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PubMed1991

Differences in the photobleaching process between 7-cis- and 11-cis-rhodopsins: a unique interaction change between the chromophore and the protein during the lumi-meta I transition.

The photochemical and subsequent thermal reactions of 7-cis-rhodopsin prepared from cattle opsin and 7-cis-retinal were investigated by low-temperature spectrophotometry and laser photolysis, and compared with those of 11-cis-rhodopsin prepared from cattle opsin and 11-cis-retinal. Low-temperature experiments revealed that the absorption maxima of batho and lumi intermediates from 7-cis-rhodopsin were at slightly shorter wavelengths than those of 11-cis-rhodopsin while the meta I intermediates of both rhodopsin isomers showed the same absorption maxima. Kinetic experiments of the photobleaching process of 7-cis-rhodopsin using picosecond and nanosecond laser pulses revealed the formation of intermediates corresponding to the batho, lumi, meta I, and meta II intermediates from 11-cis-rhodopsin. An intermediate of 7-cis-rhodopsin corresponding to photorhodopsin (a precursor of bathorhodopsin), however, was not detected. Batho and lumi intermediates from 7-cis-rhodopsin had shorter lifetimes (approximately 40 ns and 300 microseconds) than those of 11-cis-rhodopsin (250 ns and 800 microseconds), but the lifetime of the meta I intermediate from 7-cis-rhodopsin was identical with that from 11-cis-rhodopsin (12 ms). These results indicate that the difference in configuration of the original chromophore between 7-cis- and 11-cis-rhodopsins is a cause of different chromophore-opsin interactions in the batho and lumi stages, while in the meta I stage the difference has disappeared by the relaxation of the protein near the chromophores. A possible interaction change between the 9-methyl group of the chromophore and its neighboring protein during the lumi-meta I transition will be discussed.

Animals↗
PubMed2001

Regulation of phototransduction in short-wavelength cone visual pigments via the retinylidene Schiff base counterion.

Short-wavelength visual pigments (SWS1) have lambda(max) values that range from the ultraviolet to the blue. Like all visual pigments, this class has an 11-cis-retinal chromophore attached through a Schiff base linkage to a lysine residue of opsin apoprotein. We have characterized a series of site-specific mutants at a conserved acidic residue in transmembrane helix 3 in the Xenopus short-wavelength sensitive cone opsin (VCOP, lambda(max) approximately 427 nm). We report the identification of D108 as the counterion to the protonated retinylidene Schiff base. This residue regulates the pK(a) of the Schiff base and, neutralizing this charge, converts the violet sensitive pigment into one that absorbs maximally in the ultraviolet region. Changes to this position cause the pigment to exhibit two chromophore absorbance bands, a major band with a lambda(max) of approximately 352-372 nm and a minor, broad shoulder centered around 480 nm. The behavior of these two absorbance bands suggests that these represent unprotonated and protonated Schiff base forms of the pigment. The D108A mutant does not activate bovine rod transducin in the dark but has a significantly prolonged lifetime of the active MetaII state. The data suggest that in short-wavelength sensitive cone visual pigments, the counterion is necessary for the characteristic rapid production and decay of the active MetaII state.

Animals↗
PubMed1994

Synergy in the spectral tuning of retinal pigments: complete accounting of the opsin shift in bacteriorhodopsin.

UV-visible and solid-state NMR studies of a series of 6-s-trans protonated Schiff bases of retinal with aniline show that the bathochromic shift induced by weakening the imine counterion is significantly greater in the 6-s-trans conformation than in the 6-s-cis conformation. Based on the observed magnitude of this coupling between the electronic effects of 6-s isomerization and imine counterion strength in the model compounds, the large opsin shift and unusual chemical shifts in light-adapted bacteriorhodopsin can be fully explained. These phenomena therefore do not require a negative point charge or polarizability effects in the chromophore binding pocket. The results are consistent with an effective center-to-center distance between the Schiff base and its counterion of about 4 A in light-adapted bacteriorhodopsin.

Aniline Compounds↗
PubMed2006

Polymorphism of visual pigment genes in the muriqui (Primates, Atelidae).

