N-terminally modified GLP1R agonists drive G protein bias via extracellular loop 3 displacement

Area of Science:

• Pharmacology
• Structural Biology
• Endocrinology

Background:

• Glucagon-like peptide-1 receptor (GLP1R) is a key target for type 2 diabetes and obesity.
• GLP1R agonists activate both G protein and β-arrestin pathways, influencing distinct receptor states.
• Understanding signaling bias is crucial for developing effective therapeutics.

Purpose of the Study:

• To develop G protein-biased GLP1R agonists through N-terminal modifications.
• To elucidate the structural basis of GLP1R biased agonism.
• To investigate the functional consequences of biased signaling on receptor trafficking and in vivo efficacy.

Main Methods:

• N-terminal modifications (acetylation, amino acid substitutions) of GLP1R agonists.
• Cryo-electron microscopy (Cryo-EM) to determine the structure of GLP1R-G_s complex.
• In vitro assays for G protein and β-arrestin signaling, receptor trafficking, and cAMP production.
• In vivo studies using diet-induced obese mice to assess glucose-lowering activity.

Main Results:

• Modified agonists, Ac-GLP1 and Ac-semaglutide, demonstrated preferential G protein signaling.
• Cryo-EM revealed outward displacement of extracellular loop 3 (ECL3) as a key feature of G protein-biased signaling.
• Modified agonists showed altered receptor trafficking, reduced β-arrestin recruitment, and sustained cAMP signaling.
• Ac-semaglutide maintained glucose-lowering effects in obese mice for three days post-administration.

Conclusions:

• N-terminal modifications can yield G protein-biased GLP1R agonists.
• Structural insights into ECL3 displacement explain the mechanism of signaling bias.
• Biased GLP1R agonists offer a promising therapeutic strategy for metabolic disorders with improved signaling profiles.