Galphaq binds two effectors separately in cells: evidence for predetermined signaling pathways.
G-proteins transduce signals along diverse pathways, but the factors involved in pathway selection are largely unknown. Here, we have studied the ability of Galpha(q) to select between two effectors-mammalian inositide-specific phospholipase Cbeta (PLCbeta) and phosphoinositide-3-kinase (PI3K)-in human embryonic kidney 293 cells. These studies were carried out by measuring interactions between eCFP- and eYFP-tagged proteins using Forster resonance energy transfer in the basal state and during stimulation. Instead of association of Galpha(q) with effectors through diffusion and exchange, we found separate and stable pools of Galpha(q)-PLCbeta and Galpha(q)-PI3K complexes existing throughout the stimulation cycle. These separate complexes existed despite the ability of Galpha(q) to simultaneously bind both effectors as determined by in vitro measurements using purified proteins. Preformed G-protein/effector complexes will limit the number of pathways that a given signal will take, which may simplify predictive models.
Golebiewska
Urszula
U
Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York 11794-8661, USA.
Scarlata
Suzanne
S
D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D031541:Fluorescence Resonance Energy Transfer; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D054799:Phospholipase C beta / Q000378:metabolism*; D011485:Protein Binding; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
D043562:Receptors, G-Protein-Coupled; D011994:Recombinant Proteins; D019869:Phosphatidylinositol 3-Kinases; D020794:Receptor Protein-Tyrosine Kinases; D054799:Phospholipase C beta; D043802:GTP-Binding Protein alpha Subunits, Gq-G11