Temperature-dependent protein backbone dynamics from auto- and cross-correlated NMR relaxation rates

The temperature dependence of nuclear magnetic resonance relaxation rates was investigated for the backbone of¹⁵N/¹³C labeled human ubiquitin in the temperature range of 20–50 °C. The¹⁵N autorelaxation rates give evidence that the potential energy functions for¹⁵N?H^N bonds are not quadratic, in agreement with results for other proteins. Cross-correlation rates arising from correlated fluctuations of two¹⁵N?H^N dipole-dipole interactions involving successive residues were obtained by the method of Pelupessy et al. (P. Pelupessy, S. Ravindranathan, G. Bodenhausen: J. Biomol. NMR 25, 265–280, 2003). The results suggest the presence of slow internal motions at 50 °C.