The thrombospondins are a family of proteins that are involved in different biological processes. For this reason, thrombospondins are called multifunctional proteins. The protein family consists of thrombospondins 1-5. A distinction is made between subgroups: Subgroup A consists of TSP1 and TSP2; subgroup B consists of TSP3, TSP4 and TSP5. TSP1 and TSP2 are homotrimers, which means that they consist of three identical subunits. TSP3, TSP4 and TSP5 are homopentamers, they consist of five identical subunits.
TSP1 was first isolated from blood platelets ( thrombocytes ) that were stimulated with thrombin . For this reason, thrombospondin was initially called a 'thrombin-sensitive protein'. TSP1 is involved in many different biological processes, such as the formation of new blood vessels ( angiogenesis ), programmed cell death ( apoptosis ), the activation of the tissue hormone TGF-β and immune regulation . TSP1 has several receptors including CD36 , CD47, and integrins .
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