HNCCH-TOCSY, a triple resonance experiment for the correlation of backbone 13C alpha and 15N resonances with aliphatic side-chain proton resonances and for measuring vicinal 13CO,1H beta coupling constants in proteins.

A 3D triple resonance experiment has been designed to provide intraresidual and sequential correlations between amide nitrogens and alpha-carbons in uniformly 13C/15N-labeled proteins. In-phase 13C alpha magnetization is transferred to the aliphatic side-chain protons via the side-chain carbons using a CC-TOCSY mixing sequence. Thus, the experiment alleviates the resonance assignment process by providing information about the amino acid type as well as establishing sequential connectivities. Leaving the carbonyl spins untouched throughout the transfer from 13C alpha to 1H beta leads to E.COSY-type cross peaks, from which the 3JH beta CO coupling constants can be evaluated. The pulse sequence is applied to oxidized Desulfovibrio vulgaris flavodoxin.