Dynamic Structure of Proteins in Solid State. 1H and 13C NMR Relaxation Study

Abstract

Temperature dependencies of ¹H non-selective NMR T₁ and T₂ relaxation times measured at two resonance frequencies and natural abundance ^l3C NMR relaxation times T_l and T_lr measured at room temperature have been studied in a set of dry and wet solid proteins—;Bacterial RNase, lysozyme and Bovine serum albumin (BSA). The proton and carbon data were interpreted in terms of a model supposing three kinds of internal motions in a protein. These are rotation of the methyl protons around the axis of symmetry of the methyl group, and fast and slow oscillations of all atoms. The correlation times of these motions in solid state are found around 10^?11, 10^?9 and 10^?6 s, respectively. All kinds of motion are characterized by the inhomogeneous distribution of the correlation times. The protein dehydration affects only the slow internal motion. The amplitude of the slow motion obtained from the carbon data is substantially less than that obtained from the proton data. This difference can be explained by taking into account different relative inter- and intra- chemical group contributions to the proton and carbon second moments. The comparison of the solid state and solution proton relaxation data showed that the internal protein dynamics in these states is different: the slow motion seems to be few orders of magnitude faster in solution.