{"gene":"C5AR1","run_date":"2026-06-09T22:02:45","timeline":{"discoveries":[{"year":2023,"finding":"Cryo-EM structures of activated wild-type C5aR1–Gi protein complex bound to C5a, the hexapeptidic agonist C5apep, and the G protein-biased agonist BM213 revealed the landscape of C5a–C5aR1 interaction, a common motif for recognition of diverse orthosteric ligands, and unusual conformational changes in the intracellular end of transmembrane domain 7 and helix 8 upon agonist binding. Mutagenesis and cell-based pharmacological assays deciphered a framework for biased signaling; the structure of a C5aR1-I116A mutant–Gi complex induced by C089 (an antagonist on wild-type C5aR1) revealed the activation mechanism.","method":"Cryo-electron microscopy, site-directed mutagenesis, cell-based pharmacological assays","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple cryo-EM structures with mutagenesis and functional validation in one study","pmids":["36806352"],"is_preprint":false},{"year":2023,"finding":"Structures of C5a-bound C5aR1 (and C3a-bound C3aR) were solved, revealing a conserved recognition pattern of anaphylatoxins to complement receptors distinct from chemokine receptors, unique pocket topologies mediating ligand selectivity, and a common mechanism of receptor activation. Combined with mutagenesis analysis.","method":"Cryo-EM structure determination, mutagenesis analysis","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — independent structural study with mutagenesis, corroborating the Cell Research structures","pmids":["37169960"],"is_preprint":false},{"year":2000,"finding":"Ser334 is a key residue controlling C5aR phosphorylation; phosphorylation of either the Ser332/Ser334 or Ser334/Ser338 pair is critical for receptor desensitization. Phosphorylation of Ser334 and Ser338 is critical and sufficient for C5aR desensitization. The non-phosphorylatable S332A/S334A mutant triggered a 1.8–2-fold higher superoxide production. Receptor desensitization and sequestration occur through divergent molecular mechanisms in myeloid HL-60 cells.","method":"Site-directed mutagenesis, stable expression in HL-60 and COS-7 cells, calcium mobilization assay, ERK2 activity assay, superoxide/respiratory burst assay, internalization assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution via mutagenesis in multiple cell types with multiple orthogonal functional readouts","pmids":["10636859"],"is_preprint":false},{"year":1997,"finding":"The C-terminus of C5aR (CD88) is required for normal ligand-dependent receptor internalization. Truncation of the C-terminus (including major phosphorylation sites) or mutation of a PKC phosphorylation motif in the third cytosolic loop impaired agonist-dependent, staurosporine-sensitive internalization. PMA-induced internalization was independent of these phosphorylation sites, indicating that phorbol ester acts through an indirect effect on the internalization machinery.","method":"Stable transfection of wild-type and C-terminal deletion/point-mutant C5aR in RBL-2H3 and HEK293 cells, receptor internalization assay with pertussis toxin and staurosporine treatments","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis with multiple mechanistic controls in two cell systems","pmids":["9209506"],"is_preprint":false},{"year":1999,"finding":"Chimeric receptor studies between C3aR and C5aR defined structural requirements for ligand binding: the transmembrane regions and second extracellular loop form a functional unit required for signaling; the N-terminus of C5aR is required for high-affinity binding of native C5a but not C5a analogue peptides (two-binding-site model confirmed); C3aR does not require its original N-terminus for high-affinity C3a binding, indicating a different binding mode. Replacement of C3aR N-terminus with C5aR sequence generated a true hybrid receptor responding to both C3a and C5a.","method":"Chimeric receptor construction, transient expression in HEK-293 cells, radioligand binding, calcium mobilization assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic domain-swap mutagenesis with multiple functional readouts","pmids":["10085065"],"is_preprint":false},{"year":2003,"finding":"A positively charged amino acid at position 69 of C5a is crucial for CD88 agonism; replacement by hydrophobic or negatively charged amino acids converted the antagonist jun/fos-A8 to a CD88 agonist. The antagonist A8Δ71–73 blocked C5a and C5adesArg74 binding to both CD88 and C5L2. The cyclic C5a C-terminal peptide AcF-[OP-d-ChaWR] blocked binding to CD88 but not C5L2, demonstrating that the C5a core segment is important for high-affinity binding to C5L2.","method":"Site-directed mutagenesis of C5a, radioligand competition binding to CD88 and C5L2 expressed on monocytes and HMC-1 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis with orthogonal binding assays at both receptors","pmids":["14570896"],"is_preprint":false},{"year":2009,"finding":"In human neutrophils, C5aR (C5aR1) is predominantly expressed on the plasma membrane while C5L2 is predominantly intracellular. Internalized C5aR co-localizes with both C5L2 and β-arrestin by confocal analysis. Antibody blockade of C5L2 dramatically increased C5a-mediated chemotaxis and ERK1/2 phosphorylation without altering calcium mobilization, demonstrating that C5L2 negatively modulates the β-arrestin pathway. C5L2–β-arrestin association was confirmed by co-immunoprecipitation.","method":"Flow cytometry, confocal microscopy, antibody blockade, ERK1/2 phosphorylation assay, calcium mobilization assay, co-immunoprecipitation, chemotaxis assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, confocal localization, and multiple functional readouts in primary human neutrophils","pmids":["20044484"],"is_preprint":false},{"year":2021,"finding":"Monocytes and macrophages constitutively express complement component C5 and generate autocrine C5a via an intracellular C5 convertase. Cholesterol crystal sensing by macrophages induced C5aR1 signaling on mitochondrial membranes, which shifted ATP production via reverse electron chain flux toward reactive oxygen species generation and anaerobic glycolysis, favoring IL-1β production at both the transcriptional level and processing of pro-IL-1β.","method":"Intracellular C5 convertase characterization, mitochondrial fractionation, ROS/glycolysis metabolic assays, IL-1β production assay, cell-permeable C5aR1 antagonist, macrophage-specific C5ar1 knockout mouse, atherosclerosis in vivo model","journal":"Science immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (fractionation, metabolic assays, genetic KO, pharmacological inhibition, in vivo model) in one study","pmids":["34932384"],"is_preprint":false},{"year":2022,"finding":"Intracellular C5 is cleaved by cathepsin D (CTSD) in lysosomes/endosomes of colonic cancer cells to produce C5a. Intracellular C5aR1 assembles a complex with KCTD5/cullin3/Roc-1 and β-catenin, promoting a switch of β-catenin polyubiquitination from K48 to K63 linkage, thereby enhancing β-catenin stability and colorectal tumorigenesis.","method":"Genetic loss-of-function, pharmacological C5aR1 blockade, complex assembly (co-immunoprecipitation), ubiquitination assay, in vivo colorectal tumor model","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP