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-Gβ5L complex, and the p44 isoform of arrestin undergo dramatic translocation to the raft upon illumination. Phosphorylation of RGS9-1 occurs exclusively in the raft. GTPγS or pertussis toxin prevent the light-mediated translocation of transducin and RGS9-1, whereas AIF4- causes both proteins to move to the raft in the dark. This shows that the Gαt-RGS9-1-Gβ5L complex has the highest affinity to rafts in the transition state of the GTPase. GTPγS 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.
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)