Related Experiment Video

Updated: Nov 11, 2025

A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
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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

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Complementary biosensors reveal different G-protein signaling modes triggered by GPCRs and non-receptor activators

Mikel Garcia-Marcos1

  • 1Department of Biochemistry, Boston University School of Medicine, Boston, United States.

Elife
|March 31, 2021
PubMed

Insights

Cytoplasmic proteins activate heterotrimeric G-proteins like G-protein-coupled receptors (GPCRs), but through distinct cellular mechanisms. This study reveals significant differences in how non-receptor activators generate signaling molecules compared to GPCRs.

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Biochemistry

Background:

  • Heterotrimeric G-proteins are crucial signaling molecules involved in physiology and disease.
  • Activation of G-proteins typically occurs via G-protein-coupled receptors (GPCRs).
  • Cytoplasmic proteins, distinct from GPCRs, also activate G-proteins, but their mechanisms remain unclear.

Purpose of the Study:

  • To elucidate the cellular mechanisms by which non-receptor guanine nucleotide exchange factors (GEFs) trigger G-protein signaling.
  • To compare the signaling output of GPCRs and non-receptor GEFs in terms of Gα-GTP and free Gβγ generation.
  • To understand how different GEFs contribute to the distinct active signaling species of heterotrimeric G-proteins.

Main Methods:

  • Systematic comparison of GPCRs with three unrelated non-receptor GEFs (GIV/Girdin, AGS1/Dexras1, Ric-8A).
  • Utilized live-cell biosensors for direct measurement of Gα-GTP and free Gβγ levels in cells.
  • Assessed the guanine nucleotide exchange factor (GEF) activity of proteins in vitro.

Main Results:

  • Non-receptor GEFs and GPCRs exhibit high divergence in generating Gα-GTP and free Gβγ in cells.
  • Despite sharing in vitro GEF activity, the cellular signaling outcomes differ significantly.
  • Live-cell biosensors revealed distinct contributions of each activator to the two active G-protein signaling species.

Conclusions:

  • Receptor and non-receptor G-protein activators employ fundamentally different mechanisms to promote signaling in cells.
  • The biochemical similarity in GEF activity does not translate to similar cellular signaling outputs.
  • Understanding these differences is key to deciphering G-protein-dependent signaling in various physiological and disease contexts.
Keywords:
BRETG-protein-coupled receptor (GPCR)GEFGIVGTPaseGirdinbiochemistrycell biologychemical biologyhuman

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