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PubMed1993

Opsin synthesis in the C57BL/6-mivit/mivit mouse model of retinal degeneration.

The capacity of photoreceptor cells to synthesize opsin was evaluated in a newly-described mouse model of retinal degeneration, the C57BL/6-mivit/mivit. The mivit/mivit mouse loses photoreceptor cells at a rate of about one row per month beginning at 8 weeks, ROS are severely disrupted at 4 months, RPE is unevenly pigmented. Retinas of affected and control mice ages 4, 6, 8, 12, 16, 20, 24, 28, 32 and 52 weeks were incubated for 2 hours in medium containing [3H] leucine. Homogenates of retina samples were subjected to SDS-PAGE using disc gels. The gels were sliced and counted by scintillation. The incorporation of [3H] leucine into opsin was compared with its incorporation into other retinal proteins. During the early time points studied, mivit/mivit retinas incorporated proportionately similar amounts of [3H] leucine into opsin versus other retinal proteins as did controls. At 12 weeks, the percentage was about 80% and it continued to decline over the succeeding weeks studied. By 1 year, the proportion of leucine incorporated into opsin versus other proteins was only about 23% the amount incorporated in controls. The results of the present study suggest that the mivit/mivit photoreceptor cells are able to synthesize opsin and the gradual decline in synthetic ability follows the gradual loss of cells and is not correlated with the disruption of ROS.

Aging↗
PubMed1995

Chlamyrhodopsin represents a new type of sensory photoreceptor.

In order to find optimal light conditions for photosynthetic growth, the green alga Chlamydomonas uses a visual system. An optical device, a rhodopsin photoreceptor and an electrical signal transduction chain that mediates between photoreceptor and flagella comprise this system. Here we present an improved strategy for the preparation of eyespot membranes. These membranes contain a retinal binding protein, which has been proposed to be the apoprotein of the phototaxis receptor. The retinal binding protein, which we named chlamyopsin, was purified and opsin-specific antibodies were raised. Using these antibodies, the opsin was localized in the eyespot region of whole cells during growth and cell division. The opsin cDNA was purified and sequenced. The sequence reveals that chlamyopsin is not a typical seven helix receptor. It shows some homology to invertebrate opsins but not to opsins from halobacteria. It contains many polar and charged residues and might function as a light-gated ion channel complex. It is likely that this lower plant rhodopsin diverged from animal opsins early in opsin evolution.

Algal Proteins↗
PubMed1988

Rhodopsin-induced experimental autoimmune uveoretinitis: dose-dependent clinicopathological features.

We have studied the clinicopathological features of experimental autoimmune uveoretinitis (EAU) induced in Lewis rats by injection of different doses of rhodopsin and its illuminated form opsin. Rhodopsin consistently appears to be more pathogenic than opsin. Injected in Freund's complete adjuvant and pertussis adjuvant 50 micrograms of rhodopsin induces a frequency of severe EAU similar to 250 micrograms of opsin. Intensity, frequency and location of ocular inflammation are markedly dose dependent. At high dose (100-250 micrograms), rhodopsin induces severe bilateral uveoretinitis in all animals, which starts with acute inflammation of the anterior eye segment at day 10-12 followed by chorioretinitis (predominantly retinitis) which results in complete elimination of the photoreceptor cells. At low dose (20 micrograms), rhodopsin induces mild transient inflammation in 60% of the animals, mainly consisting of mild posterior retinitis which starts at day 20 and leads to a typical multiple focal destruction of the photoreceptor cells. Intermediate doses cause an intermediate type of disease. Omission of pertussis adjuvant lowers the frequency of severe disease at low doses of rhodopsin, delays its onset and changes its features. The last characteristic has been observed in particular at intermediate doses (50-100 micrograms). In these cases, EAU usually starts by cell infiltration of the vitreous, while the anterior segment is only mildly affected. Without pertussis adjuvant the pathogenicity of opsin is low. Even in both adjuvants severe EAU can only be evoked by a high dose of opsin. Although there exists a marked difference in uveitogenicity between rhodopsin and opsin, the immunogenicity is similar and seems not to be correlated with their pathogenicity.

