A NEW 3D HN(CA)HA EXPERIMENT FOR OBTAINING FINGERPRINT H(N)-H-ALPHA CROSS PEAKS IN N-15-LABELED AND C-13-LABELED PROTEINS

A new 3D H-1-N-15-C-13 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 C-13(alpha) 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 H-1(N) to N-15, C-13(alpha), H-1(alpha) and back to the H-1(N). In the sequence described, transverse C-13(alpha) coherence is present only for a length of ca. I/1J(C(alpha)-H(alpha). This reduces loss of signal due to transverse relaxation. We tested the technique on uniformly N-15- and C-13-enriched T4 lysozyme.