¹³C-{¹H} NMR/NOE and Multiplet Relaxation Data in Modeling Protein Dynamics of a Collagen ¹³C-Enriched Glycine GXX Repeat Motif Hexadecapeptide

¹³C-NMR (75 MHz) multiple! spin-lattice (T₁) relaxation and ¹³-{¹H} nuclear Overhauser measurements have been performed on a ¹³C-glycine-XX repeating hexadecapeptide, i.e., GVKGDKGNPGWPGAPY, from the triple helix domain of collagen type IV. The data have been analyzed using a formalism that considers both autocorrelation and cross-correlation dipolar spectral densities. Several motional models were tested for consistency with the data. The terminal glycine, G1, and nonterminal glycines, G4, G7, G10, and G13, were found to have distinctly different motional properties that could not be explained simultaneously by any one model. Results indicate that most glycines rotate more isotropically than the N-terminal glycine. Analysis of the experimental data using several rotational models indicates that internal motions in the peptide are important to terminal, as well as nonterminal, ¹³C-glycine relaxation. The character of the rotational motion of nonterminal glycines varies considerably with temperature. Although simple rotational diffusion models can describe terminal glycine motion, consideration of multiple internal rotations are necessary to fully describe nonterminal glycine rotations.