ROTATIONAL DIFFUSION ANISOTROPY OF PROTEINS FROM SIMULTANEOUS ANALYSIS OF N-15 AND C-13(ALPHA) NUCLEAR-SPIN RELAXATION

Current methods of determining the rotational diffusion tensors of pro teins in solution by NMR spectroscopy exclusively utilize relaxation r ate constants for backbone amide N-15 spins. However, the distribution s of orientations of N-H bond vectors are not isotropic in many protei ns, and correlations between bond vector orientations reduce the accur acy and precision of rotational diffusion tensors extracted from N-15 spin relaxation data. The inclusion of both C-13(alpha) and N-15 Spin relaxation rate constants increases the robustness of the diffusion te nsor analysis because the orientations of the C-alpha-H-alpha bond vec tors differ from the orientations of the N-H bond vectors. Theoretical and experimental results for calbindin D-9k, granulocyte colony stimu lating factor, and ubiquitin, three proteins with different distributi ons of N-H and C-alpha-H-alpha bond vectors, are used to illustrate th e advantages of the simultaneous utilization of C-13(alpha) and N-15 r elaxation data.