Two simple NMR experiments for measuring dipolar couplings in asparagine and glutamine side chains.

Residual dipolar couplings are now widely used for structure determination of biological macromolecules. Until recently, the main focus has been on measurement of dipolar couplings in the protein main chain. However, with the aim of more complete protein structure, it is also essential to have information on the orientation of protein side chains. In addition, residual dipolar couplings can potentially be employed to study molecular dynamics. In this Communication, two simple NH(2) and spin-state edited experiments are presented for rapid and convenient determination of five residual dipolar couplings from (15)N, (1)H correlation spectrum in asparagine and glutamine side chains. The pulse sequences are demonstrated on two proteins, 30.4-kDa Cel6A in diluted liquid crystal phase and 18-kDa human cardiac troponin C in water.