Slow backbone dynamics of chicken villin headpiece subdomain probed by NMR C'-N cross-correlated relaxation.

We have investigated slow correlated motions of neighboring carbonyl and nitrogen nuclei in the backbone of chicken villin headpiece subdomain. Cross-correlated chemical shift modulation experiments were performed at three temperatures where the protein remains in its folded state. The results at 8 degrees C demonstrate the presence of microseconds to milliseconds timescale motions for a number of residues belonging both to helices and unstructured regions. As the temperature is raised, the motions become progressively less visible. The reduction of the contributions of slow motions into the cross-correlated relaxation rate with the rise in temperature is caused by the increase of the chemical exchange rate constants for the slow motion processes.