Influence of cross-correlation between the chemical shift anisotropies of pairs of nuclei on multiple-quantum relaxation rates in macromolecules

The relaxation of multiple-quantum coherence due to intramolecular dipole–dipole and chemical shift anisotropy (CSA) relaxation mechanisms is described. It is shown that cross-correlation between the CSAs of the active spins can affect the relaxation of 1H–15N two-spin coherences in the protein backbone. An experiment that enables this effect to be monitored is discussed. Data are presented for perdeuterated 15N-labelled human dynamic light chain 1 protein (hdlc1). An analysis of the results yields a value for the CSA of the active 1H.