Accurate measurement of H-N-H-alpha residual dipolar couplings in proteins

A method for accurately measuring H-N-H-alpha residual dipolar couplings is described. Using this technique, both the sign and magnitude of the coupli ng can be determined easily. Residual dipolar coupling between H-N(i)-H-alp ha(i) and H-N(i)-H-alpha(i-1) were measured for the FK506 binding protein c omplexed to FK506, The experimental values were in excellent agreement with predictions based on an X-ray crystal structure of the protein/ligand comp lex, suggesting that these residual dipolar couplings will provide accurate structural constraints for the refinement of protein structures determined by NMR. (C) 1999 Academic Press.