ANALYSIS OF P-31 MAS NMR-SPECTRA AND TRANSVERSAL RELAXATION OF BACTERIOPHAGE-M13 AND TOBACCO MOSAIC-VIRUS

Phosphorus magic angle spinning nuclear magnetic resonance (NMR) spect ra and transversal relaxation of M13 and TMV are analyzed by use of a model, which includes both local backbone motions of the encapsulated nucleic acid molecules and overall rotational diffusion of the rod-sha ped virions about their length axis. Backbone motions influence the si deband intensities by causing a fast restricted reorientation of the p hosphodiesters. To evaluate their influence on the observed sideband p atterns, we extend the model that we used previously to analyze nonspi nning P-31 NMR lineshapes (Magusin, P.C.M.M., and M. A. Hemminga, 1993 a. Biophys. J. 64:1861-1868) to magic angle spinning NMR experiments. Backbone motions also influence the conformation of the phosphodiester s, causing conformational averaging of the isotropic chemical shift, w hich offers a possible explanation for the various linewidths of the c enterband and the sidebands observed for M13 gels under Various condit ions. The change of the experimental lineshape of M13 as a function of temperature and hydration is interpreted in terms of fast restricted fluctuation of the dihedral angles between the POC and the OCH planes on both sides of the P-31 nucleus in the nucleic acid backbone. Backbo ne motions also seem to be the main cause of transversal relaxation me asured at spinning rates of 4 kHz or higher. At spinning rates less th an 2 kHz, transversal relaxation is significantly faster. This effect is assigned to slow, overall rotation of the rod-shaped M13 phage abou t its length axis. Equations are derived to simulate the observed depe ndence of T-2e on the spinning rate.