Thermal Activation and Photoactivation of Visual Pigments

Ala-Laurila, Petri; Donner, Karl Johan; Koskelainen, Ari

doi:10.1529/biophysj.103.035626

Cited by 77 publications

(105 citation statements)

References 59 publications

(93 reference statements)

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“…1 These two assumptions have been partially validated by the favorable comparison between the predicted energy storage and calorimetry measurements (see section 3), as well as by the agreement between the experimental and predicted changes in NMR chemical shifts due to 11-cis/all-trans isomerization (see section 7). Furthermore, the implemented assumptions are consistent with the recent observation of thermal activation of visual pigments, 26 indicating that activation by light and by heat may in fact follow the same molecular route.…”

Section: Isomerization Processsupporting

confidence: 83%

Computational Studies of the Primary Phototransduction Event in Visual Rhodopsin

2006

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This Account addresses recent advances in the elucidation of the detailed molecular rearrangements due to the primary photochemical event in rhodopsin, a prototypical G-protein-coupled receptor (GPCR) responsible for the signal transmission cascade in the vertebrate vision process. The reviewed studies provide fundamental insight on long-standing problems regarding the assembly and function of the individual residues and bound water molecules that form the rhodopsin active site, a center that catalyzes the 11-cis/all-trans isomerization of the retinyl chromophore in the primary step of the phototransduction mechanism. Emphasis is placed on the authors' recent computational studies, based on state-of-the-art quantum mechanics/molecular mechanics (QM/MM) hybrid methods, addressing the structural refinement of the retinyl chromophore binding site in high-resolution X-ray structures of bovine visual rhodopsin, the energy storage mechanism, and the molecular origin of spectroscopic changes due to the primary photochemical event.

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Section: Isomerization Processsupporting

confidence: 83%

Computational Studies of the Primary Phototransduction Event in Visual Rhodopsin

2006

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“…Thus, in gNinaB the all-trans to 11-cis isomerization can be easily driven by the oxidative cleavage of carotenoids. The surplus energy is surprisingly high, exceeding even the activation energy of ϩ45 kcal/mol (26), for photoisomerization of the chromophore of native rhodopsin. In contrast, the negative free energy of retinyl ester hydrolysis providing energy to drive the endothermic isomerization by RPE65 is only slightly greater than 4.1 kcal/mol (27).…”

Section: Discussionmentioning

confidence: 90%

NinaB combines carotenoid oxygenase and retinoid isomerase activity in a single polypeptide

Oberhauser

Voolstra

Bangert

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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In animals, successful production of the visual chromophore (11-cis-retinal or derivatives thereof such as 11-cis-3-hydroxy-retinal) is essential for photoreceptor cell function and survival. These carotenoid-derived compounds must combine with a protein moiety (the opsin) to establish functional visual pigments. Evidence from cell culture systems has implicated that the retinal pigment epithelium protein of 65 kDa (RPE65) is the long-sought all-trans to 11-cis retinoid isomerase. RPE65 is structurally related to nonheme iron oxygenases that catalyze the conversion of carotenoids into retinoids. In vertebrate genomes, two carotenoid oxygenases and RPE65 are encoded, whereas in insect genomes only a single representative of this protein family, named NinaB (denoting neither inactivation nor afterpotential mutant B), is encoded. We here cloned and functionally characterized the ninaB gene from the great wax moth Galleria mellonella. We show that the recombinant purified enzyme combines isomerase and oxygenase (isomerooxygenase) activity in a single polypeptide. From kinetics and isomeric composition of cleavage products of asymmetrical carotenoid substrates, we propose a model for the spatial arrangement between substrate and enzyme. In Drosophila, we show that carotenoid-isomerooxygenase activity of NinaB is more generally found in insects, and we provide physiological evidence that carotenoids such as 11-cis-retinal can promote visual pigment biogenesis in the dark. Our study demonstrates that trans/cis isomerase activity can be intrinsic to this class of proteins and establishes these enzymes as key components for both invertebrate and vertebrate vision. RPE65 ͉ vision ͉ visual chromophoreA nimal visual pigments (rhodopsins) are bipartite G-proteincoupled receptors consisting of an opsin moiety and a carotenoid-derived retinylidene chromophore (1). Two fundamental issues in the pathway for visual chromophore production have resisted molecular analysis for a long time: first, the oxidative cleavage of C 40 carotenoids into C 20 retinoids; and second, the all-trans to 11-cis isomerization of retinoids.The molecular basis for the oxidative cleavage was resolved by cloning and characterization of NinaB (denoting neither inactivation nor afterpotential mutant B), which converts carotenoids into retinoids in Drosophila melanogaster (2, 3). Thereafter, several related carotenoid-15,15Ј-oxygenases (CMO1) have been identified and characterized in vertebrates including human beings (4-7). In addition, in vertebrates a second type of carotenoid-oxygenase, carotenoid-9Ј,10Ј-monooxygenase (CMO2) has been identified that cleaves carotenoids asymmetrically (8, 9), although its physiological function is not yet fully understood.The isomerization problem concerns the questions of how the visual chromophore is produced to establish functional visual pigments and, in vertebrates, how the all-trans visual photoproduct is isomerized back to the 11-cis chromophore, to maintain visual responsiveness. Recently, evidence in cell cultur...

