Temperature dependence of 1HN-1HN distances in ubiquitin as studied by exact measurements of NOEs.

Although NMR relaxation phenomena provide a great deal of insight into local molecular dynamics, the dynamic picture of biomacromolecules is still largely incomplete, as no method is available to detect motions between atoms that are far apart in the sequence. Our recent investigations (Vögeli et al. J. Am. Chem. Soc. 2009, 131 (47), 17215−17225) indicate that extraction of exact effective distances from NOE rates might allow the determination of such motions. Using this approach, we measured exact effective distances between amide protons in (15)N,(13)C,(2)H-labeled ubiquitin at three temperatures (284, 307, and 326 K). Comparisons among the three data sets reveal that, whereas the correlation-time-corrected cross-relaxation rates increase by 18% from 284 to 307 K, those at 326 K increase by 32% as compared to those at 284 K. Because theoretical considerations indicate that the NOE is largely insensitive to fast motion, as long as the local order parameter (e.g., S(NH)(2)) is larger than 0.5, the effective distance can be calculated from the NOE using its [linear span]r(-6)[linear span] dependency. Doing so, the average NOE increases translate into effective distance changes of 2.4% and 4.0% in the temperature ranges measured. The data presented demonstrate that the determination of quantitative NOEs is a powerful tool for extracting small structural and dynamical changes in a biomolecule.