22gk
C5a bound C5aR2 in complex with beta-arrestin1
Structural highlights
DiseaseCO5_HUMAN Defects in C5 are the cause of complement component 5 deficiency (C5D) [MIM:609536. A rare defect of the complement classical pathway associated with susceptibility to severe recurrent infections, predominantly by Neisseria gonorrhoeae or Neisseria meningitidis. Note=An association study of C5 haplotypes and genotypes in individuals with chronic hepatitis C virus infection shows that individuals homozygous for the C5_1 haplotype have a significantly higher stage of liver fibrosis than individuals carrying at least 1 other allele (PubMed:15995705). FunctionCO5_HUMAN Activation of C5 by a C5 convertase initiates the spontaneous assembly of the late complement components, C5-C9, into the membrane attack complex. C5b has a transient binding site for C6. The C5b-C6 complex is the foundation upon which the lytic complex is assembled. Derived from proteolytic degradation of complement C5, C5 anaphylatoxin is a mediator of local inflammatory process. It induces the contraction of smooth muscle, increases vascular permeability and causes histamine release from mast cells and basophilic leukocytes. C5a also stimulates the locomotion of polymorphonuclear leukocytes (chemokinesis) and direct their migration toward sites of inflammation (chemotaxis). Publication Abstract from PubMedC5a, 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 beta-arrestin 1-bound C5aR2 and C5aR1 stimulated by C5a or its metabolite C5a(desArg). By combining structural analysis with functional assays, we identified the key structural determinants that prevent G protein coupling and confer intrinsic bias toward beta-arrestins. Comparative analysis elucidated the distinct ligand recognition mechanism of C5aR2 and explained the retained affinity of C5a(desArg) 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. Atypical signaling, ligand recognition and selective agonist discovery of complement receptor C5aR2.,Qin J, Cai C, Shan M, Zhou S, Shen Q, Zhu T, Zhao M, Mei Y, Ji F, Shen DD, Zang SK, Zhang H, Xu H, Yang M, Wang WW, Xiao R, Yang B, Mao C, Shao Z, Wu H, Lu Q, Zhang Y Cell Res. 2026 Jul 3. doi: 10.1038/s41422-026-01273-1. PMID:42399467[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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