Melatonin receptors are G protein-coupled receptors (GPCR) which bind melatonin.[1] Three types of melatonin receptors have been cloned. The MT1 (or Mel1A or MTNR1A) and MT2 (or Mel1B or MTNR1B) receptor subtypes are present in humans and other mammals,[2] while an additional melatonin receptor subtype MT3 (or Mel1C or MTNR1C) has been identified in amphibia and birds.[3] The receptors are crucial in the signal cascade of melatonin. In the field of chronobiology, melatonin has been found to be a key player in the synchrony of biological clocks. Melatonin secretion by the pineal gland has circadian rhythmicity regulated by the suprachiasmatic nucleus (SCN) found in the brain. The SCN functions as the timing regulator for melatonin; melatonin then follows a feedback loop to decrease SCN neuronal firing. The receptors MT1 and MT2 control this process.[4] Melatonin receptors are found throughout the body in places such as the brain, the retina of the eye, the cardiovascular system, the liver and gallbladder, the colon, the skin, the kidneys, and many others.[5] In 2019, X-ray crystal and cryo-EM structures of MT1 and MT2 were reported.[6][7][8][9]
^Reppert SM (December 1997). "Melatonin receptors: molecular biology of a new family of G protein-coupled receptors". Journal of Biological Rhythms. 12 (6): 528–531. doi:10.1177/074873049701200606. PMID9406026. S2CID6501856.
^Reppert SM, Weaver DR, Godson C (March 1996). "Melatonin receptors step into the light: cloning and classification of subtypes". Trends in Pharmacological Sciences. 17 (3): 100–102. doi:10.1016/0165-6147(96)10005-5. PMID8936344.