Colour vision varies within the family Atelidae (Primates, Platyrrhini), which consists of four genera with the following cladistic relationship: {Alouatta[Ateles (Lagothrix and Brachyteles)]}. Spider monkeys (Ateles) and woolly monkeys (Lagothrix) are characteristic of platyrrhine monkeys in possessing a colour vision polymorphism. The polymorphism results from allelic variation of the single-locus middle-to-long wavelength (M/L) cone opsin gene on the X-chromosome. The presence in the population of alleles coding for different M/L photopigments results in a variety of colour vision phenotypes. Such a polymorphism is absent in howling monkeys (Alouatta), which, alone among platyrrhines, acquired uniform trichromatic vision similar to that of Old World monkeys, apes, and humans through opsin gene duplication. Dietary and morphological similarities between howling monkeys and muriquis (Brachyteles) raise the possibility that the two genera share a similar form of colour vision, uniform trichromacy. Yet parsimony predicts that the colour vision of Brachyteles will resemble the polymorphism present in Lagothrix and Ateles. Here we test this assumption. We obtained DNA from the blood or faeces of 18 muriquis and sequenced exons 3 and 5 of the M/L opsin gene. Our results affirm the existence of a single M/L cone opsin gene in the genus Brachyteles. We detected three alleles with predicted lambdamax values of 530, 550, and 562 nm. Two females were heterozygous and are thus predicted to have different types of M/L cone pigment. We discuss the implication of this result towards understanding the evolutionary ecology of trichromatic vision.

Animals↗
PubMed1989

Transplantation of photoreceptors to light-damaged retina.

We investigated the possibility of reconstructing light-damaged retinas by photoreceptor transplantation. The outer nuclear layer containing the photoreceptor cells was eliminated in adult albino rat retinas by exposure to constant high-level illumination. Photoreceptors for transplantation were harvested from neonatal rats using a novel isolation technique that maintained the cellular organization of the outer nuclear layer. Transplantation was accomplished using a transcorneal approach to the subretinal space, which minimized trauma to the eye. The retina reattached to the back of the eye with transplanted photoreceptors interposed between the retina and the overlying tissues. Prelabelling with fluorescent dye enabled positive identification of the transplanted cells. The transplanted photoreceptors appeared to survive transplantation for at least 6 weeks and were immunohistochemically reactive for opsin. The antibody staining for opsin identifies the transplanted cells as photoreceptors and indicates that they are still capable of producing visual pigment and therefore may have the capacity to transduce light. These findings indicate that photoreceptors can be transplanted to form a new outer nuclear layer in a damaged mature retina.

Animals↗
PubMed1992

Evidence for the transport of opsin in the connecting cilium and basal rod outer segment in rat retina: rapid-freeze, deep-etch and horseradish peroxidase labelling studies.

In order to clarify the pathway of opsin transport in the connecting cilium and basal rod outer segment, we examined rat rod cells by a rapid-freeze and deep-etch technique and also examined the uptake of horseradish peroxidase into isolated retina. The distribution of intramembrane particles on the P-face of the cilium indicated that the ciliary plasma membrane has similar opsin content to the basal rod outer segment plasma membrane. Dilated cisternae were detected below the stack of disk membranes at the basal rod outer segment in fresh retina. The fine structure of the P-face and true surface of these cisternae was identical to that of the disk membrane. Uptake of horseradish peroxidase was detected in the cisternae or in both cisternae and most basal disk, indicating that the cisternae are formed prior to the disk membrane. In the distal part of connecting cilium, we found axially oriented infoldings on the P-face of the plasma membrane, and subplasmalemmal tubules or cisternae adjacent and parallel to them. Such subplasmalemmal membranes were labeled by exogenous horseradish peroxidase, suggesting that the infoldings are invaginating plasma membrane. These results may indicate that opsin molecules are conveyed on the ciliary plasma membrane, and that this opsin-rich plasma membrane is internalized in the distal connecting cilium to form dilated cisternae, which subsequently change to the disk membranes.

Animals↗
PubMed2004

Salmonid opsin sequences undergo positive selection and indicate an alternate evolutionary relationship in oncorhynchus.

Positive selection can be demonstrated by statistical analysis when non-synonymous nucleotide substitutions occur more frequently than synonymous substitutions (dN>dS). This pattern of sequence evolution has been observed in the rhodopsin gene of cichlids. Mutations in opsin genes resulting in amino acid (AA) replacement appear to be associated with the evolution of specific color patterns and the evolution of courtship behaviors. Within fish, AA replacements in opsin proteins have improved vision at great depths and have occurred in deep-sea species. Salmonids experience diverse photic environments during their life history. Furthermore, sexual selection has resulted in species-specific male and female coloration during spawning. To look for evidence of positive selection in salmonid opsins, we sequenced the RH1, RH2, LWS, SWS1, and SWS2 genes from six Pacific salmon species as well as the Atlantic salmon. These salmonids include landlocked and migratory species and species that vary in their coloration during spawning. In each opsin gene comparison from all species sampled, traditional dN:dS analysis did not indicate positive selection. However, the more sensitive Creevey-McInerney statistical analysis indicates that RH1 and RH2 experienced positive selection early in the evolution and speciation of salmonids.

