Rhodopsin

This MedLibrary.org supplementary page on Rhodopsin is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:

Related Sponsors

BM Pharmacy Generic pharmaceuticals at unbeatable prices. Insomnia, men's health, hair health, pain control. bmpharmacy.com
Online Pharmacy Carisoprodol, tadalafil, sildenafil, vardenafil and more... xlpharmacy.com
MedBasket.com Discreet. Inexpensive. Fast shipping. Great selection. What more can we say? medbasket.com
Frugalmed 2000 reasons to shop with us first. frugalmed.com
Ads by Tiva

This article is about the visual rhodopsin of vertebrates. For other types of rhodopsin, see retinylidene protein.
Rhodopsin (opsin 2, rod pigment) (retinitis pigmentosa 4, autosomal dominant)
Sensory rhodopsin II (rainbow colored) embedded in a lipid bilayer (heads red and tails blue) with Transducin below it. Gtα is colored red, Gtβ blue, and Gtγ yellow. There is a bound GDP molecule in the Gtα-subunit and a bound retinal (black) in the rhodopsin. The N-terminus terminus of rhodopsin is red and the C-terminus blue. Presumed anchoring of transducin to the membrane has been drawn in black.
Available structures: 1eds, 1edx, 1f88, 1gzm, 1hzx, 1jfp, 1l9h, 1ln6, 1u19, 2g87, 2hpy, 2i35, 2i36, 2i37
Identifiers
Symbols RHO; MGC138309; MGC138311; OPN2; RP4
External IDs OMIM: 180380 MGI: 97914 HomoloGene: 68068
RNA expression pattern

More reference expression data
Orthologs
Human Mouse
Entrez 6010 212541
Ensembl ENSG00000163914 ENSMUSG00000030324
Uniprot P08100 Q8K0D8
Refseq NM_000539 (mRNA)
NP_000530 (protein)		 NM_145383 (mRNA)
NP_663358 (protein)
Location Chr 3: 130.73 - 130.74 Mb Chr 6: 115.9 - 115.9 Mb
Pubmed search [1] [2]

Rhodopsin, also known as visual purple, is a pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G-protein coupled receptor family and are extremely sensitive to light, enabling vision in low-light conditions. Exposed to white light, the pigment immediately photobleaches, and it takes about 30 minutes to regenerate fully in humans.

Contents

Structure

Rhodopsin consists of the protein moiety opsin and a reversibly covalently bound cofactor, retinal. Opsin, a bundle of seven transmembrane helices, binds retinal, a photoreactive chromophore, in a central pocket. Retinal is produced in the retina from Vitamin A. Isomerization of 11-cis-retinal into all-trans-retinal by light induces a conformational change in opsin that activates the associated G protein and triggers a second messenger cascade.

Rhodopsin of the rods most strongly absorbs green-blue light and therefore appears reddish-purple, which is why it is also called "visual purple". It is responsible for monochromatic vision in the dark.

Bovine rhodopsin

Several closely related opsins, the photopsins, exist that differ only in a few amino acids and in the wavelengths of light that they absorb most strongly. These pigments are found in the different types of the cone cells of the retina and are the basis of color vision. Humans have three different other opsins beside rhodopsin, with absorption maxima for yellowish-green (photopsin I), green (photopsin II), and bluish-violet (photopsin III) light.

The photoisomerization of rhodopsin has been studied in detail via x-ray crystallography on rhodopsin crystals. A first photoproduct called photorhodopsin forms within 200 femtoseconds after irradiation followed within picoseconds by a second one called bathorhodopsin with distorted all-trans bonds. This intermediate can be trapped and studied at cryogenic temperatures. Several models (e.g. the bicycle-pedal mechanism, hula-twist mechanism) attempt to explain how the retinal group can change its conformation without clashing with the enveloping rhodopsin protein pocket.123

Bleaching

The threshold is best determined by increasingly bright light on a white surface. When a certain number of equally bright flashes is reported (not all of them), the threshold frequency can be determined. Receptors absorb light and gradually convert the vibrational energy derived from the light into electricity, which is passed on to the bipolar cells. Maximum absorption corresponds to maximum sensitivity to light in the dark-adapted eye. In animals, the threshold sensitivity must be determined with unbiased means, such as the response of the pupil or, better yet, the electrical processes in the retina. The electroretinogram (ERG) is a record of changes between two electrodes: one on the cornea and one on a different body part, as triggered by eye illumination.

