Protein backbone dynamics through 13C′-13Cα cross-relaxation in NMR spectroscopy

Internal dynamics of proteins are usually characterized by the analysis of N-15 relaxation rates that reflect the motions of NHN vectors. It was suggested a decade ago that additional information on backbone motions can be obtained by measuring cross-relaxation rates associated with intra-residue C'C-alpha vectors. Here we propose a new approach to such measurements, based on the observation of the transfer between two-spin orders 2N(z)C'(z) and 2N(z)C(z)(alpha) R. This amounts to " anchoring" the C'(z) and C-z(a) R operators to the N-z term from the amide of the next residue. In combination with symmetrical reconversion, this method greatly reduces various artifacts. The experiment is carried out on human ubiquitin at 284.1 K, where the correlation time is 7.1 ns. The motions of the C'C-alpha vector appear more restricted than those of the NHN vector.