Activation of Visual Pigments by Light and Heat

Luo, Dong; Yue, Wendy W.S.; Ala-Laurila, Petri; Yau, King Wai

doi:10.1126/science.1200172

Cited by 110 publications

(189 citation statements)

References 35 publications

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“…The common PSB11 chromophore of melanopsins and rhodopsins does not guarantee that the same mechanism operates in both photoreceptors. This not only concerns light-induced activation but also thermal activation: a process whose rate limits the photoreceptor light sensitivity and that is currently associated with thermal, rather than photochemical, PSB11 isomerization (19)(20)(21)(22)(23)(24).…”

Section: Significancementioning

confidence: 99%

Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins

Rinaldi

Melaccio

Gozem

et al. 2014

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

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Comparative modeling and ab initio multiconfigurational quantum chemistry are combined to investigate the reactivity of the human nonvisual photoreceptor melanopsin. It is found that both the thermal and photochemical isomerization of the melanopsin 11-cis retinal chromophore occur via a space-saving mechanism involving the unidirectional, counterclockwise twisting of the =C11H-C12H= moiety with respect to its Lys340-linked frame as proposed by Warshel for visual pigments [Warshel A (1976) Nature 260 (5553):679-683]. A comparison with the mechanisms documented for vertebrate (bovine) and invertebrate (squid) visual photoreceptors shows that such a mechanism is not affected by the diversity of the three chromophore cavities. Despite such invariance, trajectory computations indicate that although all receptors display less than 100 fs excited state dynamics, human melanopsin decays from the excited state ∼40 fs earlier than bovine rhodopsin. Some diversity is also found in the energy barriers controlling thermal isomerization. Human melanopsin features the highest computed barrier which appears to be ∼2.5 kcal mol −1 higher than that of bovine rhodopsin. When assuming the validity of both the reaction speed/quantum yield correlation discussed by Warshel, Mathies and coworkers [Weiss RM, Warshel A (1979) J Am Chem Soc 101:6131-6133; Schoenlein RW, Peteanu LA, Mathies RA, Shank CV (1991) Science 254(5030):412-415] and of a relationship between thermal isomerization rate and thermal activation of the photocycle, melanopsin turns out to be a highly sensitive pigment consistent with the low number of melanopsincontaining cells found in the retina and with the extraretina location of melanopsin in nonmammalian vertebrates.F or a long time it was assumed that the human retina contains only two types of photoreceptor cells: the rods and cones responsible for dim-light and daylight vision, respectively. However, recent studies have revealed the existence of a small number of intrinsically photosensitive retinal ganglion cells (ipRGCs) that regulate nonvisual photoresponses (1). ipRGCs express an atypical opsin-like protein named melanopsin (2, 3) which plays a role in the regulation of unconscious visual reflexes and in the synchronization of endogenous physiological responses to the dawn/dusk cycle (circadian rhythms) (4, 5).Melanopsins are unique among vertebrate photoreceptors because their amino acid sequence shares greater similarity to invertebrate than vertebrate rhodopsin (i.e., the photoreceptor of rods) (6, 7). Like rhodopsins, melanopsins feature an up-down bundle architecture of seven transmembrane α-helices incorporating the 11-cis isomer of retinal as a covalently bound protonated Schiff base (PSB11 in Fig. 1A). Light-induced (i.e., photochemical) isomerization of PSB11 to its all-trans isomer (PSBAT) triggers an opsin conformational change that, ultimately, activates the receptor and signaling cascade (8, 9). However, similar to invertebrate and in contrast to vertebrate rhodopsins, melanopsins are bistable ...

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Section: Significancementioning

confidence: 99%

Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins

Rinaldi

Melaccio

Gozem

et al. 2014

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

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“…Rhodopsins with absorption at the red edge of the spectrum (XL-iodopsins) are found in flies, mollusks, fish, and in some birds. At this spectral range, thermal isomerization increases, producing significant background at high rhodopsin concentrations (3). On the other end of the spectrum, the UVAabsorbing pigment is of limited use because UV-transparent lenses promote damage of the retina.…”

mentioning

confidence: 99%

A Photochromic Histidine Kinase Rhodopsin (HKR1) That Is Bimodally Switched by Ultraviolet and Blue Light

Luck

Mathes

Bruun

et al. 2012

Journal of Biological Chemistry

111

148

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Background: Microbial rhodopsins in Chlamydomonas are employed for photoorientation and developmental processes. Results: HKR1 is a UVA-absorbing rhodopsin that is bimodally switched between a UV-and a blue light-absorbing isoform with different light colors. Conclusion:The chromophore of the dark-adapted UV state contains a deprotonated Schiff base stabilized by a 13-cis,15-anti conformation. Significance: This is the initial characterization of the first member of a novel rhodopsin family.

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“…Therefore, the incident light must propagate through five reflecting and scattering layers of cell bodies and neural processes before reaching the photoreceptors. This 'inverted' retinal structure is expected to cause blurring of the image and reduction in the photon flux reaching the photoreceptors, thus reducing their sensitivity [6][7][8][9] . It has been recently reported that retinal Müller cells act as light guides serving to transfer light across the retina, from the vitreo-retinal border towards the photoreceptors [10][11][12] .…”

mentioning

confidence: 99%

Müller cells separate between wavelengths to improve day vision with minimal effect upon night vision

et al. 2014

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Vision starts with the absorption of light by the retinal photoreceptors-cones and rods. However, due to the 'inverted' structure of the retina, the incident light must propagate through reflecting and scattering cellular layers before reaching the photoreceptors. It has been recently suggested that Müller cells function as optical fibres in the retina, transferring light illuminating the retinal surface onto the cone photoreceptors. Here we show that Müller cells are wavelength-dependent wave-guides, concentrating the green-red part of the visible spectrum onto cones and allowing the blue-purple part to leak onto nearby rods. This phenomenon is observed in the isolated retina and explained by a computational model, for the guinea pig and the human parafoveal retina. Therefore, light propagation by Müller cells through the retina can be considered as an integral part of the first step in the visual process, increasing photon absorption by cones while minimally affecting rod-mediated vision.

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Activation of Visual Pigments by Light and Heat

Cited by 110 publications

References 35 publications

Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins

Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins

A Photochromic Histidine Kinase Rhodopsin (HKR1) That Is Bimodally Switched by Ultraviolet and Blue Light

Müller cells separate between wavelengths to improve day vision with minimal effect upon night vision

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