Animals↗
PubMed1995

Constitutive activation of phototransduction by K296E opsin is not a cause of photoreceptor degeneration.

The missense mutation Lys-296-->Glu (K296E) in the rhodopsin gene produces an opsin with no chromophore binding site and therefore is not activated by light. Nevertheless, the mutant opsin constitutively activates transducin in vitro and causes photoreceptor degeneration in vivo, possibly by continuously activating the phototransduction cascade, analogous to constant exposure to environmental light. We studied the K296E mutation in eight lines of transgenic mice. Each line developed photoreceptor degeneration with the rate of degeneration increasing monotonically as the ratio of mutant:wild-type opsin mRNA increased. At no time in the course of degeneration was there endogenous light adaptation in the retina as measured by the electroretinogram. The mutant opsin was found to be invariably phosphorylated and stably bound to arrestin. Light-independent activation of transducin was demonstrated only after the removal of arrestin and dephosphorylation of K296E opsin. Thus, K296E opsin in vivo does not activate the phototransduction cascade because it is shut off by photoreceptor inactivation mechanisms. Our data show that the K296E mutation does not cause photoreceptor degeneration by continuous activation of phototransduction.

Animals↗
PubMed2005

The signaling pathway in photoresponses that may be mediated by visual pigments in erythrophores of Nile tilapia.

The ability to increase the synthesis or vary the distribution of pigment in response to light is an important feature of many pigment cells. Unlike other light-sensitive pigment cells, erythrophores of Nile tilapia change the direction of pigment migration depending on the peak wavelength of incident light: light near 365, 400 or 600 nm induces pigment aggregation, while dispersion occurs in response to light at 500 nm. How these phenomena are achieved is currently unknown. In the present study, the phototransduction involved in the pigment dispersion caused by light at 500 nm or the aggregation by light at 600 nm was examined, using pertussis toxin, cholera toxin, blockers of ion channels, various chemicals affecting serial steps of signaling pathways and membrane-permeable cAMP analog. The results show that light-induced bidirectional movements in tilapia erythrophores may be controlled by cytosolic cAMP levels via Gi- or Gs-type G proteins. In addition, RT-PCR demonstrated for the first time the expression of mRNAs encoding red and green opsins in tilapia fins, only where erythrophores exist. Here, we suggest that multiple cone-type visual pigments may be present in the erythrophores, and that unique cascades in which such opsins couple to Gi or Gs-type G proteins are involved in the photoresponses in these pigment cells. Thus, tilapia erythrophore system seems to be a nice model for understanding the photoresponses of cells other than visual cells.

Animals↗
PubMed1984

Opsin-induced experimental autoimmune retinitis in rats.

Experimental autoimmune retinitis has been induced in Lewis rats by injection of opsin in mycobacterial adjuvant and Hemophilus pertussis adjuvant. Clinical, histopathological and immunological parameters of the disease are reported. Two types of opsin were prepared from purified bovine retina outer segments, one type in Triton X-100 and the other in lithium dodecyl sulfate. Both preparations were free from S-antigen. Dodecyl sulfate-denaturated-opsin displayed lower antigenicity and pathogenicity than Triton-opsin. Triton-opsin (250 micrograms) induced moderate to severe non-granulomatous uveitis (predominantly retinitis) in 70% of the Lewis rats at the end of the second week after injection. The photoreceptor cell layer was destructed within a few days. This group displayed high responses to opsin in the lymphocyte transformation test. In view of observed histological features, the possible early involvement of vasoactive factors is discussed. Low opsin doses (50 or 100 micrograms) seldomly induced severe retinitis, while the incidence of mild pathology was low. Lewis rats appeared to be more susceptible for the development of experimental autoimmune retinitis than Wistar rats.

Animals↗
PubMed1997

Cloning and expression of the red visual pigment gene of goat (Capra hircus).

We have cloned and sequenced the red opsin gene, rCh, of goat (Capra hircus). When rCh is expressed in cultured cells and reconstituted with 11-cis retinal, the resulting visual pigment has a wavelength of maximal absorption (lambda max) of 553 nm. This result and the deduced aa sequence of the goat red opsin suggest that the lambda max values of the red pigments of goat and human are based mainly on Y277 and T285. The slightly lower lambda max value of the red pigment in goat than in human (approximately 560 nm) can be explained by a single aa difference between the goat (A180) and human (S180) red pigments.

