COMPARISON OF DIFFERENT MODES OF 2-DIMENSIONAL REVERSE-CORRELATION NMR FOR THE STUDY OF PROTEINS

Different two-dimensional NMR schemes for generating 1H-detected 1H15N and 1H13C correlation spectra are compared. It is shown that the resolution in the dimension that represents the 13C or 15N chemical shift depends on the type of correlation scheme used. For 15N NMR studies of proteins, it is found that experiments that involve 15N single-quantum coherence offer improved resolution compared to multiple-quantum correlation experiments, mainly because the 1H1H dipolar broadening of the multiple-quantum coherence is stronger than the heteronuclear dipolar broadening of 15N, but also because of the presence of unresolved J splittings in the F1 dimension of the multiple-quantum correlation spectra. For 13C, the heteronuclear dipolar interaction is much larger and the 1H13C multiple-quantum relaxation is slower than the 13C transverse relaxation; however, because of the presence of 1H1H J couplings in the F1 dimension of such spectra, in practice the multiple-quantum type correlation experiments often offer no gain or even a small loss in resolution, compared to experiments that use transverse 13C magnetization during the evolution period. A modified pulse scheme that increases F1 resolution by elimination of scalar relaxation of the second kind is proposed. Experiments for the proteins calmodulin, uniformly enriched with 15N, and staphylococcal nuclease, labeled with 13C in the Cα position of all Pro residues are demonstrated. © 1990.