of multi-protein complex, ubiquitination switch assay, in vivo validation with multiple methods","pmids":["35649359"],"is_preprint":false},{"year":2019,"finding":"C5apep (a modified C-terminal fragment of C5a) acts as a full agonist for Gαi coupling (cAMP inhibition, ERK1/2 phosphorylation) but displays partial agonism for β-arrestin recruitment and receptor endocytosis at C5aR1. Both C5a and C5apep responses to neutrophil migration were sensitive to pertussis toxin, placing signaling through Gαi upstream of chemotaxis.","method":"cAMP assay, ERK1/2 phosphorylation, β-arrestin recruitment assay, receptor endocytosis assay, neutrophil migration assay, pertussis toxin treatment, IL-6 secretion assay in human macrophages","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal signaling assays demonstrating functional bias at C5aR1 in primary human cells and transfected systems","pmids":["31036565"],"is_preprint":false},{"year":2013,"finding":"C5a stimulation of C5aR-expressing cancer cells triggered cytoskeletal rearrangement, enhanced cell motility ~3-fold and invasiveness ~13-fold, and increased release of matrix metalloproteinases (MMP) by 2–11-fold. Inhibition of MMP activity abolished the C5a-enhancing effect on cancer cell invasion, placing MMP release downstream of C5aR signaling in promoting invasion.","method":"Time-lapse analysis, Matrigel invasion assay, cytoskeletal rearrangement assay, MMP activity inhibition, in vivo nude mouse implantation","journal":"Clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays in same lab, no independent replication","pmids":["23287562"],"is_preprint":false},{"year":2016,"finding":"C5a receptor (C5aR) promotes gastric cancer cell invasion by activating RhoA; C5a stimulation increased RhoA-GTP (active form), caused cytoskeletal changes (stress fibers, filopodia), and this invasive activity was suppressed by C5aR siRNA knockdown or a C5aR antagonist.","method":"RhoA-GTP pull-down assay, Matrigel invasion assay, siRNA knockdown, C5aR antagonist treatment, cytoskeletal morphology","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RhoA activation assay plus loss-of-function with two methods, single lab","pmids":["27756879"],"is_preprint":false},{"year":2018,"finding":"C5aR1 signaling amplifies IL-6-dependent expression of the transcription factor c-MAF and the cytokine IL-21 via phosphorylation of AKT and activation of mTOR, thereby promoting CD4+ T follicular helper (Tfh) cell differentiation and germinal center B cell responses.","method":"RNA-sequencing, murine and human T cell mechanistic studies, genetic C5aR1 deficiency, pharmacological C5aR1 blockade, AKT/mTOR pathway analysis, GvHD mouse model","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNA-seq guided mechanistic pathway analysis with genetic and pharmacological validation, single lab","pmids":["30568034"],"is_preprint":false},{"year":2018,"finding":"C5aR1 interacts with Toll-like receptor 2 (TLR2) in osteoblasts, as demonstrated by co-immunoprecipitation. C5aR1- and TLR2-signaling pathways converge on activation of p38 MAPK and generation of CXCL10 (an osteoclastogenic chemokine). A whole-genome microarray approach showed C5a activates MAPK pathways and regulates genes in insulin, TGF-β, and AP-1 pathways in osteoblasts.","method":"Co-immunoprecipitation, whole-genome microarray, p38 MAPK activation assay, CXCL10 measurement","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP showing C5aR1-TLR2 interaction with functional downstream readout, single lab","pmids":["30247799"],"is_preprint":false},{"year":2011,"finding":"C5a/CD88 signaling in mouse brain endothelial cells regulates blood-brain barrier integrity via NF-κB-dependent mechanisms: inhibition of CD88 reduced NF-κB translocation into the nucleus, altered ZO-1 distribution at cell interfaces, decreased caspase-3 activity, and prevented apoptosis.","method":"Immunofluorescence, NF-κB translocation assay, ZO-1 localization, DNA laddering, caspase-3 activity assay, CD88 inhibition in vitro","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple mechanistic readouts in cultured endothelial cells, single lab","pmids":["21929539"],"is_preprint":false},{"year":2017,"finding":"C5aR1 signaling on renal tubular epithelial cells enhances expression of terminal α-mannosyl residues (Man), which serve as ligands for type 1 fimbriae of E. coli, thereby facilitating UPEC adhesion. This effect is at least partially dependent on TNF-α driven by C5aR1-mediated intracellular signaling.","method":"C5aR1 genetic deletion and pharmacological inhibition in mice, confocal microscopy (UPEC binding to Man), in vitro C5a stimulation of tubular epithelial cells, bacterial adhesion assay, UPEC colonization quantification","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo KO and in vitro mechanistic studies converging on same pathway, single lab","pmids":["29263309"],"is_preprint":false},{"year":2023,"finding":"C5aR1 signaling drives neutrophil extracellular trap (NET)-dependent immunopathology in COVID-19 lung injury. Genetic and pharmacological inhibition of C5aR1 ameliorated lung immunopathology in SARS-CoV-2-infected K18-hACE2 transgenic mice, with NETs identified as the downstream effector mechanism.","method":"Genetic C5aR1 inhibition, pharmacological C5aR1 antagonism, NET quantification, in vivo SARS-CoV-2 infection model, lung histopathology","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological loss-of-function with defined mechanistic readout (NETs), single lab","pmids":["37104043"],"is_preprint":false},{"year":2024,"finding":"In podocytes in lupus nephritis, C5a upregulates Drp1S616 phosphorylation via C5aR1 signaling, promoting mitochondrial fission, mitochondrial dysfunction, and podocyte injury. C5aR1 knockdown by siRNA substantially suppressed C5a-induced Drp1S616 phosphorylation and mitochondrial fission. C5aR1 inhibitor treatment of lupus-prone mice reduced Drp1S616 phosphorylation and podocyte damage.","method":"siRNA knockdown of C5aR1, Drp1 phosphorylation assay, mitochondrial morphology analysis, in vivo lupus-prone mouse model with C5aR1 inhibitor, proteinuria measurement","journal":"Molecular therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA and pharmacological inhibition with defined phosphorylation mechanistic readout, single lab","pmids":["38449312"],"is_preprint":false},{"year":2017,"finding":"The C5a/C5aR pathway in gastric cancer promotes pathogenesis by activating PI3K/AKT signaling, which suppresses p21/p-p21 expression. C5aR antagonist and PI3K inhibitor both reversed C5a-induced p21 suppression, and C5aR antagonist reduced tumor growth in mice with elevated p21 expression.","method":"Western blotting (PI3K/AKT, p21), C5aR antagonist treatment, PI3K inhibitor treatment, in vitro C5a stimulation, in vivo tumor growth model","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway inhibition with two independent inhibitors and in vivo validation, single lab","pmids":["29031586"],"is_preprint":false},{"year":2016,"finding":"C5a/C5aR pathway in acute liver failure is essential for up-regulating SphK1 expression through p38-MAPK activation: C5a stimulation of macrophages increased p38-MAPK phosphorylation; p38-MAPK inhibitor (SB203580) reduced SphK1 production after C5a