Animals↗
PubMedDate not supplied

Erratum: Temporal and spatial patterns of opsin gene expression in the zebrafish (Danio rerio): corrections with additions.

We report here a reexamination of the developmental expression of cone opsins in the zebrafish retina. The red- and blue-sensitive opsins appear at 51 h postfertilization (hpf) whereas ultraviolet (UV) opsin is not seen until after 55 hpf. More cells show red cone opsin expression than blue at 51 and 55 hpf, indicating the sequence of cone opsin expression in zebrafish is first red, then blue, and finally UV. Curiously, morphological development of the cones is in reverse order; UV cones appear quite mature by day 6-7 postfertilization (pf), but morphologically, red cones do not appear adult-like until 15-20 days pf.

Animals↗
PubMed2000

The spatial and temporal expression of outer segment proteins during development of Macaca monkey cones.

PURPOSE: To characterize the spatial and temporal expression of key structural and phototransduction cascade proteins in the monkey cone outer segment (OS). METHODS: Retinas from Macaca monkeys from ages fetal day (Fd) 89 through adulthood were double labeled using immunofluorescence for short (S) or long/medium (L/M) wavelength-sensitive cone opsin and either a structural protein (peripherin) or a phototransduction cascade protein (alpha-transducin [alpha-T], phosphodiesterase [PDE], or rhodopsin kinase [RK]). The spatial and temporal patterns of expression for each protein at each age were determined and graphed as a percentage of retinal coverage. RESULTS: In both cone types, opsins and phototransduction proteins appear first in the fovea and last at the retinal edge. Peripherin appears concomitantly with opsin in both S and L/M cones, but S cones express peripherin and opsin 1 to 3 weeks before neighboring L/M cones. Alpha-T, PDE, and RK are expressed together in the L/M cone OS shortly after L/M opsin appears. Phototransduction proteins are not expressed in S cones until 1 to 3 weeks after the appearance of S opsin and at the same time that neighboring cones are expressing both L/M opsin and phototransduction proteins. CONCLUSIONS: The concomitant appearance of opsin and peripherin strongly suggests roles in promoting the structural integrity of the developing OS. Phototransduction cascade proteins appear in the developing OS at the same time as one another, but after opsin. The significant lag between their expression and that of S cone opsin indicates that phototransduction proteins are not essential for OS formation, nor does opsin expression trigger their expression. The different temporal but similar spatial expression patterns of phototransduction proteins within S and L/M cones suggests that some local signal(s) coordinates their appearance.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1997

Cloning and characterization of the pineal gland-specific opsin gene of marine lamprey (Petromyzon marinus).

We have cloned and sequenced the pineal gland-specific opsin (P opsin) gene, p(Pm), of marine lamprey, P. marinus. The deduced P opsin, P(Pm), consisting of 444 aa, is about 90 aa longer than the orthologous opsins of chicken, pigeon, and American chameleon. The evolution of P(Pm) is characterized not only by a significantly higher rate of aa replacement than the other P opsins but also by a larger number of unique aa replacements at highly conserved sites in the nonTM region. These changes in P(Pm) might have been important in achieving marine lamprey-specific interaction between P(Pm) and other proteins in the pineal gland.

Amino Acid Sequence↗
PubMed1998

Constitutive activation of opsin by mutation of methionine 257 on transmembrane helix 6.

Rhodopsin is a member of the large family of G protein-coupled receptors (GPCR's). Constitutive activity of GPCR's, defined as ligand-independent signaling, has been recognized as an important feature of receptor function and has also been implicated in the molecular pathophysiology of a number of human diseases. Rhodopsin has evolved a unique mechanism to minimize receptor basal activity. The chromophore 11-cis-retinal, which acts as an inverse agonist in rhodopsin, is covalently bound to the receptor to ensure extremely low receptor signaling in the dark. In this study, we replaced Met257 in TM helix 6 of opsin with each of the remaining 19 amino acids. Only mutant opsin M257R failed to be expressed in COS-cell membranes. Each of the remaining 18 mutant opsins, with the exception of M257L, was significantly constitutively active. Two mutants in particular, M257Y and M257N, displayed very high levels of constitutive activity. In addition, the double-site mutants with substitutions of both Met257 and Glu113 in TM helix 3 tended to be much more constitutively active than the sums of the activities of the individual single-site mutants. Based on existing structural models of rhodopsin, we conclude that Met257 may form an important and specific interhelical interaction with a highly conserved NPXXY motif in TM helix 7, which stabilizes the inactive receptor conformation by preventing TM helix 6 movement in the absence of all-trans-retinal. Furthermore, we are able to show that the pharmacological properties of the large number (approximately 50) of mutant opsins that we have characterized to date support the two-state model of GPCR function. These results suggest that rhodopsin and other GPCR's share a common mechanism of receptor activation that involves specific changes in helix-helix interactions.

