melanocortin receptor subtype 3, member of the class A family of seven-transmembrane G protein-coupled receptors
The melanocortin receptor (MCR) subfamily is a member of the class A family of seven-transmembrane G-protein coupled receptors. MCRs bind a group of pituitary peptide hormones known as melanocortins, which include adrenocorticotropic hormone (ACTH) and the different isoforms of melanocyte-stimulating hormones. There are five known subtypes of the MCR subfamily. MC1R is involved in regulating skin pigmentation and hair color. ACTH (adrenocorticotropic hormone) is the only endogenous ligand for MC2R, which shows low sequence similarity with other melanocortin receptors. Mutations in MC2R cause familial glucocorticoid deficiency type 1, in which patients have elevated plasma ACTH and low cortisol levels. MC3R is expressed in many parts of the brain and peripheral tissues and involved in the regulation of energy homeostasis. MC4R is expressed primarily in the central nervous system and involved in both eating behavior and sexual function. MC5R is widely expressed in peripheral tissues and is mainly involved in the regulation of exocrine gland function.