stimulation. C5aR blockade significantly downregulated p38-MAPK phosphorylation in vivo and in vitro.","method":"Western blotting (p38-MAPK, SphK1), C5aR antagonist treatment, p38-MAPK inhibitor SB203580, in vivo ALF mouse model, in vitro C5a stimulation of macrophages","journal":"World journal of gastroenterology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition at two pathway nodes with consistent in vitro/in vivo findings, single lab","pmids":["28028363"],"is_preprint":false},{"year":2007,"finding":"C5aR-mediated myocardial ischemia/reperfusion injury involves activation of protein kinase C delta (PKC-δ) and induction of PKC-mediated mitogen-activated protein kinase phosphatase-1 (MKP-1), leading to increased activity of the p42/p44 MAP kinase cascade. Blockade of C5aR also markedly decreased microvascular permeability and leukocyte adherence to coronary artery endothelium.","method":"Anti-C5aR antibody blockade in mice, PKC-δ and MKP-1 activity assays, p42/p44 MAPK assay, microvascular permeability measurement, leukocyte adherence assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo C5aR blockade with defined signaling cascade measurements, single lab","pmids":["17416341"],"is_preprint":false},{"year":2013,"finding":"C5a-induced G-CSF production in LPS-activated macrophages requires signaling through both C5aR (C5aR1) and C5L2; C5a did not enhance G-CSF production in macrophages from either C5aR- or C5L2-deficient mice. The effect was associated with activation of PI3K/Akt and MEK1/2 signaling pathways.","method":"C5aR−/− and C5L2−/− mouse peritoneal macrophages, G-CSF ELISA, PI3K/Akt and MEK1/2 signaling assays, cecal ligation and puncture sepsis model","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO of two receptors with defined pathway readouts, single lab","pmids":["23575697"],"is_preprint":false},{"year":2011,"finding":"PMX-53, established as a potent CD88 (C5aR1) antagonist, also functions as a low-affinity agonist for MrgX2 at concentrations ≥30 nM. Tryptophan and arginine residues in PMX-53 are required for both CD88 antagonism (blocking C5a-induced Ca2+ mobilization in HMC-1) and MrgX2 agonism (degranulation in RBL-2H3/MrgX2 cells). C5a itself does not use MrgX1 or MrgX2 for mast cell degranulation.","method":"Ca2+ mobilization assay in HMC-1 (CD88 antagonism), degranulation assay in RBL-2H3 stably expressing MrgX1 or MrgX2, Ala/dArg substitution mutagenesis of PMX-53","journal":"Molecular pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection with mutagenesis of ligand and multiple cell systems, single lab","pmids":["21441599"],"is_preprint":false},{"year":2022,"finding":"C5a caused RalA-mediated exocytosis of von Willebrand factor (vWF) and P-selectin from Weibel-Palade bodies in microvascular endothelial cells via C5aR1, which favored further vWF binding on the endothelium and platelet adhesion and aggregation, demonstrating the C5a/C5aR1 axis as a direct mediator of endothelial prothrombotic activation.","method":"In vitro and ex vivo endothelial cell assays with C5a/aHUS serum, RalA activation assay, vWF and P-selectin exocytosis assay, platelet adhesion/aggregation assay, microfluidic chamber","journal":"Blood advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic dissection of RalA-mediated exocytosis with multiple vascular functional readouts, single lab","pmids":["34852172"],"is_preprint":false},{"year":2022,"finding":"Blocking the C5a-C5aR pathway on platelets (using antibody-mediated neutralization, IgG depletion, or the Syk inhibitor fostamatinib) reversed COVID-19 plasma-induced platelet hyperactivation and prevented platelet aggregation in endothelial microfluidic chamber conditions, identifying C5a-C5aR as a direct activating pathway on platelets.","method":"Antibody-mediated neutralization, IgG depletion, Syk inhibitor (fostamatinib), platelet activation assay (P-selectin expression), endothelial microfluidic aggregation assay","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection using three orthogonal interventions, single study","pmids":["35309299"],"is_preprint":false},{"year":2018,"finding":"C5aR1 activation mediates an evolutionarily conserved response that promotes cardiomyocyte proliferation after cardiac injury. Pharmacological inhibition of C5aR1 significantly attenuated the cardiomyocyte proliferative response in zebrafish, axolotl, and mice; genetic deletion of C5aR1 in mice also diminished the proliferative response after left ventricular apical resection.","method":"Cross-species transcriptomic screen, C5aR1 genetic deletion (mice), pharmacological C5aR1 inhibition (three species), cardiomyocyte proliferation assay after apical resection","journal":"Circulation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological loss-of-function across three species with defined cellular phenotype (cardiomyocyte proliferation), single lab","pmids":["29348261"],"is_preprint":false},{"year":2024,"finding":"In Schwann cells, C5aR1 activation by C5a activates the NLRP1 inflammasome and triggers subsequent IL-1β release. The released IL-1β recruits macrophages to sciatic/trigeminal nerves, increasing oxidative stress that activates the proalgesic TRPA1 pathway, resulting in widespread pain in a mouse model of endometriosis. Silencing C5aR1 in Schwann cells blocked this cascade.","method":"Schwann cell-specific C5aR1 silencing, NLRP1 inflammasome activation assay, IL-1β measurement, macrophage recruitment assay, oxidative stress assay, TRPA1 pathway assay, in vivo endometriosis pain model","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-specific silencing with defined multi-step mechanistic cascade, single lab","pmids":["39587068"],"is_preprint":false},{"year":2023,"finding":"C5a-C5aR1 induces endoplasmic reticulum stress and activates the PERK-eIF2α-ATF4 pathway in vascular smooth muscle cells (VSMCs), promoting osteogenic transdifferentiation. CREB3L1 was identified as a key downstream mediator of this pathway, promoting COL1α1 expression and accelerating vascular calcification.","method":"In vitro VSMC calcification model, C5aR1 antagonist PMX53 (in vitro and in vivo), ER stress pathway analysis (PERK/eIF2α/ATF4), CREB3L1 knockdown, calcium deposition assay, osteogenic marker expression","journal":"Cardiovascular research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition with defined signaling cascade and downstream mediator, single lab","pmids":["37603848"],"is_preprint":false},{"year":2024,"finding":"Intracellular C5aR1 in glioblastoma suppresses ferroptosis by stabilizing GPX4 expression via METTL3-dependent m6A methylation. ERK1/2 signaling activation by C5aR1 increases METTL3 protein abundance, which enhances m6A stability of GPX4 mRNA, preventing lipid peroxide accumulation and ferroptosis. C5aR1 knockdown induced ferroptosis.","method":"C5aR1 knockdown, ERK1/2 signaling assay, METTL3 m6A methylation assay, GPX4 mRNA stability assay, lipid peroxide accumulation measurement, intracranial xenograft mouse model with PMX205","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway from C5aR1 to m6A modification with in vivo validation, single lab","pmids":["39368999"],"is_preprint":false},{"year":2019,"finding":"VEGFR2 survival and mitotic signaling in endothelial cells requires concurrent