Melatonin receptor type 1 and type 2 (MT1 and MT2)

The **melatonin receptor type 1 (MT1)** and **type 2 (MT2)** are closely related **G protein–coupled receptors** that serve as the primary molecular targets of the neurohormone melatonin. These receptors help to regulate **circadian rhythms**, synchronize **sleep–wake cycles**, and influence REM and NREM sleep phases. MT1 and MT2 are both expressed in the central nervous system, with distinct anatomic and functional distributions. MT1 is primarily implicated in regulation of REM sleep, while MT2 facilitates NREM sleep. Both play roles in broader physiological regulation and are therapeutic targets for **insomnia**, **mood disorders**, and **type 2 diabetes**[1][2][3][4][5][6][7]. Additionally, certain polymorphisms in the MT2 (MTNR1B) receptor have been linked to increased diabetes risk. Both MT1 and MT2 share a canonical seven-transmembrane architecture, common to class A GPCRs, but exhibit unique ligand access mechanisms and differing binding pockets, which complicate efforts to create highly selective subtype-specific drugs. Their pharmacology is clinically relevant due to approved drugs such as ramelteon (for primary chronic insomnia), tasimelteon (for non-24-hour sleep-wake disorder), and agomelatine (for major depression). These receptors are considered valuable therapeutic targets due to their central roles in sleep regulation and potential disease associations, but challenges remain in achieving selectivity and minimizing off-target effects[1][2][3][4][5][6][7].

Other names

Melatonin receptor 1Melatonin receptor 2MTNR1A (MT1)MTNR1B (MT2)Melatonin receptor type 1AMelatonin receptor type 1B

Agonists (both selective and non-selective) mimic endogenous melatonin, activating MT1 and/or MT2 to regulate circadian rhythm, sleep architecture, and downstream signaling pathways[1][2][3][4][6]. Modulation of Gi/o protein signaling cascades, decreasing cAMP levels and affecting downstream targets[2]. Allosteric regulation (potential, based on membrane-buried channels and possible co-receptor interactions)[3][6].