Role of carbohydrate in stabilizing the triple-helix in a model for a deep-sea hydrothermal vent worm collagen

The glycopeptide Ac-(Gly-Pro-Thr(beta-Gal))(10)-NH2 forms a collagen-like triple-helix. A H-1 NMR structural analysis is reported for the peptides Ac-(Gly-Pro-Thr)(n)-NH2 and Ac-(Gly-Pro-Thr(beta-Gal))(n)-NH2, where n = 1, 5, and 10. NMR assignments for the individual peptides are made using one- and two-dimensional TOCSY, ROESY, and NOESY experiments. The NMR and corroborating CD data show that Ac-(Gly-Pro-Thr)(n)-NH2, n = 1, 5, or 10, as well as Ac-(Gly-Pro-Thr(beta-Gal))(n)-NH2, n = I or 5 peptides are unable to form collagen-like triple-helical structures. Furthermore, the equilibrium ratio of cis to trans isomers of the Pro residues is unaffected by the presence of carbohydrate. For Ac-(Gly-Pro-Thr(beta-Gal))(10)-NH2, the kinetics of amide I H exchange with solvent deuterium indicate a slow rate of exchange for both the Gly and the Thr amide. The data are thus consistent with a model in which the carbohydrate stabilizes the triple helix through an occlusion of water molecules and by hydrogen bonding but not through an influence on the cis to trans isomer ratio.