trissin receptor and related proteins, member of the class A family of seven-transmembrane G protein-coupled receptors
This subgroup represents the Drosophila melanogaster trissin receptor and closely related invertebrate proteins which are a member of the class A family of seven-transmembrane G-protein coupled receptors. The cysteine-rich trissin has been shown to be an endogenous ligand for the orphan CG34381 in Drosophila melanogaster. Trissin is a peptide composed of 28 amino acids with three intrachain disulfide bonds with no significant structural similarities to known endogenous peptides. Cysteine-rich peptides are known to have antimicrobial or toxicant activities, although frequently their mechanism of action is poorly understood. Since the expression of trissin and its receptor is reported to predominantly localize to the brain and thoracicoabdominal ganglion, trissin is predicted to behave as a neuropeptide. 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.