Differential Modulation of GLP-1R by Dietary Ginsenosides Points to a Putative Extracellular Allosteric Site

The glucagon-like peptide-1 receptor (GLP-1R) is a class B G protein-coupled receptor (GPCR) central to metabolic regulation, and its potential modulation by dietary phytochemicals is increasingly recognized as physiologically relevant. Understanding how such compounds interact with GLP-1R is important for clarifying mechanisms that may contribute to gut-to-brain signaling. In this study, we examined three structurally related dietary ginsenosides, Rg1, Rg2, and Rg3, as potential modulators of GLP-1R using luciferase reporter assays and computational analyses. Despite sharing similar molecular weights, a common dammarane scaffold, and comparable sugar moieties, the three ginsenosides displayed distinct effects on GLP-1R activity: Rg2 and Rg3 potently reduced receptor activation in a dose-dependent manner when co-administered with Exendin-4, whereas Rg1 had minimal effect. Computational screening of the GLP-1R structure for binding sites identified a putative extracellular pocket on the protein that can accommodate these compounds, while molecular docking and binding free energy calculations provided predicted affinities qualitatively reflecting the phytochemicals' experimental activities. These findings point to a plausible extracellular mechanism through which dietary ginsenosides may influence GLP-1R responsiveness at the intestinal interface. Our results point to the possibility that non-absorbed phytochemicals can differentially modulate gut-expressed receptors, suggesting a novel pathway for dietary signaling relevant to ethnopharmacology and metabolic health.