BACKBONE DYNAMICS OF (PRO-HYP-GLY)(10) AND A DESIGNED COLLAGEN-LIKE TRIPLE-HELICAL PEPTIDE BY N-15 NMR RELAXATION AND HYDROGEN-EXCHANGE MEASUREMENTS

The backbone dynamics of specific residues in two collagen-like triple -helical peptides with (X-Y-Gly)n sequences have been investigated usi ng two-dimensional inverse-detected N-15 NMR relaxation measurements a nd hydrogen-exchange experiments. One peptide, (POG)10, has the highes t possible imino acid content and is considered to be a very stable pr ototype of a triple helix. The second peptide, (POG)3ITGARGLAGPOG(POG) 3 (denoted T3-785), models an imino acid poor region of type III colla gen and contains 12 residues from near the unique collagenase cleavage site. N-15 relaxation parameters and hydrogen-exchange data were obta ined for a glycine residue in the center of (POG)10 and for the tripep tide unit Gly-Leu-Ala in the middle of T3-785. Analysis of the relaxat ion data of the rodlike triple-helical peptides required the assumptio n of anisotropic overall motion, and the model-free approach of Lipari and Szabo (1982) was used to derive overall motional parameters and t he order parameter, S2, that describes the amplitudes of the internal motion. First the mobilities of the Gly, Leu, and Ala residues in pept ide T3-785 were compared. Both hydrogen-exchange methods and relaxatio n measurements indicated that the residue in the Y position (Ala) is m ore mobile than residues in the Gly and X positions (Leu). The slower exchange rates of Gly and Leu compared to that of Ala are consistent w ith the two-hydrogen-bonded model for the triple helix. Then the backb one mobilities of the central Gly residue were compared for the two pe ptides (POG)10 and T3-785. In this case, N-15 relaxation measurements give different results from hydrogen exchange. The glycine residues in the trimer form of both T3-785 and (POG)10 have high values for the o rder parameter (near 0.85), suggesting similar small-amplitude interna l motions and rigid backbones in both peptides. In contrast to the sim ilar values of the order parameters, hydrogen-exchange data indicate t hat the central Gly exchanges at a faster rate in the trimer form of T 3-785 than in (POG)10. These results suggest that a Gly in the imino a cid rich environment of (POG)10 is dynamically different from a Gly in the imino acid poor environment of T3-785 and that the difference lie s in the slower motion related to stability, rather than the faster mo tion on the picosecond time scale. This sequence-dependent difference in dynamical properties may have important consequences for recognitio n processes in collagen.