Journal: Cell Res / Year: 2026 Title: Atypical signaling, ligand recognition and selective agonist discovery of complement receptor C5aR2. Authors: Jiao Qin / Chenxi Cai / Mayu Shan / Suqing Zhou / Qingya Shen / Tianyi Zhu / Mingming Zhao / Yang Mei / Fanghan Ji / Dan-Dan Shen / Shao-Kun Zang / Huibing Zhang / Haomang Xu / Ming Yang / ...Authors: Jiao Qin / Chenxi Cai / Mayu Shan / Suqing Zhou / Qingya Shen / Tianyi Zhu / Mingming Zhao / Yang Mei / Fanghan Ji / Dan-Dan Shen / Shao-Kun Zang / Huibing Zhang / Haomang Xu / Ming Yang / Wei-Wei Wang / Rong Xiao / Bing Yang / Chunyou Mao / Zhenhua Shao / Haijing Wu / Qianjin Lu / Yan Zhang / Abstract: C5a, the most potent anaphylatoxin in the complement system, exerts its effects through the canonical G protein-coupled receptor C5aR1 and the arrestin-coupled receptor C5aR2. Despite the critical ...C5a, the most potent anaphylatoxin in the complement system, exerts its effects through the canonical G protein-coupled receptor C5aR1 and the arrestin-coupled receptor C5aR2. Despite the critical role of C5aR2 in immunomodulation, the molecular mechanisms underlying its biased signaling, ligand recognition, and associated pathophysiology remain poorly understood. Here, we report cryo-electron microscopy structures of β-arrestin 1-bound C5aR2 and C5aR1 stimulated by C5a or its metabolite C5a. By combining structural analysis with functional assays, we identified the key structural determinants that prevent G protein coupling and confer intrinsic bias toward β-arrestins. Comparative analysis elucidated the distinct ligand recognition mechanism of C5aR2 and explained the retained affinity of C5a for C5aR2. These findings guided the rational design of ZQ105, a highly selective C5aR2 agonist. Leveraging ZQ105 as a chemical probe, functional studies revealed that selective C5aR2 activation induces distinct pro-inflammatory responses and receptor internalization in neutrophils. This study provides novel structural insights into transducer engagement and ligand recognition by C5aR2, yielding a valuable pharmacological tool for exploring C5aR2-related pathophysiological processes.
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