Theory of rhodopsin activation: probable charge redistribution of excited state chromophore

Nakanishi, Koji; Derguini, Fadila; Rao, V. Jayathirtha; Zarrilli, Gerald R.; Okabe, Masami; Lien, Thoai Hung; Johnson, Randy L.; Foster, Kenneth W.; Saranak, Jureepan

doi:10.1351/pac198961030361

Cited by 25 publications

(15 citation statements)

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“…The present results rule out efficient photoexcitation by 11-cislocked retinals in rods. This is in contrast to results with Chlamydomonas, where analogue 4 was reported to produce sensitivity 55 times greater than analogue 3 and 1.8 times greater than retinal 1 (25)(26)(27).…”

Section: Discussioncontrasting

confidence: 99%

Sensitization of bleached rod photoreceptors by 11-cis-locked analogues of retinal.

Corson

Cornwall

MacNichol

et al. 1990

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

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Photoactivation of rhodopsin initiates both excitation and adaptation in vertebrate rod photoreceptors. Bleaching of rhodopsin to free opsin and all-trans-retinal in isolated rods produces a stable desensitization (bleaching adaptation) that is much larger than expected from pigment depletion alone. In our experiments, a 93% bleach produced a 500-fold increase in the light intensity required for saturation of the light response. This component of adaptation was 32-fold larger than the 16-fold increase expected from pigment depletion alone.11-cis-Retinal, when delivered to isolated rods from liposomes, combines with free opsin to form a bleachable photopigment that fully restores sensitivity. 11-cis-Locked analogues of retinal combine with opsin to form unbleachable pigments in isolated bleached rods from the tiger salamander. They restore sensitivity to a substantial (16-to 25-fold) but incomplete extent. The analogues apparently relieve a stable component of adaptation when they interact with opsin. Because these analogues do not detectably excite rods, the structural requirements of both retinal and opsin for the relief of adaptation are different from those of excitation. The biochemical basis of light adaptation resulting from pigment bleaching and the minimum structural requirements of retinal for its relief remain to be determined.

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Section: Discussioncontrasting

confidence: 99%

Sensitization of bleached rod photoreceptors by 11-cis-locked analogues of retinal.

Corson

Cornwall

MacNichol

et al. 1990

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

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“…From this large set of reconstitution experiments the authors came to surprising conclusions, which initiated a wide confusion among rhodopsin researchers: (i) protonation of the imine N is not required for rhodopsin activation; (ii) no particular regiospecific isomerisation is required; and (iii) the rhodopsin can be activated even when retinal is replaced by hexenal or hexanal, which contain only one C = C double bond or even none at all. They proposed that rhodopsin might be activated by a 'charge redistribution of the excited state chromophore' [7,9]. Later, by using a light scattering assay and different motion analysis systems, three groups independently analysed flash-induced behavioural responses by using a mutant named CC2359, which is completely blind under all known conditions.…”

Section: Controversial Perspectives About the Rhodopsin Photoreceptormentioning

confidence: 99%

Photophobic responses and phototaxis in Chlamydomonas are triggered by a single rhodopsin photoreceptor

Kröger

Hegemann

1994

FEBS Letters

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The rhodopsin nature of the photoreceptor for the behavioural light responses in Chlamydomonas has originally been revealed by action spectroscopy. Meanwhile most physiological experiments and the identification of all-truns-retinal in cell extracts favour that this chlamyrhodopsin contains an all-trans-type retinal chromophore with strong similarity to the light sensors SR I and SRI1 from Halobacteriu. Reconstitution of retinal-deficient cells with ['HIretinal identified a single retinal protein with a MW of 30,000. Chlamyrhodopsin triggers a photoreceptor current in the eyespot region resulting in direction changes or phototaxis. Furthermore, when the light stimulus oversteps a critical level, two flagellar currents appear, which are the basis for photophobic responses. The physiological, electrophysiological and biochemical experiments suggest that all behavioural responses are triggered by a single rhodopsin-type receptor.

