Abstract
Collagen is a right-handed triple helix consisting of three left-handed PPⅡ helices interacted by hydrogen bonding. It involves many repeats of the tripeptide sequence : Pro-Hyp-Gly, and thus we use it as the peptide model to investigate the stability of collagen. A series of host-guest collagen peptides, (Pro-Hyp-Gly)n-Pro- Hyp-Xaa-(Pro-Hyp-Gly)m, where Xaa is β-Ala, L-Ala, D-Ala, and sarcosine, were prepared to investigate the effects of a prolonged backbone, the side chain steric strain, and the hydrogen bond breaking on collagen stability. CD and NMR measurements indicated that the mutated peptides formed less stable triple helices compared to the wild type peptide, but the destabilizing effects at different sites were different. Our data have shown that the mutation at the N-terminus destabilized the triple helix more than that at the C-terminus. We suggest that coming across the N-terminal mutation while folding from the C- to N-terminus would significantly disperse the triple helix, but it could skip the C-terminal mutation site and then hold on folding at the other site to form a larger section of Pro-Hyp-Gly repeats. The substitution of a sarcosine at the middle site of a collagen peptide could still form a triple helix, suggesting that the hydrogen bond-breaking has less destabilization effects than the perturbation of backbone. Moreover, the kinetic studies have shown that steric effects of the side chains might be the main factor retarding the folding of a triple helix.