Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Opsins”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources
PubMed1989

Circadian rhythm and light regulate opsin mRNA in rod photoreceptors.

Disk membranes in the outer segment of rod photoreceptors are continuously renewed, being assembled at the outer segment base, displaced outward by new disks and eventually shed at the tip. In lower vertebrates, disk assembly occurs with a diurnal rhythm with 2-4% of the outer segment length produced daily. We have discovered that in toad and fish retinas the level of mRNA for opsin, the most abundant protein in rod disks, fluctuates with a daily rhythm and is regulated both by light and by a circadian oscillator. The mRNA level rises before light onset, remains high during the light phase of a diurnal cycle and decreases four to tenfold during the dark phase. In constant darkness, mRNA elevation occurs during subjective daytime. At night, rod opsin mRNA can be elevated by exposure to light.

Animals↗
PubMed2004

Opsin expression: new mechanism for modulating colour vision.

Each cone photoreceptor in the retina responds to light in a limited range of wavelengths, giving it a spectral phenotype. This phenotype is determined by the most prevalent of the photoreceptor's visual-pigment proteins (opsins) and is assumed to remain unchanged during an animal's lifetime. Here we show that in the Pacific pink salmon, Oncorhynchus gorbuscha, single cones can switch their spectral phenotype from ultraviolet to blue by regulating the production of the appropriate opsins as the fish grow older. This photoreceptor plasticity may operate to modulate colour vision as the salmon's lifestyle changes.

Animals↗
PubMed2002

Trans-specific evolution of opsin alleles and the maintenance of trichromatic colour vision in Callitrichine primates.

Many New World (NW) primates possess a remarkable polymorphism in an X-linked locus, which encodes for the visual pigments (opsins) used for colour vision. Females that are heterozygous for opsin alleles of different spectral sensitivity at this locus have trichromatic colour vision, whereas homozygous females and males are dichromatic, with poor colour discrimination in the red-green range. Here we describe an extensive survey of allelic variation in both exons and introns at this locus within and among species of the Callitrichines (marmosets and tamarins). All five genera of Callitrichines have the X-linked polymorphism, and only the three functional allelic classes described previously (with maximum wavelength sensitivities at about 543 nm, 556 nm and 563 nm) were found among the 16 species and 233 or more X-chromosomes sampled. In spite of the homogenizing effects of gene conversion, phylogenetic analyses provide direct evidence for trans-specific evolution of alleles over time periods of at least 5-6 million years, and up to 14 million years (estimated from independent phylogenies). These conclusions are supported by the distribution of insertions and deletions in introns. The maintenance of polymorphism over these time periods requires an adaptive explanation, which must involve a heterozygote advantage for trichromats. The lack of detection of alleles that are recombinant for spectral sensitivity suggests that such alleles are suboptimal. The two main hypotheses for the selective advantage of trichromacy in primates are frugivory for ripe fruits and folivory for young leaves. The latter can be discounted in Callitrichines, as they are not folivorous.

Alleles↗
PubMed2002

The effect of selection on a long wavelength-sensitive (LWS) opsin gene of Lake Victoria cichlid fishes.

In East African Lake Victoria >200 endemic species of haplochromine fishes have been described on the basis of morphological and behavioral differences. Yet molecular analysis has failed to reveal any species-specific differences among these fishes in either mitochondrial or nuclear genes. Although the genes could be shown to vary, the variations represent trans-species polymorphisms not yet assorted along species lines. Nevertheless, fixed genetic differences must exist between the species at loci responsible for the adaptive characters distinguishing the various forms from one another. Here we describe variation and fixation at the long wavelength-sensitive (LWS) opsin locus, which is selection-driven, adaptive, and if not species- then at least population-specific. Because color is one of the characters distinguishing species of haplochromine fishes and color perception plays an important part in food acquisition and mate choice, we suggest that the observed variation and fixation at the LWS opsin locus may have been involved in the process that has led to the spectacular species divergence of haplochromine fishes in Lake Victoria.

Adaptation, Physiological↗
PubMed1988

Opsin exhibits cGMP-activated single-channel activity.

Low concentrations of cGMP evoked reversible single-channel currents in patches excised from liposomes that contained purified bovine opsin. Two elementary conductances, of 32 and 17 pS, were observed in the presence of 10-200 microM cGMP. Both individual channel openings (mean open times, approximately 1.6 ms for the 32-pS conductance and approximately 1.0 ms for the 17-pS conductance) and bursts of openings (mean burst duration, approximately 2-3 ms for the large events) were observed. The cGMP-activated channel activity could be observed in the presence or absence of Ca2+. These results raise the possibility that opsin or rhodopsin, an opsin/rhodopsin isoform, or an opsin/isoform multimer serves as a cGMP-modulated pore in the rod outer segment.

