Structural and Functional Basis of G Protein-Coupled Receptor 35 Activation by Pyrroloquinoline Quinone

Pyrroloquinoline quinone (PQQ), an o-quinone-type nutrient, has been shown to exert diverse beneficial effects on the biochemical and physiological processes of mammals. However, the molecular mechanisms underlying these effects remain incompletely understood. Here, through screening of metabolite-sensing G protein-coupled receptors (GPCRs)─which respond to metabolites produced by gut microbiota or derived from nutrients─we found that PQQ selectively activates G-protein-coupled receptor 35 (GPR35) and characterized the molecular basis of its ligand recognition. Using a transforming growth factor α shedding assay, we demonstrated that PQQ selectively activated GPR35, a class A rhodopsin-like GPCR expressed in various tissues, including adipose tissue and the gastrointestinal tract. PQQ also promoted β-arrestin 1 recruitment to the plasma membrane, further supporting its role as a GPR35 agonist. Direct binding of PQQ to GPR35 was demonstrated using a clickable photoaffinity probe derived from PQQ. Molecular docking simulation and site-directed mutagenesis revealed that the 2-carboxylic acid moiety of PQQ forms critical hydrogen bonds with Arg100, Tyr101, and Arg151 of GPR35. Additionally, Phe163 appears to contribute to π-H interaction with PQQ. These findings indicate that PQQ functions as a food-derived agonist of GPR35 and provide new insights into the molecular mechanisms underlying the potential beneficial effects of PQQ.