, L.E. A new class of CEST experiment based on selecting different magnetization components at the start and end of the CEST relaxation element: an application to 1H CEST. J Biomol NMR 70, 93–102 (2018). https://doi.org/10.1007/s10858-017-0161-2
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DOI: https://doi.org/10.1007/s10858-017-0161-2