Animals↗
PubMed2003

Ligand channeling within a G-protein-coupled receptor. The entry and exit of retinals in native opsin.

Deactivation of light-activated rhodopsin (metarhodopsin II) involves, after rhodopsin kinase and arrestin interactions, the hydrolysis of the covalent bond of all-trans-retinal to the apoprotein. Although the long-lived storage form metarhodopsin III is transiently formed, all-trans-retinal is eventually released from the active site. Here we address the question of whether the release results in a retinal that is freely diffusible in the lipid phase of the photoreceptor membrane. The release reaction is accompanied by an increase in intrinsic protein fluorescence (release signal), which arises from the relief of the fluorescence quenching imposed by the retinal in the active site. An analogous fluorescence decrease (uptake signal) was evoked by exogenous retinoids when they non-covalently bound to native opsin membranes. Uptake of 11-cis-retinal was faster than formation of the retinylidene linkage to the apoprotein. Endogenous all-trans-retinal released from the active site during metarhodopsin II decay did not generate the uptake signal. The data show that in addition to the retinylidene pocket (site I) there are two other retinoidbinding sites within opsin. Site II involved in the uptake signal is an entrance site, while the exit site (site III) is occupied when retinal remains bound after its release from site I. Support for a retinal channeling mechanism comes from the rhodopsin crystal structure, which unveiled two putative hydrophobic binding sites. This mechanism enables a unidirectional process for the release of photoisomerized chromophore and the uptake of newly synthesized 11-cis-retinal for the regeneration of rhodopsin.

Animals↗
PubMed2003

Organization of the G protein-coupled receptors rhodopsin and opsin in native membranes.

G protein-coupled receptors (GPCRs), which constitute the largest and structurally best conserved family of signaling molecules, are involved in virtually all physiological processes. Crystal structures are available only for the detergent-solubilized light receptor rhodopsin. In addition, this receptor is the only GPCR for which the presumed higher order oligomeric state in native membranes has been demonstrated (Fotiadis, D., Liang, Y., Filipek, S., Saperstein, D. A., Engel, A., and Palczewski, K. (2003) Nature 421, 127-128). Here, we have determined by atomic force microscopy the organization of rhodopsin in native membranes obtained from wild-type mouse photoreceptors and opsin isolated from photoreceptors of Rpe65-/- mutant mice, which do not produce the chromophore 11-cis-retinal. The higher order organization of rhodopsin was present irrespective of the support on which the membranes were adsorbed for imaging. Rhodopsin and opsin form structural dimers that are organized in paracrystalline arrays. The intradimeric contact is likely to involve helices IV and V, whereas contacts mainly between helices I and II and the cytoplasmic loop connecting helices V and VI facilitate the formation of rhodopsin dimer rows. Contacts between rows are on the extracellular side and involve helix I. This is the first semi-empirical model of a higher order structure of a GPCR in native membranes, and it has profound implications for the understanding of how this receptor interacts with partner proteins.

Animals↗
PubMed2005

Photoreceptors of Nrl -/- mice coexpress functional S- and M-cone opsins having distinct inactivation mechanisms.

The retinas of mice null for the neural retina leucine zipper transcription factor (Nrl-/-) contain no rods but are populated instead with photoreceptors that on ultrastructural, histochemical, and molecular criteria appear cone like. To characterize these photoreceptors functionally, responses of single photoreceptors of Nrl-/- mice were recorded with suction pipettes at 35-37 degrees C and compared with the responses of rods of WT mice. Recordings were made either in the conventional manner, with the outer segment (OS) drawn into the pipette ("OS in"), or in a novel configuration with a portion of the inner segment drawn in ("OS out"). Nrl-/- photoreceptor responses recorded in the OS-out configuration were much faster than those of WT rods: for dim-flash responses tpeak = 91 ms vs. 215 ms; for saturating flashes, dominant recovery time constants, tau(D) = 110 ms vs. 240 ms, respectively. Nrl-/- photoreceptors in the OS-in configuration had reduced amplification, sensitivity, and slowed recovery kinetics, but the recording configuration had no effect on rod response properties, suggesting Nrl-/- outer segments to be more susceptible to damage. Functional coexpression of two cone pigments in a single mammalian photoreceptor was established for the first time; the responses of every Nrl-/- cell were driven by both the short-wave (S, lambda(max) approximately 360 nm) and the mid-wave (M, lambda(max) approximately 510 nm) mouse cone pigment; the apparent ratio of coexpressed M-pigment varied from 1:1 to 1:3,000 in a manner reflecting a dorso-ventral retinal position gradient. The role of the G-protein receptor kinase Grk1 in cone pigment inactivation was investigated in recordings from Nrl-/-/Grk1-/- photoreceptors. Dim-flash responses of cells driven by either the S- or the M-cone pigment were slowed 2.8-fold and 7.5-fold, respectively, in the absence of Grk1; the inactivation of the M-pigment response was much more seriously retarded. Thus, Grk1 is essential to normal inactivation of both S- and M-mouse cone opsins, but S-opsin has access to a relatively effective, Grk1-independent inactivation pathway.

