Melanopsin receptor (OPN4)

Melanopsin receptor (OPN4) is a G protein-coupled receptor (GPCR) photopigment encoded by the OPN4 gene and predominantly expressed in intrinsically photosensitive retinal ganglion cells (ipRGCs) of the mammalian retina[1][2][3][4][5]. It plays a crucial role in non-image-forming photoreception, especially the regulation of circadian rhythms by transmitting information about environmental light to the brain's suprachiasmatic nucleus (the master circadian clock)[1][2][4]. Melanopsin is maximally sensitive to blue light (~480 nm), couples predominantly to Gq/11-type G proteins, and activates downstream signaling that results in cellular depolarization and calcium influx—a process distinct from classical rod and cone photoreceptors[1][2][3][5]. Mutations or deficiencies in OPN4 are linked to disorders such as Seasonal Affective Disorder and impairments in circadian entrainment[1][3][4]. Melanopsin's non-visual (photoentrainment, pupillary response) and potential visual (contribution to optokinetic response) functions make it a specialized molecular target in chronobiology and ophthalmology, though there are currently no clinically approved drugs targeting OPN4 directly[3][4][5].

Other names

melanopsinopsin 4OPN4MOPmelanopsin receptormelanopsin-opsinopn4Opsin-4

Light-dependent activation via G protein-coupled signaling cascade (Gq/11, sometimes Gi/o) leading to membrane depolarization and increase in intracellular calcium[1][2][3][5]