title: Signal-dependent translocation of transducin, RGS9-1-Gbeta5L complex, and arrestin to detergent-resistant membrane rafts in photoreceptors.
abstract: Many lines of evidence show that membranes contain microdomains, "lipid rafts", that are different from the rest of the membrane in specific lipid and protein composition. In several biological systems, they were shown to be necessary for trafficking and signal transduction. Here, we investigate if lipid rafts have a role in the regulation of the G protein-mediated pathway underlying vertebrate phototransduction. Photoreceptor membranes contain detergent-resistant membrane (DRM) rafts. Rhodopsin and cGMP phosphodiesterase are found in raft and nonraft portions of the membrane; guanylate cyclase is found exclusively in the raft. Distribution of these proteins does not change in the light or dark. In contrast, the G protein transducin, the RGS9-1-Gbeta5L complex, and the p44 isoform of arrestin undergo dramatic translocation to the raft upon illumination. Phosphorylation of RGS9-1 occurs exclusively in the raft. GTPgammaS or pertussis toxin prevent the light-mediated translocation of transducin and RGS9-1, whereas AlF(minus sign)(4) causes both proteins to move to the raft in the dark. This shows that the Galphat-RGS9-1-Gbeta5L complex has the highest affinity to rafts in the transition state of the GTPase. GTPgammaS binds to transducin at a significantly slower rate in the raft, indicating that this translocation results in a reduced rhodopsin-transducin coupling. Thus, an external signal can rearrange components of a G protein pathway in specific domains of the cell membrane, changing its signaling properties. These findings could reveal a novel mechanism utilized by the cells for regulation of G protein-mediated signal transduction.
authors.affiliation: Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, Miami, FL 33136, USA.
authors.forename: K Saidas
authors.initials: KS
authors.lastname: Nair
authors.forename: Nagaraj
authors.initials: N
authors.lastname: Balasubramanian
authors.forename: Vladlen Z
authors.initials: VZ
authors.lastname: Slepak
mesh_terms: D000818:Animals; D019393:Arrestin / Q000378:metabolism*; D003902:Detergents; D044387:GTP-Binding Protein beta Subunits; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D046911:Macromolecular Substances; D021962:Membrane Microdomains / Q000378:metabolism; D010766:Phosphorylation; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D020710:RGS Proteins / Q000378:metabolism*; D012243:Rhodopsin / Q000378:metabolism; D012374:Rod Cell Outer Segment / Q000378:metabolism; D015398:Signal Transduction; D015293:Transducin / Q000378:metabolism*; D014785:Vision, Ocular
chemical_list: D019393:Arrestin; D003902:Detergents; D044387:GTP-Binding Protein beta Subunits; C094668:Gnb5 protein, mouse; D046911:Macromolecular Substances; D020710:RGS Proteins; C116925:regulator of g-protein signaling 9; D012243:Rhodopsin; D020962:Heterotrimeric GTP-Binding Proteins; D015293:Transducin