Circular Dichroism of Metaiodopsin II and Its Binding to Transducin: A Comparative Study between Meta II Intermediates of Iodopsin and Rhodopsin

Okada, Tetsuji; Matsuda, Takehisa; Kandori, Hideki; Fukada, Yoshitaka; Yoshizawa, Tôru; Shichida, Yoshinori

doi:10.1021/bi00182a024

Cited by 54 publications

(55 citation statements)

References 34 publications

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“…These results are consistent with both the conservation of the amino acid regions in rhodopsin and the Xenopus violet pigment that are involved in transducin binding 2 and with the high homology (76%) between bovine rod and cone transducin (10) and suggest that the conformations of the violet pigment and its enzymatically active state are very similar to those of rhodopsin. These results are consistent with the similarities found between the MetaII photointermediates of chicken red cone opsin and rhodopsin using circular dichroism (25).…”

Section: Discussionsupporting

confidence: 81%

Activation of Transducin by a Xenopus Short Wavelength Visual Pigment

Starace

Knox

1997

Journal of Biological Chemistry

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Phototransduction in cones differs significantly from that in rods in sensitivity, kinetics, and recovery following exposure to light. The contribution that the visual pigment makes in determining the cone response was investigated biochemically by expressing a Xenopus violet cone opsin (VCOP) cDNA in COS1 cells and assaying the light-dependent activation of transducin. Light-exposed VCOP stimulated [35 S]guanosine 5-(␥-thio)triphosphate nucleotide exchange on bovine rod transducin in a time-dependent manner with a half-time for activation of 0.75 min, similar to that of bovine rhodopsin. In exhaustive binding assays, VCOP and rhodopsin activity showed similar concentration dependence with half-maximal activation occurring at 0.02 mol of pigment/mol of transducin. Although VCOP was able to activate as many as 12 transducins per photoisomerization, rhodopsin catalyzed significantly more. When assays were performed with > 420 nm illumination, VCOP exhibited rapid regeneration and high affinity for the photoregenerated 11-cis-retinal. Recycling of the chromophore and reactivation of the pigment resulted in multiple activations of transducin, whereas a maximum of 1 transducin per VCOP was activated under brief illumination. The decay of the active species formed following photobleaching was complete in <5 min, ϳ10-fold faster than that of rhodopsin. In vitro, VCOP activated rod transducin with kinetics and affinity similar to those of rhodopsin, but the active conformation decayed more rapidly and the apoprotein regenerated more efficiently with VCOP than with rhodopsin. These properties of the violet pigment may account for much of the difference in response kinetics between rods and cones.Photopic vision is mediated by specialized photoreceptor cone cells that function at high levels of illumination, respond to rapid changes in light, and permit color discrimination (1, 2). Each cone cell expresses a cone opsin. The cone opsins are members of a larger family of visual pigments (3-5) and share significant amino acid sequence homology with the rod pigment rhodopsin (6). Among the cone pigments, the short wavelength pigments (Group S, with wavelengths of peak absorbance ( max ) 1 ϳ 415-440 nm) permit vision in the violet/blue region of the spectrum and are represented by the mammalian blue, chicken violet, and Xenopus violet pigments.2 Although cone cells expressing Group S pigments are in the minority in the vertebrate retina, they are an integral part of vision. For example, in blue monochromats, i.e. humans with red-green pigment mutations, the blue opsin is the sole mediator of photopic vision (7,8).The phototransduction mechanisms have been extensively investigated in rods (for reviews see Refs. 2 and 9). Following absorption of light and isomerization of 11-cis-retinal to alltrans-retinal, rhodopsin undergoes a series of conformational changes that eventually leads to a transient state, coincident with metarhodopsin(II) (MetaII), that activates the second messenger cascade (9). MetaII interacts with the heterot...

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Section: Discussionsupporting

confidence: 81%

Activation of Transducin by a Xenopus Short Wavelength Visual Pigment

Starace

Knox

1997

Journal of Biological Chemistry

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“…Such light intensities would exhaust/saturate the capacity of cones to inactivate their phototransduction cascade by GRK1 and arrestin, and termination of the cone light response would likely be dominated by the spontaneous decay of cone visual pigment. Consistent with this notion, the time constant of cone response decay at 3.6% is 2.8 s, comparable with the rate of decay of photoactivated cone pigment (51). Thus, our results are consistent with the notion that the capacity of mammalian cones to inactivate the phototransduction cascade saturates at a relatively dim light, bleaching only ϳ1% of their pigment.…”

Section: Discussionsupporting

confidence: 80%

Regulation of Mammalian Cone Phototransduction by Recoverin and Rhodopsin Kinase

Sakurai

Chen

Khani

et al. 2015

Journal of Biological Chemistry

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Background: Calcium-mediated feedback to phototransduction is critical for modulating cone responses under different lighting conditions. Results: The calcium-binding protein recoverin potentiates dim light sensitivity, whereas increasing expression of its target, GRK1, delays response shutoff in cones. Conclusion: Recoverin and GRK1 levels modulate cone phototransduction. Significance: Cone pigment inactivation regulates cone responses in dim light but not in bright light.