After a certain length of time in the light, little or no rhodopsin is available, but is replenished in the dark. Rhodopsin can be derived from rod-only animals such as the rat or guinea pig, but not the cone-only retina of the chicken. Cone pigments are not as easily extracted or identified.

The higher rod sensitivity may be due to concentration of pigment (for more efficient light capture) or efficiency of light-to-electrical energy conversion. Organization of retinal receptors and neurons are crucial for the study of sensitivity.

Different wavelengths give different sensitivities, e.g., blue-green over orange. At the threshold for white light, only white is seen, but when the intensity is increased to a certain point, color is perceived. The difference between these is the photochromatic interval. Since the rods are extremely insensitive to red light, this interval is zero for red light, which means that sensation of color and light are at the same intensity. 4

Rhodopsin and retinal disease

Mutation of the rhodopsin gene is a major contributor to various retinopathies such as retinitis pigmentosa. The disease-causing protein generally aggregates with ubiquitin in inclusion bodies, disrupts the intermediate filament network and impairs the ability of the cell to degrade non-functioning proteins which leads to photoreceptor apoptosis.5 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.6 Several other pathological states relating to rhodopsin have been discovered including poor post-Golgi trafficking, dysregulative activation, rod outer segment instability and arrestin binding.6

Microbial rhodopsins

Main article: Bacterial rhodopsins

Some prokaryotes express proton pumps called bacteriorhodopsin, proteorhodopsin, xanthorhodopsin to carry out phototrophy.7 Like rhodopsin, these contain retinal and have seven transmembrane alpha helices; however they are not coupled to a G protein. Bacterial halorhodopsin is a light-activated chloride pump.7 Finally, an alga is known to have an opsin that contains its own monolithic light-gated ion channel, channelrhodopsin. While bacteriorhodopsin, halorhodopsin, and channelrhodopsin all have significant sequence homology to one another, they have no detectable sequence identity to G-protein coupled receptor (GPCR) family where rhodopsins belong. Nevertheless, bacterial rhodopsins and GPCR are possibly evolutionary related, based on similarity of their three-dimensional structures. Therefore, they have been assigned to the same superfamily in Structural Classification of Proteins.8

References

  1. ^ 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. 
  2. ^ 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. 
  3. ^ 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. 
  4. ^ "eye, human."Encyclopædia Britannica. 2008. Encyclopædia Britannica 2006 Ultimate Reference Suite DVD
  5. ^ Saliba RS, Munro PM, Luthert PJ, Cheetham ME (July 2002). "The cellular fate of mutant rhodopsin: quality control, degradation and aggresome formation". J. Cell. Sci. 115 (Pt 14): 2907–18. PMID 12082151, http://jcs.biologists.org/cgi/pmidlookup?view=long&pmid=12082151. 
  6. ^ a b Mendes HF, van der Spuy J, Chapple JP, Cheetham ME (April 2005). "Mechanisms of cell death in rhodopsin retinitis pigmentosa: implications for therapy". Trends Mol Med 11 (4): 177–85. doi:10.1016/j.molmed.2005.02.007. PMID 15823756. 
  7. ^ a b Bryant DA, Frigaard NU (November 2006). "Prokaryotic photosynthesis and phototrophy illuminated". Trends Microbiol. 14 (11): 488–96. doi:10.1016/j.tim.2006.09.001. PMID 16997562. 
  8. ^ http://scop.mrc-lmb.cam.ac.uk/scop/data/scop.b.g.e.b.html.

