G protein-coupled receptors 26 and 78, member of the class A family of seven-transmembrane G protein-coupled receptors
Orphan G-protein coupled receptor 26 (GPR26) and GPR78 are constitutively active and coupled to increased cAMP formation. They are closely related based on sequence homology and comprise a conserved subgroup within the class A G-protein coupled receptor (GPCR) superfamily. Both receptors are widely expressed in selected tissues of the brain but their endogenous ligands are unknown. GPR26 knockout mice showed increased levels of anxiety- and depression-like behaviors, whereas GPR78 has been implicated in susceptibility to bipolar affective disorder and schizophrenia. Members of this subgroup contain the highly conserved Asp-Arg-Tyr/Phe (DRY/F) motif found in the third transmembrane helix (TM3) of the rhodopsin-like class A receptors which is important for efficient G protein-coupled signal transduction. 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.
Comment:based on the structures of some class A family members with bound ligands (peptides or chemicals), agonists, or antagonists
Comment:Small-molecule chemical ligands tend to bind deeper within the receptor core, compared to a peptide ligand neurotensin, which binds towards the extracellular surface of its receptor.
Jiyao W et al.(2023). "The conserved domain database in 2023.",