Synthesis of (Pro-Hyp-Gly) n of defined molecular weights Evidence for the stabilization of collagen triple helix by hydroxypyroline

Abstract

(Pro-Hyp-Gly) 5 and (Pro-Hyp-Gly) 10 were synthesized by repeated condensation of tert-butyloxycarbonyl(Boc)-Pro-Hyp[benzyl(Bzl)]-Gly on a Merrifield resin followed by cleavage of the peptides from the resin with HF. The solution properties of the peptides were then compared with those of (Pro-Pro-Gly) 5 and (Pro-Pro-Gly) 10 synthesized previously. The peptides containing hydroxyproline were similar to those that did not, in that they formed triple-helical structures analogous to the triple-helical structure of collagen. At low temperatures the peptides showed a high degree of negative optical rotation and there was a relatively sharp change in optical rotation as the temperature was increased. The T m was about 5 °C for (Pro-Hyp-Gly) 5 and about 58 °C for (Pro-Hyp-Gly) 10. Ultracentrifugation studies were consistent with the conclusion that the temperature-dependent changes in optical rotation reflected a transition between triple-stranded and single-stranded forms of the peptides. The major difference between the peptides containing hydroxyproline and those that did not was that the T m values for the hydroxyproline-containing peptides were higher by about 35 °C. The results indicated that the hydroxyprolyl residues preceding glycyl residues in the peptides stabilize the triple-helical structure, and they suggested therefore that hydroxyproline may perform a similar function in collagen.