title: Transducin activation state controls its light-dependent translocation in rod photoreceptors.
abstract: Light-dependent redistribution of transducin between the rod outer segments (OS) and other photoreceptor compartments including the inner segments (IS) and synaptic terminals (ST) is recognized as a critical contributing factor to light and dark adaptation. The mechanisms of light-induced transducin translocation to the IS/ST and its return to the OS during dark adaptation are not well understood. We have probed these mechanisms by examining light-dependent localizations of the transducin-alpha subunit (Gtalpha)in mice lacking the photoreceptor GAP-protein RGS9, or expressing the GTPase-deficient mutant GtalphaQ200L. An illumination threshold for the Gtalpha movement out of the OS is lower in the RGS9 knockout mice, indicating that the fast inactivation of transducin in the wild-type mice limits its translocation to the IS/ST. Transgenic GtalphaQ200L mice have significantly diminished levels of proteins involved in cGMP metabolism in rods, most notably the PDE6 catalytic subunits, and severely reduced sensitivity to light. Similarly to the native Gtalpha, the GtalphaQ200L mutant is localized to the IS/ST compartment in light-adapted transgenic mice. However, the return of GtalphaQ200L to the OS during dark adaptation is markedly slower than normal. Thus, the light-dependent translocations of transducin are controlled by the GTP-hydrolysis on Gtalpha, and apparently, do not require Gtalpha interaction with RGS9 and PDE6.
authors.affiliation: Department of Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA.
authors.forename: Vasily
authors.initials: V
authors.lastname: Kerov
authors.forename: Desheng
authors.initials: D
authors.lastname: Chen
authors.forename: Mustapha
authors.initials: M
authors.lastname: Moussaif
authors.forename: Yu-Jiun
authors.initials: YJ
authors.lastname: Chen
authors.forename: Ching-Kang
authors.initials: CK
authors.lastname: Chen
authors.forename: Nikolai O
authors.initials: NO
authors.lastname: Artemyev
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000235:genetics; D001692:Biological Transport; D003623:Dark Adaptation / Q000502:physiology; D004151:Dipeptides / Q000276:immunology; D005455:Fluorescent Antibody Technique; D020558:GTP Phosphohydrolases / Q000172:deficiency / Q000378:metabolism; D015870:Gene Expression; D018698:Glutamic Acid / Q000276:immunology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D006868:Hydrolysis; D008027:Light; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D016296:Mutagenesis; D020710:RGS Proteins / Q000172:deficiency / Q000502:physiology; D012160:Retina / Q000737:chemistry; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D015293:Transducin / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D004151:Dipeptides; D020710:RGS Proteins; C116925:regulator of g-protein signaling 9; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D018698:Glutamic Acid; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D015293:Transducin