High-affinity agonists reveal recognition motifs for the MRGPRD GPCR.

The human MRGPRD protein is a member of the Mas-related G protein-coupled receptors (MRGPRs) that is involved in the sensing of pain, itch, and other inflammatory stimuli. As with other MRGPRs, MRGPRD is a relatively understudied receptor with few known agonists. The most potent small-molecule agonist of MRGPRD reported so far is β-alanine, with an affinity in the micromole range, which largely restricts its functional study. Here, we report two MRGPRD agonists, EP-2825 and EP-3945, that are approximately 100-fold more potent than β-alanine and determine the structures of MRGPRD-Gq in complex with EP-2825 and EP-3945, respectively. The structures reveal distinct agonist binding modes of MRGPRD and large conformational plasticity of the orthosteric pocket. Collectively, the discovery of high-affinity MRGPRD agonists and their distinct binding modes will facilitate the functional study and the structure-based design of ligands targeting this understudied receptor.