A new 3D HN(CA)HA experiment for obtaining fingerprint HN-Halpha peaks in 15N- and 13C-labeled proteins.

A new 3D 1H-15N-13C triple resonance experiment is presented that provides in-phase absorptive cross peaks between amide protons and alpha-protons of the same and the sequentially preceding residue. The experiment yields similar connectivities as those described previously by Montelione and Wagner (1990a) (J. Magn. Reson., 87, 183-188) and Kay et al. (1991) (J. Magn. Reson., 91, 84-92). However, the pulse sequence was designed to minimize the time that transverse coherence of the 13Calpha nucleus is present, since this nucleus has the shortest transverse relaxation time of all the nuclei involved in these experiments. This is achieved by using a coherence transfer pathway from 1HN to 15N, 13Calpha, 1Halpha and back to the 1HN. In the sequence described, transverse 13Calpha coherence is present only for a length of ca. 1/1J(Calpha-Halpha). This reduces loss of signal due to transverse relaxation. We tested the technique on uniformly 15N- and 13C-enriched T4 lysozyme.