Theoritical studies on the molecular structure of collagen and related polypeptides

Abstract

In Section 1.5, it is seen that hydroxyproline residues can give added stability to the collagen fibers by forming both intra- as well as intermolecular hydrogen bonds involving the ?-hydroxyl group.

2.4 Conclusion

It is a well-known fact that only the imino-acid residues occurring in the third position in the repeating sequence – Gly–X–Y – of collagen are hydroxylated at the C? atom, and that the hydroxyl group is always attached in the trans orientation. The theoretical studies reported here on the role of hydroxyproline in collagen clearly indicate that only a hydroxyl group occurring in this position and orientation can lend added stability to the collagen structure by participating in both intra- as well as inter-triple-helical hydrogen bonds.

The intramolecular hydrogen bonds can only be formed via a water molecule as an intermediary, while the intermolecular hydrogen bond can be formed directly under conditions of low humidity, and via a water molecule when the collagen is in the wet state.

Thus, it is clear that the hydroxyproline residues, in addition to stabilizing the collagen structure due to the stereochemical properties of the pyrrolidine rings, also give added stability by virtue of their ?-hydroxyl groups forming additional hydrogen bonds. As mentioned earlier, recent experimental evidence from thermal denaturation studies on unhydroxylated and hydroxylated collagen samples fully supports this idea.