Further reading

  • Humphries P, Kenna P, Farrar GJ (1992). "On the molecular genetics of retinitis pigmentosa.". Science 256 (5058): 804–8. doi:10.1126/science.1589761. PMID 1589761. 
  • Edwards SC (1995). "Involvement of cGMP and calcium in the photoresponse in vertebrate photoreceptor cells.". The Journal of the Florida Medical Association 82 (7): 485–8. PMID 7673885. 
  • al-Maghtheh M, Gregory C, Inglehearn C, et al. (1993). "Rhodopsin mutations in autosomal dominant retinitis pigmentosa.". Hum. Mutat. 2 (4): 249–55. doi:10.1002/humu.1380020403. PMID 8401533. 
  • Garriga P, Manyosa J (2002). "The eye photoreceptor protein rhodopsin. Structural implications for retinal disease.". FEBS Lett. 528 (1-3): 17–22. doi:10.1016/S0014-5793(02)03241-6. PMID 12297272. 
  • Mendes HF, van der Spuy J, Chapple JP, Cheetham ME (2005). "Mechanisms of cell death in rhodopsin retinitis pigmentosa: implications for therapy.". Trends in molecular medicine 11 (4): 177–85. doi:10.1016/j.molmed.2005.02.007. PMID 15823756. 
  • Inglehearn CF, Keen TJ, Bashir R, et al. (1993). "A completed screen for mutations of the rhodopsin gene in a panel of patients with autosomal dominant retinitis pigmentosa.". Hum. Mol. Genet. 1 (1): 41–5. PMID 1301135. 
  • Farrar GJ, Findlay JB, Kumar-Singh R, et al. (1993). "Autosomal dominant retinitis pigmentosa: a novel mutation in the rhodopsin gene in the original 3q linked family.". Hum. Mol. Genet. 1 (9): 769–71. PMID 1302614. 
  • Robinson PR, Cohen GB, Zhukovsky EA, Oprian DD (1992). "Constitutively active mutants of rhodopsin.". Neuron 9 (4): 719–25. doi:10.1016/0896-6273(92)90034-B. PMID 1356370. 
  • Fujiki K, Hotta Y, Hayakawa M, et al. (1992). "Point mutations of rhodopsin gene found in Japanese families with autosomal dominant retinitis pigmentosa (ADRP).". Jpn. J. Hum. Genet. 37 (2): 125–32. doi:10.1007/BF01899733. PMID 1391967. 
  • Olsson JE, Gordon JW, Pawlyk BS, et al. (1992). "Transgenic mice with a rhodopsin mutation (Pro23His): a mouse model of autosomal dominant retinitis pigmentosa.". Neuron 9 (5): 815–30. doi:10.1016/0896-6273(92)90236-7. PMID 1418997. 
  • Andréasson S, Ehinger B, Abrahamson M, Fex G (1993). "A six-generation family with autosomal dominant retinitis pigmentosa and a rhodopsin gene mutation (arginine-135-leucine).". Ophthalmic paediatrics and genetics 13 (3): 145–53. PMID 1484692. 
  • Inglehearn CF, Lester DH, Bashir R, et al. (1992). "Recombination between rhodopsin and locus D3S47 (C17) in rhodopsin retinitis pigmentosa families.". Am. J. Hum. Genet. 50 (3): 590–7. PMID 1539595. 
  • Fishman GA, Stone EM, Gilbert LD, Sheffield VC (1992). "Ocular findings associated with a rhodopsin gene codon 106 mutation. Glycine-to-arginine change in autosomal dominant retinitis pigmentosa.". Arch. Ophthalmol. 110 (5): 646–53. PMID 1580841. 
  • Keen TJ, Inglehearn CF, Lester DH, et al. (1992). "Autosomal dominant retinitis pigmentosa: four new mutations in rhodopsin, one of them in the retinal attachment site.". Genomics 11 (1): 199–205. PMID 1765377. 
  • Dryja TP, Hahn LB, Cowley GS, et al. (1991). "Mutation spectrum of the rhodopsin gene among patients with autosomal dominant retinitis pigmentosa.". Proc. Natl. Acad. Sci. U.S.A. 88 (20): 9370–4. doi:10.1073/pnas.88.20.9370. PMID 1833777. 
  • Gal A, Artlich A, Ludwig M, et al. (1992). "Pro-347-Arg mutation of the rhodopsin gene in autosomal dominant retinitis pigmentosa.". Genomics 11 (2): 468–70. PMID 1840561. 
  • Sung CH, Davenport CM, Hennessey JC, et al. (1991). "Rhodopsin mutations in autosomal dominant retinitis pigmentosa.". Proc. Natl. Acad. Sci. U.S.A. 88 (15): 6481–5. PMID 1862076. 
  • Jacobson SG, Kemp CM, Sung CH, Nathans J (1991). "Retinal function and rhodopsin levels in autosomal dominant retinitis pigmentosa with rhodopsin mutations.". Am. J. Ophthalmol. 112 (3): 256–71. PMID 1882937. 
  • Sheffield VC, Fishman GA, Beck JS, et al. (1991). "Identification of novel rhodopsin mutations associated with retinitis pigmentosa by GC-clamped denaturing gradient gel electrophoresis.". Am. J. Hum. Genet. 49 (4): 699–706. PMID 1897520. 