Animals↗
PubMed1996

Calcium-activated opsin phosphatase activity in retinal rod outer segments.

We describe the presence in bovine retinal rod outer segments of a phosphatase which dephosphorylates phosphoopsin with an efficiency similar to that of PP2A, and which is stimulated by submicromolar levels of Ca2+ (half-maximal activation, 0.4-0.5 microM). This enzyme is designated CA2+ -activated opsin phosphatase (CAOP). CAOP has a molecular mass of 70-75 kDa as determined by gel filtration on Superose 12 and exhibits reversible Ca2+ -dependent oligomerization. An unidentified protein of approximately 25 kDa is necessary for full activity of CAOP and for cooperative binding of Ca2+ (h > 2). CAOP does not require Mg2+ and is inhibited by okadaic acid (median inhibitory concentration > 25 microM), which suggests that it is related to the PP1/2A/2b class of protein phosphatases. Like PP2B, CAOP is inhibited by trifluoperazine (median inhibitory concentration 40 microM), but calmodulin has no effect on CAOP activity, and CAOP is inhibited by mastoparan at much higher concentrations than PP2b. This combination of properties suggests that CAOP is not identical to any characterized protein phosphatase. Since the cytoplasmic concentration of Ca2+ -sensitive opsin phosphatase activity suggests that light-dependent Ca2+ levels may control rhodopsin dephosphorylation.

Animals↗
PubMed1988

Immunoreactive opsin and glial fibrillary acidic protein in persistent hyperplastic primary vitreous.

An 8-month-old boy had an anterior type of persistent hyperplastic primary vitreous in the right eye. Results of needle biopsy, performed because of elevated intraocular pressure, disclosed clusters of blastic cells. The eye was enucleated on the suspicion of retinoblastoma. Histological examination showed retrolental fibrovascular tissue and retinal dysplasia. Immunoreactive opsin was detected in the innermost structures and in photoreceptor-like cells of rosettes. We conclude that photoreceptor cells differentiated to express opsin, even when neighbouring cells were abnormally arranged. An immunocytochemical study of glial fibrillary acidic protein demonstrated glial proliferation in the inner layer of the retina but not in the preretinal space.

Eye↗
PubMed2004

Ciliary photoreceptors with a vertebrate-type opsin in an invertebrate brain.

For vision, insect and vertebrate eyes use rhabdomeric and ciliary photoreceptor cells, respectively. These cells show distinct architecture and transduce the light signal by different phototransductory cascades. In the marine rag-worm Platynereis, we find both cell types: rhabdomeric photoreceptor cells in the eyes and ciliary photoreceptor cells in the brain. The latter use a photopigment closely related to vertebrate rod and cone opsins. Comparative analysis indicates that both types of photoreceptors, with distinct opsins, coexisted in Urbilateria, the last common ancestor of insects and vertebrates, and sheds new light on vertebrate eye evolution.

Amino Acid Sequence↗
PubMed2005

Impaired opsin targeting and cone photoreceptor migration in the retina of mice lacking the cyclic nucleotide-gated channel CNGA3.