Animals↗
PubMed2002

Different structural organization of the encephalopsin gene in man and mouse.

Encephalopsin, also called Panopsin, is a recently discovered extraretinal photoreceptor, which may play a role in non-visual photic processes such as the entrainment of circadian rhythm or the regulation of pineal melatonin production. Based on RT-PCR data and comparative genomic sequence analysis, we show that the human OPN3 gene consists of six exons and expresses various splice variants, while the murine homologue contains four exons and produces just one splice form. Furthermore, the human OPN3 gene overlaps with the neighboring KMO gene on a genomic as well as on an RNA level, whereas the corresponding genes in mouse lie close together but do not overlap. This finding is of particular interest, since differences in gene organization between man and mouse, that have been reported so far, occur within gene clusters, i.e. the number of genes within a certain cluster may differ between man and mouse. OPN3 provides an exception to this rule, since it is positionally uncoupled from other genes of the opsin family.

3' Flanking Region↗
PubMed1997

Interconversion of red opsin isoforms by the cyclophilin-related chaperone protein Ran-binding protein 2.

Ran-binding protein 2 (RanBP2) (type II) is a retinal cyclophilin-related protein that binds Ran-GTPase. Type I cyclophilin is a shorter, alternatively spliced isoform of RanBP2. Recently, we showed that the Ran-binding domain 4 (RBD4)/cyclophilin (CY) supradomain of RanBP2 acts both in vitro and in vivo as a specific chaperone for bovine red/green opsin (R/G opsin). R/G opsin undergoes a stable modification of its electrophoretic mobility upon binding to RanBP2. This modification is likely due to cis-trans isomerization of one or more proline residues in the opsin protein. Here, we show that expression of human red opsin in Escherichia coli and COS cells results in the production of still a third electrophoretic variant of this protein. This variant was converted to the RBD4 binding-competent form of opsin through direct interaction with RBD4/CY, both in vivo and in vitro. We suggest that these distinct opsin species may represent kinetically or thermodynamically trapped prolyl conformers that can be interconverted by concerted action of the RBD4 and CY domains of RanBP2. We also show that the C-terminal half of RBD4 is the binding domain for bovine R/G opsin and that coexpression of human red opsin with type I cyclophilin in vivo enhances the production of functional visual pigment. These observations imply that prolyl isomerization may have importance beyond its role in protein folding, possibly as a molecular switch modulated by cyclophilin for the loading of opsin onto RanBP2 during visual pigment processing in cones.

Amino Acid Isomerases↗
PubMed1984

[Heat denaturation of opsin in warm-blooded animals as a possible mechanism of light-induced retinal damage].

The rate of thermal denaturation of bovine and rat opsin in the photoreceptor membranes was studied within a wide temperature range (between 37 and 70 degrees C). It was found that the rate of thermal denaturation of opsin at a physiological temperature (37 degrees C) might be commensurable or even exceed the known rate of rhodopsin renewal produced by photoreceptor disk formation and shedding. Lipid peroxidation caused an increase in the rate of opsin denaturation at a physiological temperature. It is assumed that accumulation of denatured opsin in the photoreceptor membranes during raised illumination together with lipid peroxidation induction may be one of the mechanisms leading to vision deterioration under raised illumination.

Animals↗
PubMed1998

Mechanisms of spectral tuning in blue cone visual pigments. Visible and raman spectroscopy of blue-shifted rhodopsin mutants.

