Phototransduction Motifs and Variations

摘要

Finally, this Review has focused on animal photoreceptors that typically signal light to the brain via opsin and a vitamin A-based chromophore. These photoreceptors belong to the overwhelming majority in the animal kingdom. There is, however, at least one other known photoprotein, namely, the blue-absorbing flavoprotein cryptochrome. In Drosophila, there is good evidence that cryptochrome absorbs light and signals it to the molecular clock mechanism (for review, Ashmore and Sehgal, 2003). In vertebrates, the two cryptochromes (CRY1 and CRY2) are components of the molecular clock, but here their role appears to be unrelated to light signaling. In a potentially fascinating development, cryptochromes have been proposed to underlie magnetic-compass orientation in birds (Mouritsen and Ritz, 2005)and insects (Yoshii et al., 2009). The recent discovery in C. elegans of UV light avoidance via a gustatory receptor also raises the possibility of yet another photoprotein. However, we must wait to see whether the receptor, lite-1, indeed absorbs light directly.