Enhancing the Sensitivity of CPMG Relaxation Dispersion to Conformational Exchange Processes by Multiple-Quantum Spectroscopy.

A triple-quantum (1) H Carr-Purcell-Meiboom-Gill NMR relaxation dispersion experiment is presented that uses methyl group probes as reporters of conformational exchange in highly deuterated, methyl-protonated proteins. Significantly larger dispersion profiles, by as much as a factor of nine, can be obtained relative to single-quantum approaches, thus offering very significant advantages in applications involving interconverting conformers with only small changes in structure or in studies of rare states that are at very low populations. Applications to a number of protein systems are presented where the utility of the method, including its improved sensitivity to chemical exchange processes, is established.