Spectral tuning by visual pigments involves the modulation of the physical properties of the chromophore (11-cis-retinal) by amino acid side chains that compose the chromophore-binding pocket. We identified 12 amino acid residues in the human blue cone pigment that might induce the required green-to-blue opsin shift. The simultaneous substitution of nine of these sites in rhodopsin (M86L, G90S, A117G, E122L, A124T, W265Y, A292S, A295S, and A299C) shifted the absorption maximum from 500 to 438 nm, accounting for 2,830 cm-1, or 80%, of the opsin shift between rhodopsin and the blue cone pigment. Raman spectroscopy of mutant pigments shows that the dielectric character and architecture of the chromophore-binding pocket are specifically altered. An increase in the number of dipolar side chains near the protonated Schiff base of retinal increases the ground-excited state energy gap via long range dipole-dipole Coulomb interaction. In addition, the W265Y substitution causes a decrease in solvent polarizability near the chromophore ring structure. Finally, two substitutions on transmembrane helix 3 (A117G and E122L) act in combination with the other substitutions to alter the binding-pocket structure, resulting in stronger interaction of the protonated Schiff base group with the surrounding dipolar groups and the counterion. Taken together, these results identify the amino acid side chains and the underlying physical mechanisms responsible for a majority of the opsin shift in blue visual pigments.

Amino Acid Sequence↗
PubMed1987

Immunocytochemical evidence of molecular photoreceptor markers in cerebellar medulloblastomas.

With the use of antisera against bovine retinal S-antigen and bovine opsin the authors demonstrate that in cerebellar medulloblastomas certain tumor cells display immunocytochemical properties characteristic of retinal photoreceptors and pinealocytes. S-antigen-like and opsin-like immunoreactions occur in nine of 28 medulloblastomas investigated. All tumors displaying S-antigen-like immunoreactive neoplastic cells also contain opsin-like immunoreactive cells; however, the opsin-like immunoreactive cells were less frequent than the S-antigen-like immunoreactive cells throughout all positive cases. The immunoreactive cells displayed several long processes. Generally, both S-antigen and opsin-like immunoreactive cells considerably vary in number among individual tumors. The results indicate that certain neoplastic cells of medulloblastoma are capable of expression of photoreceptor-specific proteins and, thus, may be closely related to tumor cells of retinoblastoma and pineocytomas previously shown to bind antisera against retinal S-antigen and opsin. No S-antigen and opsin-like immunoreaction was found in malignant teratomas and germinomas of the pineal gland, oat cell tumors, astrocytomas, ependymomas, oligodendrogliomas, glioblastomas, gangliogliomas, gangliocytoma, ganglioneuroblastomas, neuroblastomas, and esthesioneuroblastoma.

Cerebellar Neoplasms↗
PubMed2002

The amino terminus of opsin translocates "posttranslationally" as efficiently as cotranslationally.

Opsin, a member of the G-protein-coupled receptor family, is a polytopic membrane protein that does not encode a cleaved amino-terminal signal sequence. The amino terminus of opsin precedes the first known targeting information, suggesting that it translocates across the endoplasmic reticulum (ER) membrane after synthesis, uncoupled from translation. However, translocation across the mammalian ER is believed to be coupled to protein synthesis. In this study we show that opsin, within a range of nascent peptide lengths, targets and translocates equally efficiently co- and posttranslationally. Longer nascent opsin peptides have a lower efficiency of cotranslational translocation but an even lower efficiency of posttranslational translocation. We also show that SRP is required for both co- and posttranslational targeting.

Animals↗
PubMed1991

Proper cotranslational insertion of visual rhodopsin into the lipid bilayer occurs in the absence of protein translocation machinery.

The insertion of visual opsin into membranes occurred during in vitro translation of opsin mRNA in wheat germ extract in the presence of either microsomes or liposomes. The rhodopsin that integrated into both types of membranes after regeneration with 11-cis-retinal was functionally active (in contrast to the nonincorporated protein). Opsin either cotranslationally translocated into microsomes or inserted into liposomes had equal sensitivity to proteolysis and yielded the same pattern of peptides, which differed substantially from the set of peptides produced during proteolysis of opsin not incorporated into membranes. Thus visual opsin does not require protein translocation machinery for proper insertion into the lipid bilayer.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1989

[Study of thermo-stabilizing effect of tocopherol on rhodopsin in the presence of fatty acids using the method of differential scanning calorimetry].

By the method of differential scanning calorimetry it was shown that the addition of arachidonic acid to photoreceptor membranes is accompanied by concentration-dependent shift of thermograms curve of rhodopsin value. Addition of tocopherol to photoreceptor membranes prevents the turbulent effect of the fatty acid on opsin and rhodopsin. The obtained data are discussed from the point of view of membrane protective properties of tocopherol.

