The collagen triple-helix: correlation of conformation with biological activities.

Collagens are distinguished from other extracellular matrix proteins by their triple-helical conformation. Triple-helical conformation has been proposed to be important for cellular activities, such as adhesion and activation, extracellular matrix assembly, and enzyme function, such as hydroxylation of collagen Lys and Pro residues and matrix metalloproteinase (MMP) catabolism of native collagens. A collagen-like triple-helix is also a necessary component of several macrophage cell surface receptors. Collagen-mediated cellular and/or enzymatic activities that (i) require an intact triple-helix, (ii) require a denatured triple-helix, or (iii) are "conformationally independent" of the state of the triple-helix have been documented. Recently developed synthetic protocols have allowed for the study of biological activities of specific collagen sequences in triple-helical conformation.