A study of protein side-chain dynamics from new 2H auto-correlation and 13C cross-correlation NMR experiments: application to the N-terminal SH3 domain from drk.

Two new NMR experiments are presented for measuring side-chain dynamics in proteins. The first method, requiring 15N, 13C, approximately 50% 2H-labeled protein, measures 2H T1 and T1p spin relaxation times at side-chain positions. A second experiment permits the straightforward measurement of 13C-1H dipole-dipole cross-correlation relaxation rates at 13C beta positions in 15N, 13C-labeled molecules. An excellent correlation is observed between order parameters, describing the amplitude of motion at these sites, obtained on the basis of 2H relaxation and dipole-dipole cross-correlation relaxation rates. Together these experiments provide a powerful approach for selecting appropriate motional models. The methods are applied to study the side-chain motional properties of the N-terminal SH3 domain from the signaling protein drk.