Mechanism of β-arrestin recruitment by the μ-opioid G protein-coupled receptor

Proc Natl Acad Sci U S A. 2020 Jul 14;117(28):16346-16355. doi: 10.1073/pnas.1918264117. Epub 2020 Jun 29.


Agonists to the μ-opioid G protein-coupled receptor (μOR) can alleviate pain through activation of G protein signaling, but they can also induce β-arrestin activation, leading to such side effects as respiratory depression. Biased ligands to μOR that induce G protein signaling without inducing β-arrestin signaling can alleviate pain while reducing side effects. However, the mechanism for stimulating β-arrestin signaling is not known, making it difficult to design optimum biased ligands. We use extensive molecular dynamics simulations to determine three-dimensional (3D) structures of activated β-arrestin2 stabilized by phosphorylated μOR bound to the morphine and D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO) nonbiased agonists and to the TRV130 biased agonist. For nonbiased agonists, we find that the β-arrestin2 couples to the phosphorylated μOR by forming strong polar interactions with intracellular loop 2 (ICL2) and either the ICL3 or cytoplasmic region of transmembrane (TM6). Strikingly, Gi protein makes identical strong bonds with these same ICLs. Thus, the Gi protein and β-arrestin2 compete for the same binding site even though their recruitment leads to much different outcomes. On the other hand, we find that TRV130 has a greater tendency to bind the extracellular portion of TM2 and TM3, which repositions TM6 in the cytoplasmic region of μOR, hindering β-arrestin2 from making polar anchors to the ICL3 or to the cytosolic end of TM6. This dramatically reduces the affinity between μOR and β-arrestin2.

Keywords: biased agonists; molecular dynamics; nonbiased agonists.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analgesics, Opioid / metabolism
  • Animals
  • Binding Sites
  • Cell Membrane / metabolism
  • Cytoplasm / metabolism
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / metabolism
  • GTP-Binding Proteins / metabolism
  • Humans
  • Mice
  • Molecular Dynamics Simulation
  • Morphine / metabolism
  • Phosphorylation
  • Protein Binding
  • Protein Domains
  • Receptors, Opioid, mu / agonists
  • Receptors, Opioid, mu / chemistry
  • Receptors, Opioid, mu / metabolism*
  • Signal Transduction
  • Spiro Compounds / metabolism
  • Thiophenes / metabolism
  • beta-Arrestin 2 / chemistry
  • beta-Arrestin 2 / metabolism*


  • ((3-methoxythiophen-2-yl)methyl)((2-(9-(pyridin-2-yl)-6-oxaspiro(4.5)decan-9-yl)ethyl))amine
  • Analgesics, Opioid
  • Receptors, Opioid, mu
  • Spiro Compounds
  • Thiophenes
  • beta-Arrestin 2
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
  • Morphine
  • GTP-Binding Proteins