Description
Cartilage Oligomeric Matrix Protein (COMP), also referred to as thrombospondin-5, is a secreted noncollagenous extracellular matrix (ECM) protein and belongs to the subgroup B of the thrombospondin protein family. The native glycoprotein incorporates five identical subunits, each with the molecular weight of 87 KDa consists of four epidermal growth factor (EGF)-like domains, eight so-called thrombospondin type 3 (T3) repeats (calcium-binding domain) and a carboxyl-terminal globular domain. A coiled-coil domain at the amino terminus mediates the pentamerization resulting in a bouquet-shaped subunit arrangement via disulfide-bonds. COMP is a component of cartilage, synovium, ligament, and tendon, and binds to other ECM proteins such as collagen I, II and IX with high affinities depending on the divalent cations Zn2+ or Ni2+. COMP is suggested to play a role in cell growth and development, and recent studies have revealed the possible mechanism that it protects cells against death by elevating members of the IAP (inhibitor of apoptosis protein) family of survival proteins. COMP mutations cause dominantly inherited chondrodysplasias Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) characterized by short stature and early-onset osteoarthrosi, and up-regulated expression of COMP are observed in rheumatoid arthritis and certain carcinomas