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retinal protein formed by the action of light on rhodopsin

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/08/20 22:14:24」(JST)

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Three-dimensional structure of bovine rhodopsin. The seven transmembrane domains are shown in varying colors. The chromophore is shown in red.

Opsins are a group of light-sensitive 35–55 kDa membrane-bound G protein-coupled receptors of the retinylidene protein family found in photoreceptor cells of the retina. Five classical groups of opsins are involved in vision, mediating the conversion of a photon of light into an electrochemical signal, the first step in the visual transduction cascade. Another opsin found in the mammalian retina, melanopsin, is involved in circadian rhythms and pupillary reflex but not in image-forming.

1 Opsin classification
2 Prokaryotic (type 1) opsins
3 Animal (type 2) opsins
- 3.1 Ciliary opsins
  - 3.1.1 Vertebrate opsins
  - 3.1.2 Encephalopsins
  - 3.1.3 Go / Gs opsins
- 3.2 Rhabdomeric opsins
- 3.3 Photoisomerases
- 3.4 Neuropsins
4 Structure and function
5 See also
6 External links
7 References

Opsin classification

There are two groups of protein termed opsins; these groups are not homologous, but have convergently evolved a similar form and function.^[1]^[2] Type I opsins are employed by prokaryotes and - as the protein component of channelrhodopsins - by some algae, whereas animals use Type II opsins. No opsins have been found outside these groups (for instance in plants, fungi, or placozoans),^[1] although as-yet unconfirmed reports of opsins in sponges^[3] would suggest that opsins were present in the ancestral metazoan.

Based on the phylogeny of their sequences, type 2 opsins can be grouped into six families; these families are very distinct, with under 20% of their sequences shared with any other subfamily. The families consist of the vertebrate opsins/encephalopsins; Go opsins; Gs opsins; invertebrate Gq opsins; the photoisomerases and neuropsins.^[4] These subfamilies can be grouped according to their expression; the first three are found in ciliary-type photoreceptor cells; Gq opsins in rhabdomeric-type photoreceptor cells; and the latter two are found elsewhere but based on their shared intron positions can be bundled together into the photoisomerases.^[4]

Prokaryotic (type 1) opsins

Like eukaryotic opsins, prokaryotic opsins have a seven transmembrane domain structure similar to that found in eukaryotic G-protein coupled receptors. Despite this similarity, there is no evidence that they are evolutionarily related, suggesting that they evolved independently of one another.^[2]

Several type 1 opsins, such as proteo- and bacteriorhodopsin, are used by various bacterial groups to harvest energy from light to carry out metabolic processes using a non-chlorophyll-based pathway. Beside that, halorhodopsins of Halobacteria and channelrhodopsins of some algae, e.g. Volvox, serve them as light-gated ion channels, amongst others also for phototactic purposes. Additionally, sensory rhodopsins exist in Halobacteria that induce a phototactic response by interacting with transducer membrane-embedded proteins that have no relation to G proteins.^[5]

Animal (type 2) opsins

Ciliary opsins

Ciliary opsins are expressed in ciliary photoreceptor cells, and include the vertebrate opsins/encephalopsins, Go and Gs opsin subfamilies.^[4] They convert light signals to nerve impulses via cyclic nucleotide gated ion channels, which work by increasing the charge differential across the cell membrane (i.e. hyperpolarization.^[1])

Vertebrate opsins

Vertebrate opsins can be further subdivided into rod opsins and four types of cone opsin, based on differential spatial expression, spectral sensitivity, and evolutionary history.^[4] Rod opsins (rhodopsins, usually denoted Rh), are used in night vision, are thermally stable, and are found in the rod photoreceptor cells. Cone opsins, employed in color vision, are less-stable opsins located in the cone photoreceptor cells. Cone opsins are further subdivided according to their absorption maxima (λ_max), the wavelength at which the highest light absorption is observed. Evolutionary relationships, deduced using the amino acid sequence of the opsins, are also frequently used to categorize cone opsins into their respective group. Both methods predict four general cone opsin groups in addition to rhodopsin.^[6]

Humans have the following set of photoreceptor proteins responsible for vision:

Rhodopsin (Rh1, OPN2, RHO) – expressed in rod cells, used in night vision
Three cone opsins (also known as photopsins) – expressed in cone cells, used in color vision
- Long Wavelength Sensitive (OPN1LW) Opsin – λ_max in the red region of the electromagnetic spectrum. Despite its name, this receptor has a secondary response in the violet high frequencies^[7]^[8]
- Middle Wavelength Sensitive (OPN1MW) Opsin – λ_max in the green region of the electromagnetic spectrum
- Short Wavelength Sensitive (OPN1SW) Opsin – λ_max in the blue region of the electromagnetic spectrum