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“…This point was confirmed with analogs showing that this charge redistribution or displacement is necessary for initiating the bacteriorhodopsin photocycle (44). Hence, it would seem reasonable for the sensory role of rhodopsins in Peranema, Chlamydomonas, and Allomyces (13,14,15,29), for which the n-hexenal is an active chromophore, that a similar charge displacement in the photoreceptor protein is sufficient to drive a conformation change and activation.…”

Section: Discussionmentioning

confidence: 73%

“…n-Hexenal was also active with rhodopsin in the bikont Chlamydomonas (13,14,15) and in the zoospore of the unikont chytridiomycete fungus Allomyces (34). In Chlamydomonas, n-hexenal recovered the sensitivity of phototaxis at 354 nm to 2.9 orders of magnitude above the background, with no loss of sensitivity relative to the native chromophore and with an action spectrum consistent for n-hexenal-opsin amply demonstrating its activity (29). Whether this property has evolved to be different in animals has not been adequately tested.…”

Section: Discussionmentioning

confidence: 90%

Photoreceptor for Curling Behavior in Peranema trichophorum and Evolution of Eukaryotic Rhodopsins

Saranak

Foster

2005

Eukaryot Cell

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When it is gliding, the unicellular euglenoid Peranema trichophorum uses activation of the photoreceptor rhodopsin to control the probability of its curling behavior. From the curled state, the cell takes off in a new direction. In a similar manner, archaea such as Halobacterium use light activation of bacterio-and sensory rhodopsins to control the probability of reversal of the rotation direction of flagella. Each reversal causes the cell to change its direction. In neither case does the cell track light, as known for the rhodopsin-dependent eukaryotic phototaxis of fungi, green algae, cryptomonads, dinoflagellates, and animal larvae. Rhodopsin was identified in Peranema by its native action spectrum (peak at 2.43 eV or 510 nm) and by the shifted spectrum (peak at 3.73 eV or 332 nm) upon replacement of the native chromophore with the retinal analog n-hexenal. The in vivo physiological activity of n-hexenal incorporated to become a chromophore also demonstrates that charge redistribution of a short asymmetric chromophore is sufficient for receptor activation and that the following isomerization step is probably not required when the rest of the native chromophore is missing. This property seems universal among the Euglenozoa, Plant, and Fungus kingdom rhodopsins. The rhodopsins of animals have yet to be studied in this respect. The photoresponse appears to be mediated by Ca 2؉ influx.Since rhodopsins sharing sequence similarities are found in bacteria, archaea, eukaryotic microorganisms, and animals, it is possible to gain insight into the evolutionary progression and diversification leading to the receptor proteins of human visual photoreceptors as well as other photoreceptors. As part of this continuing project on the evolution and mechanisms of visual systems, the light-dependent responses of Peranema have been studied with respect to behavior, action spectra, the mechanism of activation, and signaling to the cell.Peranema trichophorum is a colorless eukaryotic phagotroph of the Euglenophyta that lives in fresh water (8). It does not have a chloroplast but rapidly deforms in shape and is very effective at capturing and eating prey (41). Peranema voraciously takes any particles into its body by phagocytosis (1). This "feeding behavior" is clearly and commonly observed under the microscope. Its life cycle is not well studied, but from light microscopic observations Peranema appears to have several distinct stages of growth. After the cells are put into fresh medium, which is initially low on waste products, one sees small round cells of about 10 to 15 m in diameter. These cells elongate into oval cells that swim freely in solution and fast in a helical euglenoid motion. Over 2 weeks, these cells elongate further to 25 to 70 m in length, remaining 10 m wide, and are seen to glide forward on a surface pulled by their leading anterior cilium, which is about the length of the cell body. (We use the word "cilium" rather than "eukaryotic flagellum" to describe the leading appendage that enables the cell to glide to e...

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Theory of rhodopsin activation: probable charge redistribution of excited state chromophore

Abstract: Abstract

Cited by 25 publications

References 0 publications

Sensitization of bleached rod photoreceptors by 11-cis-locked analogues of retinal.

Sensitization of bleached rod photoreceptors by 11-cis-locked analogues of retinal.

Photophobic responses and phototaxis in Chlamydomonas are triggered by a single rhodopsin photoreceptor

Photoreceptor for Curling Behavior in Peranema trichophorum and Evolution of Eukaryotic Rhodopsins

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