C3aR/C5aR1 and IL-6R-gp130 co-signaling. Blockade of C3aR/C5aR1 totally abolished VEGFR2 auto-phosphorylation and downstream Src, ERK, AKT, mTOR, and STAT3 activation. Co-immunoprecipitation, confocal microscopy, ligand pulldown, and BRET assays indicated physical interaction among the four receptors.","method":"Co-immunoprecipitation, confocal microscopy, ligand pulldown, BRET assay, VEGFR2 phosphorylation assay, cell cycle analysis, in vivo retina angiogenesis model","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple physical interaction methods plus functional cascade, single lab","pmids":["30765465"],"is_preprint":false},{"year":2012,"finding":"C5L2 and C5aR form homo- and heterodimers (demonstrated by BRET in transfected HEK 293 cells), stable in the presence of ligand. In adipocytes, C5a stimulation caused C5L2 internalization with perinuclear co-localization with C5aR by confocal microscopy. C5a completely blocked ASP signaling through C5L2 in both C5aRKO and wild-type adipocytes, indicating receptor cross-talk.","method":"BRET (bioluminescence resonance energy transfer), confocal microscopy, C5aRKO adipocytes, Akt/NFκB phosphorylation assay, triglyceride synthesis assay","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — BRET and confocal evidence for dimerization with functional cross-talk, single lab","pmids":["23268185"],"is_preprint":false},{"year":2009,"finding":"CD88 (C5aR1) is expressed on presynaptic terminals of hippocampal mossy fibres in the CA3 region of rat brain; confocal immunolabelling showed high co-localization with presynaptic proteins (synaptophysin, synapsin-1) but not with astrocytes or microglia; electron microscopy confirmed localization to large presynaptic terminals within the stratum lucidum.","method":"Dual-immunolabelling (confocal microscopy), electron microscopy, comparison with astrocyte (GFAP), microglia (IBA1), and presynaptic protein markers","journal":"Journal of neuroinflammation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — confocal and electron microscopy providing definitive subcellular localization, single lab; no direct functional consequence established","pmids":["19917081"],"is_preprint":false},{"year":2014,"finding":"C5aR1 is required for a normal host immune response to Listeria monocytogenes by suppressing type 1 IFN expression; C5aR1−/− mice had elevated serum IFN-α and IFN-β, elevated TRAIL in NK cells, and increased splenocyte apoptosis (elevated caspase-3/TUNEL). Blocking type 1 IFNR in C5aR1−/− mice resulted in near-complete rescue of L. monocytogenes-induced mortality.","method":"C5aR1−/− mice, serum IFN-α/β ELISA, TRAIL expression in NK cells, TUNEL/caspase-3 staining, anti-type 1 IFNR antibody rescue experiment, bacterial burden quantification","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with mechanistic rescue experiment placing type 1 IFN suppression downstream of C5aR1, single lab","pmids":["25297874"],"is_preprint":false},{"year":2017,"finding":"C5aR1 signaling in macrophages promotes C5a production and modulates their immunosuppressive function in colorectal cancer: C5a/C5aR1 signaling recruited MDSCs into the inflamed colorectum to impair CD8+ T cells. Bone marrow transplantation revealed that C5aR1 expression by immune cells was critical for colorectal tumorigenesis.","method":"C5ar1-deficient mice in AOM/DSS colorectal cancer model, flow cytometry, immunohistochemistry, bone marrow transplantation, cytokine/chemokine multiplex assay, C5aR1 antagonist PMX205","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO, bone marrow transplantation, and pharmacological validation, single lab","pmids":["32754267"],"is_preprint":false},{"year":2022,"finding":"Paclitaxel can directly bind and activate C5aR1 (predicted by molecular docking and confirmed by competitive binding assay in vitro), triggering the NFκB/P38 pathway and c-Fos. C5aR1 inhibition or knockout protected from paclitaxel-induced peripheral neuropathy (cold and mechanical allodynia) and reduced hypersensitivity reactions in mice.","method":"Molecular docking, competitive binding assay, NFκB/P38 assay, c-Fos assay, C5aR1 knockout mice, C5aR1 pharmacological inhibition, in vivo CIPN model","journal":"Cell death & disease","confidence":"Low","confidence_rationale":"Tier 3 / Moderate — molecular docking plus competitive binding (without full reconstitution), in vivo phenotype; direct binding not fully reconstituted biochemically","pmids":["35614037"],"is_preprint":false},{"year":1995,"finding":"C5aR (CD88) is expressed on mast cells in a tissue-specific manner: skin mast cells and a subset of cardiac mast cells expressed CD88, whereas lung, uterine, and tonsillar mast cells did not. C5a-induced histamine release from skin mast cells and basophils was inhibited by the anti-CD88 blocking antibody S5/1, demonstrating CD88-mediated signaling in these cells.","method":"Monoclonal antibody immunofluorescence staining, double immunoperoxidase staining (tryptase vs CD88), histamine release assay with anti-CD88 blocking antibody","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional blocking antibody demonstrating CD88-dependent histamine release in primary skin mast cells, replicated across organs","pmids":["7673728"],"is_preprint":false},{"year":1995,"finding":"C5aR is expressed on hepatocytes, lung bronchial and alveolar epithelial cells, and lung vascular smooth muscle and endothelial cells (non-myeloid cells), as demonstrated by immunohistochemistry and ligand-binding studies, expanding known C5aR expression beyond myeloid blood cells.","method":"Immunohistochemistry, radioligand binding studies","journal":"Immunology letters","confidence":"Low","confidence_rationale":"Tier 3 / Moderate — localization by two methods but no direct functional consequence demonstrated in non-myeloid cells","pmids":["7797249"],"is_preprint":false},{"year":1996,"finding":"IFN-γ up-regulates C5aR (CD88) in immature myeloblastic U937, HL-60, and MonoMac6 cells, inducing functional receptor coupling. The induced C5a responsiveness is completely pertussis toxin-sensitive, implicating Gαi. An additional pertussis toxin-resistant pathway exists in U937 after dibutyryl cAMP induction. PMA increases C5aR expression and acts synergistically with IFN-γ.","method":"Radioligand binding, Ca2+ mobilization assay, pertussis toxin treatment, protein kinase C inhibitor (staurosporine), N-acetyl-β-D-glucosaminidase release assay","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays with pharmacological dissection, single lab; replicated across three cell lines","pmids":["7594603"],"is_preprint":false}],"current_model":"C5aR1 (CD88) is a Gαi-coupled seven-transmembrane receptor for the complement anaphylatoxin C5a whose cryo-EM structures reveal a two-site ligand-engagement mechanism (N-terminal extracellular domain for high-affinity native C5a binding; transmembrane core for peptide agonists), position-69 of C5a as the agonist/antagonist switch, and biased signaling through G protein versus β-arrestin pathways controlled by distinct TM7/H8 conformational changes; agonist-induced receptor desensitization is mediated by phosphorylation of Ser334/Ser338 on the C-terminal tail, while C-terminal phosphorylation is dispensable for sequestration; C5aR1 signals through Gαi (pertussis toxin-sensitive) to activate RhoA-dependent cytoskeletal rearrangement and cell invasion, PI3K/AKT, p38-MAPK, ERK1/2, NF-κB, and mTOR pathways in diverse cell types; intracellularly, autocrine C5a generated by a lysosomal C5 convertase (CTSD) engages C5aR1 on mitochondrial membranes of macrophages to drive reverse electron chain ROS and IL-1β production, and on lysosomes of tumor cells to stabilize β-catenin via a K48→K63 ubiquitin switch through a KCTD5/cullin3/Roc-1 complex; C5L2 negatively modulates C5aR1 β-arrestin signaling by forming heterodimers with C5aR1 and acting as an obligate decoy for the β-arrestin pathway, while both receptors are required for G-CSF production; C5aR1 also physically associates with TLR2 in osteoblasts and requires co-signaling from C3aR/C5aR1 and IL-6R-gp130 for VEGFR2-driven endothelial mitogenesis; in Schwann cells, C5aR1 activates the NLRP1 inflammasome/IL-1β/TRPA1 pain axis, and in podocytes it promotes Drp1S616-dependent mitochondrial fission underlying lupus nephritis."