Effect of the -Gly-3(S)-hydroxyprolyl-4(R)-hydroxyprolyl- tripeptide unit on the stability of collagen model peptides

In order to evaluate the role of 3(S)-hydroxyproline [3(S)-Hyp] in the triple-helical structure, we produced a series of model peptides with nine tripeptide units including 0-9 3(S)-hydroxyproline residues. The sequences are H-(Gly-Pro-4(R)Hyp)(l)-(Gly-3(S)Hyp-4(R)Hyp)(m)-(Gly-Pro-4(R)Hyp)(n)-OH, where (l, m, n) = (9, 0, 0), (4, 1, 4), (3, 2, 4), (3, 3, 3), (1, 7, 1) and (0, 9, 0). All peptides showed triple-helical CD spectra at room temperature and thermal transition curves. Sedimentation equilibrium analysis showed that peptide H-(Gly-3(S)Hyp-4(R)Hyp)(9)-OH is a trimer. Differential scanning calorimetry showed that replacement of Pro residues with 3(S)Hyp residues decreased the transition enthalpy, and the transition temperature increases by 4.5 degrees C from 52.0 degrees C for the peptide with no 3(S)Hyp residues to 56.5 degrees C for the peptide with nine 3(S)Hyp residues. The refolding kinetics of peptides H-(Gly-3(S)Hyp-4(R)Hyp)(9)-OH, H-(Gly-Pro-4(R)Hyp)(9)-OH and H-(Gly-4(R)Hyp-4(R)Hyp)(9)-OH were compared, and the apparent reaction orders of refolding at 10 degrees C were n = 1.5, 1.3 and 1.2, respectively. Replacement of Pro with 3(S)Hyp or 4(R)Hyp has little effect on the refolding kinetics. This result suggests that the refolding kinetics of collagen model peptides are influenced mainly by the residue in the Yaa position of the -Gly-Xaa-Yaa- repeated sequence. The experiments indicate that replacement of a Pro residue by a 3(S)Hyp residue in the Xaa position of the -Gly-Xaa-4(R)Hyp- repeat of collagen model peptides increases the stability, mainly due to entropic factors.