A family of five distinct gene products, thrombospondins (TSP) 1–4 and cartilage oligomeric matrix protein, that are extracellular calcium-binding proteins involved in cell proliferation, adhesion, and migration. Thrombospondin I (TSP1, 1170 aa) is a homotrimeric glycoprotein (450 kDa) found in the α granules of platelets, and synthesized and secreted for incorporation into the extracellular matrix by a variety of cells including endothelial cells, fibroblasts, smooth muscle cells, and type II pneumocytes. It binds heparin, and various extracellular matrix components. TSP 2 (1172 aa) is similar in properties to TSP1. TSP 1 and 2 promote synaptogenesis in the central nervous system. TSP 3 (956 aa) is a developmentally regulated heparin binding protein. TSP 4 (961 aa) also has heparin-binding properties but differs in being a potential integrin ligand.
Subjects: Chemistry — Medicine and Health.