C-13 NUCLEAR-MAGNETIC-RESONANCE RELAXATION-DERIVED PSI, PHI BOND ROTATIONAL ENERGY BARRIERS AND ROTATIONAL RESTRICTIONS FOR GLYCINE C-13(ALPHA)-METHYLENES IN A GXX-REPEAT HEXADECAPEPTIDE

Spin-lattice relaxation of C-13 multiplet spectra and {H-1}-C-13 nucle ar Overhauser enhancement (NOE) coefficients of selectively C-13-enric hed glycines in a collagen GXX-repeat motif hexadecapeptide, G1VKG4DKG 7NPG10WPG13APY, has been investigated. Data have been collected at two C-13 Larmor frequencies (90 and 150 MHz) over the temperature range f rom 5 to 70-degrees-C. Relaxation data indicate that the most restrict ed internal rotations are at G7 and G10. Mobility of other glycine res idues can be arranged in the order G4, G13, and G1. G1 glycine shows t he least change in motional anisotropy with temperature. Several motio nal models have been used to explain the experimental data. While any one model is not completely satisfactory in describing all experimenta l parameters, only the model of restricted internal diffusion yields t he observed positive sign for the cross-correlated spectral densities. Energetic and angular limits of PSI,PHI bond rotational motions deriv ed from relaxation data and the restricted diffusion model are in good agreement with those calculated as Ramachandran potentional energy pr ofiles. G1 rotational energy barriers for overall tumbling and interna l rotation are approximately equal, suggesting strong interaction betw een the N-terminus and water. Internal rotational parameters for GV an d GG dipeptides confirm this view. Nonterminal glycine internal motion s are apparently less dependent on water-peptide interactions.