Temperature dependence of protein backbone motion from carbonyl 13C and amide 15N NMR relaxation

The NMR spin-lattice relaxation rate (R-1) and the rotating-frame spin-lattice relaxation rate (R-1p) of amide N-15 and carbonyl C-13 (C-13') of the uniformly C-13- and N-15-labeled ubiquitin were measured at different temperatures and field strengths to investigate the temperature dependence of overall rotational diffusion and local backbone motion. Correlation between the order S-NH(2), and that of the carbonyl carbon, C was investigated. The effective S-C(2), was estimated from parameter of the N-H vector, the direct fit of the experimental relaxation rates and from the slope of 2R(2) - R-1 vs. B-2 using Lipari-Szabo formalism. The average S' decreased by 5.9%, while the average S-C(2), decreased by 4.6% from 15 to 47 degrees C. At the extreme low and high temperatures the difference in the temperature dependence of the order parameters vanishes. At the intermediate temperatures they do not change by the same amount but they follow the same trend. On the same peptide plane along the protein sequence, S', and S-NH(2) are highly correlated. The results suggest that fast local motion experienced at the site of the N-H vector and carbonyl nucleus is more complicated than previously thought and it cannot be easily described by one single type of motion in a broad range of temperature. Published by Elsevier Inc.