Related Experiment Video
Updated: Sep 16, 2026

A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
Published on: February 20, 2018
Structural basis for small-molecule agonism at GCGR and GIPR via a conserved intracellular allosteric site
Qian He1,2,3, Hong Shan2,3, Wen Hu2,3
1Research Center for Medicinal Structural Biology, National Research Center for Translational Medicine • Shanghai, State Key Laboratory of Medical Genomics, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200025, China.
Abstract:
The glucagon receptor (GCGR) and gastric inhibitory polypeptide receptor (GIPR) are class B GPCRs that regulate glucose homeostasis and energy balance, making them key targets for type 2 diabetes and obesity. Achieving preferential Gs signaling at these receptors with small molecules remains an unmet challenge. Here, we report SIM1, developed through optimization of the PCO371 scaffold, which exhibits preferential Gs signaling at GCGR and GIPR with minimal detectable β-arrestin recruitment and substantially improved efficacy at GIPR. Cryo-EM structures of SIM1-GCGR-Gs (2.53 Å) and SIM1-GIPR-Gs (2.74 Å) reveal a shared intracellular allosteric interface at the receptor-G protein coupling region, distinct from extracellular peptide recognition. Structural comparison with GLP1R suggests that intracellular conformational constraints contribute to differential SIM1 responsiveness, which is restored by targeted mutations. Guided by these insights, analogs SIM2 and SIM3 exhibited up to 20-fold enhanced potency while maintaining an apparent preferential Gs signaling profile. These findings reveal a conserved intracellular allosteric activation mechanism across multiple class B GPCRs and identify SIM1 and its analogs as valuable chemical tools for investigating receptor-specific intracellular allosteric regulation and G protein-preferential signaling.
Related Concept Videos
GPCRs Regulate Adenylyl Cylase Activity
Two...
Transducer Mechanism: G Protein–Coupled Receptors
GPCRs are also called heptahelical, 7TM, or...
G Protein-coupled Receptors
GPCRs are also called heptahelical, 7TM, or serpentine receptors, and consist of seven (H1-H7) transmembrane alpha-helices that span the bilayer to form a cylindrical core. The transmembrane helices are connected by three extracellular loops and three...
G Protein-coupled Receptors
GPCRs are also called heptahelical, 7TM, or serpentine receptors, and consist of seven (H1-H7) transmembrane alpha-helices that span the bilayer to form a cylindrical core. The transmembrane helices are connected by three extracellular loops and three...
Activation and Inactivation of G Proteins
G Protein-coupled Receptors

