In the vertebrate retina, cone photoreceptors are responsible for day/color vision and rod photoreceptors for night vision. Although the molecular mechanism for visual excitation in cones is not as well understood as in rods, it is generally believed to involve a GTP-binding protein (G-protein)-coupled pathway regulated by a battery of cone-specific proteins. Like all large G-proteins, the conespecific G-protein, cone transducin, is presumed to contain an alpha subunit and a tightly-bound beta-gamma subunit. The a subunit of cone transducin is encoded by a cDNA (alpha(c)) highly homologous to its rod counterpart, as is the beta component (beta(3)3) of a newly identified bovine retinal cone transducin beta-gamma complex. Its associated gamma subunit appears to be a novel protein. The bovine retinal cone transducin beta-gamma complex also has been observed to bind a 34 kDa phosphoprotein which is immunologically related to phosducin, the 33 kDa phosphoprotein of rod photoreceptors. This 34 kDa protein could be a cone-specific phosducin playing an important role in the cone function. To better understand the structure and interaction of these cone transduction components, this research project seeks (1) to determine the primary structure of the cone transducin gamma subunit and its distribution in the retina; (2) to purify the cone transducin alpha subunit by novel subtractive affinity chromatography for reconstitution studies with the purified cone transducin beta-gamma complex; (3) to determine whether the 34 kDa phosducin-like protein is a cone-specific phosducin by elucidating its primary structure and determining its distribution in the retina; (4) to characterize the phosphorylation of this 34 kDa protein, in vitro and in situ, and its interaction with the cone transducin beta-gamma complex; and (5) to generate monoclonal antibodies against the gamma polypeptide and the 34 kDa protein as specific probes for this and future investigations. Results from these studies will provide information and specific tools for investigating the molecular mechanism of cone phototransduction. Systematic studies correlating activity with structure in reconstituted cone or rod transduction components may lead to a better understanding of their physiology and, furthermore, to new insight into the molecular mechanism of transmembrane signaling in general. Finally, these studies will provide the conceptual basis and the specific probes needed for studying the role of cone proteins in blindness caused by age-related macular degeneration.
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| Chen, F; Lee, R H (1997) Phosducin and betagamma-transducin interaction I: effects of post-translational modifications. Biochem Biophys Res Commun 233:370-4 |
| Ong, O C; Yamane, H K; Phan, K B et al. (1995) Molecular cloning and characterization of the G protein gamma subunit of cone photoreceptors. J Biol Chem 270:8495-500 |
