The microbiota generates diverse metabolites to modulate host physiology and disease, but their protein targets and mechanisms of action have not been fully elucidated. To address this challenge, we explored microbiota-derived indole metabolites and developed photoaffinity chemical reporters for proteomic studies. We identified many potential indole metabolite-interacting proteins, including metabolic enzymes, transporters, immune sensors and G protein-coupled receptors. Notably, we discovered that aromatic monoamines can bind the orphan receptor GPRC5A and stimulate β-arrestin recruitment. Metabolomic and functional profiling also revealed specific amino acid decarboxylase-expressing microbiota species that produce aromatic monoamine agonists for GPRC5A-β-arrestin recruitment. Our analysis of synthetic aromatic monoamine derivatives identified 7-fluorotryptamine as a more potent agonist of GPRC5A. These results highlight the utility of chemoproteomics to identify microbiota metabolite-interacting proteins and the development of small-molecule agonists for orphan receptors.

微生物群产生多种代谢物来调节宿主生理和疾病，但它们的蛋白质靶点和作用机制尚未完全阐明。为了应对这一挑战，我们探索了微生物群衍生的吲哚代谢物，并开发了用于蛋白质组研究的光亲和化学报告基因。我们鉴定了许多潜在的吲哚代谢物相互作用蛋白，包括代谢酶、转运蛋白、免疫传感器和 G 蛋白偶联受体。值得注意的是，我们发现芳香族单胺可以结合孤儿受体 GPRC5A 并刺激 β-arrestin 募集。代谢组学和功能分析还揭示了表达特定氨基酸脱羧酶的微生物群物种，这些微生物群产生用于 GPRC5A-β-arrestin 募集的芳香单胺激动剂。我们对合成芳香族单胺衍生物的分析确定 7-氟色胺是 GPRC5A 更有效的激动剂。这些结果强调了化学蛋白质组学在识别微生物代谢物相互作用蛋白以及孤儿受体小分子激动剂的开发方面的实用性。