Rhodopsin

visual purple
Rhodopsin (also known as visual purple) is a light-sensitive receptor protein involved in visual phototransduction.wikipedia
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Biological pigment

pigmentpigmentspigmentation
Rhodopsin is a biological pigment found in the rods of the retina and is a G-protein-coupled receptor (GPCR).
Carotenes: alpha and beta carotene, lycopene, rhodopsin

Paul Hargrave

Its amino acid sequence and physical structure were established in the early 1980s by the laboratories of Yuri Ovchinnikov in Russia and Paul Hargrave in the United States.
Paul Hargrave (born 1938) is an American biochemist whose laboratory work established key features of the structure of rhodopsin.

G protein-coupled receptor

G protein-coupled receptorsGPCRG protein-coupled
Rhodopsin is a biological pigment found in the rods of the retina and is a G-protein-coupled receptor (GPCR). Scotopsin is an opsin, a light-sensitive G protein coupled receptor that embeds in the lipid bilayer of cell membranes using seven protein transmembrane domains.
More recently, an alternative classification system called GRAFS (Glutamate, Rhodopsin, Adhesion, Frizzled/Taste2, Secretin) has been proposed.

Vitamin A

Avitamins ARAE
Retinal is produced in the retina from vitamin A, from dietary beta-carotene.
Vitamin A is needed by the retina of the eye in the form of retinal, which combines with protein opsin to form rhodopsin, the light-absorbing molecule necessary for both low-light (scotopic vision) and color vision.

Rod cell

rodsrodrod cells
Rhodopsin is a biological pigment found in the rods of the retina and is a G-protein-coupled receptor (GPCR).
The pigment, called rhodopsin (conopsin is found in cone cells) comprises a large protein called opsin (situated in the plasma membrane), attached to which is a covalently bound prosthetic group: an organic molecule called retinal (a derivative of vitamin A).

Melanopsin

melanopsin (Opn4)Opn4Opsin 4, Melanopsin
The remaining opsin, melanopsin, is found in photosensitive ganglion cells and absorbs blue light most strongly.
In the mammalian retina, there are two additional categories of opsins, both involved in the formation of visual images: rhodopsin and photopsin (types I, II, and III) in the rod and cone photoreceptor cells, respectively.

Franz Christian Boll

Rhodopsin was discovered by Franz Christian Boll in 1876.
Boll is remembered for the discovery of rhodopsin, when he noticed that the light-sensitive pigment in the rods of the retina had a tendency to fade in the presence of illumination.

Opsin

opsinsSWS1 and M/LWS
Scotopsin is an opsin, a light-sensitive G protein coupled receptor that embeds in the lipid bilayer of cell membranes using seven protein transmembrane domains.
Rhodopsin (Rh1, OPN2, RHO) – expressed in rod cells, used in night vision

Photopsin

iodopsinporphyropsinclassical type 2 opsin genes
The photopsins are found in the cone cells of the retina and are the basis of color vision.
Iodopsin, the cone pigment system in chicken retina, is a close analog of the visual purple rhodopsin that is used in night vision.

Transducin

Isomerization of 11-cis-retinal into all-trans-retinal by light sets off a series of conformational changes ('bleaching') in the opsin, eventually leading it to a form called metarhodopsin II (Meta II), which activates an associated G protein, transducin, to trigger a cyclic guanosine monophosphate (cGMP) second messenger cascade.
Light leads to conformational changes in rhodopsin, which in turn leads to the activation of transducin.

George Wald

Wald, George
The intermediates formed during this process were first investigated in the laboratory of George Wald, who received the Nobel prize for this research in 1967.
His further experiments showed that when the pigment rhodopsin was exposed to light, it yielded the protein opsin and a compound containing vitamin A. This suggested that vitamin A was essential in retinal function.

Protein

proteinsprotein synthesisproteinaceous
Rhodopsin consists of two components, a protein molecule also called scotopsin and a covalently-bound cofactor called retinal.
Hybrid methods combining standard molecular dynamics with quantum mechanical mathematics explored the electronic states of rhodopsins.

