Visual transduction

Rdzanowska, M and Rozanowski, B, 2008. Visual transduction and age-related changes in lipofuscin. In Tombran-Tink, J and Barnstable, CJ (Eds.), Ophthalmology Research The Visual Transduction Cascade. The Humana Press Inc., Totowa, NJ, pp. 405 146. 

The sensitivity of receptor systems is subject to modification. When a signal is present continuously, desensitization of the receptor system results (Fig. 12-lc) when the stimulus falls below a certain threshold, the system again becomes sensitive. Think of what happens to your visual transduction system when you walk from bright sunlight into a darkened room or from darkness into the light. 

The formation of metarhodopsin II is fast enough to be an obligatory step in visual transduction. It clearly is associated with changes in the interactions between rhodopsin and its surroundings. A reasonable hypothesis, therefore, is that the changes in protein structure allow metarhodopsin II to initiate an interaction with some other component of the disk membrane. We explore the nature of this component in the following sections. 

Burns, M.E. and Arshavsky, V.Y. (2005). Beyond counting photons trials and trends in vertebrate visual transduction. Neuron 48 387-401. 

Nakanishi K (2000) Recent bioorganic studies on rhodopsin and visual transduction. Chem Pharm Bull 48, 1399-1409. 

Hardie R.C. and Raghu P. (2001) Visual transduction in Drosophila. Science 413, 186-193. 

Palczewski K and Saari JC (1997) Activation and inactivation steps in the visual transduction pathway. Curent Opinions in Neurobiology , 500. ... 

Cliabre M and Deterre P (1989) Molecular mechanisms of visual transduction. European Journal of Biochemistry 179,255-66. 

Fukada, Y., et al. (1994). Effects of carboxyl methylation of photoreceptor G protein gamma-subunit in visual transduction. J Biol Chem 269 5163-5170. 

In both types of photoreceptor cells, the outer segment contains all components of the visual transduction cascade which is one of the best studied examples of... 

Montell, C. (1999) Visual transduction in Drosophila. Annu. Rev. Cell Dev. Biol. 15, 231-268. 

Pugh, E.N. Jr. and Lamb, T. (2000) Phototransducin in vertebrate rods and cones Molecular mechanism of amplification, recovery and light adaptation. In Molecular Mechanism in Visual Transduction. D.G. Stavenga, W.J. Degrip and E.N. Pugh Jr., eds. (Amsterdam, The Netherlands Elsevier Science Publishers B.V.),pp. 183-255. 

Crouch, R.K. and J.-X. Ma. The role of vitamin A in visual transduction. In Vitamin A and Retinoids Am Update of Biological Aspects and Clinical Applications, edited by M.A. Livrea, Boston, Birkhauser Verlag, pp. 59-72, 2000. 

The visual transduction pathway is the best characterized G-protein-coupled signal transduction system. Study of the visual receptor, rhodopsin, over the past several decades has made it the archetype of the growing superfamily of heptahelical G-protein-coupled receptors (reviewed in Litman Mitchell, 1996a). The preeminent position of rhodopsin in this important superfamily will likely increase with the recent publication of the three-dimensional structure of rhodopsin (Palczewski et al., 2000). Many neurotransmitter receptors, as well as the olfactory and taste receptors, are members of this superfamily. Therefore, the effect of lipid membrane composition on various steps in visual signaling will be reviewed in some detail in this chapter. Given the similarity in mode of signaling, the observations made for the vision system should be of general applicability to other members of this receptor superfamily. 

Litman BJ. Niu SL, Polozova A, Mitchell DC. The role of docosahexaenoic acid containing phospholipids in modulating G protein-coupled signaling pathways Visual transduction. Mol Cell Neuorsci, In Press. 2001. 

Kraft TW, Schneeweis DM. Schnaft JL. Visual transduction in human rod photoreceptors. J Physiol 1993 464 747-765. 

The visual transduction system of retinal membranes contains a plethora of prenylated proteins. One of the prenylated components is a protein called transducin. This protein is a member of a family of G proteins that contain three distinct subunits (a, P, and y) and function in mediating signal transduction from cell membrane receptors to downstream effector proteins. In the case of visual transduction, photoactivation of rhodopsin leads to a conformational change that is sensed by transducin. In the absence of photoactivation of rhodopsin, transducin exists in a resting state in which Gt)P is bound to its a-subunit. Photoactivated rhodopsin catalyzes the exchange of GDP bound to transducin with GTP. This GTP-bound activated transducin then stimulates the enzymatic activity of another membrane-bound protein termed cyclic GMP phosphodiesterase. The latter... 

Another famesylated protein involved in visual transduction is rhodopsin kinase. This enzyme selectively phosphorylates photoactivated rhodopsin and this terminates its interaction with transducin. Thus, rhodopsin kinase is responsible for terminating the visual process in those retinal cells that have been activated by light, so that one does not continue to see what one has seen in the past. Like transducin, famesylated rhodopsin kinase binds weakly to membranes, but translocation to the membranes is enhanced when rhodopsin is photoactivated, and this requires that rhodopsin kinase be famesylated (Inglese et al., 1992). 

---