Rodopsin

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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 OMIM180380 MGI97914 HomoloGene68068 GeneCards: RHO Gene
Pregled RNK izražavanja
PBB GE RHO 206454 s at tn.png
PBB GE RHO 206455 s at tn.png
podaci
Ortolozi
Vrsta Čovek Miš
Entrez 6010 212541
Ensembl ENSG00000163914 ENSMUSG00000030324
UniProt P08100 Q8K0D8
RefSeq (mRNA) NM_000539 NM_145383
RefSeq (protein) NP_000530 NP_663358
Lokacija (UCSC) Chr 3:
130.73 - 130.74 Mb
Chr 6:
115.9 - 115.9 Mb
PubMed pretraga [1] [2]

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[uredi - уреди]

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]

Goveđi rodopsin

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[uredi - уреди]

  1. 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. 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. 
  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. 
  4. Kolb H, Fernandez E, Nelson R, Jones BW (1. 3. 2010.). "Webvision: Photoreceptors". University of Utah. http://webvision.med.utah.edu/photo1.html. 
  5. 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. 
  6. 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. 
  7. 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. 
  8. "Monomeric G-Protein-Coupled Receptor as a Functional Unit - Biochemistry (ACS Publications)". http://pubs.acs.org/doi/abs/10.1021/bi050720o. 

Literatura[uredi - уреди]

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  • Stuart JA, Brige RR (1996). Lee AG. ur. Rhodopsin and G-Protein Linked Receptors, Part A (Vol 2, 1996) (2 Vol Set). Greenwich, Conn: JAI Press. str. 33-140. 
  • Litmann BJ, Mitchell DC (1996). Lee AG. ur. Rhodopsin and G-Protein Linked Receptors, Part A (Vol 2, 1996) (2 Vol Set). Greenwich, Conn: JAI Press. str. 1-32. 
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Spoljašnje veze[uredi - уреди]