PURPOSE: To characterize molecular and cellular changes in the mouse retina caused by the genetic deletion of the cone cyclic nucleotide-gated channel (CNG) subunit CNGA3. METHODS: Retinas of wild-type and CNGA3-deficient (CNGA3(-/-)) mice from 9 days up to 22 months of age were analyzed by immunohistochemistry, electron microscopy, and molecular biological methods. RESULTS: CNGA3(-/-) cones failed to transport opsins into outer segments, downregulated various proteins of the phototransduction cascade, and induced apoptotic death. Loss of CNGA3 did not affect the transcription of cone-specific genes. Cone degeneration was evident from the second postnatal week on, and it proceeded significantly faster in the ventral than in the dorsal part of the retina. Ventral cones were completely missing after the third postnatal month, whereas residual dorsal cones were present, even in 22-month-old knockout mice. CNGA3(-/-) cone somata exhibited profoundly delayed migration during postnatal development. At the time of eye opening, most CNGA3(-/-) cones had displaced somata localized close to or in the outer plexiform layer. These cones lacked the characteristic synaptic pedicle, but revealed synapselike contacts to second-order neurons at their somata. At later stages, most of the surviving CNGA3(-/-) cones had correctly located somata and morphologically normal synapses. CONCLUSIONS: The loss of CNGA3 impairs the targeting of cone opsins and the expression of other visual cascade proteins. In addition, CNGA3 appears to be essential for normal postnatal migration of cone somata. After loss of cone outer segment proteins, CNGA3(-/-) cones induce apoptotic cell death.

Animals↗
PubMed2006

Active and passive displacement of transmembrane domains both occur during opsin biogenesis at the Sec61 translocon.

We used a site-specific crosslinking approach to study the membrane integration of the polytopic protein opsin at the endoplasmic reticulum. We show that transmembrane domain 1 occupies two distinct Sec61-based environments during its integration. However, transmembrane domains 2 and 3 exit the Sec61 translocon more rapidly in a process that suggests a displacement model for their integration where the biosynthesis of one transmembrane domain would facilitate the exit of another. In order to investigate this hypothesis further, we studied the integration of the first and third transmembrane domains of opsin in the absence of any additional C-terminal transmembrane domains. In the case of transmembrane domain 1, we found that its lateral exit from the translocon is clearly dependent upon the synthesis of subsequent transmembrane domains. By contrast, the lateral exit of the third transmembrane domain occurred independently of any such requirement. Thus, even within a single polypeptide chain, distinct transmembrane domains display different requirements for their integration through the endoplasmic reticulum translocon, and the displacement of one transmembrane domain by another is not a global requirement for membrane integration.

Amino Acid Sequence↗
PubMed2002

Constraints of opsin structure on the ligand-binding site: studies with ring-fused retinals.

Ring-fused retinal analogs were designed to examine the hula-twist mode of the photoisomerization of the 9-cis retinylidene chromophore. Two 9-cis retinal analogs, the C11-C13 five-membered ring-fused and the C12-C14 five-membered ring-fused retinal derivatives, formed the pigments with opsin. The C11-C13 ring-fused analog was isomerized to a relaxed all-trans chromophore (lambda(max) > 400 nm) at even -269 degrees C and the Schiff base was kept protonated at 0 degrees C. The C12-C14 ring-fused analog was converted photochemically to a bathorhodopsin-like chromophore (lambda(max) = 583 nm) at -196 degrees C, which was further converted to the deprotonated Schiff base at 0 degrees C. The model-building study suggested that the analogs do not form pigments in the retinal-binding site of rhodopsin but form pigments with opsin structures, which have larger binding space generated by the movement of transmembrane helices. The molecular dynamics simulation of the isomerization of the analog chromophores provided a twisted C11-C12 double bond for the C12-C14 ring-fused analog and all relaxed double bonds with a highly twisted C10-C11 bond for the C11-C13 ring-fused analog. The structural model of the C11-C13 ring-fused analog chromophore showed a characteristic flip of the cyclohexenyl moiety toward transmembrane segments 3 and 4. The structural models suggested that hula twist is a primary process for the photoisomerization of the analog chromophores.

Chromatography, High Pressure Liquid↗
PubMed2000

Late retinal progenitor cells show intrinsic limitations in the production of cell types and the kinetics of opsin synthesis.

The seven major cell classes of the vertebrate neural retina arise from a pool of multipotent progenitor cells. Several studies suggest a model of retinal development in which both the environment and the progenitor cells themselves change over time (). To test this model, we used a reaggregate culture system in which a labeled population of progenitor cells from the postnatal rat retina were cultured with an excess of embryonic retinal cells. The labeled cells were then assayed for their cell fate choices and their kinetics of rod differentiation, as measured by opsin synthesis. The kinetics of opsin synthesis remained unchanged, but fewer postnatal cells adopted the rod cell fate when cultured with embryonic cells. There was an increase in the percentage of bipolar cells produced by postnatal progenitor cells, indicating a possible respecification of fate. The increase in bipolar cells could occur even after progenitor cells had completed their terminal mitoses. These alterations in cell fates appeared to be caused at least in part by a secreted factor released by the embryonic cells that requires the LIFRbeta/gp130 complex for signaling. Finally, although surrounded by 20-fold more embryonic cells, the postnatal cells did not choose to adopt any fates normally produced only by embryonic cells.

