Farnesylation of retinal transducin underlies its translocation during light adaptation.
G proteins are posttranslationally modified by isoprenylation: either farnesylation or geranylgeranylation. The gamma subunit of retinal transducin (Talpha/Tbetagamma) is selectively farnesylated, and the farnesylation is required for light signaling mediated by transducin in rod cells. However, whether and how this selective isoprenylation regulates cellular functions remain poorly understood. Here we report that knockin mice expressing geranylgeranylated Tgamma showed normal rod responses to dim flashes under dark-adapted conditions but exhibited impaired properties in light adaptation. Of note, geranylgeranylation of Tgamma suppressed light-induced transition of Tbetagamma from membrane to cytosol, and also attenuated its light-dependent translocation from the outer segment to the inner region, an event contributing to retinal light adaptation. These results indicate that, while the farnesylation of transducin is interchangeable with the geranylgeranylation in terms of the light signaling, the selective farnesylation is important for visual sensitivity regulation by providing sufficient but not excessive membrane anchoring of Tbetagamma.
Kassai
Hidetoshi
H
Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan.
Aiba
Atsu
A
Nakao
Kazuki
K
Nakamura
Kenji
K
Katsuki
Motoya
M
Xiong
Wei-Hong
WH
Yau
King-Wai
KW
Imai
Hiroo
H
Shichida
Yoshinori
Y
Satomi
Yoshinori
Y
Takao
Toshifumi
T
Okano
Toshiyuki
T
Fukada
Yoshitaka
Y
D000221:Adaptation, Ocular / Q000502:physiology*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D015350:Contrast Sensitivity / Q000235:genetics; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D010775:Photic Stimulation; D017368:Protein Prenylation / Q000235:genetics*; D021122:Protein Subunits / Q000378:metabolism; D021381:Protein Transport / Q000235:genetics; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D015293:Transducin / Q000235:genetics / Q000378:metabolism*; D014785:Vision, Ocular / Q000502:physiology*
D017261:Glycosylphosphatidylinositols; D021122:Protein Subunits; D015293:Transducin