Retina

retinal diseasesretinasretinal
Rhodopsin is a biological pigment found in the rods of the retina and is a G-protein-coupled receptor (GPCR). Retinal is produced in the retina from vitamin A, from dietary beta-carotene.
Rhodopsin

Retinal

retinaldehydeall-trans-retinalretinylidene
Rhodopsin consists of two components, a protein molecule also called scotopsin and a covalently-bound cofactor called retinal.
3) 11-cis-retinal + aporhodopsin → rhodopsin + H 2 O; forms Schiff base linkage to lysine, -CH=N + H-,

Lysine

Lyslysine degradationlysine biosynthesis
These domains form a pocket where the photoreactive chromophore, retinal, lies horizontally to the cell membrane, linked to a lysine residue in the seventh transmembrane domain of the protein.
In opsins like rhodopsin and the visual opsins (encoded by the genes OPN1SW, OPN1MW, and OPN1LW), retinaldehyde forms a Schiff base with a conserved lysine residue, and interaction of light with the retinylidene group causes signal transduction in color vision (See visual cycle for details).

Archaerhodopsin

Some prokaryotes express proton pumps called bacteriorhodopsins, archaerhodopsins, proteorhodopsins, and xanthorhodopsins to carry out phototrophy.
They function similarly to the mammalian protein Rhodopsin, but are structurally distinct.

Schiff base

azomethineSchiff base linkageSchiff base reaction
In rhodopsin, the aldehyde group of retinal is covalently linked to the amino group of a lysine residue on the protein in a protonated Schiff base (-NH + =CH-).
Similarly, the cofactor retinal forms a Schiff base in rhodopsins, including human rhodopsin (via Lysine 296), which is key in the photoreception mechanism.

Visual phototransduction

phototransductionvisual cyclephototransducing
Rhodopsin (also known as visual purple) is a light-sensitive receptor protein involved in visual phototransduction.
Finally, it is oxidized to 11-cis retinal before traveling back to the rod outer segment where it is again conjugated to an opsin to form new, functional visual pigment (rhodopsin).

Retinitis pigmentosa

pigmentary retinopathyretinitis pigmentosa sine pigmento
Mutation of the rhodopsin gene is a major contributor to various retinopathies such as retinitis pigmentosa.
In 1989, a mutation of the gene for rhodopsin, a pigment that plays an essential part in the visual transduction cascade enabling vision in low-light conditions, was identified.

Channelrhodopsin

channelrhodopsin-2channelrhodopsins
Unicellular flagellate algae contain channelrhodopsins that act as light-gated cation channels when expressed in heterologous systems.
Channelrhodopsins are a subfamily of retinylidene proteins (rhodopsins) that function as light-gated ion channels.

Cryptochrome

cryptochromesCRY1CRY
Humans have eight other opsins besides rhodopsin, as well as cryptochrome (light-sensitive, but not an opsin).
However, the lateral neurons receive light information through both the blue light CRY pathway and the rhodopsin pathway.

Proteorhodopsin

Some prokaryotes express proton pumps called bacteriorhodopsins, archaerhodopsins, proteorhodopsins, and xanthorhodopsins to carry out phototrophy.
Some members of the family, Homologous rhodopsin-like pigments, i.e. bacteriorhodopsin (of which there are more than 800 types) have Sensory Functions like opsins, integral for visual phototransduction.

Arrestin

β-arrestinarrestinsb-arrestin
Meta II is deactivated rapidly after activating transducin by rhodopsin kinase and arrestin.
Arrestin-2 was the first non-visual arrestin cloned. It was first named β-arrestin simply because between two GPCRs available in purified form at the time, rhodopsin and β 2 -adrenergic receptor, it showed preference for the latter.

Bacteriorhodopsin

bacteriorhodopsinsArchaerhodopsin 3
Some prokaryotes express proton pumps called bacteriorhodopsins, archaerhodopsins, proteorhodopsins, and xanthorhodopsins to carry out phototrophy.
They have similarities to vertebrate rhodopsins, the pigments that sense light in the retina.

Congenital stationary night blindness

Other mutations on rhodopsin lead to X-linked congenital stationary night blindness, mainly due to constitutive activation, when the mutations occur around the chromophore binding pocket of rhodopsin.
Only three rhodopsin mutations have been found associated with congenital stationary night blindness (CSNB).