EXPERIMENTAL CHARACTERIZATION OF MODELS FOR BACKBONE PICOSECOND DYNAMICS IN PROTEINS - QUANTIFICATION OF NMR AUTO-CORRELATION AND CROSS-CORRELATION RELAXATION MECHANISMS INVOLVING DIFFERENT NUCLEI OF THE PEPTIDE PLANE

NMR relaxation parameters were measured for the peptide-plane carbonyl and nitrogen nuclei for the protein Escherichia coil flavodoxin. A po or correlation between the general order parameters of the C'-C alpha vector (Zeng, L.; Fischer, M. W. F.; Zuiderweg, E. R. P. J. Biomol. NM R 1996, 7, 157-162) and the N-NH vector was observed. We interpret thi s lack of correlation in this nearly spherical protein as evidence of local or semilocal anisotropic motion. A new experiment is introduced from which the cross-correlation between the carbonyl chemical shift a nisotropy relaxation and carbonyl-C alpha dipole-dipole relaxation is obtained. We show theoretically that the three relaxation measurements , reporting on the dynamics of the C'-C alpha vector, N-NH vector, and CSA tensor components behave differently under anisotropic motion. Th e cross-correlation order parameter formalism for dipolar cross-correl ation spectral densities, as introduced by Daragan and Mayo (Daragan, V. A.; Mayo, K. H. J. Magn. Reson. B 1995, 107, 274-278), has been ext ended to include cross-correlations between nonaxial chemical shift an isotropy and dipole-dipole relaxation. By analyzing our experimental d ata with the theoretical models for anisotropic local motion, dynamic models were obtained for the peptide planes of 32 residues of E. coli flavodoxin.