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A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
Published on: February 20, 2018
Galphaq binds two effectors separately in cells: evidence for predetermined signaling pathways
Urszula Golebiewska1, Suzanne Scarlata
1Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York 11794-8661, USA.
Biophysical Journal
|June 3, 2008
Summary
G-protein pathway selection was studied using Galpha(q) and its effectors, phospholipase Cbeta (PLCbeta) and phosphoinositide-3-kinase (PI3K). Separate, stable G-protein/effector complexes form, limiting signal transduction pathways.
Area of Science:
- Cellular signaling
- Molecular biology
- Biochemistry
Background:
- G-proteins mediate diverse cellular signals, but pathway selection mechanisms remain unclear.
- Understanding how G-protein alpha subunits (Galpha) choose between effectors is crucial for deciphering signal transduction.
- Galpha(q) is known to interact with multiple downstream effectors, including PLCbeta and PI3K.
Purpose of the Study:
- To investigate the pathway selection mechanism of Galpha(q) between phospholipase Cbeta (PLCbeta) and phosphoinositide-3-kinase (PI3K).
- To determine if Galpha(q) forms distinct complexes with PLCbeta and PI3K in living cells.
- To elucidate the dynamics of G-protein/effector interactions during signal transduction.
Main Methods:
- Utilized human embryonic kidney 293 cells expressing eCFP- and eYFP-tagged proteins.
- Employed Förster resonance energy transfer (FRET) to measure protein-protein interactions in real-time.
- Performed in vitro binding assays with purified proteins to assess simultaneous effector binding.
Main Results:
- Identified separate and stable complexes of Galpha(q)-PLCbeta and Galpha(q)-PI3K throughout the stimulation cycle.
- Observed that these complexes form independently and do not appear to involve diffusion and exchange.
- Demonstrated that Galpha(q) can simultaneously bind both PLCbeta and PI3K in vitro, despite forming separate complexes in cells.
Conclusions:
- Pre-formed G-protein/effector complexes dictate pathway usage, rather than dynamic exchange.
- This complex formation limits the number of signaling pathways activated by a single G-protein.
- Findings simplify predictive models of G-protein-mediated signal transduction.
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