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PubMed1989

Purification of cone visual pigments from chicken retina.

A novel method for purification of chicken cone visual pigments was established by use of a 3-[(3-cholamidopropyl)dimethylammonio]-1- propanesulfonate-phosphatidylcholine (CHAPS-PC) mixture. Outer segment membranes isolated from chicken retinas were extracted with 0.75% CHAPS supplemented with 1.0 mg/mL phosphatidylcholine (CHAPS-PC system). After the extract was diluted to 0.6% CHAPS, it was loaded on a concanavalin A-Sepharose column. Elution from the column with different concentrations of methyl alpha-mannoside yielded three fractions: the first was composed of chicken violet, blue, and red in roughly equal amounts, the second predominantly contained chicken red, and the third was rhodopsin with a small amount of chicken green, which was separated from rhodopsin by DEAE-Sepharose column chromatography. Since CHAPS has little absorbance at both ultraviolet and visible regions, we could demonstrate the absolute absorption spectra of chicken red (92%) and rhodopsin (greater than 96%) in these regions. The maximum of the difference spectrum between either chicken red or rhodopsin and its photoproduct (all-trans-retinal oxime plus opsin) was determined to be 571 or 503 nm, respectively. Although chicken green was contaminated with a small amount of rhodopsin having a similar spectral shape, the maximum of its difference spectrum was located at 508 nm by taking advantage of the difference in susceptibility against hydroxylamine between these pigments. Although chicken blue and chicken violet were minor pigments present in the first fraction from the concanavalin A column, their maxima in the difference spectra were determined to be at 455 and 425 nm, respectively, by a partial bleaching method.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Advantage of dichromats over trichromats in discrimination of color-camouflaged stimuli in nonhuman primates.

Due to a middle- to long-wavelength-sensitive (M/LWS) cone opsin polymorphism, there is considerable phenotypic variation in the color vision of New World monkeys. Many females have trichromatic vision, whereas some females and all males have dichromatic vision. The selective pressures that maintain this polymorphism are unclear. In the present study we compared the performance of dichromats and trichromats in a discrimination task. We examined tri- and dichromatic individuals of two species: brown capuchin monkeys (Cebus apella) and long-tailed macaques (Macaca fascicularis). We also examined one protanomalous chimpanzee (Pan troglodytes). The subjects' task was to discriminate a circular pattern from other patterns in which textural elements differed in orientation and thickness from the background. After they were trained with stimuli of a single color, the subjects were presented with color-camouflaged stimuli with a green/red mosaic overlaid onto the pattern. The dichromatic monkeys and the protanomalous chimpanzee selected the correct stimulus under camouflaged conditions at rates significantly above chance levels, while the trichromats did not. These findings demonstrate that dichromatic nonhuman primates possess a superior visual ability to discriminate color-camouflaged stimuli, and that such an ability may confer selective advantages with respect to the detection of cryptic foods and/or predators.

Animals↗
PubMed1992

Primary structures of chicken cone visual pigments: vertebrate rhodopsins have evolved out of cone visual pigments.

The chicken retina contains rhodopsin (a rod visual pigment) and four kinds of cone visual pigments. The primary structures of chicken red (iodopsin) and rhodopsin have been determined previously. Here we report isolation of three cDNA clones encoding additional pigments from a chicken retinal cDNA library. Based on the partial amino acid sequences of the purified chicken visual pigments together with their biochemical and spectral properties, we have identified these clones as encoding the chicken green, blue, and violet visual pigments. Chicken violet was very similar to human blue not only in absorption maximum (chicken violet, 415 nm; human blue, 419 nm) but also in amino acid sequence (80.6% identical). Interestingly, chicken green was more similar (71-75.1%) than any other known cone pigment (42.0-53.7%) to vertebrate rhodopsins. The fourth additional cone pigment, chicken blue, had relatively low similarity (39.3-54.6%) in amino acid sequence to those of the other vertebrate visual pigments. A phylogenetic tree of vertebrate visual pigments constructed on the basis of amino acid identity indicated that an ancestral visual pigment evolved first into four groups (groups L, S, M1, and M2), each of which includes one of the chicken cone pigments, and that group Rh including vertebrate rhodopsins diverged from group M2 later. Thus, it is suggested that the gene for scotopic vision (rhodopsin) has evolved out of that for photopic vision (cone pigments). The divergence of rhodopsin from cone pigments was accompanied by an increase in negative net charge of the pigment.

