G-protein-coupled receptor GPR139, member of the class A family of seven-transmembrane G protein-coupled receptors
GPR139, a vertebrate orphan receptor, is very closely related to GPR142, but they have different expression patterns in the brain and in other tissues. These receptors couple to inhibitory G proteins and activate phospholipase C. Studies suggested that dimer formation may be required for their proper function. GPR142 is predominantly expressed in pancreatic beta-cells and plays an important role in mediating insulin secretion and maintaining glucose homeostasis, whereas GPR139 is expressed almost exclusively in the brain and is suggested to play a role in the control of locomotor activity. Tryptophan and phenylalanine have been identified as putative endogenous ligands of GPR139. These orphan receptors are phylogenetically clustered with invertebrate FMRFamide receptors such as Drosophila melanogaster DrmFMRFa-R.