Measurement of Three-bond, 13C'-13Cβ 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'Cβ, between carbonyl and aliphatic Cβ carbons in ubiquitin, uniformly enriched with 13C and 15N. A Karplus relation, 3JC'Cβ = 1.28 cos2(φ - 120o) -1.02 cos(φ - 120o) +0.30 Hz, is obtained by correlating the 3JC'Cβ values measured for human ubiquitin with backbone φ angles from its crystal structure. As predicted, the new Karplus parametrization yields 3JC'Cβ 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