Biased allosteric modulation of formyl peptide receptor 2 leads to distinct receptor conformational states for pro- and anti-inflammatory signaling.

BACKGROUND AND PURPOSE

Formyl peptide receptor 2 (FPR2) is a Class A G protein-coupled receptor (GPCR) that interacts with multiple ligands and transduces both proinflammatory and anti-inflammatory signals. These ligands include weak agonists and modulators that are produced during inflammation. The present study investigates how prolonged exposure to FPR2 modulators influence receptor signaling.

EXPERIMENTAL APPROACH

Fluorescent biosensors of FPR2 were constructed based on single-molecule fluorescent resonance energy transfer (FRET) and used for measurement of ligand-induced receptor conformational changes. These changes were combined with FPR2-mediated signaling events and used as parameters for the conformational states of FPR2. Ternary complex models were developed to interpret ligand concentration-dependent changes in FPR2 conformational states.

KEY RESULTS

Incubation with Ac, an anti-inflammatory ligand of FPR2, decreased FRET intensity at picomolar concentrations. In comparison, WKYMVm (W-pep) and Aβ, both proinflammatory agonists of FPR2, increased FRET intensity. Preincubation with Ac at 10 pM diminished W-pep-induced Ca flux but potentiated W-pep-stimulated β-arrestin2 membrane translocation and p38 MAPK phosphorylation. The opposite effects were observed with 10 pM of Aβ. Neither Ac nor Aβ competed for W-pep binding at the picomolar concentrations.

CONCLUSIONS AND IMPLICATIONS

The results support the presence of two allosteric binding sites on FPR2, each for Ac and Aβ, with high and low affinities. Sequential binding of the two allosteric ligands at increasing concentrations induce different conformational changes in FPR2, providing a novel mechanism by which biased allosteric modulators alter receptor conformations and generate pro- and anti-inflammatory signals.