CPMG relaxation dispersion NMR experiments measuring glycine 1Hα and 13Cα chemical shifts in the ‘invisible’ excited states of proteins
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Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion NMR experiments are extremely powerful for characterizing millisecond time-scale conformational exchange processes in biomolecules. A large number of such CPMG experiments have now emerged for measuring protein backbone chemical shifts of sparsely populated (>0.5%), excited state conformers that cannot be directly detected in NMR spectra and that are invisible to most other biophysical methods as well. A notable deficiency is, however, the absence of CPMG experiments for measurement of 1Hα and 13Cα chemical shifts of glycine residues in the excited state that reflects the fact that in this case the 1Hα, 13Cα spins form a three-spin system that is more complex than the AX 1Hα–13Cα spin systems in the other amino acids. Here pulse sequences for recording 1Hα and 13Cα CPMG relaxation dispersion profiles derived from glycine residues are presented that provide information from which 1Hα, 13Cα chemical shifts can be obtained. The utility of these experiments is demonstrated by an application to a mutant of T4 lysozyme that undergoes a millisecond time-scale exchange process facilitating the binding of hydrophobic ligands to an internal cavity in the protein.
KeywordsCPMG Relaxation dispersion Excited protein states T4 lysozyme Millisecond dynamics
This work was supported by funds from the Canadian Institutes of Health Research (CIHR) in the form of a research grant to LEK and postdoctoral fellowships to DFH and PL (Protein Folding Training Grant). LEK holds a Canada Research Chair in Biochemistry.
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