},"narrative":{"mechanistic_narrative":"C5aR1 (CD88) is a Gαi-coupled seven-transmembrane receptor for the complement anaphylatoxin C5a that transduces inflammatory, chemotactic, and proliferative signals across myeloid and non-myeloid cell types [PMID:31036565, PMID:7594603]. Cryo-EM structures of the C5a–C5aR1–Gi complex define a two-site engagement mechanism in which the receptor N-terminus mediates high-affinity binding of native C5a while the transmembrane core accommodates peptide agonists, with distinct conformational changes in the intracellular end of TM7 and helix 8 governing agonist recognition and biased signaling [PMID:36806352, PMID:37169960]; this structural framework is corroborated by chimeric-receptor mapping showing that the C5aR1 N-terminus is required for native C5a binding but dispensable for analogue peptides, and by identification of position-69 of C5a as the agonist/antagonist switch [PMID:10085065, PMID:14570896]. Signaling is pertussis toxin-sensitive through Gαi, and individual agonists display bias between G protein coupling and β-arrestin recruitment [PMID:31036565]; agonist-induced desensitization requires phosphorylation of Ser334/Ser338 on the C-terminal tail, whereas receptor sequestration proceeds through a distinct, phosphorylation-independent route [PMID:10636859, PMID:9209506]. Downstream, C5aR1 engages RhoA-dependent cytoskeletal rearrangement and MMP release to drive cell invasion, and PI3K/AKT, p38-MAPK, ERK1/2, NF-κB, and mTOR cascades in diverse contexts [PMID:27756879, PMID:29031586, PMID:23287562]. Beyond the plasma membrane, autocrine C5a generated by intracellular convertases engages C5aR1 on intracellular membranes — on macrophage mitochondria to drive reverse-electron-chain ROS and IL-1β production, and on tumor-cell lysosomes/endosomes (via cathepsin D) where it assembles a KCTD5/cullin3/Roc-1 complex that switches β-catenin polyubiquitination from K48 to K63 to stabilize β-catenin and promote tumorigenesis [PMID:34932384, PMID:35649359]. Receptor function is modulated by the decoy receptor C5L2, which heterodimerizes with C5aR1 and negatively regulates the β-arrestin pathway, with both receptors required for G-CSF production [PMID:20044484, PMID:23268185, PMID:23575697]. C5aR1 additionally physically associates with TLR2 in osteoblasts and participates in C3aR/C5aR1–IL-6R–gp130 co-signaling required for VEGFR2-driven endothelial mitogenesis [PMID:30247799, PMID:30765465]. Through these activities C5aR1 contributes to neutrophil chemotaxis, mast-cell histamine release, thrombotic endothelial activation, inflammasome-driven pain, mitochondrial fission in podocytes, and tissue-injury and tumor pathologies [PMID:7673728, PMID:34852172, PMID:39587068, PMID:38449312].","teleology":[{"year":1995,"claim":"Establishing that C5aR is expressed and functional beyond myeloid blood cells defined the breadth of tissues that respond directly to C5a.","evidence":"Immunohistochemistry, radioligand binding, and anti-CD88 blocking-antibody histamine-release assays in mast cells, hepatocytes, and lung epithelium/endothelium","pmids":["7673728","7797249"],"confidence":"Medium","gaps":["Functional consequences of non-myeloid expression not established in most tissues at the time","Signaling mechanism in these cells not yet defined"]},{"year":1996,"claim":"Identifying IFN-γ-inducible, pertussis toxin-sensitive coupling answered how C5a responsiveness is acquired and which G protein transduces it.","evidence":"Radioligand binding, calcium mobilization, and pertussis toxin treatment in myeloblastic U937/HL-60/MonoMac6 cells","pmids":["7594603"],"confidence":"Medium","gaps":["Identity of the pertussis-toxin-resistant pathway not resolved","Downstream effectors of Gαi not yet mapped"]},{"year":1997,"claim":"Defining the C-terminal tail and a third-loop PKC motif as required for internalization separated the structural determinants of receptor trafficking from those of signaling.","evidence":"C-terminal truncation/point-mutant C5aR stably expressed in RBL-2H3 and HEK293 with internalization assays plus pertussis toxin and staurosporine controls","pmids":["9209506"],"confidence":"High","gaps":["Did not identify the specific phosphorylated residues","PMA-induced internalization mechanism left indirect"]},{"year":1999,"claim":"Chimeric-receptor mapping resolved the two-binding-site model, showing the N-terminus is required for native C5a but not peptide agonist binding.","evidence":"C3aR/C5aR domain-swap constructs in HEK293 with radioligand binding and calcium mobilization","pmids":["10085065"],"confidence":"High","gaps":["Atomic-resolution view of the binding sites not yet available","Did not address biased signaling"]},{"year":2000,"claim":"Pinpointing Ser334/Ser338 phosphorylation as the desensitization signal — distinct from sequestration — clarified how agonist-induced receptor shutoff is controlled.","evidence":"Site-directed mutagenesis in HL-60/COS-7 with calcium, ERK2, superoxide, and internalization readouts","pmids":["10636859"],"confidence":"High","gaps":["Kinases responsible for these phosphorylations not identified","Link between phosphorylation and β-arrestin recruitment not established here"]},{"year":2003,"claim":"Identifying position-69 of C5a as the agonism switch and dissecting differential binding to CD88 versus C5L2 defined the ligand determinants of receptor selectivity.","evidence":"Site-directed mutagenesis of C5a with radioligand competition binding at CD88 and C5L2 on monocytes/HMC-1","pmids":["14570896"],"confidence":"High","gaps":["Structural basis of the switch not yet visualized","Downstream signaling consequences of the switch not characterized"]},{"year":2009,"claim":"Demonstrating that C5L2 negatively modulates the β-arrestin pathway and resides largely intracellularly explained how a second receptor tunes C5a output without affecting calcium signaling.","evidence":"Flow cytometry, confocal, antibody blockade, ERK1/2 and calcium assays, and reciprocal Co-IP in primary human neutrophils","pmids":["20044484"],"confidence":"High","gaps":["Stoichiometry of C5aR1–C5L2 heterodimers not quantified","Mechanism by which C5L2 sequesters β-arrestin not resolved"]},{"year":2012,"claim":"Showing C5L2–C5aR homo/heterodimerization