REVIEW : Signal transduction mechanism in photoreceptor cells

The molecular mechanism of the visual transduction pathway in vertebrate photoreceptor cells Vertebrate photoreceptor cells, rods and cones, are specially designed and differentiated neuroal cells for detecting light signals. Both cells are composed of three compartments, the outer segment, inner segment and synapse. The outer segments contain all of the protein components for producing electrical signals in response to a capture of a photon. Rhodopsin, a photoreceptor protein in rods, absorbs light and undergoes a photobleaching intermediates activating GTP binding protein called transducin. Activated transducin in turn activates cGMP phosphodiesterase that hydrolyzes cytosolic cGMP. The closure of cGMP gated on the plasma membrane results in the generation of hyperpolarized membrane potential. This light-triggered cascade reaction is terminated and completely restored to the dark levels by another enzymatically controlled reaction. Photoactivated rhodopsin is phosphorylated by rhodopsin kinase. The regulatory protein called arrestin specifically binds and makes a stable complex with the phosphorylated photolyzed rhodopsin preventing transducin activation. Membrane associated all-trans retinol dehydrogenase metabolizes phosphorylated photolyzed rhodopsin to phosphorylated opsin after removol of arrestin from the complex. Phosphorylated opsin is dephosphorylated by prorein prosphatase 2A and regenerates with 11-cis-retinal. I have engaged in research exploring rhodopsin phosphorylation and posttranslational modifications of transducin γ subunit, and found some novel insights in this fields. In this article, I reviewed the latest information regarding the molecular basis of the visual transduction pathway in the photoreceptor cells