Key domains and residues of the receptor MRGPRX1 recognizing the peptide ligand BAM8-22.

Mas-related G protein-coupled receptors (Mrgprs) are a newly discovered class of G protein-coupled receptors consisting of more than 50 members in recent years. MRGPRX1 can be activated by bovine adrenal medulla peptide 8-22 (BAM8-22), triggering Ca2+ influx and then causing pain and itch. It is very important for the discovery of analgesic and antipruritic drugs to elucidate the molecular mechanism of MRGPRX1 recognizing BAM8-22. Here, we identified the functional domains and residues of the receptor MRGPRX1 activating BAM8-22 through molecular model, mutation and living cell calcium imaging. The molecular docking predicted that BAM8-22 interacted with N-terminal, TM4, TM5, TM6 and ECL3 of MRGPRX1. Both ECL3 and TM6 domains were further revealed to play a critical role in the BAM8-22-induced MRGPRX1 activation, whereas TM3 region performed a secondary function. Moreover, the mutation F237A of MRGPRX1 completely lost the activation ability of BAM8-22. These results were consistent with the cryogenic electron microscopy (cryo-EM) structure of MRGPRX1-Gαq in complex with BAM8-22 reported most recently. Taken together, our work shows insights into the molecular mechanism of the interaction between the receptor MRGPRX1 and the peptide agonist BAM8-22, and will also provide some valuable clues for the design of analgesic and antipruritic drugs targeting MRGPRX1.