A SUITE OF TRIPLE-RESONANCE NMR EXPERIMENTS FOR THE BACKBONE ASSIGNMENT OF N-15, C-13, H-2 LABELED PROTEINS WITH HIGH-SENSITIVITY

A suite of NMR pulse schemes is presented for the assignment of HN, N-15, C-13(alpha), and C-13(beta) resonances in N-15, C-13, H-2 labeled proteins. The experiments exploit the line narrowing of the C-13 spins caused by the substitution of deuterons for bound protons and are therefore well suited for application to molecules with masses on the order of 30-40 kDa where standard triple resonance experiments may fail completely or provide spectra of poor sensitivity. The methods are demonstrated on a 37 kDa ternary complex of a N-15, C-13, and similar to 70% H-2 labeled sample of trp-repressor, the corepressor 5-methyltryptophan, and a 20 basepair trp-operator DNA fragment. All of the experiments in the family presented provide well over 95% of the expected intra- and/or inter-residue correlations. Carbon relaxation measurements of the complex indicate that the use of deuteration increases the average C-13(alpha) T-2 value from 16.5 to 130 ms.