What are the structural features common to all collagen molecules
The definitive structural feature of all collagen molecules is the triple helix. This unique conformation is due to three polypeptide chains (α-chains) twisted around each other into a right-handed major helix. Extending from the amino and carboxyl terminal ends of both helical domains of the α-chains are nonhelical components called telopeptides. In the major interstitial collagens, the helical domains are continuous, whereas in the other collagen classes, the helical domains may be interrupted by 1 to 12 nonhelical segments.
The primary structure of the helical domain of the α-chain is characterized by the repeating triplet Gly– X – Y . X and Y can be any amino acid but are most frequently proline and hydroxyproline, respectively. Overall, approximately 25% of the residues in the triple helical domains consist of proline and hydroxyproline. Hydroxylysine is also commonly found. In the most abundant interstitial collagens (type I and II), the triple helical region contains about 1000 amino acid residues (Gly– X –Y) 333