Arachidonic Acid↗
PubMed1980

Site of attachment of 11-cis-retinal in bovine rhodopsin.

A dipeptide containing the binding site for retinal in bovine rhodopsin has been isolated and its sequence determined. Rhodopsin containing [11-3H]retinal was prepared in chromatographically pure form, and the [3H]retinal was reductively linked to its binding site on opsin by using borane--dimethylamine. The [3H]retinylopsin in octyl glucoside was exhaustively digested with Pronase, and its peptides were separated on silica gel in chloroform/methanol/ammonia [Bownds, D. (1967) Nature (London) 216, 1178--1181] followed by silica gel thin-layer chromatography in two solvent systems. The major retinyl peptide was shown to be alanyl-N epsilon-retinyllysine by amino acid composition, 3H content, and amino acid sequence analysis. The retinyl binding site is located in the carboxyl-terminal region of rhodopsin: when rod cell disk membranes containing [3H]retinal rhodopsin were digested with thermolysin and then reacted with sodium borohydride or borane--dimethylamine, [3H]retinal was reduced onto the F2 (Mr congruent to 6000) fragment, which derives from rhodopsin's carboxyl-terminal region.

Animals↗
PubMed1996

The patterning and onset of opsin expression in vertebrate retinae.

A fascinating area of current research for developmental biologists concerns the patterning of complex tissues. The distribution of photoreceptors across the vertebrate retina is an excellent example of patterning in a tractable model system. Recent studies defining photoreceptor distribution in developing and mature tissue have set the stage for mechanistic studies of the control of patterning.

Aging↗
PubMed1999

Non-visual photoreception by a variety of vertebrate opsins.

Extraretinal photoreceptors in animals are involved in a variety of physiological functions such as photo-entrainment of circadian rhythm, photoperiodicity and body colour change. We have identified pinopsin in the chicken pineal gland as a typical 'non-visual' photoreceptive molecule. Pinopsin with bound 11-cis-retinal shows a blue-light sensitivity (lambda max = 468 nm), and it may play a role in synchronizing the phase of the endogenous circadian oscillator with an environmental dark-light cycle. Pinopsin is not a unique pineal opsin in animals. In the zebrafish, we have detected expression of two rhodopsin genes, the nucleotide sequences of which are very similar but distinct from each other. One is canonical rhodopsin expressed in the retina, and the other is expressed in the pineal gland. The latter gene is widely distributed among teleosts, and we named it 'exo-rhodopsin' after extraocular rhodopsin. On the other hand, our effort to identify the 'deep brain opsin' responsible for the photoperiodic gonadal response resulted in the identification of two kinds of opsins; pinopsin in the toad anterior preoptic nucleus and rhodopsin in the pigeon lateral septum. Both of these opsins are localized in the cerebrospinal fluid-contacting neurons in the brain of the two animals. We also identified VAL opsin in zebrafish retinal horizontal cells, which have not been considered as photoreceptive cells. It has become evident that animals employ a wide variety of photoreceptive molecules for 'non-visual' purposes.

Amino Acid Sequence↗
PubMed1983

Opsin-immunoreactive outer segments in the pineal and parapineal organs of the lamprey (Lampetra fluviatilis), the eel (Anguilla anguilla), and the rainbow trout (Salmo gairdneri).

