Annexins in Bruch’s Memberane and Drusen

Abstract

Annexins (also known as lipocortins) are a family of calcium and phospholipid-binding proteins. At least 20 members of this family are known, and they have a wide range of potential functions, such as vesicular transport and trafficking, endocytosis, exocytosis and cellcell adhesion. Annexins have molecular weights ranging between 30 and 40kDA (the exception is annexin VI which is 66kDA) and possess striking structural features. To qualify as an annexin, a protein must have 1) the presence of a conserved 70 amino acid domain repeated either 4 or 8 times in the overall structure (annexin VI has an 8 repeating amino acid domain; whereas the rest have 4), 2) the ability to bind phosopholipids in the presence of calcium. Annexins are exported from the cytosol to the exterior of cells across the plasma membrane by an unknown mehanism. When located extracellular, some annexins have been shown to function as receptors for other extracellular proteins: annexin II binds to tenascin and tissue plasminogen activator, while annexin V binds to collagen (Kojima, 1997).