Rodopsin

Rodopsin (opsin 2, štap pigment) (retinitis pigmentosa 4, autosomno dominantan)
	; Senzorni rodopsin II (duginih boja) smešten u lipidnom dvosloju (glave crveno i repovi plavo) sa transducinom ispod njega. Gtα je obojen crveno, Gtβ plavo, i Gtγ žuto. GDP molekul je vezan u Gtα-podjedinici i kovalento vezani retinal (crno ) je u rodopsinu. N-terminus rodopsina je crven i C-terminus je plav. Pretpostavljeno ankerisanje transducina za membranu je prikazano u crnoj boji.
Dostupne strukture
	1eds, 1edx, 1f88, 1gzm, 1hzx, 1jfp, 1l9h, 1ln6, 1u19, 2g87, 2hpy, 2i35, 2i36, 2i37
Identifikatori
Simboli	RHO; MGC138309; MGC138311; OPN2; RP4
Vanjski ID	OMIM: 180380 MGI: 97914 HomoloGene: 68068 GeneCards: RHO Gene
Ontologija gena
Molekularna funkcija	• rodopsinu-slična receptorska aktivnost • receptorska aktivnost
Celularna komponenta	• fotoreceptorski spoljašnji segment • membrana plazme • integralno sa membranom plazme
Biološki proces	• signalni put G-protein spregnutog receptora • vizuelna percepcija • fototransdukcija, vidljiva svetlost • rodopsin posredovana signalizacija • protein-hromofor veza • respons na stimulus
Pregled RNK izražavanja
	podaci
Ortolozi

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Rodopsin, mrežnjačin purpur, je pigment retine koji je odgovoran za formiranje fotoreceptorskih ćelija, i za prve događaje u percepciji svetlosti. Rodopsini pripadaju familiji G-protein spregnutih receptora i ekstremno su senzitivni na svetlost, što omogućava vid u slabo-osvetljenoj sredini.^[1] Exposed to light, the pigment immediately photobleaches, and it takes about 30 minutes^[2] to regenerate fully in humans.

Struktura

Rodopsin se sastoji od proteinskog dela opsina i reverzibilno kovalentno vezanog kofaktor, retinala. Opsin, svežanj sedam transmembranskih heliksa međusobno povezanih proteinskim petljama, vezuje retinal (fotoreaktivni hromofor), koji je lociran u centralnoj šupljini na lizinskom ostatku sedmog heliksa. Retinal zauzima horizontalan položaj u odnosu na membranu. Svaki spoljašnji segment diska sadrži hiljade vizuelnih molekula pigmenta. Oko polovine opsina je unutar lipidnog dvosloja. Retinal nastaje u retini iz Vitamina A, dijetarnog beta-karotena. Izomerizacija 11-cis-retinala u sve-trans-retinal pod uticajem svetlosti indukuje konformacionu promenu (beljenje) u opsina, koja se nastavlja sa metarodopsinom II, koji aktivira vezani G protein transducin, i započinje kaskadu sekundarnih glasnika.^[2]^[3]^[4]

Rodopsin štapića najsnažnije apsorbuje zeleno-plavu svetlost, i zato izgleda crvenkasto-ljubičasto. On se naziva "vizuelno ljubičasto". Rodopsin je odgovoran za monohromatski vid u tami.^[2]

Nekoliko blisko srodnih opsina postoji. Oni se razlikuju u nekoliko aminokiselina, i konsekventno u talasnoj dužini svetlosti koju najjače apsorbuju. Kod čoveka postoje četiri različita opsina pored rodopsina. Fotopsini se nalazi u različitim tipovima koničnih ćelija retine, i oni su baza raspoznavanja boja. Oni imaju maksimume apsorpcije za žuto-zeleno (fotopsin I), zeleno (fotopsin II), i plavo-ljubičasto (fotopsin III) svetlo. Preostali opsin (melanopsin) se nalazi u fotosenzitivnim ganglionskim ćelijama, i apsorbuje najjače plavu svetlost.

Struktura rodopsina je detaljno proučena putem rendgenske strukturne analize kristala rodopsina. Fotoizomerizaciona dinamika je bila istražena putem FTIR spektroskopije i UV/Vis spektroskopije. Prvi fotoprodukt, fotorodopsin, se formira u toku 200 femtosekundi nakon iradijacije, čemu sledi u toku nekoliko pikosekundi drugi, batorodopsin, sa deformisanim sve-trans vezama. Taj intermedijar može da bude zarobljen i studiran na kriogenim temperaturama. Više modela (npr. mehanizam pedala bicikla, hula-tvist mehanizam) pokušava da objasni kako retinalna grupa može da promeni svoju konformaciju bez sudaranja sa okružujućim rodopsin proteinskim džepom.^[5]^[6]^[7]

Nedavni nalazi indiciraju da rodopsin funkcionače kao monomer, a ne kao dimer, mada je to dugo vremena bila ustaljena paradigma za G-spregnute proteinske receptore.^[8]

Reference

↑ Litmann BJ, Mitchell DC (1996). „Rhodopsin structure and function”. u: Lee AG. Rhodopsin and G-Protein Linked Receptors, Part A (Vol 2, 1996) (2 Vol Set). Greenwich, Conn: JAI Press. str. 1-32. ISBN 978-1-55938-659-3.
↑ ^2,0 ^2,1 ^2,2 Stuart JA, Brige RR (1996). „Characterization of the primary photochemical events in bacteriorhodopsin and rhodopsin”. u: Lee AG. Rhodopsin and G-Protein Linked Receptors, Part A (Vol 2, 1996) (2 Vol Set). Greenwich, Conn: JAI Press. str. 33-140. ISBN 978-1-55938-659-3.
↑ Hofmann KP, Heck M (1996). „Light-induced protein-protein interactions on the rod photoreceptor disc membrane”. u: Lee AG. Rhodopsin and G-Protein Linked Receptors, Part A (Vol 2, 1996) (2 Vol Set). Greenwich, Conn: JAI Press. str. 141-198. ISBN 978-1-55938-659-3.
↑ Kolb H, Fernandez E, Nelson R, Jones BW (1. 3. 2010.). „Webvision: Photoreceptors”. University of Utah. Arhivirano iz originala na datum 2000-08-16.
↑ Nakamichi H, Okada T (June 2006). „Crystallographic analysis of primary visual photochemistry”. Angew. Chem. Int. Ed. Engl. 45 (26): 4270-3. DOI:10.1002/anie.200600595. PMID 16586416.
↑ Schreiber M, Sugihara M, Okada T, Buss V (June 2006). „Quantum mechanical studies on the crystallographic model of bathorhodopsin”. Angew. Chem. Int. Ed. Engl. 45 (26): 4274-7. DOI:10.1002/anie.200600585. PMID 16729349.
↑ Weingart O (September 2007). „The twisted C11-C12 bond of the rhodopsin chromophore--a photochemical hot spot”. J. Am. Chem. Soc. 129 (35): 10618-9. DOI:10.1021/ja071793t. PMID 17691730.
↑ „Monomeric G-Protein-Coupled Receptor as a Functional Unit - Biochemistry (ACS Publications)”.

Literatura

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