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A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
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Direct Modulation of Heterotrimeric G Protein-coupled Signaling by a Receptor Kinase Complex.
Meral Tunc-Ozdemir1, Daisuke Urano1, Dinesh Kumar Jaiswal1
1Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599.
The Journal of Biological Chemistry
|May 29, 2016
Summary
Plant G protein signaling uses leucine-rich repeat receptor-like kinases (LRR RLKs) to activate signaling pathways, unlike animal G protein-coupled receptors (GPCRs). This study reveals LRR RLKs phosphorylate AtRGS1, modulating G protein activity in response to external signals.
Area of Science:
- Plant molecular biology
- Cell signaling
- G protein-coupled receptor research
Background:
- Heterotrimeric G protein complexes in plants and protists can activate spontaneously, independent of canonical G protein-coupled receptors (GPCRs).
- In Arabidopsis, the regulator of G protein signaling 1 (AtRGS1), a 7-transmembrane protein, maintains the G protein complex in an inactive (GDP-bound) state.
- The mechanism by which a single G protein modulator orchestrates diverse biological responses remains unclear.
Purpose of the Study:
- To investigate the role of plant leucine-rich repeat receptor-like kinases (LRR RLKs) in modulating G protein signaling.
- To elucidate how plant LRR RLKs discriminate signals and activate G protein pathways, contrasting with animal GPCR mechanisms.
- To understand the specific activation of G protein signaling by pathogen-associated molecular patterns (PAMPs) via FLS2 and BAK1.
Main Methods:
- Investigated the interaction between LRR RLKs and the G protein regulator AtRGS1.
- Examined the ligand-dependent phosphorylation of AtRGS1 by LRR RLKs.
- Utilized flagellin peptide 22 (flg22) as a PAMP to study FLS2 and BAK1-mediated G protein activation.
Main Results:
- Plant LRR RLKs, not GPCRs, are proposed to provide signal discrimination for G protein activation.
- LRR RLKs phosphorylate AtRGS1 in a ligand-dependent manner, thereby modulating G protein activity.
- Pathogen-associated molecular pattern flagellin peptide 22 directly activates G protein signaling through the LRR RLKs FLS2 and its co-receptor BAK1.
Conclusions:
- Plant G protein signaling activation diverges significantly from animal pathways, relying on LRR RLKs for signal specificity.
- The phosphorylation of AtRGS1 by LRR RLKs is a key mechanism for integrating external stimuli into G protein-mediated responses.
- FLS2 and BAK1 play a crucial role in initiating G protein signaling cascades in response to pathogen detection.
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