Structural insights into the ligand modulation of MRGPRX4 conformational plasticity.

Chronic pruritus is a debilitating condition with limited treatment options, particularly in cholestatic liver diseases, where bile acid dysregulation is a known trigger. Although Mas-related G protein-coupled receptor X4 (MRGPRX4) has recently been identified as a key mediator of bile acid-induced pruritus, the structural mechanisms underlying its inhibition remain poorly understood, hindering the development of therapeutic antagonists. Here, we report the cryo-electron microscopy structures of MRGPRX4 in three distinct states: agonist-bound state, antagonist-bound state, and apo state. Our structures reveal a previously unrecognized antagonist-binding site that is structurally distinct from those engaged by agonists. Complementary functional assays and molecular dynamics simulations further demonstrate that the extracellular pocket of MRGPRX4 undergoes pronounced ligand-dependent conformational rearrangements upon binding to both the agonist and the antagonist. Collectively, these findings elucidate the conformational plasticity underlying MRGPRX4 activity modulation and establish a structural framework for the rational design of MRGPRX4 antagonists that target chronic pruritus.