Cross-correlated relaxation enhanced 1H-13C NMR spectroscopy of methyl groups in very high molecular weight proteins and protein complexes

A comparison of HSQC and HMQC pulse schemes for recording H-1-C-13 correlation maps of protonated methyl groups in highly deuterated proteins is presented. It is shown that HMQC correlation maps can be as much as a factor of 3 more sensitive than their HSQC counterparts and that the sensitivity gains result from a TROSY effect that involves cancellation of intra-methyl dipolar relaxation interactions. H-1-C-13 correlation spectra are recorded on U-[N-15,H-2], lledelta1-[C-13,H-1] samples of (i) malate synthase G, a 723 residue protein, at 37 and 5degreesC, and of (ii) the protease ClpP, comprising 14 identical subunits, each with 193 residues (305kDa), at 5degreesC. The high quality of HMQC spectra obtained in short measuring times strongly suggests that methyl groups will be useful probes of structure and dynamics in supramolecular complexes.