Simultaneous measurement of 3JHN,Hα and 3JHα,Hβ coupling constants in 13C,15N-labeled proteins

A triple-resonance NMR pulse sequence termed HA[HB,HN](CACO)NH is proposed that provides two types of (3)J(HH) coupling constants sharing the Cn proton in amino acid spin systems. The experiment is of the quantitative J correlation-type and takes advantage of the favorable relaxation properties of H-1(a)-C-13(alpha) multiple-quantum coherence as compared to schemes relying on antiphase magnetization. The problem of signal overlap is considerably reduced by calculating J values from cross-peak-cross-peak intensity ratios rather than referencing diagonal peaks. Application to flavodoxin from Desulfovibrio vulgaris yields a total of 282 (3)J(H alpha,H beta) and (3)J(HN,H alpha) coupling constants, normally determined in two separate experiments, to be used in conjunction with heteronuclear couplings to derive angular constraints for the protein's backbone and side chains. While 3J(H alpha,H beta) coupling constants indicate some extent of conformational averaging not in accord with fixed side chain torsion, excellent correlation of the experimental 3J(HN,H alpha) values with X-ray derived phi torsional angles in flavodoxin is observed.