Encephalopsins

This type of opsin is expressed throughout the mammalian heart

It is also expressed in ciliary photoreceptor cells in annelids, and in the brains of some insects.^[4]

Go / Gs opsins

These opsins, absent from higher vertebrates and arthropods, are found in the ciliary photoreceptor cells of molluscs and basal chordates (amphioxus); and in cnidarians, respectively.^[4]

Rhabdomeric opsins

Arthropods and molluscs use Gq opsins. Arthropods appear to attain colour vision in a similar fashion to the vertebrates, by the use of three (or more) distinct groups of opsin, distinct both in terms of phylogeny and spectral sensitivity.^[4] The Gq opsin melanopsin is also expressed in vertebrates, where it is responsible for the maintenance of circadian rhythms.^[4]

Unlike ciliary opsins, these are associated with canonical transient receptor potential ion channels; these lead to the electric potential difference across a cell membrane being eradicated (i.e. depolarization).^[1]

The identification of the crystal structure of squid rhodopsin^[9] is likely to further our understanding of its function in this group.

Arthropods do use different opsins in their different eye types, but at least in Limulus the opsins expressed in lateral and in compound eyes are 99% identical and presumably diverged recently.^[10]

Photoisomerases

This class of opsins are not coupled to a G-protein, and thus serve to traffic retinal around in response to light, rather than directly in signal-induction.^[4]

Neuropsins

These opsins are found in nervous tissue in mammals, and despite some genetic similarities to photoisomerases, their function has not yet been identified.^[4]

Name	Gene	Notes
Melanopsin	OPN4	best studied novel opsin involved in circadian rhythms and pupillary reflex
Pineal Opsin (Pinopsin)^[11]		wide range of expression in the brain, most notably in the pineal region
Vertebrate Ancient (VA) opsin^[12]		has three isoforms VA short (VAS), VA medium (VAM), and VA long (VAL). It is expressed in the inner retina, within the horizontal and amacrine cells, as well as the pineal organ and habenular region of the brain
Parapinopsin (PP) Opsin ^[13]
Extraretinal (or extra-ocular) Rhodopsin-Like Opsins (Exo-Rh)^[14]		Rhodopsin-like protein expressed in the pineal region
Encephalopsin or Panopsin	OPN3	originally found in human and mice tissue with a very wide range of expression (brain, testes, heart, liver, kidney, skeletal muscle, lung, pancreas and retina)
Teleost Multiple Tissue (TMT) Opsin^[15]		Teleost fish opsin with a wide range of expression
Peropsin or "Retinal pigment epithelium-derived rhodopsin homolog"	RRH	expressed in the retinal pigment epithelium (RPE) cells
Retinal G protein coupled receptor	RGR	expressed in the retinal pigment epithelium (RPE) and Müller cells
Neuropsin	OPN5

Structure and function

Opsin proteins covalently bind to a vitamin A-based retinaldehyde chromophore through a Schiff base linkage to a lysine residue in the seventh transmembrane alpha helix. In vertebrates, the chromophore is either 11-cis-retinal (A1) or 11-cis-3,4-didehydroretinal (A2) and is found in the retinal binding pocket of the opsin. The absorption of a photon of light results in the photoisomerisation of the chromophore from the 11-cis to an all-trans conformation. The photoisomerization induces a conformational change in the opsin protein, causing the activation of the phototransduction cascade. The opsin remains insensitive to light in the trans form. It is regenerated by the replacement of the all-trans retinal by a newly synthesized 11-cis-retinal provided from the retinal epithelial cells. Opsins are functional while bound to either chromophore, with A2-bound opsin λ_max being at a longer wavelength than A1-bound opsin.

Opsins contain seven transmembrane α-helical domains connected by three extra-cellular and three cytoplasmic loops. Many amino acid residues, termed functionally conserved residues, are highly conserved between all opsin groups, indicative of important functional roles. All residue positions discussed henceforth are relative to the 348 amino acid bovine rhodopsin crystallized by Palczewski et al.^[16] Lys296 is conserved in all known opsins and serves as the site for the Schiff base linkage with the chromophore. Cys138 and Cys110 form a highly conserved disulfide bridge. Glu113 serves as the counterion, stabilizing the protonation of the Schiff linkage between Lys296 and the chromophore. The Glu134-Arg135-Tyr136 is another highly conserved motif, involved in the propagation of the transduction signal once a photon has been absorbed.