Amino Acid Sequence↗
PubMed2001

First identification and localization of a visual pigment in Hydra (Cnidaria, Hydrozoa).

The cnidarian Hydra does not possess identified photoreceptive structures or specialized cells for light detection; nevertheless, it shows a marked photosensitivity. So far no evidence has been previously reported about the localization of the proteins involved in the photoresponse. We used polyclonal antibodies and immunofluorescence microscopy on whole-mount Hydra to identify a putative rhodopsin-like protein. Our results show an immunoreactivity in the ectodermal layer of Hydra, which corresponds in position to the nervous epidermal sensory cells. These data provide the first identification of a rhodopsin-like protein in a phylogenetically old invertebrate and give a new insight into the Hydra photoreceptive response.

Animals↗
PubMed2001

Molecular evolution of the cone visual pigments in the pure rod-retina of the nocturnal gecko, Gekko gekko.

We have isolated a full-length cDNA encoding a putative ultraviolet (UV)-sensitive visual pigment of the Tokay gecko (Gekko gekko). This clone has 57 and 59% sequence similarities to the gecko RH2 and MWS pigment genes, respectively, but it shows 87% similarity to the UV pigment gene of the American chameleon (Anolis carolinensis). The evolutionary rates of amino acid replacement are significantly higher in the three gecko pigments than in the corresponding chameleon pigments. The accelerated evolutionary rates reflect not only the transition from cones to rods in the retina but also the blue-shift in the absorption spectra of the gecko pigments.

Amino Acid Sequence↗
PubMed1993

Nanosecond laser photolysis of iodopsin, a chicken red-sensitive cone visual pigment.

The photobleaching process of iodopsin (a chicken red-sensitive cone visual pigment) purified in a detergent system containing CHAPS and phosphatidylcholine was investigated by means of nanosecond laser photolysis at room temperature. Excitation of iodopsin with a nanosecond laser pulse (wavelength, 560 nm; pulse width, 17 ns) resulted in the formation of at least four intermediates on the nanosecond to millisecond time scale. The earliest intermediate detected had an absorption maximum at 571 nm, which was very close to that of original iodopsin (lambda max = 567 nm), and remarkably blue-shifted as compared with that of bathoiodopsin [lambda max = 625 nm; Kandori et al. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 8908-8912]. The intermediate, named BL-iodopsin, converted to the next intermediate, lumiiodopsin (lambda max = 535 nm), with a time constant of 130 ns. The BL intermediate had an absorption maximum just between batho- and lumiiodopsins, and an extinction coefficient comparable with these intermediates. These properties are different from those of the corresponding intermediate of rhodopsin [BL(BSI)-rhodopsin], suggesting that the binding of chloride to iodopsin, but not to rhodopsin, has an influence upon changes of the chromophore-opsin interaction in the early stage of photobleaching of iodopsin. Lumiiodopsin converted to metaiodopsin I (lambda max < 500 nm) with a time constant of 230 microseconds, and then to metaiodopsin II (lambda max = 390 nm) with a time constant of 6 ms. A thermal equilibrium between metaiodopsin I and II was established, but unlike meta intermediates of rhodopsin, they showed little temperature dependence.

Animals↗
PubMed1999

Spectral tuning in the human blue cone pigment.