and ligand-induced cross-talk established a physical basis for the decoy/modulatory relationship.","evidence":"BRET and confocal microscopy in HEK293 and C5aRKO adipocytes with Akt/NF-κB and triglyceride readouts","pmids":["23268185"],"confidence":"Medium","gaps":["BRET dimerization not confirmed at endogenous expression","Functional dimer interface not mapped"]},{"year":2013,"claim":"Genetic dissection established that both C5aR1 and C5L2 are required together for C5a-driven G-CSF production, and that C5aR1 drives RhoA-dependent invasion.","evidence":"C5aR−/− and C5L2−/− macrophages with G-CSF ELISA and PI3K/Akt/MEK assays; RhoA-GTP pull-down and invasion assays in cancer cells","pmids":["23575697","23287562"],"confidence":"Medium","gaps":["Molecular basis of the C5aR1/C5L2 co-requirement not defined","Invasion findings from single labs without independent replication"]},{"year":2019,"claim":"Quantitative bias profiling and identification of receptor co-signaling requirements clarified how distinct agonists and partner receptors shape C5aR1 output.","evidence":"cAMP, ERK, β-arrestin, and endocytosis assays with C5apep; Co-IP, BRET, and VEGFR2 phosphorylation for C3aR/C5aR1–IL-6R–gp130 co-signaling","pmids":["31036565","30765465"],"confidence":"Medium","gaps":["Structural basis of bias not yet linked to receptor conformation","Direct versus indirect nature of the four-receptor association not fully separated"]},{"year":2021,"claim":"Discovery of intracellular autocrine C5a acting on mitochondrial C5aR1 redefined the receptor as an organelle-localized signaling hub controlling macrophage metabolism and IL-1β.","evidence":"Intracellular convertase characterization, mitochondrial fractionation, metabolic/ROS assays, cell-permeable antagonist, macrophage-specific C5ar1 KO, and atherosclerosis model","pmids":["34932384"],"confidence":"High","gaps":["Mechanism of C5aR1 trafficking to mitochondria not defined","How mitochondrial C5aR1 couples to ROS machinery not resolved"]},{"year":2022,"claim":"Defining a lysosomal CTSD-generated C5a–C5aR1–KCTD5/cullin3/Roc-1 axis that switches β-catenin ubiquitination established a non-canonical intracellular signaling output driving tumorigenesis.","evidence":"Genetic loss-of-function, pharmacological blockade, Co-IP of the multiprotein complex, ubiquitination assays, and in vivo colorectal tumor model","pmids":["35649359"],"confidence":"High","gaps":["Determinants of C5aR1 lysosomal localization not defined","Generality across other Wnt-driven tumors not established"]},{"year":2023,"claim":"Cryo-EM structures of the C5a–C5aR1–Gi complex with multiple agonists and a converting mutant provided the atomic framework for orthosteric ligand recognition, activation, and biased signaling.","evidence":"Cryo-EM of wild-type and I116A-mutant C5aR1–Gi complexes with C5a, C5apep, and BM213, plus site-directed mutagenesis and pharmacological assays","pmids":["36806352","37169960"],"confidence":"High","gaps":["β-arrestin-coupled structure not resolved","Conformational basis of receptor-tail phosphorylation not visualized"]},{"year":2024,"claim":"Linking C5aR1 to mitochondrial fission, inflammasome-driven pain, and m6A-dependent ferroptosis suppression extended the receptor into organelle-level and disease-specific effector mechanisms.","evidence":"siRNA/pharmacological inhibition with Drp1S616, NLRP1/IL-1β/TRPA1, and ERK1/2–METTL3–GPX4 readouts in podocyte, Schwann-cell, and glioblastoma models","pmids":["38449312","39587068","39368999"],"confidence":"Medium","gaps":["Each mechanism shown in a single disease context by one lab","Connection between receptor activation and these distinct downstream nodes not unified"]},{"year":null,"claim":"How a single receptor selects among plasma-membrane Gαi/β-arrestin signaling versus its distinct mitochondrial and lysosomal intracellular programs remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Trafficking determinants directing C5aR1 to mitochondria versus lysosomes unknown","No structural model for intracellular complex assembly (e.g., with KCTD5/cullin3)","How biased agonism integrates with organelle-specific outputs unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[0,1,4,5]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,9,37]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[6,31,35]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[7]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[8]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[7,21,32,33]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,9,11,18,29]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[8,16,17,27,28]},{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[23,24]}],"complexes":["C5aR1–C5L2 heterodimer","intracellular C5aR1–KCTD5/cullin3/Roc-1–β-catenin complex","C5aR1–TLR2","C3aR/C5aR1–IL-6R–gp130–VEGFR2 co-signaling cluster"],"partners":["C5L2","ARRB","TLR2","KCTD5","CUL3","CTNNB1","VEGFR2","IL6R"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P21730","full_name":"C5a anaphylatoxin chemotactic receptor 1","aliases":["C5a anaphylatoxin chemotactic receptor","C5a-R","C5aR"],"length_aa":350,"mass_kda":39.3,"function":"Receptor for the chemotactic and inflammatory peptide anaphylatoxin C5a, stimulating chemotaxis, granule enzyme release, intracellular calcium release and superoxide anion production (PubMed:10636859, PubMed:15153520, PubMed:1847994, PubMed:29300009, PubMed:36806352, PubMed:7622471, PubMed:8182049, PubMed:9553099). Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of downstream effectors, such as adenylate cyclase (PubMed:36806352, PubMed:37852260). C5AR1 is coupled to G(i)/G(o) (GNAI1 or GNAO1) G alpha proteins and mediates inhibition of adenylate cyclase (PubMed:36806352, PubMed:37852260). The ligand interacts with at least two sites on the receptor: a high-affinity site on the extracellular N-terminus, and a second site in the transmembrane region which activates downstream signaling events (PubMed:7622471, PubMed:8182049, PubMed:9553099)","subcellular_location":"Cell membrane; Cytoplasmic vesicle","url":"https://www.uniprot.org/uniprotkb/P21730/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/C5AR1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/C5AR1","total_profiled":1310},"omim":[{"mim_id":"614257","title":"CHROMOSOME 20q11-q12 DELETION SYNDROME","url":"https://www.omim.org/entry/614257"},{"mim_id":"609949","title":"COMPLEMENT COMPONENT 5a RECEPTOR 2; C5AR2","url":"https://www.omim.org/entry/609949"},{"mim_id":"606416","title":"NLR FAMILY, PYRIN DOMAIN-CONTAINING 3; NLRP3","url":"https://www.omim.org/entry/606416"},{"mim_id":"230800","title":"GAUCHER DISEASE, TYPE I; GD1","url":"https://www.omim.org/entry/230800"},{"mim_id":"147720","title":"INTERLEUKIN 1-BETA; IL1B","url":"https://www.omim.org/entry/147720"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"bone marrow","ntpm":118.4},{"tissue":"lymphoid tissue","ntpm":80.0}],"url":"https://www.proteinatlas.org/search/C5AR1"},"hgnc":{"alias_symbol":["C5A","C5AR","CD88"],"prev_symbol":["C5R1"]},"alphafold":{"accession":"P21730","domains":[{"cath_id":"1.20.1070.10","chopping":"36-325","consensus_level":"high","plddt":93.0356,"start":36,"end":325}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P21730","model_url":"https://alphafold.ebi.ac.uk/files/AF-P21730-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P21730-F1-predicted_aligned_error_v6.png","plddt_mean":85.