Semi-constant-time HMSQC (SCT-HMSQC-HA) for the measurement of (3)J(HNH alpha) couplings in N-15-labeled proteins

A simple method for accurately measuring 3J(HNH alpha) coupling constants i n N-15-labeled proteins is described. This semi-constant-time HMSQC-HA expe riment combines the rapidity and convenience of the recently introduced CT- HMQC-HA scheme (Postingl and Otting, J. Biomol, NMR 12, 319-324 (1998)) wit h the high resolution and robustness of the HSQC experiment. The proposed m ethod is demonstrated for the 76-residue human ubiquitin and Saccharopolysp ora erythraea calerythrin (176 residues). Our results imply that the SCT-HM SQC-HA experiment is suitable also for proteins with less favorable NMR pro perties due to its good resolution and sensitivity. (C) 2000 Academic Press .