The first determination of the absolute absorption maximum of the human blue cone visual pigment is presented. After expression in COS cells, reconstitution with 11-cis-retinal, and purification, the blue pigment exhibits an absolute absorption maximum of 414 nm. The pigment reacts rapidly with hydroxylamine in the dark and is capable of activating bovine rod transducin in a light-dependent manner. Products of mutations of proposed spectral tuning residues in the blue pigment do not behave as predicted when using rhodopsin mutants as a model. Mutations of amino acids in the ring portion of the chromophore binding pocket of rhodopsin serve well as a predictive model for mutations in the blue pigment, but mutations near the Schiff base do not.

Animals↗
PubMed2005

Elephants and human color-blind deuteranopes have identical sets of visual pigments.

Being the largest land mammals, elephants have very few natural enemies and are active during both day and night. Compared with those of diurnal and nocturnal animals, the eyes of elephants and other arrhythmic species, such as many ungulates and large carnivores, must function in both the bright light of day and dim light of night. Despite their fundamental importance, the roles of photosensitive molecules, visual pigments, in arrhythmic vision are not well understood. Here we report that elephants (Loxodonta africana and Elephas maximus) use RH1, SWS1, and LWS pigments, which are maximally sensitive to 496, 419, and 552 nm, respectively. These light sensitivities are virtually identical to those of certain "color-blind" people who lack MWS pigments, which are maximally sensitive to 530 nm. During the day, therefore, elephants seem to have the dichromatic color vision of deuteranopes. During the night, however, they are likely to use RH1 and SWS1 pigments and detect light at 420-490 nm.

Animals↗
PubMed2003

Demonstration of a sensory rhodopsin in eubacteria.

We report the first sensory rhodopsin observed in the eubacterial domain, a green light-activated photoreceptor in Anabaena (Nostoc) sp. PCC7120, a freshwater cyanobacterium. The gene encoding the membrane opsin protein of 261 residues (26 kDa) and a smaller gene encoding a soluble protein of 125 residues (14 kDa) are under the same promoter in a single operon. The opsin expressed heterologously in Escherichia coli membranes bound all-trans retinal to form a pink pigment (lambda max 543 nm) with a photochemical reaction cycle of 110 ms half-life (pH 6.8, 18 degrees C). Co-expression with the 14 kDa protein increased the rate of the photocycle, indicating physical interaction with the membrane-embedded rhodopsin, which we confirmed in vitro by affinity enrichment chromatography and Biacore interaction. The pigment lacks the proton donor carboxylate residue in helix C conserved in known retinylidene proton pumps and did not exhibit detectable proton ejection activity. We detected retinal binding to the protein in Anabaena membranes by SDS-PAGE and autofluorography of 3H-labelled all-trans retinal of reduced membranes from the organism. We conclude that Anabaena rhodopsin functions as a photosensory receptor in its natural environment, and suggest that the soluble 14 kDa protein transduces a signal from the receptor. Therefore, unlike the archaeal sensory rhodopsins, which transmit signals by transmembrane helix-helix interactions with membrane-embedded transducers, the Anabaena sensory rhodopsin may signal through a soluble cytoplasmic protein, analogous to higher animal visual pigments.

Amino Acid Sequence↗
PubMed2006

RPE65 gene delivery restores isomerohydrolase activity and prevents early cone loss in Rpe65-/- mice.

