Dynamic structure of proteins in solid state. 1H and 13C NMR relaxation study.

Temperature dependencies of 1H non-selective NMR T1 and T2 relaxation times measured at two resonance frequencies and natural abundance 13C NMR relaxation times T1 and T1r 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.

Overall and internal protein dynamics in solution studied by the nonselective proton relaxation.

A new algorithm for the analysis of nonselective proton relaxation data in protein solution is presented. T1 and T2 of protein protons in lysozyme and RNase solutions were measured at three resonance frequencies--11, 27 and 90 MHz. In addition we measured water T1 dispersions in lysozyme solutions over the frequency range of 10 kHz--10 MHz on a field-cycling installation. It was found that the correlation function of protein Brownian tumbling as a whole is nonexponential: in addition to a component with the usual correlation time tau t it contained also a component with a correlation time exceeding tau t by approximately an order of magnitude and with a small relative amplitude. The experiment shows that the parameters of the slow component of the tumbling correlation function depend both on the concentration and on the pH of the protein solution. To explain the results obtained one must take into account the interprotein electrostatic interactions in solution. All protein molecules in solution experience electrostatic torques from their neighbors and this gives rise to an anisotropy in the protein Brownian tumbling. The lifetime of this anisotropy is controlled by the translational diffusion of proteins.

On mechanisms of water nuclear magnetic relaxation in protein solutions.

To describe water nuclear magnetic relaxation in protein solutions a new modification of two-state model has been advanced. It is assumed that the hydration water molecules take part in two type rotation motions: fast anisotropic and slow isotropic ones, each of them can be characterized by a single correlation time. A transition of water molecule from bound state into bulk water is considered as defect arousing and is described by defect diffusion model. The model advanced allows one to describe both frequency and temperature dependences of water spin-lattice relaxation times in protein solutions and to get an information on microdynamic parameters of hydration water molecules such as life time, fraction, hindrance of local motion, etc.