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

Internal dynamics of proteins are usually characterized by the analysis of ¹⁵N relaxation rates that reflect the motions of NH^N 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^α vectors. Here we propose a new approach to such measurements, based on the observation of the transfer between two-spin orders 2N_zC′_z and 2N_zC _z^α. This amounts to "anchoring" the C′_z and C_z^α 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^α vector appear more restricted than those of the NH^N vector.