PURPOSE: Recent in vitro evidence has shown that RPE65 is the isomerohydrolase that converts all-trans retinyl ester to 11-cis retinal, the chromophore for visual pigments in vertebrates. Homozygous RPE65 knockout (Rpe65-/-) mice lack 11-cis retinoids and have early cone degeneration. The purpose of this study is to determine whether RPE65 gene delivery restores the isomerohydrolase activity and normal profile of endogenous retinoids in Rpe65-/- mice. METHODS: Adenovirus-expressing RPE65 (Ad-RPE65) was injected into the subretinal space of Rpe65-/- mice. The expression of RPE65 was determined by immunohistochemistry and Western blot analysis. The isomerohydrolase activity was measured in vitro in eyecup homogenates. Endogenous retinoid profile in the eyecups was analyzed by high-performance liquid chromatography (HPLC). Photoreceptor-specific gene expression was determined with real-time RT-PCR. Cone degeneration was determined by cone-specific staining and counting cones in flatmounted retina. RESULTS: High levels of RPE65 expression from the Ad-RPE65 injection generated robust isomerohydrolase activity in the eyecup of Rpe65-/- mice, at levels comparable to those in wild-type (wt) mice. Consequently, the RPE65 gene delivery resulted in substantial amounts of 11-cis retinal in Rpe65-/- mice. The RPE65 gene delivery prevented the downregulation of cone-specific genes, including both cone opsins and cone tranducin alpha subunit in Rpe65-/- mice. Moreover, the Ad-RPE65 injection also prevented massive cone degeneration at early ages of Rpe65-/- mice. CONCLUSIONS: RPE65 gene delivery generates isomerohydrolase activity and restores retinoid profile in Rpe65-/- mice. Regeneration of 11-cis retinal is essential for survival of cone photoreceptors.

Adenoviridae↗
PubMed1994

Sequence divergence analysis for the prediction of seven-helix membrane protein structures: II. A 3-D model of human rhodopsin.

A three-dimensional (3-D) model of the transmembrane domain of human rhodopsin was predicted from the sequence divergence analysis of 42 sequences of rhodopsins and visual pigments without a template. The prediction steps include multiple sequence alignment, calculation of a variability profile of the aligned sequences, use of the variability profile to identify the boundaries of transmembrane regions, their secondary structure and packing shape in a helix bundle, prediction of side-chain conformations and structure refinement. The identification of the retinal binding site was assisted by its known covalent linkage with K296. The structural features of the predicted 3-D model are in good agreement with a low resolution electron density map of bovine rhodopsin and with residues in contact with retinal as determined experimentally.

Amino Acid Sequence↗
PubMed1998

Tetrachromacy, oil droplets and bird plumage colours.

There is a growing body of data on avian eyes, including measurements of visual pigment and oil droplet spectral absorption, and of receptor densities and their distributions across the retina. These data are sufficient to predict psychophysical colour discrimination thresholds for light-adapted eyes, and hence provide a basis for relating eye design to visual needs. We examine the advantages of coloured oil droplets, UV vision and tetrachromacy for discriminating a diverse set of avian plumage spectra under natural illumination. Discriminability is enhanced both by tetrachromacy and coloured oil droplets. Oil droplets may also improve colour constancy. Comparison of the performance of a pigeon's eye, where the shortest wavelength receptor peak is at 410 nm, with that of the passerine Leiothrix, where the ultraviolet-sensitive peak is at 365 nm, generally shows a small advantage to the latter, but this advantage depends critically on the noise level in the sensitivity mechanism and on the set of spectra being viewed.

Adaptation, Ocular↗
PubMed1993

Light-induced binding of proteins to rhabdomeric membranes in the retina of crayfish (Procambarus clarkii).

Light-induced protein interaction as part of the process of visual transduction in arthropods with rhabdomeric photoreceptors was investigated biochemically by using crayfish retina. Two kinds of retinal buffer soluble proteins (one of 40 kDa and the other of 46 kDa) were found to bind to the irradiated rhabdomeric membranes both in vitro and in vivo. The proteins bound to the membranes in the presence of metarhodopsin. An antibody against mouse arrestin (S-antigen) cross-reacted with the 40 kDa protein. These results suggest that the binding of the proteins to the membranes is caused by the formation of metarhodopsin, and that the 40 kDa protein has a similar structure to arrestin.

Animals↗
PubMed1995

Defective intracellular transport is the molecular basis of rhodopsin-dependent dominant retinal degeneration.

