A structural basis for how ligand binding site changes can allosterically regulate GPCR signaling and engender functional selectivity.
SCIENCE SIGNALING(2020)
摘要
Signaling bias is the propensity for some agonists to preferentially stimulate G protein-coupled receptor (GPCR) signaling through one intracellular pathway versus another. We previously identified a G protein-biased agonist of the D2 dopamine receptor (D2R) that results in impaired beta-arrestin recruitment. This signaling bias was predicted to arise from unique interactions of the ligand with a hydrophobic pocket at the interface of the second extracellular loop and fifth transmembrane segment of the D2R. Here, we showed that residue Phe189 within this pocket (position 5.38 using Ballesteros-Weinstein numbering) functions as a microswitch for regulating receptor interactions with beta-arrestin. This residue is relatively conserved among class A GPCRs, and analogous mutations within other GPCRs similarly impaired beta-arrestin recruitment while maintaining G protein signaling. To investigate the mechanism of this signaling bias, we used an active-state structure of the beta(2)-adrenergic receptor (beta 2R) to build beta 2R-WT and beta 2R-Y199(5.38A) models in complex with the full beta 2R agonist BI-167107 for molecular dynamics simulations. These analyses identified conformational rearrangements in beta 2R-Y199(5.38A) that propagated from the extracellular ligand binding site to the intracellular surface, resulting in a modified orientation of the second intracellular loop in beta 2R-Y199(5.38A), which is predicted to affect its interactions with beta-arrestin. Our findings provide a structural basis for how ligand binding site alterations can allosterically affect GPCR-transducer interactions and result in biased signaling.
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