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

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