Amino Acid Sequence↗
PubMed1984

Opsin-immunoreactive outer segments of photoreceptors in the eye and in the lumen of the optic nerve of the hagfish, Myxine glutinosa.

Opsin-immunoreactive sites in the eye and optic nerve of the hagfish, Myxine glutinosa, were studied by use of light-microscopic pre- and postembedding peroxidase-antiperoxidase or avidin-biotin-peroxidase techniques, and the immuno-electron-microscopic protein A-gold method. At the light-microscopic level, a strong opsin immunoreaction was obtained on the outer segments of the photoreceptor cells with sheep and rat antibodies against bovine (rhod)opsin. These outer segments were located in the marginal photoreceptor space and in follicles of the retina, as well as in the tubular lumen of the optic nerve. Ultrastructurally, two classes of outer segments can be distinguished; most of them exhibited a strong antiopsin reaction, while certain elements lacked immunoreactivity with the antisera employed. The protein A-gold particles marked opsin-immunoreactive sites on the photoreceptor membranes. The presence of opsin-immunoreactive material in the retina and optic nerve of the hagfish strengthens the view that this primitive eye lacking a cornea, lens and vitreous body is engaged in light perception. The morphological similarity between the eye and pineal tissue is discussed in connection with the absence of a pineal organ in this species.

Animals↗
PubMed1994

The human blue opsin promoter directs transgene expression in short-wave cones and bipolar cells in the mouse retina.

Transgenic mouse lines were generated using either 3.8 or 1.1 kb of 5' upstream flanking sequence from the human blue opsin gene fused to the lacZ or human growth hormone reporter gene. Mice were analyzed for appropriate cell-specific and developmental expression patterns. In 13 independently derived lines of animals, transgene expression was limited to photoreceptor and inner nuclear layer cells. Photoreceptors were identified as cone cells based on morphological criteria and colocalization of transgene expression with the cone-associated marker, peanut agglutinin lectin. More specifically, transgene-positive photoreceptors were identified as short-wave cone cells (S-cones) by using the short-wave color opsin-specific antibody, OS-2. Reporter-gene-positive cells of the inner nuclear layer were identified as bipolar cells based on morphological criteria. Transgenes and the endogenous mouse short-wave opsin gene were transcriptionally coactivated at embryonic day 13. These results show that 3.8 or 1.1 kb of human blue opsin upstream flanking sequences are capable of directing expression in short-wave cone cells in a spatially and temporally appropriate fashion and that the human blue opsin gene is the homologue of the short-wave-sensitive pigment, S-opsin, in the short-wave cones of the mouse retina. Expression in the bipolar cells may reflect regulatory mechanisms that are common to these cells and to the cone photoreceptors.

Animals↗
PubMed2006

Glycine receptors in a population of adult mammalian cones.

Glycinergic interplexiform cells provide a feedback signal from the inner retina to the outer retina. To determine if cones receive such a signal, glycine was applied on cultured porcine cone photoreceptors recorded with the patch clamp technique. A minor population of cone photoreceptors was found to generate large currents in response to puff application of glycine. These currents reversed close to the calculated equilibrium potential for chloride ions. These glycine-elicited currents were sensitive to strychnine but not to picrotoxin consistent with the expression of alpha-beta-heteromeric glycine receptors. Glycine receptors were also activated by taurine and beta-alanine. The glycine receptor antibody mAb4a labelled a minority of the cone photoreceptors identified by an antibody specific for cone arrestin. Finally, expression of the beta subunit of the glycine receptor was demonstrated by single cell RT-PCR in a similar proportion (approximately 13%) of cone photoreceptors freshly isolated by lectin-panning. The identity of cone photoreceptors was assessed by their specific expression of the cone arrestin mRNA. The population of cone photoreceptors expressing the glycine receptor was not correlated to a specific colour-sensitive subtype as demonstrated by single cell RT-PCR experiments using primers for S opsin, cone arrestin and glycine receptor beta subunit. This glycine receptor expression in a minority of cones defines a new cone population suggesting an unexpected role for glycine in the visual information processing in the outer retina.

Animals↗