National Natural Science Foundation of China (NSFC)
China
Citation
Journal: EMBO J / Year: 2026 Title: Structural insight into ligand binding and activation of the orphan GPCR Mas1. Authors: Yumu Zhang / Qiuying Wang / Heng Liu / Hong Shan / Yimin Gu / Jiaqi Yang / Yuan Gao / Kai Wu / Dehua Yang / H Eric Xu / Abstract: The Mas1 receptor, an orphan class A G-protein-coupled receptor (GPCR), plays pivotal roles in cardiovascular and anti-inflammatory regulation. Despite its therapeutic relevance, the structural ...The Mas1 receptor, an orphan class A G-protein-coupled receptor (GPCR), plays pivotal roles in cardiovascular and anti-inflammatory regulation. Despite its therapeutic relevance, the structural mechanisms underlying Mas1 ligand binding and activation remain poorly understood. Here, we report cryo-EM structures of Mas1 bound to two chemically distinct agonists-neuropeptide FF (NPFF) and synthetic small-molecule AR234958-captured in complex with inhibitory G proteins. These structures reveal a conserved orthosteric binding pocket accommodating both ligands through shared hydrophobic interactions. Unlike many other class A GPCRs that rely on direct W toggle switch engagement, Mas1 adopts a non-canonical activation strategy driven by a ligand-induced hydrophobic compression plane involving residues Y248, L87, I84, and L266 at the bottom of the ligand binding pocket. This mechanism transmits mechanical tension to promote TM6 displacement and G protein coupling. Functional mutagenesis validates this model, identifying two transmembrane helix 6 (TM6) residues, M244 and F237, as critical molecular switches. Comparative analyses of Mas1-related receptors, MRGPRX1-X4, reveal conserved features and mechanistic divergence within this subfamily. These findings provide a structural framework for understanding Mas1 pharmacology and rational design of selective therapeutics.
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