Measurement of three-bond, 13C'-13C beta J couplings in human ubiquitin by a triple resonance, E. COSY-type NMR technique.

A [CO]HN(CA)CB-E.COSY pulse scheme is described for measurement of three-bond couplings, 3JC'C beta, between carbonyl and aliphatic C beta carbons in ubiquitin, uniformly enriched with 13C and 15N. A Karplus relation, 3JC'C beta = 1.28 cos2(phi - 120 degrees) -1.02 cos(phi - 120 degrees) + 0.30 Hz, is obtained by correlating the 3JC'C beta values measured for human ubiquitin with backbone phi angles from its crystal structure. As predicted, the new Karplus parametrization yields 3JC'C beta values slightly larger than previously obtained by quantitative J correlation [Hu, J.-S. and Bax, A. (1997) J. Am. Chem. Soc., 119, 6360-6368], but considerably smaller than what has been reported on the basis of other E.COSY-type measurements carried out on flavodoxin.