MULTIPLE-QUANTUM LINE NARROWING FOR MEASUREMENT OF H-ALPHA-H-BETA J-COUPLINGS IN ISOTOPICALLY ENRICHED PROTEINS

Uniform C-13 enrichment of proteins is commonly used for NMR studies of proteins that are not amenable to conventional homonuclear 2D NMR spectroscopy. In such studies, the one-bond H-1-C-13 dipolar interaction is usually the dominant source of H-1 line broadening. H-1-C-13 zero- and double-quantum coherences are, to first order, not affected by this dipolar relaxation mechanism. The relatively long relaxation time of such H-1(alpha)-C-13(alpha) multiple-quantum coherences is exploited for measurement of H-alpha-H-beta J couplings in a sample of uniformly C-13-enriched calcium-free calmodulin (16.7 kD) and a sample of TGF-beta 1 (25 kDa). J(H-alpha-H-beta) provides information on the stereospecific resonance assignment for residues with nonequivalent H-beta methylene protons and on the chi(1) torsion angles.