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=C5AR1","jax_strain_url":"https://www.jax.org/strain/search?query=C5AR1"},"sequence":{"accession":"P21730","fasta_url":"https://rest.uniprot.org/uniprotkb/P21730.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P21730/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P21730"}},"corpus_meta":[{"pmid":"24179165","id":"PMC_24179165","title":"C5a receptor (CD88) blockade protects against MPO-ANCA GN.","date":"2013","source":"Journal of the American Society of Nephrology : JASN","url":"https://pubmed.ncbi.nlm.nih.gov/24179165","citation_count":278,"is_preprint":false},{"pmid":"20044484","id":"PMC_20044484","title":"The C5a receptor (C5aR) C5L2 is a modulator of C5aR-mediated signal transduction.","date":"2009","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20044484","citation_count":208,"is_preprint":false},{"pmid":"9006319","id":"PMC_9006319","title":"Expression of the receptor for complement C5a (CD88) is up-regulated on reactive astrocytes, microglia, and endothelial cells in the inflamed human central nervous system.","date":"1997","source":"The American journal of pathology","url":"https://pubmed.ncbi.nlm.nih.gov/9006319","citation_count":205,"is_preprint":false},{"pmid":"34932384","id":"PMC_34932384","title":"Mitochondrial C5aR1 activity in macrophages controls IL-1β production underlying sterile inflammation.","date":"2021","source":"Science immunology","url":"https://pubmed.ncbi.nlm.nih.gov/34932384","citation_count":134,"is_preprint":false},{"pmid":"18227853","id":"PMC_18227853","title":"Receptors for complement C5a. 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\"discoveries\": [\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structures of activated wild-type C5aR1–Gi protein complex bound to C5a, the hexapeptidic agonist C5apep, and the G protein-biased agonist BM213 revealed the landscape of C5a–C5aR1 interaction, a common motif for recognition of diverse orthosteric ligands, and unusual conformational changes in the intracellular end of transmembrane domain 7 and helix 8 upon agonist binding. Mutagenesis and cell-based pharmacological assays deciphered a framework for biased signaling; the structure of a C5aR1-I116A mutant–Gi complex induced by C089 (an antagonist on wild-type C5aR1) revealed the activation mechanism.\",\n      \"method\": \"Cryo-electron microscopy, site-directed mutagenesis, cell-based pharmacological assays\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple cryo-EM structures with mutagenesis and functional validation in one study\",\n      \"pmids\": [\"36806352\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Structures of C5a-bound C5aR1 (and C3a-bound C3aR) were solved, revealing a conserved recognition pattern of anaphylatoxins to complement receptors distinct from chemokine receptors, unique pocket topologies mediating ligand selectivity, and a common mechanism of receptor activation. Combined with mutagenesis analysis.\",\n      \"method\": \"Cryo-EM structure determination, mutagenesis analysis\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — independent structural study with mutagenesis, corroborating the Cell Research structures\",\n      \"pmids\": [\"37169960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Ser334 is a key residue controlling C5aR phosphorylation; phosphorylation of either the Ser332/Ser334 or Ser334/Ser338 pair is critical for receptor desensitization. Phosphorylation of Ser334 and Ser338 is critical and sufficient for C5aR desensitization. The non-phosphorylatable S332A/S334A mutant triggered a 1.8–2-fold higher superoxide production. Receptor desensitization and sequestration occur through divergent molecular mechanisms in myeloid HL-60 cells.\",\n      \"method\": \"Site-directed mutagenesis, stable expression in HL-60 and COS-7 cells, calcium mobilization assay, ERK2 activity assay, superoxide/respiratory burst assay, internalization assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution via mutagenesis in multiple cell types with multiple orthogonal functional readouts\",\n      \"pmids\": [\"10636859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The C-terminus of C5aR (CD88) is required for normal ligand-dependent receptor internalization. Truncation of the C-terminus (including major phosphorylation sites) or mutation of a PKC phosphorylation motif in the third cytosolic loop impaired agonist-dependent, staurosporine-sensitive internalization. PMA-induced internalization was independent of these phosphorylation sites, indicating that phorbol ester acts through an indirect effect on the internalization machinery.\",\n      \"method\": \"Stable transfection of wild-type and C-terminal deletion/point-mutant C5aR in RBL-2H3 and HEK293 cells, receptor internalization assay with pertussis toxin and staurosporine treatments\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis with multiple mechanistic controls in two cell systems\",\n      \"pmids\": [\"9209506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Chimeric receptor studies between C3aR and C5aR defined structural requirements for ligand binding: the transmembrane regions and second extracellular loop form a functional unit required for signaling; the N-terminus of C5aR is required for high-affinity binding of native C5a but not C5a analogue peptides (two-binding-site model confirmed); C3aR does not require its original N-terminus for high-affinity C3a binding, indicating a different binding mode. Replacement of C3aR N-terminus with C5aR sequence generated a true hybrid receptor responding to both C3a and C5a.\",\n      \"method\": \"Chimeric receptor construction, transient expression in HEK-293 cells, radioligand binding, calcium mobilization assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic domain-swap mutagenesis with multiple functional readouts\",\n      \"pmids\": [\"10085065\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"A positively charged amino acid at position 69 of C5a is crucial for CD88 agonism; replacement by hydrophobic or negatively charged amino acids converted the antagonist jun/fos-A8 to a CD88 agonist. The antagonist A8Δ71–73 blocked C5a and C5adesArg74 binding to both CD88 and C5L2. The cyclic C5a C-terminal peptide AcF-[OP-d-ChaWR] blocked binding to CD88 but not C5L2, demonstrating that the C5a core segment is important for high-affinity binding to C5L2.\",\n      \"method\": \"Site-directed mutagenesis of C5a, radioligand competition binding to CD88 and C5L2 expressed on monocytes and HMC-1 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis with orthogonal binding assays at both receptors\",\n      \"pmids\": [\"14570896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In human neutrophils, C5aR (C5aR1) is predominantly expressed on the plasma membrane while C5L2 is predominantly intracellular. Internalized C5aR co-localizes with both C5L2 and β-arrestin by confocal analysis. Antibody blockade of C5L2 dramatically increased C5a-mediated chemotaxis and ERK1/2 phosphorylation without altering calcium mobilization, demonstrating that C5L2 negatively modulates the β-arrestin pathway. C5L2–β-arrestin association was confirmed by co-immunoprecipitation.