GPCR-mediated β-arrestin activation deconvoluted with single-molecule precision

Area of Science:

• Molecular and Cellular Biology
• Biochemistry
• Pharmacology

Background:

• Beta-arrestins play a critical role in G protein-coupled receptor (GPCR) signaling termination and initiation of distinct downstream pathways.
• Understanding beta-arrestin regulation is key to modulating GPCR-mediated cellular responses.

Purpose of the Study:

• To investigate the conformational states of beta-arrestin and the mechanisms governing its activation by phosphorylated GPCRs.
• To elucidate the role of receptor phosphorylation patterns and agonism in beta-arrestin activation.

Main Methods:

• Single-molecule fluorescence resonance energy transfer (smFRET) imaging to observe beta-arrestin conformational dynamics.
• Biochemical assays using phosphopeptides mimicking phosphorylated receptor tails.
• Cellular investigations to assess beta-arrestin activation in a physiological context.

Main Results:

• Beta-arrestin exists in a strongly autoinhibited basal state.
• Engagement with phosphopeptides releases the beta-arrestin tail, inducing distinct conformations.
• Unexpectedly, beta-arrestin binding to phosphorylated receptors is inefficient without agonist-promoted receptor activation, suggesting a sequestered C-tail release mechanism.
• Receptor agonism and C-tail release are critical determinants of beta-arrestin activation rate and efficiency.

Conclusions:

• Beta-arrestin activation is a complex process regulated by both receptor phosphorylation and agonist binding.
• The synergistic interplay between phosphorylation patterns and agonism dictates the specificity and strength of downstream beta-arrestin signaling.
• These findings provide novel insights into GPCR signaling and offer potential targets for therapeutic intervention.