External links

Wikimedia Commons has media related to:


v • d • e
Transmembrane receptor: G protein-coupled receptors
Class A: Rhodopsin like
α1 (A, B, D) • α2 (A, B, C) • β1 • β2 • β3
CysLT (1, 2) • LTB4 (1, 2) • FPRL1 • OXE • Prostaglandin (DP, EP (1, 2, 3, 4), PGF) • Prostacyclin • Thromboxane
B/W (1, 2) • FF (1, 2) • S • Y (1, 2, 4, 5) • Neuromedin (B, U (1, 2)) • Neurotensin (1, 2)
GPR (1, 3, 4, 6, 12, 15, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 31, 32, 33, 34, 35, 37, 39, 42, 44, 45, 50, 52, 55, 61, 62, 63, 65, 68, 75, 77, 78, 82, 83, 84, 85, 87, 88, 92, 101, 103, 119, 120, 132, 135, 139, 141, 142, 146, 148, 149, 150, 151, 152, 153, 160, 161, 162, 171, 172A, 173, 174, 176, 177, 182)
Adenosine (A1, A2a, A2b, A3) • P2Y (1, 2, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14)
(all but 5-HT3) 5-HT1 (A, B, D, E, F) • 5-HT2 (A, B, C) • 5-HT (4, 5A, 6, 7)
Other
Acetylcholine (M1, M2, M3, M4, M5) • Adrenomedullin • Anaphylatoxin (C3a, C5a) • Angiotensin (1, 2) • Apelin • Bile acid • Bombesin (BRS3, GRPR, NMBR) • Bradykinin (B1, B2) • Cannabinoid (CB1, CB2) • Chemokine • Cholecystokinin (A, B) • Dopamine (D1, D2, D3, D4, D5) • EBI2 • Endothelin (A, B) • Estrogen • Formyl peptide (1, L1, L2) • Free fatty acid (1, 2, 3, 4) • FSH • Galanin (1, 2, 3) • Gonadotropin-releasing hormone (1, 2) • Ghrelin • Histamine (H1, H2, H3, H4) • Kisspeptin • Luteinizing hormone/choriogonadotropin • Lysophospholipid (1, 2, 3, 4, 5, 6, 7, 8) • MAS (1, 1L, D, E, F, G, X1, X2, X3, X4) • Melanocortin (1, 2, 3, 4, 5) • MCHR (1, 2) • Melatonin (1A, 1B) • Motilin • Opioid (Delta, Kappa, Mu, Nociceptin, but not Sigma) • Olfactory • Opsin (3, 4, 5, 1LW, 1MW, 1SW, RGR, RRH) • Orexin (1, 2) • Oxytocin • Oxoglutarate • PAF • Prokineticin (1, 2) • Prolactin-releasing peptide • Protease-activated (1, 2, 3, 4) • Relaxin (1, 2, 3, 4) • Somatostatin (1, 2, 3, 4, 5) • SREB • Succinate • TAAR (1, 2, 3, 5, 6, 8, 9) • Tachykinin (1, 2, 3) • Thyrotropin • Thyrotropin-releasing hormone • Urotensin-II • Vasopressin (1A, 1B, 2)
Class B: Secretin like
GPR (56, 64, 97, 98, 110, 111, 112, 113, 114, 115, 116, 123, 124, 125, 126, 128, 133, 143, 144, 157)
Other
Class C: Metabotropic
glutamate / pheromone
TAS1R (1, 2, 3) • TAS2R (1, 3, 4, 5, 8, 9, 10, 12, 13, 14, 16, 38, 39, 40, 41, 43, 44, 45, 46, 47, 48, 49, 50)
Other
Calcium-sensing receptor • GABA B (1, 2) • Glutamate receptor (Metabotropic glutamate (1, 2, 3, 4, 5, 6, 7, 8)) • GPRC6A • GPR (156, 158, 179) • RAIG (1, 2, 3, 4)
Frizzled / Smoothened
Frizzled (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) • Smoothened
v • d • e
Eye proteins
Opsin (retinylidene protein)
Rhodopsin - Melanopsin - Photopsin
Crystallin
Other

Wikipedia content modification information:

  • This page was last modified on 31 October 2008, at 16:14.

Wikipedia Authorship and Review

Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.

Wikipedia Usage Guidelines

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Rhodopsin".

The URL for this specific entry is:

All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.