Cone opsin (OPN1) (OPN1)

Cone opsins, also known as photopsins, are a group of light-sensitive G protein-coupled receptors (GPCRs) located in the outer segments of cone photoreceptor cells in the retina. They are responsible for mediating color vision and visual acuity under bright light (photopic) conditions. In humans, there are three types of cone opsins: Short-wave-sensitive (S-opsin/OPN1SW), Medium-wave-sensitive (M-opsin/OPN1MW), and Long-wave-sensitive (L-opsin/OPN1LW), which respond to blue, green, and red light respectively (UniProt: P03999, P04000, P04001). Each opsin protein is associated with the chromophore 11-cis-retinal; light absorption triggers the isomerization of retinal to all-trans-retinal, initiating a biochemical cascade that results in a neural signal (PubMed: 29130302). Mutations in the genes encoding these opsins lead to various vision disorders, including color blindness and blue cone monochromacy (NIH: GeneReviews). Current therapeutic research is heavily focused on gene therapy approaches using viral vectors to deliver functional opsin genes to the retina to restore vision in affected individuals (ClinicalTrials.gov: NCT04220892).

Other names

PhotopsinIodopsinVisual pigmentColor opsinShort-wave-sensitive opsin 1Medium-wave-sensitive opsin 1Long-wave-sensitive opsin 1OPN1LWOPN1MWOPN1SW

Cone opsins act as light-sensitive G protein-coupled receptors. Upon photon absorption, the 11-cis-retinal chromophore isomerizes to all-trans-retinal, triggering a conformational change to the active Metarhodopsin II state. This state activates the G-protein transducin (Gt), which then stimulates cGMP phosphodiesterase (PDE6). The resulting decrease in intracellular cGMP levels leads to the closure of cyclic nucleotide-gated (CNG) channels, causing membrane hyperpolarization and a reduction in glutamate release at the synaptic terminal (PubMed: 29130302, UniProt: P03999).