Cone opsin (also known as photopsin) (Varies by cone type (L-opsin, M-opsin, S-opsin for long, medium, and short wavelength cones, respectively))

Cone cell photopigments (opsins/photopsins) are light-sensitive G protein-coupled receptors located in the outer segment membranes of cone photoreceptor cells in the retina[2][3][4]. These molecules consist of an opsin protein—a transmembrane protein with seven transmembrane domains arranged in a barrel-like structure[1]—bound to the chromophore retinal (an oxidized derivative of vitamin A)[4]. Three distinct cone opsin variants exist, each with different peak wavelength sensitivities: L-opsin (red/long wavelength), M-opsin (green/medium wavelength), and S-opsin (blue/short wavelength)[4][7]. When photons strike the photopigment, they trigger photoisomerization of the retinal chromophore, causing a conformational change in the opsin that initiates the phototransduction cascade, ultimately generating electrical signals that enable color vision and daylight sight[3][4]. Unlike rod photopigments (rhodopsin), cone opsins reside on open disc membranes that remain continuous with the cell's plasma membrane, allowing rapid molecular exchange and supporting the high metabolic demands of daylight vision[3]. Mutations in cone opsin genes and dysregulation of cone opsin expression are associated with color blindness, enhanced S-cone syndrome, and other inherited retinal dystrophies, making cone opsins relevant targets for understanding and potentially treating retinal disease[3].

Other names

PhotopsinIodopsinCone pigmentL-opsinM-opsinS-opsinRed opsin (L-cone)green opsin (M-cone)blue opsin (S-cone)

Cone opsins function as light-activated GPCRs. When photons are absorbed by the retinal chromophore bound within the opsin's transmembrane barrel structure[1], the opsin undergoes a conformational change from 11-*cis*-retinal to all-*trans*-retinal[3]. This activated opsin binds to the G-protein transducin, initiating a phototransduction cascade that ultimately modulates cGMP-gated ion channels and generates electrical signals[3][4].