Excess of Gbetae over Gqalphae in vivo prevents dark, spontaneous activity of Drosophila photoreceptors.
Drosophila melanogaster photoreceptor cells are capable of detecting single photons. This utmost sensitivity is critically dependent on the maintenance of an exceedingly low, dark, spontaneous activity of photoreceptor cells. However, the underlying mechanisms of this hallmark of phototransduction are not fully understood. An analysis of the Drosophila visual heterotrimeric (alphabetagamma) Gq protein revealed that wild-type Drosophila flies have about a twofold excess of Gbeta over Galpha subunits of the visual Gq protein. Studies of Gbetae mutants in which the excess of Gbeta was genetically eliminated showed dramatic dark, spontaneous activity of the photoreceptor cells, whereas concurrent genetic reduction of the Galpha subunit, which restored the excess of Gbeta, abolished this effect. These results indicate that an excess of Gbeta over Galpha is a strategy used in vivo for the suppression of spontaneous activity, thereby yielding a high signal to noise ratio, which is characteristic of the photoreceptor light response. This mechanism could be relevant to the regulation of G protein signaling in general.
Elia
Natalie
N
Department of Biological Chemistry, Kühne Minerva Center for Studies of Visual Transduction, Institute of Life Sciences, The Hebrew University, Givat Ram, Jerusalem 91904, Israel.
Frechter
Shahar
S
Gedi
Yinon
Y
Minke
Baruch
B
Selinger
Zvi
Z
D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D019281:Dimerization; D004330:Drosophila / Q000235:genetics / Q000502:physiology*; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000235:genetics / Q000502:physiology*; D044387:GTP-Binding Protein beta Subunits / Q000502:physiology*; D044388:GTP-Binding Protein gamma Subunits / Q000502:physiology; D008027:Light; D009154:Mutation; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D012243:Rhodopsin / Q000378:metabolism; D015398:Signal Transduction
D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D012243:Rhodopsin; D043802:GTP-Binding Protein alpha Subunits, Gq-G11