Biased Signaling of the G-Protein-Coupled Receptor β2AR Is Governed by Conformational Exchange Kinetics

Structure. 2020 Mar 3;28(3):371-377.e3. doi: 10.1016/j.str.2020.01.001. Epub 2020 Jan 23.


G-protein-coupled receptors (GPCRs) mediate a wide range of human physiological functions by transducing extracellular ligand binding events into intracellular responses. GPCRs can activate parallel, independent signaling pathways mediated by G proteins or β-arrestins. Whereas "balanced" agonists activate both pathways equally, "biased" agonists dominantly activate one pathway, which is of interest for designing GPCR-targeting drugs because it may mitigate undesirable side effects. Previous studies demonstrated that β-arrestin activation is associated with transmembrane helix VII (TM VII) of GPCRs. Here, single-molecule fluorescence spectroscopy with the β2-adrenergic receptor (β2AR) in the ligand-free state showed that TM VII spontaneously fluctuates between one inactive and one active-like conformation. The presence of the β-arrestin-biased agonist isoetharine prolongs the dwell time of TM VII in the active-like conformation compared with the balanced agonist formoterol, suggesting that ligands can induce signaling bias by modulating the kinetics of receptor conformational exchange.

Keywords: G-protein-coupled receptor; biased signaling; conformational dynamics; single-molecule fluorescence spectroscopy; β(2)-adrenergic receptor.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Binding Sites / drug effects
  • Humans
  • Isoetharine / pharmacology*
  • Kinetics
  • Models, Molecular
  • Protein Binding / drug effects
  • Protein Conformation
  • Protein Domains
  • Protein Structure, Secondary
  • Receptors, Adrenergic, beta-2 / chemistry*
  • Receptors, Adrenergic, beta-2 / metabolism*
  • Signal Transduction
  • Single Molecule Imaging
  • Spectrometry, Fluorescence
  • beta-Arrestins / metabolism*


  • ADRB2 protein, human
  • Receptors, Adrenergic, beta-2
  • beta-Arrestins
  • Isoetharine