The pineal complex of Lampetra fluviatilis, Anguilla anguilla and Salmo gairdneri was studied by means of the indirect immunohistochemical antiopsin reaction. Opsin-immunoreactive material was demonstrated in the outer segments of the photoreceptor cells in the pineal organ of all three species investigated. In the lamprey, the opsin-positive outer segments were located in the lumen of the pineal vesicle and atrium. In the two teleost species, the immunoreactive outer segments were observed in abundance in the pineal end-vesicle and stalk. These structures were found to accumulate in the prominent initial portion of the pineal stalk of the eel. In the rainbow trout, immunoreactive outer segments occurred in the wide orifice of the pineal recess at the roof of the third ventricle. In addition, outer segments of photoreceptor cells of the parapineal organ ("parapinealocytes") displayed opsin immunoreactivity. In the lamprey, opsin immunoreactivity was restricted to the central portion of the ventral parapineal retina, while the parapinealocytes in the lateral portions did not bind the antibody. In the two teleosts, immunoreactive outer segments displayed a scattered pattern. These immunocytochemical results provide direct evidence that the photosensitivity of the pineal demonstrated electrophysiologically in lampreys and teleosts (cf. Dodt 1973) is based on an opsin-containing photopigment. The presence of opsin in cells of the parapineal organ strengthens the view that also this organ may be capable of direct light perception. In the lamprey, the exclusive opsin immunoreactivity of a circumscribed group of parapineal cells suggests the existence of two types of parapinealocytes. The significance of opsin-containing photoreceptor outer segments occurring in the most proximal portion of the teleost pineal stalk is discussed, especially with regard to the interpretation of results obtained from pinealectomy experiments.

Animals↗
PubMed1988

Synthesis of functional bovine opsin in insect cells under control of the baculovirus polyhedrin promoter.

In vitro expression of cDNA encoding bovine opsin is accomplished using the baculovirus expression vector system. Full-length opsin was synthesized which was recognized by poly- and monoclonal antisera raised against bovine rhodopsin. Upon infection with a recombinant virus, 1 x 10(6) insect cells produced up to 3 micrograms opsin. Incubation of the in vitro synthesized opsin with 11-cis retinal produced a hydroxylamine-stable, photosensitive pigment.

Animals↗
PubMed2006

Spectral sensitivity of melatonin suppression in the zebrafish pineal gland.

The pineal gland of the zebrafish (Danio rerio) is a clock-containing photoreceptive organ. Superfused pineal glands kept in darkness display rhythmic melatonin production that lasts for days, with high melatonin levels during the night and low levels during the day. Nocturnal light, however, evokes an acute suppression of melatonin synthesis in the photoreceptor cells. Towards characterizing zebrafish pineal photopigment that is involved in the acute melatonin suppression we have measured the spectral sensitivity of melatonin-suppression response in superfused pineal glands. The effect of 2 h light exposure of seven wavelengths (lambdaavg 408, 460, 512, 560, 608, 660 and 697+/-10-15 nm) at multiple irradiances (10(7)-10(14) photons/cm2/s) was determined, and an action spectrum was plotted. The resultant action spectrum provides evidence for the involvement of multiple photopigments in melatonin suppression. The most efficient melatonin-suppression response was achieved by exposure to light of around 512 nm; however, another peak of lower irradiance sensitivity was observed in the middle to long wavelengths. Opsins-specific RT-PCR analysis confirmed the expression of exo-rhodopsin and visual red-sensitive opsin in the pineal gland, while other zebrafish visual opsins as well as VA and VAL opsins were not detected. Dartnall monograms for exo-rhodopsin and visual red-sensitive opsin account for most but not all of the spectral sensitivity features. Therefore, additional pineal photopigments may contribute to the melatonin-suppression response in the pineal gland.

Animals↗
PubMed2003

Cone pigment variations in four genera of new world monkeys.

Previous research revealed significant individual variations in opsin genes and cone photopigments in several species of platyrrhine (New World) monkeys and showed that these in turn can yield significant variations in color vision. To extend the understanding of the nature of color vision in New World monkeys, electroretinogram flicker photometry was used to obtain spectral sensitivity measurements from representatives of four platyrrhine genera (Cebus, Leontopithecus, Saguinus, Pithecia). Animals from each genus were found to be polymorphic for middle to long-wavelength (M/L) sensitive cones. The presence of a short-wavelength sensitive photopigment was established as well so these animals conform to the earlier pattern in predicting that all male monkeys are dichromats while, depending on their opsin gene array, individual females can be either dichromatic or trichromatic. Across subjects a total of five different M/L cone pigments were inferred with a subset of three of these present in each species.

Adaptation, Ocular↗