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Agonist concentration-dependent changes in FPR1 conformation lead to biased signaling for selective activation of

Junlin Wang1, Richard D Ye1

  • 1Kobilka Institute of Innovative Drug Discovery and School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen, Guangdong 518172, China.

Proceedings of the National Academy of Sciences of the United States of America
|July 25, 2022
PubMed

Insights

The bacteria-derived peptide fMet-Leu-Phe (fMLF) triggers distinct phagocyte responses based on concentration. Low fMLF levels promote migration, while high levels activate bacteria-killing functions by altering receptor signaling.

Area of Science:

  • Immunology
  • Cell Biology
  • Biochemistry

Background:

  • The bacteria-derived formyl peptide fMet-Leu-Phe (fMLF) is a potent chemoattractant for phagocytes, crucial for immune responses.
  • fMLF exhibits dual activity: inducing chemotaxis at low concentrations and stimulating degranulation and superoxide production at higher concentrations.
  • The underlying mechanism for fMLF's concentration-dependent activation of distinct cellular functions remains poorly understood.

Purpose of the Study:

  • To elucidate the mechanism by which fMLF activates distinct phagocyte functions at different concentrations.
  • To investigate the concentration-dependent conformational changes in the formyl peptide receptor 1 (FPR1) induced by fMLF.
  • To understand how these receptor dynamics translate into specific cellular outcomes like migration and bacterial killing.

Main Methods:

  • Utilized a bioluminescence resonance energy transfer (BRET)-based FPR1 biosensor to monitor receptor conformational changes.
  • Exposed neutrophil-like HL-60 cells to varying concentrations of fMLF (subnanomolar to micromolar).
  • Assessed cellular responses including polarization, migration, intracellular calcium (Ca2+) dynamics, degranulation, superoxide production, ERK1/2 phosphorylation, and β-arrestin2 translocation.

Main Results:

  • fMLF at subnanomolar and micromolar concentrations induced distinct conformational changes in FPR1.
  • Low fMLF concentrations promoted rapid HL-60 cell polarization, migration, and development of an intracellular Ca2+ gradient.
  • High fMLF concentrations (nanomolar to micromolar) activated the PLC-β pathway, leading to uniform Ca2+ rise, degranulation, superoxide production, and inhibited chemotaxis.
  • Elevated ERK1/2 phosphorylation and β-arrestin2 translocation correlated with diminished chemotaxis at fMLF concentrations above 1 nM.

Conclusions:

  • fMLF concentration dictates FPR1 signaling pathways, switching phagocyte function from migration to bactericidal activity.
  • Distinct FPR1 conformational states mediate different cellular responses, providing a mechanism for concentration-dependent signaling.
  • This concentration-dependent switch is critical for effective host defense against bacterial invasion.
Keywords:
GPCRsbiased signalingcalcium mobilizationphagocytes

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