Abstact

UNLABELLED β-arrestins (βarrs) are key regulators of G protein-coupled receptors (GPCRs), essential for modulating signaling pathways and physiological processes. While current pharmacological strategies target GPCR orthosteric and allosteric sites, as well as G protein transducers, comparable tools for studying βarrs are lacking. Here, we present the discovery and characterization of novel small-molecule allosteric inhibitors of βarrs through comprehensive biophysical, biochemical, pharmacological, and structural analyses. These inhibitors disrupt βarr interactions with agonist-activated GPCRs, impairing receptor internalization, desensitization, and βarr-mediated physiological functions. A cryo-EM structure of βarr1 in complex with the allosteric inhibitor Cmpd-5, complemented by molecular dynamics simulations and mutagenesis studies, reveals that Cmpd-5 binds within a cryptic cleft formed by the middle, C-, and lariat loops-a critical site for βarr activation and recruitment to GPCRs. Thus, Cmpd-5 acts as a molecular lock, hindering βarr1 activation via an allosteric mechanism. These findings introduce novel strategies and tools for probing βarr functions. HIGHLIGHTS Small molecule strategies for modulating βarr functions in both GPCR-dependent and independent contexts.Modulators disrupt βarr interaction with GPCRs, impairing their critical functions.Cryo-EM structures reveal the allosteric inhibitor Cmpd-5 binding to a cryptic pocket between the N and C domains in the central crest of βarr1, inhibiting its activation.Structural analyses, including cryo-EM, MD simulations, and mutagenesis, reveal a unique βarr1 conformation induced by Cmpd-5, shedding light on its mechanism of allosteric inhibition.