Animals↗
PubMed2001

Extended photoreceptor viability by light stress in the RCS rats but not in the opsin P23H mutant rats.

PURPOSE: To determine the effect of light stress on retinal function and long-term photoreceptor viability in Royal College of Surgeons (RCS) rats and the applicability of the light treatment to the opsin P23H mutant rats. METHODS: RCS rats at postnatal day (P)23 were illuminated with 120 foot-candles (fc) white light for 10 hours. Photoreceptor survival and basic fibroblast growth factor (bFGF) expression were measured at P60 and P83. Retinal function was evaluated by electroretinography. Opsin P23H transgenic rats were treated with light at P28 and analyzed at P70 for photoreceptor viability, ultrastructure, and bFGF expression. RESULTS: Light-treated RCS rats at P60 had four to five rows of nuclei versus one to two rows in untreated littermates. The average amplitude of the ERG b-wave was 28 microV in treated rats, compared with 6 microV in untreated littermates. By P83 there was still significant preservation of the ONL in treated rats. Immunoblot analysis showed a high expression of bFGF in the treated retinas even 2 months after treatment. Illumination of P23H rats at P28 with 120 fc white light for 10 hours caused substantial photoreceptor cell death, although bFGF expression was upregulated. Lowered illumination dosages continued to cause photoreceptor damage until levels were reached that neither caused damage nor enhanced survival. CONCLUSIONS: Although light stress promotes photoreceptor survival and function in the RCS rat, it elicits death signals in the P23H rats that may not be overcome by survival-promoting factors. Therefore, use of light stress to promote photoreceptor survival should be considered with regard to sensitivity of the mutation to light damage.

Animals↗
PubMed2002

Opsin-G11-mediated signaling pathway for photic entrainment of the chicken pineal circadian clock.

Light is a major environmental signal for entrainment of the circadian clock, but little is known about the intracellular phototransduction pathway triggered by light activation of the photoreceptive molecule(s) responsible for the phase shift of the clock in vertebrates. The chicken pineal gland and retina contain the autonomous circadian oscillators together with the photic entrainment pathway, and hence they represent useful experimental models for the clock system. Here we show the expression of G11alpha, an alpha subunit of heterotrimeric G-protein, in both tissues by cDNA cloning, Northern blot, and Western blot analyses. G11alpha immunoreactivity was colocalized with pinopsin in the chicken pineal cells and also with rhodopsin in the outer segments of retinal photoreceptor cells, suggesting functional coupling of G11alpha with opsins in the clock-containing photosensitive tissues. The physical interaction was examined by coimmunoprecipitation experiments, the results of which provided evidence for light- and GTP-dependent coupling between rhodopsin and G11alpha. To examine whether activation of endogenous G11 leads to a phase shift of the oscillator, Gq/11-coupled m1-type muscarinic acetylcholine receptor (mAChR) was ectopically expressed in the cultured pineal cells. Subsequent treatment of the cells with carbamylcholine (CCh), an agonist of mAChR, induced phase-dependent phase shifts of the melatonin rhythm in a manner very similar to the effect of light. In contrast, CCh treatment induced no measurable effect on the rhythm of nontransfected (control) cells or cells expressing G(i/o)-coupled m2-type mAChR, indicating selectivity of the G-protein activation. Together, our results demonstrate the existence of a G11-mediated opsin-signaling pathway contributing to the photic entrainment of the circadian clock.

Animals↗
PubMed2005

[Molecular dynamics simulation of dark-adapted rhodopsin and free opsin].

Molecular dynamics simulation was carried out for the rhodopsin protein to investigate its conformational changes in respect to inclusion of 11-cis retinal chromophore. Molecular dynamics calculations were performed within the time frame 3000 ps. Totally, 3 X 10(6) configurations ofrhodopsin and free opsin were analyzed and compared. It has been shown that the 11-cis retinal rearrangement (adaptation) in opsin strongly affects the surrounding amino acid residues of protein binding pocket and the protein cytoplasmic region. The extracellular part, however, shows comparatively little changes. On basis of the simulation results obtained we propose a molecular mechanism for the rhodopsin protein function as a G-protein-coupled receptor in the state of darkness. We discuss the role of the retinal chromophore as a ligand-antagonist stabilizing the inactive conformation of rhodopsin.

Animals↗