DETERMINATION OF THE PROTEIN BACKBONE DIHEDRAL ANGLE-PSI FROM A COMBINATION OF NMR-DERIVED CROSS-CORRELATION SPIN RELAXATION RATES

A sensitive triple resonance NMR experiment Is presented for the measu rement of the protein backbone dihedral angle psi based on cross-corre lated spin relaxation between C-13(alpha)-H-1(alpha) and N-15-(HN)-H-1 dipolar interactions in N-15,C-13-labeled proteins. In general, as ma ny as four yi values can be consistent with a single cross-correlation rate. However, in many cases, the ambiguity can be significantly redu ced (for example, from four to two) when a combination of cross-correl ation relaxation rates are employed. This is illustrated by considerin g rates derived from (Calpha-1Halpha)-C-13/N-15-(HN)-H-1 dipolar and f rom C-13(alpha)-H-1(alpha) dipolar/carbonyl chemical shift anisotropy relaxation mechanisms for the proteins ubiquitin and CheY. Using a dat abase of psi values obtained from high-resolution X-ray structures, it is shown that for values in the range -50 degrees less than or equal to psi less than or equal to 40 degrees a single psi can be obtained t o high probability.