G protein-coupled receptor 88, member of the class A family of seven-transmembrane G protein-coupled receptors
GPR88, an orphan G protein-coupled receptor, is predominantly and almost exclusively expressed within medium spiny neurons (MSNs) of the brain's striatum in both human and rodents; thus it is also called Striatum-specific GPCR (STRG). The striatum is known to involve in motor coordination, reward-based decision making, and response learning. GPR88 is shown to co-localize with both dopamine D1 and D2 receptors and displays the highest sequence similarity to receptors for biogenic amines such as dopamine and serotonin. GPR88 knockout mice showed abnormal behaviors observed in schizophrenia, such as disrupted sensorimotor gating, increased stereotypic behavior and locomotor activity in response to treatment with dopaminergic compounds such as apomorphine and amphetamine, respectively, suggesting a role for GPR88 in dopaminergic signaling. Furthermore, the transcriptional profiling studies showed that GPR88 expression is altered in a number of psychiatric disorders such as depression, drug addiction, bipolar and schizophrenia, providing further evidence that GPR88 plays an important role in CNS signaling pathways related to psychiatric disorder. 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.