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Thromboxane receptor
The thromboxane receptor (TP) also known as the prostanoid TP receptor is a protein that in humans is encoded by the TBXA2R gene, The thromboxane receptor is one among the five classes of prostanoid receptors and was the first eicosanoid receptor cloned. The TP receptor derives its name from its preferred endogenous ligand thromboxane A2.〔
The TP receptor is a G-protein coupled receptor coupled to the G protein Gq. The initial purification and cloning of the TP receptor established this protein as a member of the G protein-coupled super family of seven-transmembrane receptors. The gene responsible for the thromboxane receptor, TBXA2R is found on chromosome 19 and spans 15 kilobases.〔TBXA2R thromboxane A2 receptor (Homo sapiens) ()〕
== Heterogeneity ==
Molecular biology findings have provided definite evidence of human TP receptor subtypes.〔 The originally cloned TP from placenta (343 amino acids in length) is known as the α isoform, and the splice variant cloned from endothelium (with 407 amino acids) is termed the β isoform.〔 The first 328 amino acids are the same for both isoforms, but the β isoform exhibits an extended C-terminal cytoplasmic domain.〔 Both isoforms functionally couple to a Gq protein leading to the phospholipase C activation, calcium release and activation of protein kinase C.〔 Nevertheless, they couple oppositely to adenylate cyclase. TPα activates adenylate cyclase while TPβ inhibits this enzyme.〔 Intrareceptor differences in C-terminal tail sequence also allow for significant differences in their ability to internalize in response to agonist exposure. For example, in HEK-293 cells, TPβ but not TPα undergoes U46619-induced G protein-coupled receptor (GRK) phosphorylation and internalization, whereas the C-terminus of TPα is not capable of being phosphorylated by GRKs.〔
The expression of α and β isoforms is not equal within or across different cell types.〔 For example, platelets express high concentrations of the α isoform (and possess residual RNA for the β isoform), while expression of the β isoform has not been documented in these cells.〔 The β isoform is expressed in human endothelium.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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