Rhodopsin

• OMIM: 180380
• UniProt: P08100

Rhodopsin, also known as visual purple because of its red color, is one of the visual pigments in the retina ( retina) of the eyes of vertebrates ( vertebrates ) and in the photoreceptors of invertebrates ( invertebrates ). In the human eye, the rhodopsin in the rods of the retina is responsible for the light-dark vision. Mutations in the opsin gene can lead to retinitis pigmentosa and congenital night blindness.

But there are also various other photoreceptors that differ in their sensitivity to light of certain wavelengths. So based color vision using the pin on three different forms of Iodopsins, which differ only slightly in their amino acid sequences.

Details

Rhodopsin is a protein consisting of rod opsin ( Skotopsin ) and the unsaturated aldehyde 11-cis -retinal is composed. The 11-cis -retinal (aldehyde of retinol ) is covalently bonded to the ε -amino group of the lysine moiety of the protein as K256 imine ( Schiff base ). An absorption maximum in the visible range is λ = 500 nm at the beginning of the visual process leads the incident light to an isomerization of the retinal (11 -cis-retinal, all-trans -retinal → ). For this purpose, only one photon of sufficient energy is needed. This results in a conformational change in opsin, which leads via the activation of the G- protein transducin for triggering the visual signal transduction.

It is the most famous and best-studied member of a protein family of G- protein coupled receptors ( GPCR). The characteristic feature of this family are seven transmembrane domains and a receptor that is activated by addition of a ligand, the G protein ( by GTP is attached to G- protein and the left in an inactive state where GDP replaced). Bovine rhodopsin was first GPCR from which was present, a crystal structure obtained by X-ray structural analysis. It therefore serves as a template for models of other GPCRs, although the match in the primary structure partially is very low. But since 21 October 2007, a crystal structure of the human β2 - adrenergic receptor is published. In June 2008, structures of the β1 - adrenergic receptor from turkey (Meleagris gallopavo ) and the rhodopsin of the Japanese flying squid followed ( Todarodes pacificus ).

Medical reference

A lack of vitamin A as a source of retinal leads to night blindness, dryness of the eye ( xerophthalmia ) and an inflammation of the cornea (keratitis ) of the eye. In children, vitamin A deficiency and blindness. This occurs because of the rice-based diet especially common in the Third World countries. The daily requirement of vitamin A is an adult 90/496/EEC ( EU Nutrition Labelling Directive ) established in accordance with European Directive with 800 micrograms.

Related Topics

A similar molecule bacteriorhodopsin, is found in halobacteria. It also contains retinal and is also composed of seven transmembrane domains. However, it is not coupled to a G protein. It is a light-driven proton pump.

In higher green plants, however, phytochrome functions as a light receptor that can occur in different states, as well as rhodopsin and the plant thus provides information about the currently existing light conditions.