Signal transduction in photoreceptors

Langmack, Keith; Saibil, Helen R.

doi:10.1042/bst0190858

Cited by 4 publications

(3 citation statements)

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“…103,104 Diminution of rhodopsin expression proportionally decreases the size of rod outer segment structures, while maintaining the same density of rhodopsin as in native discs, 98,105 whereas overexpression of rhodopsin results in enlargement of these structures that ultimately causes their instability. [105][106][107] Early work using biophysical approaches by Chabre 108 (Laboratoire de Biophysique Moléculaire et Cellulaire, Grenoble, France), Saibil 109 (Department of Biological Sciences and ISMB Birkbeck College, London, UK), and Cone, 110 and Poo 111 (Johns Hopkins University) suggested that rhodopsin is monomeric and moves rapidly within the discs. Such mobility was arguably required for high speed phototransduction.…”

Section: Rhodopsin Is Critical For the Organization Of Rod Outer Segmmentioning

confidence: 99%

Chemistry and Biology of the Initial Steps in Vision: The Friedenwald Lecture

Palczewski¹

2014

Invest. Ophthalmol. Vis. Sci.

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Visual transduction is the process in the eye whereby absorption of light in the retina is translated into electrical signals that ultimately reach the brain. The first challenge presented by visual transduction is to understand its molecular basis. We know that maintenance of vision is a continuous process requiring the activation and subsequent restoration of a vitamin A-derived chromophore through a series of chemical reactions catalyzed by enzymes in the retina and retinal pigment epithelium (RPE). Diverse biochemical approaches that identified key proteins and reactions were essential to achieve a mechanistic understanding of these visual processes. The three-dimensional arrangements of these enzymes' polypeptide chains provide invaluable insights into their mechanisms of action. A wealth of information has already been obtained by solving high-resolution crystal structures of both rhodopsin and the retinoid isomerase from pigment RPE (RPE65). Rhodopsin, which is activated by photoisomerization of its 11-cis-retinylidene chromophore, is a prototypical member of a large family of membrane-bound proteins called G protein-coupled receptors (GPCRs). RPE65 is a retinoid isomerase critical for regeneration of the chromophore. Electron microscopy (EM) and atomic force microscopy have provided insights into how certain proteins are assembled to form much larger structures such as rod photoreceptor cell outer segment membranes. A second challenge of visual transduction is to use this knowledge to devise therapeutic approaches that can prevent or reverse conditions leading to blindness. Imaging modalities like optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) applied to appropriate animal models as well as human retinal imaging have been employed to characterize blinding diseases, monitor their progression, and evaluate the success of therapeutic agents. Lately two-photon (2-PO) imaging, together with biochemical assays, are revealing functional aspects of vision at a new molecular level. These multidisciplinary approaches combined with suitable animal models and inbred mutant species can be especially helpful in translating provocative cell and tissue culture findings into therapeutic options for further development in animals and eventually in humans. A host of different approaches and techniques is required for substantial progress in understanding fundamental properties of the visual system.

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Section: Rhodopsin Is Critical For the Organization Of Rod Outer Segmmentioning

confidence: 99%

Chemistry and Biology of the Initial Steps in Vision: The Friedenwald Lecture

Palczewski¹

2014

Invest. Ophthalmol. Vis. Sci.

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“…5 and 6), a feedback pathway with Ca2+ as an inhibitor of rhodopsin-Gq activation is unlikely. Regarding receptor activation of the Gq, squid rhodopsin is homologous to other rhodopsins and to G-protein-coupled receptors, but has a proline-rich C-terminal extension [28,29]. This C-terminal tail is not present in Drosophila rhodopsin, and does not appear to play a role in G-protein activation or specificity.…”

Section: Discussionmentioning

confidence: 99%

Activation of the GTP-binding protein Gq by rhodopsin in squid photoreceptors

Nobes

Baverstock

Saibil

1992

Biochemical Journal

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Photoaffinity labelling by a GTP analogue has been used to identify a 42 kDa band as the major G alpha subunit in squid photoreceptor membranes, recently identified by partial sequence analysis to be a member of the Gq sub-group of GTP-binding proteins [Pottinger, Ryba, Keen & Findlay (1991) Biochem. J. 279, 323-326]. Guanine-nucleotide-binding displacement analysis gave a stoichiometry of 1 G-protein per 12.5 rhodopsin molecules, the same as in vertebrate rod photoreceptors. Binding was not detected above background in the dark, but was rapidly activated by light. Unlike vertebrate transducin, this G-protein is very temperature-sensitive. GTP binding is maximal at temperatures less than 10 degrees C and is much decreased after several minutes above 18 degrees C. The light-stimulated GTPase rate is maximal around 10 degrees C, above which the loss of binding sites counteracts the increase in hydrolytic rate per site. Earlier studies described light-sensitive G alpha components of 40 and 45 kDa, by ADP-ribosylation in the presence of cholera and pertussis toxins. These are now shown to be very minor components, as the prolonged treatment at elevated temperature required for ADP-ribosylation is sufficient to inactivate the major G alpha totally. Unlike the minor G alpha components, the 42 kDa G alpha is not inhibited by Ca2+.

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“…Os fotorreceptores são neurônios especializados responsáveis pelo início do processamento da informação visual na retina, capazes de converter energia luminosa em energia eletroquímica, por meio de uma série de cascatas bioquímicas. Tal processo inicia-se a partir da interação entre fótons e moléculas presentes em regiões específicas dos fotorreceptores Langmack & Saibil, 1991). Os fotorreceptores clássicos são encontrados na camada de fotorreceptores da retina externa dos vertebrados.…”

Section: Os Fotorreceptores E O Início Do Processamento Visualunclassified

Análise genética dos pigmentos visuais da Tartaruga-de-Orelha-Vermelha,Trachemys scriptaelegans (Testudine, Emydidae)

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Signal transduction in photoreceptors

Cited by 4 publications

References 1 publication

Chemistry and Biology of the Initial Steps in Vision: The Friedenwald Lecture

Chemistry and Biology of the Initial Steps in Vision: The Friedenwald Lecture

Activation of the GTP-binding protein Gq by rhodopsin in squid photoreceptors

Análise genética dos pigmentos visuais da Tartaruga-de-Orelha-Vermelha,Trachemys scriptaelegans (Testudine, Emydidae)

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