Reactome | Photons induce isomerization of 11c-retinyl to at-retinyl

Photons induce isomerization of 11c-retinyl to at-retinyl

Stable Identifier

R-HSA-74101

Type

Reaction [transition]

Species

Homo sapiens

Compartment

photoreceptor disc membrane, extracellular region

Synonyms

Rhodopsin activation

ReviewStatus

5/5

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Photons induce isomerization of 11c-retinyl to at-retinyl

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The visual pigment rhodopsin consists of a seven transmembrane helix protein, opsin (RHO), to which an 11-cis-retinal (11cRAL) chromophore is bound as a protonated Schiff base (Hargrave et al. 1983, Nathans & Hogness 1984, Ovchinnikov et al. 1983). The covalent bond between opsin and its 11-cis-retinyl (11c-retinyl) ligand, which is unique among G protein coupled receptors, helps to confer extraordinary stability in darkness (Baylor et al. 1984). 11cRAL is an inverse agonist, that quenches the weak ability of opsin to activate transducin G protein (Gt). Upon photon absorption, the bound 11c-retinyl group isomerizes in a few hundred femtoseconds (Schoenlein et al. 1991) and with a high quantum efficiency of 0.7 (Dartnall 1968) to the bound all-trans-retinyl (at-retinyl) isomer. Then in the next few milliseconds, opsin undergoes a rearrangement in structure that renders it catalytically active (MII aka metarhodopsin II or R*) (Emeis et al. 1982). The isomerisation is a very fast photochemical process (femtoseconds) followed by slower events (Smith 2010).

Mutations in RHO can give rise to autosomal dominant or recessive forms of retinitis pigmentosa or autosomal dominant congenital stationary night blindness (https://sph.uth.edu/retnet/). Retinitis pigmentosa is a progressive form of blindness marked by an initial degeneration of rods, followed by the secondary loss of cones.

Literature References

PubMed ID	Title	Journal	Year
6679757	[Visual rhodopsin. III. Complete amino acid sequence and topography in a membrane] Feĭgina, MIu, Ovchinnikov, IuA, Artamonov, ID, Abdulaev, NG, Bogachuk, AS	Bioorg. Khim.	1983
20192770	Structure and activation of the visual pigment rhodopsin Smith, SO	Annu Rev Biophys	2010
6342691	The structure of bovine rhodopsin Wang, JK, Rao, JK, Argos, P, McDowell, JH, Juszczak, E, Curtis, DR, Hargrave, PA, Fong, SL	Biophys. Struct. Mech.	1983
6288450	Complex formation between metarhodopsin II and GTP-binding protein in bovine photoreceptor membranes leads to a shift of the photoproduct equilibrium Reichert, J, Kühn, H, Emeis, D, Hofmann, KP	FEBS Lett.	1982
6512705	The photocurrent, noise and spectral sensitivity of rods of the monkey Macaca fascicularis Nunn, BJ, Schnapf, JL, Baylor, DA	J. Physiol. (Lond.)	1984
6589631	Isolation and nucleotide sequence of the gene encoding human rhodopsin. Hogness, DS, Nathans, J	Proc Natl Acad Sci U S A	1984
1925597	The first step in vision: femtosecond isomerization of rhodopsin Peteanu, LA, Shank, CV, Schoenlein, RW, Mathies, RA	Science	1991
5315589	The photosensitivities of visual pigments in the presence of hydroxylamine Dartnall, HJ	Vision Res.	1968