Collagens at a glance

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Abstract
Collagens contain three polypeptide (α) chains, displaying an extended polyproline-II conformation, a right-handed supercoil and a one-residue stagger between adjacent chains (Brodsky and Persikov, 2005). Each polypeptide chain has a repeating Gly-X-Y triplet in which glycyl residues occupy every third position and the X and Y positions are frequently occupied by proline and 4-hydroxyproline, respectively. The three α chains are held together by interchain hydrogen bonds. Highly ordered hydration networks surround the triple helices. The significance of these interactions to collagen stability remains a matter of debate. Some collagens have interruptions (containing numerous residues) and imperfections (one to three residues) in the triple helix. The conformational changes derived from some simple imperfections have been visualised in crystal structures of model peptides (Bella et al., 2006). Integrin adhesion sequences [e.g. Arg-Gly-Asp (RGD) and Gly-Phe-O-Gly-Arg, where O is hydroxyproline] occur in the triple helical domain of several collagens and contribute to integrin-ligand-binding specificity (Bella and Humphries, 2005).