Certain amino acid residues, termed spectral tuning sites, have a strong effect on λ_max values. Using site-directed mutagenesis, it is possible to selectively mutate these residues and investigate the resulting changes in light absorption properties of the opsin. It is important to differentiate spectral tuning sites, residues that affect the wavelength at which the opsin absorbs light, from functionally conserved sites, residues important for the proper functioning of the opsin. They are not mutually exclusive, but, for practical reasons, it is easier to investigate spectral tuning sites that do not affect opsin functionality. For a comprehensive review of spectral tuning sites see Yokoyama^[17] and Deeb.^[18] The impact of spectral tuning sites on λ_max differs between different opsin groups and between opsin groups of different species.

External links

Review of opsins and current research: Shichida, Y.; Matsuyama, T. (2009). "Evolution of opsins and phototransduction". Philosophical transactions of the Royal Society of London. Series B, Biological sciences 364 (1531): 2881–2895. doi:10.1098/rstb.2009.0051. PMC 2781858. PMID 19720651. edit
Illustration at Baldwin-Wallace College
Opsin at the US National Library of Medicine Medical Subject Headings (MeSH)

References

^ ^a ^b ^c ^d Plachetzki, D.; Fong, C.; Oakley, T. (2010). "The evolution of phototransduction from an ancestral cyclic nucleotide gated pathway". Proceedings. Biological sciences / the Royal Society 277 (1690): 1963–1969. doi:10.1098/rspb.2009.1797. PMC 2880087. PMID 20219739. edit
^ ^a ^b Fernald, R. D. (2006). "Casting a genetic light on the evolution of eyes". Science 313 (5795): 1914–1918. Bibcode:2006Sci...313.1914F. doi:10.1126/science.1127889. PMID 17008522. edit
^ "Porifera: Amphimedon queenslandica (sponge) .. 1 opsin". GenomeWiki. University of California Santa Cruz (UCSC) Genome Bioinformatics Group.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j Shichida, Y.; Matsuyama, T. (2009). "Evolution of opsins and phototransduction". Philosophical transactions of the Royal Society of London. Series B, Biological sciences 364 (1531): 2881–2895. doi:10.1098/rstb.2009.0051. PMC 2781858. PMID 19720651. edit
^ Römpler, H.; Stäubert, C.; Thor, D.; Schulz, A.; Hofreiter, M.; Schöneberg, T. (2007). "G protein-coupled time travel: evolutionary aspects of GPCR research". Molecular interventions 7 (1): 17–25. doi:10.1124/mi.7.1.5. PMID 17339603. edit
^ Terakita, A. (2005). "The opsins". Genome Biology 6 (3): 213. doi:10.1186/gb-2005-6-3-213. PMC 1088937. PMID 15774036. edit
^ Mathpages http://www.mathpages.com/home/kmath579/kmath579.htm
^ University of California excerpts from "Theory of Color"
^ Murakami, M.; Kouyama, T. (2008). "Crystal structure of squid rhodopsin". Nature 453 (7193): 363. Bibcode:2008Natur.453..363M. doi:10.1038/nature06925. PMID 18480818. edit
^ Smith, W. C.; Price, D. A.; Greenberg, R. M.; Battelle, B. A. (1993). "Opsins from the lateral eyes and ocelli of the horseshoe crab, Limulus polyphemus". Proceedings of the National Academy of Sciences of the United States of America 90 (13): 6150–6154. Bibcode:1993PNAS...90.6150S. doi:10.1073/pnas.90.13.6150. PMC 46885. PMID 8327495. edit
^ Okano T, Yoshizawa T, Fukada Y (1994). "Pinopsin is a chicken pineal photoreceptive molecule". Nature 372 (6501): 94–97. Bibcode:1994Natur.372...94O. doi:10.1038/372094a0. PMID 7969427.
^ Philp AR, Garcia-Fernandez JM, Soni BG, Lucas RJ, Bellingham J, Foster RG (2000). "Vertebrate ancient (VA) opsin and extraretinal photoreception in the Atlantic salmon (Salmo salar)". J. Exp. Biol. 203 (Pt 12): 1925–36. PMID 10821749.
^ Blackshaw S, Snyder SH (1997). "Parapinopsin, a novel catfish opsin localized to the parapineal organ, defines a new gene family". J. Neurosci. 17 (21): 8083–92. PMID 9334384.
^ Mano H, Kojima D, Fukada Y (1999). "Exo-rhodopsin: a novel rhodopsin expressed in the zebrafish pineal gland". Brain Res. Mol. Brain Res. 73 (1–2): 110–118. doi:10.1016/S0169-328X(99)00242-9. PMID 10581404.
^ Moutsaki P, Whitmore D, Bellingham J, Sakamoto K, David-Gray ZK, Foster RG (2003). "Teleost multiple tissue (tmt) opsin: a candidate photopigment regulating the peripheral clocks of zebrafish?". Brain Res. Mol. Brain Res. 112 (1–2): 135–145. doi:10.1016/S0169-328X(03)00059-7. PMID 12670711.
^ Palczewski K et al. (2000). "Crystal Structure of Rhodopsin: A G Protein-Coupled Receptor". Science 289 (5480): 739–745. Bibcode:2000Sci...289..739P. doi:10.1126/science.289.5480.739. PMID 10926528.
^ Yokoyama S (2000). "Molecular evolution of vertebrate visual pigments". Progress in Retinal and Eye Research 19 (4): 385–419. doi:10.1016/S1350-9462(00)00002-1. PMID 10785616.
^ Deeb SS (2005). "The molecular basis of variation in human color vision". Clinical genetics 67 (5): 369–377. doi:10.1111/j.1399-0004.2004.00343.x. PMID 15811001.

