Chemical shift anisotropy tensors of carbonyl, nitrogen, and amide proton nuclei in proteins through cross-correlated relaxation in NMR spectroscopy

The principal components and orientations of the chemical shift anisotropy (CSA) tensors; of the carbonyl (U), nitrogen (N), and amide proton (H-N) nuclei of 64 distinct amide bonds in human ubiquitin have been determined in isotropic solution by a set of 14 complementary auto- and cross-correlated relaxation rates involving the CSA interactions of the nuclei of interest and several dipole-dipole (DID) interactions. The CSA parameters thus obtained depend to some degree on the models used for local motions. Three cases have been considered: restricted isotropic diffusion, three-dimensional Gaussian axial fluctuations (3D-GAF), and independent out-of-plane motions of the NHN vectors with respect to the peptide planes.