Thermal denaturation of collagen revisited

We have recently re-examined the-characteristic sharp denaturation temperat ure of the collagen molecule and fibre. It has been generally accepted for many years that denaturation is an equilibrium process involving the ruptur e of hydrogen bonds. We have now proposed-that-the process is an irreversib le rate process, in which uncoupling of the alpha-chains initially occurs i n a thermally labile domain devoid of hydroxyproline. The domain is located near the C-terminal and following alignment of the molecules in the quarte r-stagger-end-overlap arrangement is located in the gap-region of the fibre . The domain appears to be conserved in type I of several animal. species, and is present in types II and III. Collagen molecules that co-polymerise t o form fibres, types V and XI, do not possess this. labile domain. Ramachandran proposed that stabilisation of-the triple helix occurred throu gh hydrogen-bonded water-bridges involving the hydroxyl group of hydroxypro line. Recent studies have been equivocal, some questioning the role of wate r bridges and of hydroxyproline, whilst recent detailed X-ray studies of-co llagen-like peptides demonstrate the presence of a stabilising sheath of hy drogen-bonded water. Our findings support the proposal of hydrogen-bonded w ater-bridge stabilising the triple helix.