Collagen

Collagen is the most abundant protein in the human body, playing a pivotal role in the structural integrity and physical properties of various tissues, including skin, bones, cartilage, and tendons. It is integral to maintaining not only the mechanical strength but also the functional capability of these tissues.

Structure and synthesis:

• Structure: Collagen is characterised by its triple-helix structure, which consists of three polypeptide chains wound around each other, forming a rope-like assembly that provides tensile strength to tissues.
• Synthesis: Collagen synthesis involves several steps, starting with the translation of collagen mRNA to form preprocollagen, which contains extra peptide sequences.
• Post-Translational Modifications: Before forming the mature collagen, the procollagen undergoes extensive post-translational modifications such as hydroxylation of proline and lysine residues, crucial for stability and secretion.
• Assembly and Secretion: Hydroxylated procollagen forms a triple helix, is processed in the Golgi apparatus, and secreted into the extracellular matrix, where it forms collagen fibres.

There are at least 28 different types of collagen, with Types I, II, III, and IV being the most common. Each type is found in specific locations and has distinct roles.

Collagen type _ Notes _ Associated conditions| I _ Bone, skin, tendon _ Osteogenesis imperfecta| II _ Hyaline cartilage, vitreous humour _ | III_ Reticular fibre, granulation tissue _ Vascular variant of Ehlers-Danlos syndrome | IV _ Basal lamina, lens, basement membrane _ Alport syndrome (mutations in the genes encoding Type IV collagen), Goodpasture's syndrome (autoimmune reaction where antibodies attack the Type IV collagen)| V _ Most interstitial tissue, placental tissue _ Classical variant of Ehlers-Danlos syndrome|