G protein-coupled receptor 149, member of the class A family of seven-transmembrane G protein-coupled receptors
GPR149 is predominantly expressed in the ovary and is present at low levels in the brain and the digestive tract (stomach and small intestine). GPR149-null mice are viable and have normal maturation of the ovarian follicle, but show enhanced fertility and ovulation. Additionally, the null mice showed increased expression levels of growth differentiation factor 9 (Gdf9) in oocytes, and upregulated expression of cyclin D2, a downstream target of FSH (follicle-stimulating hormone) receptor signaling pathways that promotes granulosa cell proliferation. GPR149 is an orphan receptor with no known endogenous ligand as yet identified. Although categorized as a member of the class A GPCRs, GPR149 lacks the first two charged amino acids of the highly conserved Asp-Arg-Tyr (DRY) motif found in the third transmembrane helix (TM3) of class A receptors which is important for efficient G protein-coupled signal transduction. Moreover, the transmembrane domains and carboxyl terminus of GPR149 show low similarities to other GPCRs. 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.