histamine subtype H2 receptor, member of the class A family of seven-transmembrane G protein-coupled receptors
This group includes histamine receptor subtype H2R, a member of histamine receptor family, which belongs to the class A of GPCRs. Histamine plays a key role as chemical mediator and neurotransmitter in various physiological and pathophysiological processes in the central and peripheral nervous system. Histamine exerts its functions by binding to four different G protein-coupled receptors (H1-H4). The H2R subtype selectively interacts with the G(s)-type G protein that activates adenylate cyclase, leading to increased cAMP production and activation of Protein Kinase A. H2R is found in various tissues such as the brain, stomach, and heart. Its most prominent role is in histamine-induced gastric acid secretion. All GPCRs have a common structural architecture comprising of seven-transmembrane (TM) alpha-helices interconnected by three extracellular and three intracellular loops. A general feature of GPCR signaling is agonist-induced conformational changes in the receptors, leading to activation of the heterotrimeric G proteins, which consist of the guanine nucleotide-binding G-alpha subunit and the dimeric G-beta-gamma subunits. The activated G proteins then bind to and activate numerous downstream effector proteins, which generate second messengers that mediate a broad range of cellular and physiological processes.
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