Retinitis pigmentosa (RP) is a group of hereditary human diseases that cause retinal degeneration and lead to eventual blindness. More than 25% of all RP cases in humans appear to be caused by dominant mutations in the gene encoding the visual pigment rhodopsin. The mechanism by which the mutant rhodopsin proteins cause dominant retinal degeneration is still unclear. Interestingly, the great majority of these mutants appear to produce misfolded rhodopsin. We now report the isolation and characterization of 13 rhodopsin mutations that act dominantly to cause retinal degeneration in Drosophila; four of these correspond to identical substitutions in human autosomal dominant RP patients. We demonstrate that retinal degeneration results from interference in the maturation of wild-type rhodopsin by the mutant proteins.

Alleles↗
PubMed2003

Direct modulation of rod photoreceptor responsiveness through a Mel(1c) melatonin receptor in transgenic Xenopus laevis retina.

PURPOSE: Retinal circadian signals may have a role in maintaining the normal function and health of photoreceptors. Melatonin is an output of the retinal circadian oscillator and provides nocturnal signaling that is mediated through specific G-protein-coupled receptors. Melatonin receptors are expressed in retinal photoreceptor cells, and this study was undertaken to test the hypothesis that melatonin directly increases photoreceptor responses through melatonin receptors. METHODS: Transgenic Xenopus laevis frogs were generated using a DNA construct containing a Xenopus opsin promoter driving expression of a melatonin Mel(1c) receptor-green fluorescent protein (GFP) fusion protein (XOP-MEL(1c)-GFP). Electroretinogram (ERG) analysis on transgenic and normal tadpole eyes was performed in response to melatonin treatment, and the eyes were subsequently examined by confocal microscopy and GFP immunocytochemistry. RESULTS: XOP-MEL(1c)-GFP transgenic frogs demonstrated GFP immunoreactivity in rod photoreceptor inner segments throughout the retina, indicating the rod-specific expression of the Mel(1c)-GFP fusion protein. ERG analysis of transgenic tadpole eyes showed that 1 to 100 nM melatonin increased the a- and b-wave amplitudes. Control transgenic (XOP-GFP) and normal frogs exhibited only modest ERG responses to 100-nM melatonin treatment. The effect of melatonin on a- and b-wave amplitudes in XOP-MEL(1c)-GFP transgenic frogs was dose dependent, with ERG responses occurring at physiological concentrations. CONCLUSIONS: The results suggest that melatonin, acting through Mel(1c) receptors on rod photoreceptor membranes, directly stimulates the responsiveness of rod photoreceptors to light. This supports the hypothesis that melatonin acts both as an intracrine and paracrine circadian signal of darkness, and binds to specific receptors in photoreceptors and other retinal cells to increase visual sensitivity.

Animals↗
PubMed2001

Vision in the ultraviolet.

Sensitivity to ultraviolet light (UV) is achieved by photoreceptors in the eye that contain a class of visual pigments maximally sensitive to light at wavelengths <400 nm. It is widespread in the animal kingdom where it is used for mate choice, communication and foraging for food. UV sensitivity is not, however, a constant feature of the visual system, and in many vertebrate species, the UV-sensitive (UVS) pigment is replaced by a violet-sensitive (VS) pigment with maximal sensitivity between 410 and 435 nm. The role of protonation of the Schiff base-chromophore linkage and the mechanism for tuning of pigments into the UV is discussed in detail. Amino acid sequence analysis of vertebrate VS/UVS pigments indicates that the ancestral pigment was UVS, with loss of UV sensitivity occurring separately in mammals, amphibia and birds, and subsequently regained by a single amino acid substitution in certain bird species. In contrast, no loss of UV sensitivity has occurred in the UVS pigments of insects.

Animals↗
PubMed1988

Selective failure of long-term survival of isolated photoreceptors from both homozygous and heterozygous rd (retinal degeneration) mice.

