Anisotropy of rotational diffusion, dipole-dipole cross-correlated NMR relaxation and angles between bond vectors in proteins

A new expression for the spectral d. function of cross-correlated dipole-dipole interference is proposed. It allows one to assess to what extent anisotropic rotational diffusion results in complications in the interpretation of cross-correlation rates. The 13Ca-1Ha vectors undergoing significant local motion were detd. The importance of rotational anisotropy for human ubiquitin was evaluated. The comparison between cross-correlation rates predicted for a set of hydrodynamic parameters with exptl. rates and angles, previously detd. by NMR, yielded information about motional processes. Flexible regions and residues featuring conformational instabilities were distinguished. The residues featuring significant local motion were located outside the area covered by calcd. cross-correlation rates. This indicated that the rigid backbone model is not sufficient to explain the corresponding cross-correlation rates. [on SciFinder (R)]