UpToDate Contents

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1. ビタミンAの概要 overview of vitamin a

English Journal

Diversity of animal opsin-based pigments and their optogenetic potential.

Koyanagi M1, Terakita A2.Author information 1Department of Biology and Geosciences, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.2Department of Biology and Geosciences, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan. Electronic address: terakita@sci.osaka-cu.ac.jp.AbstractMost animal opsin-based pigments are typical G protein-coupled receptors (GPCR) and consist of a protein moiety, opsin, and 11-cis retinal as a chromophore. More than several thousand opsins have been identified from a wide variety of animals, which have multiple opsin genes. Accumulated evidence reveals the molecular property of opsin-based pigments, particularly non-conventional visual pigments including non-visual pigments. Opsin-based pigments are generally a bistable pigment having two stable and photointerconvertible states and therefore are bleach-resistant and reusable, unlike vertebrate visual pigments which become bleached. The opsin family contains Gt-coupled, Gq-coupled, Go-coupled, Gs-coupled, Gi-coupled, and Gi/Go-coupled opsins, indicating the existence of a large diversity of light-driven GPCR-signaling cascades. It is suggested that these molecular properties might contribute to different physiologies. In addition, various opsin based-pigments, especially nonconventional visual pigments having different molecular characteristics would facilitate the design and development of promising optogenetic tools for modulating GPCR-signaling, which is involved in a wide variety of physiological responses. We here introduce molecular and functional properties of various kinds of opsins and discuss their physiological function and also their potentials for optogenetic applications. This article is part of a Special Issue entitled: Retinal proteins - you can teach an old dog new tricks.
Biochimica et biophysica acta.Biochim Biophys Acta.2014 May;1837(5):710-716. doi: 10.1016/j.bbabio.2013.09.003. Epub 2013 Sep 13.
Most animal opsin-based pigments are typical G protein-coupled receptors (GPCR) and consist of a protein moiety, opsin, and 11-cis retinal as a chromophore. More than several thousand opsins have been identified from a wide variety of animals, which have multiple opsin genes. Accumulated evidence re
PMID 24041647

Cone visual pigments.

Imamoto Y1, Shichida Y2.Author information 1Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.2Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan. Electronic address: shichida@rh.biophys.kyoto-u.ac.jp.AbstractCone visual pigments are visual opsins that are present in vertebrate cone photoreceptor cells and act as photoreceptor molecules responsible for photopic vision. Like the rod visual pigment rhodopsin, which is responsible for scotopic vision, cone visual pigments contain the chromophore 11-cis-retinal, which undergoes cis-trans isomerization resulting in the induction of conformational changes of the protein moiety to form a G protein-activating state. There are multiple types of cone visual pigments with different absorption maxima, which are the molecular basis of color discrimination in animals. Cone visual pigments form a phylogenetic sister group with non-visual opsin groups such as pinopsin, VA opsin, parapinopsin and parietopsin groups. Cone visual pigments diverged into four groups with different absorption maxima, and the rhodopsin group diverged from one of the four groups of cone visual pigments. The photochemical behavior of cone visual pigments is similar to that of pinopsin but considerably different from those of other non-visual opsins. G protein activation efficiency of cone visual pigments is also comparable to that of pinopsin but higher than that of the other non-visual opsins. Recent measurements with sufficient time-resolution demonstrated that G protein activation efficiency of cone visual pigments is lower than that of rhodopsin, which is one of the molecular bases for the lower amplification of cones compared to rods. In this review, the uniqueness of cone visual pigments is shown by comparison of their molecular properties with those of non-visual opsins and rhodopsin. This article is part of a Special Issue entitled: Retinal Proteins - You can teach an old dog new tricks.
Biochimica et biophysica acta.Biochim Biophys Acta.2014 May;1837(5):664-673. doi: 10.1016/j.bbabio.2013.08.009. Epub 2013 Sep 7.
Cone visual pigments are visual opsins that are present in vertebrate cone photoreceptor cells and act as photoreceptor molecules responsible for photopic vision. Like the rod visual pigment rhodopsin, which is responsible for scotopic vision, cone visual pigments contain the chromophore 11-cis-reti
PMID 24021171

