collagen: translation
Major structural protein (285 kD) of extracellular matrix. An unusual protein both in amino acid composition (very rich in glycine (30%), proline, hydroxyproline, lysine, and hydroxylysine; no tyrosine or tryptophan), structure (a triple helical arrangement of 95 kD polypeptides giving a tropocollagen molecule, dimensions 300nm x 0.5nm), and resistance to proteases. Most types are fibril-forming with characteristic quarter-stagger overlap between molecules producing an excellent tension-resisting fibrillar structure. Type IV, characteristic of basal lamina does not form fibrils. Many different types of collagen are now recognized. Some are glycosylated (glucose-galactose dimer on the hydroxylysine), and nearly all types can be crosslinked through lysine side-chains. See dermatosparaxis, Ehlers-Danlos syndrome, scurvy.