Description
Collagen is the most abundant protein in mammals, accounting for nearly 30% of body protein content. Collagen is an extracellular scaffolding protein found in skin, tendons, bone, cartilage, ligaments and muscles, amongst other tissues. There are more than twenty different characterized types of collagen, but the fibrilous types I, II and III comprise more than 90% of the total collagen in mammals. Collagen has a triple helical structure, consisting of three 'preprocollagen' strands with a repeating Gly-X-Hyp tripeptide sequence, where X is any amino acid and Hyp is hydroxyproline, a post-translationally modified amino acid formed from proline by the enzyme prolyl-4-hydroxylase. In animals, hydroxyproline is found almost entirely in collagen (which contains approximately 12-14% hydroxyproline by mass) and contributes to its structural rigidity and high tensile strength. Hydroxyproline is thus a direct measure of the amount of collagen present in tissues. Many diseases are believed to affect collagen turnover, including tumor invasion and metastasis, rheumatoid arthritis, cardiopulmonary fibrosis and muscular dystrophy.
