Collagen: Structure and Synthesis

Key points

• • Collagen is the most abundant protein in the body and the main structural protein of skin, bone, tendon, cartilage and blood-vessel walls.
• • Its basic unit is a triple helix of three chains wound together, made strong by a repeating sequence in which every third amino acid is glycine.
• • It is rich in the modified amino acids hydroxyproline and hydroxylysine, made by prolyl and lysyl hydroxylase enzymes that need vitamin C as a cofactor.
• • Because vitamin C is needed to build strong collagen, a lack of it (scurvy) gives weak collagen, with bleeding gums, loose teeth and poor wound healing.
• • There are several types for different jobs: type I in bone, skin and tendon; type II in cartilage; type III in blood vessels; and type IV in basement membranes.
• • Inherited faults in collagen or its processing enzymes cause disease: brittle bones in osteogenesis imperfecta (type I) and stretchy skin and loose joints in Ehlers-Danlos syndrome.