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A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
Published on: February 20, 2018
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Class B1 GPCR activation by an intracellular agonist
Kazuhiro Kobayashi1, Kouki Kawakami2, Tsukasa Kusakizako1
1Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan.
Nature
|June 7, 2023
Summary
Researchers discovered a new intracellular binding pocket in G protein-coupled receptors (GPCRs). This finding reveals how biased agonists selectively activate signaling pathways, offering new drug development avenues.
Area of Science:
- Structural Biology
- Pharmacology
- Biochemistry
Background:
- G protein-coupled receptors (GPCRs) typically bind ligands in orthosteric pockets, triggering conformational changes and activating G proteins and β-arrestins.
- Adverse effects from signaling necessitate understanding selective transducer activation.
- Intracellular-biased agonists, binding within the receptor's intracellular cavity, are of recent interest for pathway-specific signaling.
Purpose of the Study:
- To elucidate the structural basis of intracellular-biased agonism.
- To provide evidence for agonist binding within the intracellular cavity of GPCRs.
- To understand the mechanism of selective G protein versus β-arrestin activation.
Main Methods:
- Cryogenic electron microscopy (cryo-EM) was used to determine the structure of a complex.
- The complex consisted of the human parathyroid hormone type 1 receptor (PTH1R), Gs, and the agonist PCO371.
- Structural analysis focused on the binding mode of PCO371 and its effect on receptor conformation.
Main Results:
- The structure revealed that the agonist PCO371 binds within an intracellular pocket of PTH1R, directly interacting with Gs.
- This binding induces an active conformation without extracellular allosteric signal propagation, stabilizing transmembrane helix 6.
- PCO371 activates 7 out of 15 class B1 GPCRs by binding to a conserved intracellular pocket.
Conclusions:
- A novel and conserved intracellular agonist-binding pocket in GPCRs has been identified.
- The study provides structural evidence for intracellular-biased agonism targeting the receptor-transducer interface.
- This mechanism preferentially facilitates G protein binding over β-arrestin binding, offering insights for selective drug development.
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