Multiple-quantum relaxation dispersion NMR spectroscopy probing millisecond time-scale dynamics in proteins: Theory and application

New relaxation dispersion experiments are presented that probe millisecond time-scale dynamical processes in proteins. The experiments measure the relaxation of H-1-N-15 multiple-quantum coherence as a function of the rate of application of either H-1 or N-15 refocusing pulses during a constant time relaxation interval. In contrast to the dispersion profiles generated from more conventional N-15(H-1) single-quantum relaxation experiments that depend on changes in N-15(H-1) Chemical shifts between exchanging states, H-1-N-15 multiple-quantum dispersions are sensitive to changes in the chemical environments of both H-1 and N-15 spins. The resulting multiple-quantum relaxation dispersion profiles can, therefore, be quite different from those generated by single-quantum experiments, so that an analysis of both single- and multiple-quantum profiles together provides a powerful approach for obtaining robust measures of exchange parameters. This is particularly the case in applications to protonated proteins where other methods for studying exchange involving amide proton spins are negatively influenced by contributions from neighboring protons. The methodology is demonstrated on protonated and perdeuterated samples of a G48M mutant of the Fyn SH3 domain that exchanges between folded and unfolded states in solution.