Composition and post-translational modi?cations
Composition of the amino acid of collagen is quite unique. Nearly one-third of its residues are Gly although another one-quarter are Pro signi?cantly higher proportions than are found in another proteins. The hydroxylated amino acids 4- hydroxyproline Hyp and 5-hydroxylysine Hyl are found only in collagen. These hydroxylated amino acids are formed from the parent amino acid through the action of lysine hydroxylase and proline hydroxylase, respectively. These enzymes have a Fe2+ ion at their active site and needs ascorbic acid like vitamin C for activity. The ascorbic acid behave as an antioxidant keeping
![990_Composition and post-translational modi?cations.png](https://www.expertsmind.com/../CMSImages/990_Composition and post-translational modi?cations.png)
Figure: Overview of the biosynthesis of collagen.
the Fe2+ ion in its decrease state. The lysine hydroxylase and Proline hydroxylase are dioxygenases by using a molecule of O2. The citric acid cycle α-Ketoglutarate intermediate is an obligatory substrate and is converted to succinate in during of the reaction. Both enzymes will hydroxylate only Lys and Pro residues which are incorporated in a polypeptide chain and then only when the residue is on the N-terminal side of Gly. The Hyp is most important in stabilizing the structure of collagen by hydrogen bond formation. In vitamin C de?ciency, Hyp and Hyl are not synthesized resulting in the weakening of the collagen ?bers. This leads to the fragile blood vessels, skin lesions and poor wound healing which are characteristic of the disease scurvy.
The other post-translational modi?cation which occurs to collagen is glycosylation. In this case the sugar residues, commonly only galactose, glucose and their disaccharides are attached to the hydroxyl group in the newly formed Hyl residues, rather than to Asn or Ser or Thr residues as occurs in the more broad- spread N- and O-linked glycosylation (see Topic H5). The quantity of attached carbohydrate in collagen varies from 0.4 to 12 percent through weight depending on the tissue in that it is synthesized.