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“…All experimental procedures were carried out in a darkroom under dim red light (>670 nm). Bovine rod outer segments (ROS) were prepared as described elsewhere (41,42). ROS were washed with isotonic and hypotonic buffer to remove both soluble and membraneassociated ROS proteins (43).…”

Section: Discussionmentioning

confidence: 99%

Photocyclic behavior of rhodopsin induced by an atypical isomerization mechanism

Gulati

Jastrzębska

Banerjee

et al. 2017

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

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Vertebrate rhodopsin (Rh) contains 11-cis-retinal as a chromophore to convert light energy into visual signals. On absorption of light, 11-cis-retinal is isomerized to all-trans-retinal, constituting a oneway reaction that activates transducin (G t ) followed by chromophore release. Here we report that bovine Rh, regenerated instead with a six-carbon-ring retinal chromophore featuring a C 11 =C 12 double bond locked in its cis conformation (Rh6mr), employs an atypical isomerization mechanism by converting 11-cis to an 11,13-dicis configuration for prolonged G t activation. Time-dependent UV-vis spectroscopy, HPLC, and molecular mechanics analyses revealed an atypical thermal reisomerization of the 11,13-dicis to the 11-cis configuration on a slow timescale, which enables Rh6mr to function in a photocyclic manner similar to that of microbial Rhs. With this photocyclic behavior, Rh6mr repeatedly recruits and activates G t in response to light stimuli, making it an excellent candidate for optogenetic tools based on retinal analog-bound vertebrate Rhs. Overall, these comprehensive structure-function studies unveil a unique photocyclic mechanism of Rh activation by an 11-cis-to-11,13-dicis isomerization.is the visual pigment found in rod outer segments of vertebrate and invertebrate photoreceptors that mediates the transformation of light into vision (1-5). By contrast, microbial Rhs mediate both the energy conversion and cell signaling required for cell survival (2, 6, 7). All classes of Rhs feature a heptahelical transmembrane structure that incorporates a covalently bound retinal chromophore, but they differ in their ability to interconvert between their two spectral absorption states driven by light exposure (2). Although vertebrate Rh undergoes a one-way photobleaching reaction of the retinal chromophore after light absorption (8), microbial Rhs exhibit an intrinsic photocyclic behavior with no chromophore release (2,8). This makes vertebrate Rhs unsuitable for optogenetic applications that require reversible control over effector ligands. Nevertheless, all Rhs require a cis-trans/trans-cis isomerization of their chromophores to trigger a protein conformational change that mediates the downstream signaling cascade or energy conversion (2,8). Previous studies on bovine Rh regenerated with sixcarbon-ring retinal chromophores (Rh6mr) featuring a locked C 11 =C 12 cis-trans isomerization (SI Appendix, Fig. S1) have implied their ability to activate the G protein transducin (G t ). These results suggest an alternative mechanism that can propagate the downstream visual cascades (9)(10)(11)(12)(13)(14). In this study, we provide direct evidence that Rh6mr can activate G t by an atypical cis-to-dicis isomerization that is also photocyclic, undergoing an 11,13-dicis-to-11-cis reisomerization. Even though it is believed that cis-trans isomerization is required to achieve the conformational change in opsin needed for G t activation, our results generalize this prerequisite to any isomerization that can achieve the same con...

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Circular Dichroism of Metaiodopsin II and Its Binding to Transducin: A Comparative Study between Meta II Intermediates of Iodopsin and Rhodopsin

Cited by 54 publications

References 34 publications

Activation of Transducin by a Xenopus Short Wavelength Visual Pigment

Activation of Transducin by a Xenopus Short Wavelength Visual Pigment

Regulation of Mammalian Cone Phototransduction by Recoverin and Rhodopsin Kinase

Photocyclic behavior of rhodopsin induced by an atypical isomerization mechanism

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