Retinas from homozygous rdle/rdle and heterozygous rdle/++ C57BL/6J mice were dissected and dissociated on postnatal day 2, when they are still essentially indistinguishable. The resulting cell suspensions were seeded on highly adhesive substrata, to which the cells attach as individual units, and grown in vitro for 2 weeks in serum-free, chemically defined media. The behavior of neurons and photoreceptors in vitro was investigated with several techniques; essentially no differences were found between rdle/rdle and rdle/++ cells. Three distinctive cell types could be recognized in cultures of both genotypes towards the end of the first week in vitro: process-free cells, multipolar neurons and rod photoreceptors. There were similarities between rdle/rdle and rdle/++ cultures in the number and morphology of photoreceptor cells, to include the presence of a cilium and a short neurite terminating in a spherule-like body. Moreover, in cultures of both genotypes, only photoreceptors showed opsin immunoreactivity and the antigen recognized by the rod-specific monoclonal antibody RET-P1. Biochemical and autoradiographic studies demonstrated that rdle/rdle and rdle/++ cells also showed similar uptakes of the putative amino acid neurotransmitters glutamate and aspartate (associated with most of the photoreceptors and only some neurons), and gamma-aminobutyric acid (associated with neurons but absent in photoreceptors). Thus, according to several parameters, the properties shown by photoreceptor cells were similar in rdle/rdle and rdle/++ cultures during the first week in vitro. Massive photoreceptor cell death was observed in both genotypes during the second week in vitro, coinciding with the time when photoreceptor degeneration occurs in vivo in rd/rd, but not in rd/+ retinas. Photoreceptor death in culture appeared to be specific, since approx. 80% of the non-photoreceptor neurons survived normally during the period when photoreceptor degeneration took place. Several reports from the literature suggest that the period around postnatal days 8-10 represents a critical stage for rd/rd photoreceptors, since they survive until this time but degenerate thereafter. Genetically normal photoreceptors apparently undergo a comparable crisis during maintenance in primary culture, suggesting the involvement of cell-cell contacts and/or retina-derived environmental signals in the survival or rod visual cells.

Amino Acids↗
PubMed2001

Characterization of human GRK7 as a potential cone opsin kinase.

PURPOSE: Homozygous inactivation of the mouse gene for GRK1 (G protein-coupled receptor kinase 1, or rhodopsin kinase) causes severe defects in the recovery of cone phototransduction. However, electroretinographic (ERG) analyses of human oguchi patients with defective GRK1 alleles showed normal or slightly abnormal photopic responses. It remains unclear why the loss of GRK1 yields such different phenotypes in the recovery of mouse and human cones. We examined the localization and enzyme activity of GRK7, the human ortholog of the seventh member of the GRK family, in an attempt to understand its potential role in photopic vision. METHODS: Bioinformatic approaches were used to identify the human GRK7 gene. Human and bovine GRK7 cDNAs were isolated by RT-PCR. Recombinant GRK7, expressed in insect cells, was used to phosphorylate activated rhodopsin. Antibodies raised against GRK7 peptides were used to examine the retina specific expression of GRK7 by immunoblotting and its subcellular localization by immunocytochemistry. RESULTS: The human GRK7 gene is located on chromosome 3q21, spans at least 10 Kb and consists of 4 exons. In human, GRK7 is expressed exclusively in the retina and is found in all retinal neurons, and specifically, in cone outer segments. Recombinant human GRK7 catalyzes rhodopsin phosphorylation in a light dependent manner. We provide evidence that GRK1 and GRK7 are co-expressed in human cones. In contrast, mouse GRK7 is expressed in many tissues including retina where photoreceptors apparently do not express GRK7. CONCLUSIONS: The presence of GRK7 in human, but not in mouse, cone outer segments suggests that GRK7 may function to provide the normal photopic vision reported by oguchi patients with a defective GRK1 gene. The absence of GRK7 expression in cone outer segments of mice is consistent with the notion that mouse cones rely solely on GRK1 to shutoff cone visual pigments.

Amino Acid Sequence↗