Light- and guanosine 5 '-3-O-(thio)triphosphate-sensitive localization of a G protein and its effector on detergent-resistant membrane rafts in rod photoreceptor outer segments

Detergent-resistant membrane microdomains in the plasma membrane, known as lipid rafts, have been implicated in various cellular processes. We report here that a low-density Triton X-100-insoluble membrane (detergent-resistan t membrane; DRM) fraction is present in bovine rod photoreceptor outer segm ents (ROS), In dark-adapted ROS, transducin and most of cGMP-phosphodiester ase (PDE) were detergent-soluble. When ROS membranes were exposed to light, however, a large portion of transducin localized in the DRM fraction. Furt hermore, on addition of guanosine 5'-3-O-(thio)triphosphate (GTP gammaS) to light-bleached ROS, transducin became detergent-soluble again. PDE was not recruited to the DRM fraction after light stimulus alone, but simultaneous stimulation by light and GTP gammaS induced a massive translocation of all PDE subunits to the DRM, A cholesterol-removing reagent, methyl-beta -cycl odextrin, selectively but partially solubilized PDE from the DRM, suggestin g that cholesterol contributes, at least in part, to the association of PDE with the DRM, By contrast, transducin was not extracted by the depletion o f cholesterol, These data suggest that transducin and PDE are likely to per form their functions in phototransduction by changing their localization be tween two distinct lipid phases, rafts and surrounding fluid membrane, on d isc membranes in an activation-dependent manner.