Diversity of visual pigments from the viewpoint of G protein activation--comparison with other G protein-coupled receptors.
The visual pigment present in the photoreceptor cells of the retina is a member of the family of G protein-coupled receptors and contains an 11-cis-retinal as a light-absorbing chromophore. Light induces conformational changes in the protein moiety of the visual pigment through cis-trans isomerization of the chromophore, which leads to the activation of a G protein-mediated signal transduction cascade that eventually generates an electrical response of the photoreceptor cells. So far, various types of visual pigments have been identified from a variety of photoreceptor cells and the structure-function relationship of visual pigments has been widely investigated by means of biophysical, biochemical and molecular biological techniques. Recent identifications of visual pigment-like proteins in the extra-ocular cells emphasize the importance of the visual pigment family as the photoreceptive molecules in not only visual but also non-visual photoreception. This article reviews the functional diversity of visual pigments from the viewpoint of the molecular mechanisms of photoreception and G protein activation. In addition, the similarity and difference of G protein activation mechanism between visual pigment and other G protein-coupled receptors are discussed for furthering our understanding of the common mechanism of G protein activation by G protein-coupled receptors.
Shichida
Yoshinori
Y
Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan. shichida@photo2.biophys.kyoto-u.ac.jp
Yamashita
Takahiro
T
D000818:Animals; D019204:GTP-Binding Proteins / Q000502:physiology*; D043562:Receptors, G-Protein-Coupled / Q000502:physiology*; D012160:Retina / Q000502:physiology*; D012168:Retinal Pigments / Q000502:physiology*; D014714:Vertebrates
D043562:Receptors, G-Protein-Coupled; D012168:Retinal Pigments; D019204:GTP-Binding Proteins