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“…and between cones of different classes (Schneeweis and Schnapf, 1999;Rieke and Baylor, 2000;Burns and Baylor, 2001;Sampath and Baylor, 2002;Ala-Laurila et al, 2004;Dunn and Rieke, 2006;Nikonov et al, 2006).…”

Section: Opsin Expression Predicts Cone Input To Horizontal and Briskmentioning

confidence: 99%

Chromatic Properties of Horizontal and Ganglion Cell Responses Follow a Dual Gradient in Cone Opsin Expression

Yin¹,

Smith²,

Sterling³

et al. 2006

J. Neurosci.

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In guinea pig retina, immunostaining reveals a dual gradient of opsins: cones expressing opsin sensitive to medium wavelengths (M) predominate in the upper retina, whereas cones expressing opsin sensitive to shorter wavelengths (S) predominate in the lower retina. Whether these gradients correspond to functional gradients in postreceptoral neurons is essentially unknown. Using monochromatic flashes, we measured the relative weights with which M, S, and rod signals contribute to horizontal cell responses. For a background that produced 4.76 log 10 photoisomerizations per rod per second (Rh*/rod/s), mean weights in superior retina were 52% (M), 2% (S), and 46% (rod). Mean weights in inferior retina were 9% (M), 50% (S), and 41% (rod). In superior retina, cone opsin weights agreed quantitatively with relative pigment density estimates from immunostaining. In inferior retina, cone opsin weights agreed qualitatively with relative pigment density estimates, but quantitative comparison was impossible because individual cones coexpress both opsins to varying and unquantifiable degrees. We further characterized the functional gradients in horizontal and brisk-transient ganglion cells using flickering stimuli produced by various mixtures of blue and green primary lights. Cone weights for both cell types resembled those obtained for horizontal cells using monochromatic flashes. Because the brisk-transient ganglion cell is thought to mediate behavioral detection of luminance contrast, our results are consistent with the hypothesis that the dual gradient of cone opsins assists achromatic contrast detection against different spectral backgrounds. In our preparation, rod responses did not completely saturate, even at background light levels typical of outdoor sunlight (5.14 log 10 Rh*/rod/s).

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Thermal Activation and Photoactivation of Visual Pigments

Cited by 77 publications

References 59 publications

Computational Studies of the Primary Phototransduction Event in Visual Rhodopsin

Computational Studies of the Primary Phototransduction Event in Visual Rhodopsin

NinaB combines carotenoid oxygenase and retinoid isomerase activity in a single polypeptide

Chromatic Properties of Horizontal and Ganglion Cell Responses Follow a Dual Gradient in Cone Opsin Expression

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