A NEW TRIPLE-RESONANCE EXPERIMENT FOR THE SEQUENTIAL ASSIGNMENT OF BACKBONE RESONANCES IN PROTEINS

A new protocol is described for obtaining intraresidual and sequential correlations between carbonyl carbons and amide H-1 and N-15 resonances of amino acids. Frequency labelling of (CO)-C-13 spins occurs during a period required for the C-13(alpha)-N-15 polarization transfer, leading to an optimized transfer efficiency. In a four-dimensional version of the experiment, C-13(alpha) chemical shifts are used to improve the dispersion of signals. The resonance frequencies of all backbone nuclei can be detected in a 3D variant in which cross peaks are split along two frequency axes. This pulse scheme is the equivalent of a five-dimensional experiment. The novel pulse sequences are applied to flavodoxin from Desulfovibrio vulgaris.