Collagen Structure & Function: Difference between revisions

Collagen synthesis begins specialized cells called fibroblasts <ref name="biosyn">PMID:PMC1367617</ref>. It is here that amino acids undergo activation; Proline is hydroxylated to Hydroxyproline and Lysine to Hydroxylysine. Peptide subunits of ~250 residues are assembled on the ribosome and are linked by carbohydrate residues to form α-chains <ref name="biosyn" />. Three α-chains then associate with each other and then further associate extracelluarly forming a molecule with a molecular weight of 360,000 <ref name="biosyn" />. Bonds are further strengthened thus forming the insoluble collagen fibril <ref name="biosyn" /> <ref name="collalike" />. During the process of collagen synthesis, free-hydroxyproline and hydroxylysine peptides appear as by-products, some of which are metabolized and may appear in urine <ref name="biosyn" />.

The triple-helical domain structure of collagens consists of three distinct α-chains and earns collagen the name "tropocollagen" <ref name="collalike">PMID:7695699</ref>. Each of these chains contain a characteristic L-handed amino acid sequence of polyproline, often termed as polyproline type II helix <ref>PMID: 19344236</ref>. The proper folding of each of these chains requires a glycine residue to be present in every third position in the polypeptide chain. For example, each α-chain is composed of multiple triplet sequences of of Gly-Y-Z in which Y and Z can be any amino acid. Y is commonly found as proline and Z is usually present as hydroxyproline (Figure 1.). The presence of hydroxyproline in the Y position is also thought to  contribute to the stability of the helical form <ref name="collalike" />.