Hsp90 inhibition protects against inherited retinal degeneration.

Aguilà M1, Bevilacqua D, McCulley C, Schwarz N, Athanasiou D, Kanuga N, Novoselov SS, Lange CA, Ali RR, Bainbridge JW, Gias C, Coffey PJ, Garriga P, Cheetham ME.Author information 1Department of Ocular Biology and Therapeutics.AbstractThe molecular chaperone Hsp90 is important for the functional maturation of many client proteins, and inhibitors are in clinical trials for multiple indications in cancer. Hsp90 inhibition activates the heat shock response and can improve viability in a cell model of the P23H misfolding mutation in rhodopsin that causes autosomal dominant retinitis pigmentosa (adRP). Here, we show that a single low dose of the Hsp90 inhibitor HSP990 enhanced visual function and delayed photoreceptor degeneration in a P23H transgenic rat model. This was associated with the induction of heat shock protein expression and reduced rhodopsin aggregation. We then investigated the effect of Hsp90 inhibition on a different type of rod opsin mutant, R135L, which is hyperphosphorylated, binds arrestin and disrupts vesicular traffic. Hsp90 inhibition with 17-AAG reduced the intracellular accumulation of R135L and abolished arrestin binding in cells. Hsf-1(-/-) cells revealed that the effect of 17-AAG on P23H aggregation was dependent on HSF-1, whereas the effect on R135L was HSF-1 independent. Instead, the effect on R135L was mediated by a requirement of Hsp90 for rhodopsin kinase (GRK1) maturation and function. Importantly, Hsp90 inhibition restored R135L rod opsin localization to wild-type (WT) phenotype in vivo in rat retina. Prolonged Hsp90 inhibition with HSP990 in vivo led to a posttranslational reduction in GRK1 and phosphodiesterase (PDE6) protein levels, identifying them as Hsp90 clients. These data suggest that Hsp90 represents a potential therapeutic target for different types of rhodopsin adRP through distinct mechanisms, but also indicate that sustained Hsp90 inhibition might adversely affect visual function.
Human molecular genetics.Hum Mol Genet.2014 Apr 15;23(8):2164-75. doi: 10.1093/hmg/ddt613. Epub 2013 Dec 2.
The molecular chaperone Hsp90 is important for the functional maturation of many client proteins, and inhibitors are in clinical trials for multiple indications in cancer. Hsp90 inhibition activates the heat shock response and can improve viability in a cell model of the P23H misfolding mutation in
PMID 24301679

Japanese Journal

A new subset of deutan colour vision defect associated with an L/M visual pigment gene array of normal order and -71C substitution in the Japanese population

The journal of biochemistry 158(3), 197-204, 2015-09
NAID 40020593497

トンボの光センサーを作るオプシン遺伝子の多様性

昆虫と自然 50(9), 24-26, 2015-08
NAID 40020591319

養殖スマEuthynnus affinisのオプシン遺伝子解析

水産増殖 = Aquaculture science 63(2), 179-189, 2015-06
NAID 40020516999

Related Pictures

★リンクテーブル★

リンク元	「網膜」「ロドプシン」「オプシン」
拡張検索	「rhodopsin kinase」「porphyropsin」

「網膜」

　　[★]

英: retina
関: 眼、眼球

図：SP.275,

組織学

10層よりなる (SP.275)

構造	層		細胞体
脈絡膜
網膜
1	色素上皮層		色素上皮細胞	pigment epithelium cell
2	杆体錐体層	rod and cone layer
3	外境界膜
4	外顆粒層	outer nuclear layer	視細胞	photoreceptor
5	外網状層	outer plexiform layer
6	内顆粒層	inner nuclear layer	双極細胞	bipolar cell
			水平細胞	horizontal cell
			アマクリン細胞	amacrine cell
7	内網状層	inner plexiform layer
8	神経節細胞層	ganglion cell layer	神経節細胞	ganglion cell
9	神経線維層	optic nerve fiber layer
10	内境界膜