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Galphaq binds to p110alpha/p85alpha phosphoinositide 3-kinase and displaces Ras
Lisa M Ballou1, Mohar Chattopadhyay, Yan Li
1Department of Medicine, Division of Hematology, Stony Brook University, Stony Brook, NY 11794, USA.
The Biochemical Journal
|November 5, 2005
Summary
G protein Gαq directly inhibits phosphoinositide 3-kinase (PI3K) signaling by binding to p110α/p85α. This interaction, dependent on GTP, competes with Ras and explains receptor-mediated PI3K inhibition in cells.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- G(q)-coupled receptor activation is known to inhibit phosphoinositide 3-kinase (PI3K) signaling.
- The precise molecular mechanism underlying this inhibition remains incompletely understood.
Purpose of the Study:
- To elucidate the direct interaction between Gαq and PI3K isoforms.
- To determine the mechanism by which Gαq inhibits PI3K signaling.
Main Methods:
- Purified protein studies using fluorescence spectroscopy to measure binding affinities.
- Co-precipitation assays with deletion mutants to identify binding domains.
- Cell-based assays to assess pathway activation.
Main Results:
- Gαq directly inhibits p110α/p85α PI3K in a GTP-dependent manner.
- Activated Gαq binds p110α/p85α PI3K with higher affinity than Gαq.GDP and competes with Ras.
- Gαq binds to the p85-binding domain of p110α, not the Ras-binding domain.
- Expression of active Gαq inhibits Ras-activated PI3K/Akt signaling but not MAPK/ERK signaling.
Conclusions:
- Gαq.GTP directly binds and inhibits p110α/p85α PI3K.
- This direct interaction provides a molecular basis for G(q)-coupled receptor-mediated inhibition of PI3K signaling in specific cell types.