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M. Kono, P. W. Goletz, R. K. Crouch; Constitutive Activity of Cone Opsins. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5432.
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© ARVO (1962-2015); The Authors (2016-present)
Human color vision generally relies on the red, green, and blue cone visual pigments to detect light and initiate the signal cascade. While there is much information on the physical properties of rhodopsin, the dim light photopigment, much less is known about the cone pigments and differences between the different classes of opsins. Thus, the purpose of this study is to determine the differences in activities between the human red, green, and blue cone opsins with and without ligands.
Human cone opsins were expressed in COS cells, and membranes isolated. The amounts of opsin were determined by slot blot analysis and probed with the anti-rhodopsin 1D4 antibody whose epitope had been appended to all the cone opsins. The ability of the opsins to activate transducin was determined using a radioactive filter binding assay. Addition of 11-cis retinal, which forms pigments with cone opsins, deactivates the opsins. The effects of noncovalently binding retinal analogs have also been tested.
The blue cone opsin is more constitutively active than both the red and green cone opsins. In addition, certain noncovalently binding ligands (e.g., beta ionone, cyclocitral, and 11-cis retinol) reduce the red/green cone opsins’ ability to activate tranducin but do not reduce transducin interaction with the blue cone opsin. The blue cone opsin often demonstrates the same general pattern of interaction with ligands as the rod opsin with the red and green cone opsins being quite different.
Despite their high homology and shared function of photon absorption to initiate the visual cascade, cone opsins can effect transducin activation differently from each other. Likewise, the red, green, and blue cone opsins are not all modulated in the same manner by noncovalently binding ligands.
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