G protein-coupled receptor 55 and similar proteins, member of the class A family of seven-transmembrane G protein-coupled receptors
GPR55 shares closest homology with GPR35, and they belong to the class A G protein-coupled receptor superfamily, which all have a common structural architecture comprising of seven-transmembrane (TM) alpha-helices interconnected by three extracellular and three intracellular loops. GPR55 has been reported to couple to G(13), G(12), or G(q) proteins. Activation of GPR55 leads to activation of phospholipase C, RhoA, ROCK, ERK, p38MAPK, and calcium release. Lysophophatidylinositol (LPI) is currently considered as the endogenous ligand for GPR55, although the receptor was initially deorphanized as a cannabinoid receptor and binds many cannabinoid ligands.