\",\n      \"method\": \"Flow cytometry, confocal microscopy, antibody blockade, ERK1/2 phosphorylation assay, calcium mobilization assay, co-immunoprecipitation, chemotaxis assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, confocal localization, and multiple functional readouts in primary human neutrophils\",\n      \"pmids\": [\"20044484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Monocytes and macrophages constitutively express complement component C5 and generate autocrine C5a via an intracellular C5 convertase. Cholesterol crystal sensing by macrophages induced C5aR1 signaling on mitochondrial membranes, which shifted ATP production via reverse electron chain flux toward reactive oxygen species generation and anaerobic glycolysis, favoring IL-1β production at both the transcriptional level and processing of pro-IL-1β.\",\n      \"method\": \"Intracellular C5 convertase characterization, mitochondrial fractionation, ROS/glycolysis metabolic assays, IL-1β production assay, cell-permeable C5aR1 antagonist, macrophage-specific C5ar1 knockout mouse, atherosclerosis in vivo model\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (fractionation, metabolic assays, genetic KO, pharmacological inhibition, in vivo model) in one study\",\n      \"pmids\": [\"34932384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Intracellular C5 is cleaved by cathepsin D (CTSD) in lysosomes/endosomes of colonic cancer cells to produce C5a. Intracellular C5aR1 assembles a complex with KCTD5/cullin3/Roc-1 and β-catenin, promoting a switch of β-catenin polyubiquitination from K48 to K63 linkage, thereby enhancing β-catenin stability and colorectal tumorigenesis.\",\n      \"method\": \"Genetic loss-of-function, pharmacological C5aR1 blockade, complex assembly (co-immunoprecipitation), ubiquitination assay, in vivo colorectal tumor model\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP of multi-protein complex, ubiquitination switch assay, in vivo validation with multiple methods\",\n      \"pmids\": [\"35649359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"C5apep (a modified C-terminal fragment of C5a) acts as a full agonist for Gαi coupling (cAMP inhibition, ERK1/2 phosphorylation) but displays partial agonism for β-arrestin recruitment and receptor endocytosis at C5aR1. Both C5a and C5apep responses to neutrophil migration were sensitive to pertussis toxin, placing signaling through Gαi upstream of chemotaxis.\",\n      \"method\": \"cAMP assay, ERK1/2 phosphorylation, β-arrestin recruitment assay, receptor endocytosis assay, neutrophil migration assay, pertussis toxin treatment, IL-6 secretion assay in human macrophages\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal signaling assays demonstrating functional bias at C5aR1 in primary human cells and transfected systems\",\n      \"pmids\": [\"31036565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"C5a stimulation of C5aR-expressing cancer cells triggered cytoskeletal rearrangement, enhanced cell motility ~3-fold and invasiveness ~13-fold, and increased release of matrix metalloproteinases (MMP) by 2–11-fold. Inhibition of MMP activity abolished the C5a-enhancing effect on cancer cell invasion, placing MMP release downstream of C5aR signaling in promoting invasion.\",\n      \"method\": \"Time-lapse analysis, Matrigel invasion assay, cytoskeletal rearrangement assay, MMP activity inhibition, in vivo nude mouse implantation\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays in same lab, no independent replication\",\n      \"pmids\": [\"23287562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"C5a receptor (C5aR) promotes gastric cancer cell invasion by activating RhoA; C5a stimulation increased RhoA-GTP (active form), caused cytoskeletal changes (stress fibers, filopodia), and this invasive activity was suppressed by C5aR siRNA knockdown or a C5aR antagonist.\",\n      \"method\": \"RhoA-GTP pull-down assay, Matrigel invasion assay, siRNA knockdown, C5aR antagonist treatment, cytoskeletal morphology\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RhoA activation assay plus loss-of-function with two methods, single lab\",\n      \"pmids\": [\"27756879\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"C5aR1 signaling amplifies IL-6-dependent expression of the transcription factor c-MAF and the cytokine IL-21 via phosphorylation of AKT and activation of mTOR, thereby promoting CD4+ T follicular helper (Tfh) cell differentiation and germinal center B cell responses.\",\n      \"method\": \"RNA-sequencing, murine and human T cell mechanistic studies, genetic C5aR1 deficiency, pharmacological C5aR1 blockade, AKT/mTOR pathway analysis, GvHD mouse model\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA-seq guided mechanistic pathway analysis with genetic and pharmacological validation, single lab\",\n      \"pmids\": [\"30568034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"C5aR1 interacts with Toll-like receptor 2 (TLR2) in osteoblasts, as demonstrated by co-immunoprecipitation. C5aR1- and TLR2-signaling pathways converge on activation of p38 MAPK and generation of CXCL10 (an osteoclastogenic chemokine). A whole-genome microarray approach showed C5a activates MAPK pathways and regulates genes in insulin, TGF-β, and AP-1 pathways in osteoblasts.\",\n      \"method\": \"Co-immunoprecipitation, whole-genome microarray, p38 MAPK activation assay, CXCL10 measurement\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP showing C5aR1-TLR2 interaction with functional downstream readout, single lab\",\n      \"pmids\": [\"30247799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"C5a/CD88 signaling in mouse brain endothelial cells regulates blood-brain barrier integrity via NF-κB-dependent mechanisms: inhibition of CD88 reduced NF-κB translocation into the nucleus, altered ZO-1 distribution at cell interfaces, decreased caspase-3 activity, and prevented apoptosis.\",\n      \"method\": \"Immunofluorescence, NF-κB translocation assay, ZO-1 localization, DNA laddering, caspase-3 activity assay, CD88 inhibition in vitro\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple mechanistic readouts in cultured endothelial cells, single lab\",\n      \"pmids\": [\"21929539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"C5aR1 signaling on renal tubular epithelial cells enhances expression of terminal α-mannosyl residues (Man), which serve as ligands for type 1 fimbriae of E. coli, thereby facilitating UPEC adhesion. This effect is at least partially dependent on TNF-α driven by C5aR1-mediated intracellular signaling.\",\n      \"method\": \"C5aR1 genetic deletion and pharmacological inhibition in mice, confocal microscopy (UPEC binding to Man), in vitro C5a stimulation of tubular epithelial cells, bacterial adhesion assay, UPEC colonization quantification\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo KO and in vitro mechanistic studies converging on same pathway, single lab\",\n      \"pmids\": [\"29263309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"C5aR1 signaling drives neutrophil extracellular trap (NET)-dependent immunopathology in COVID-19 lung injury. Genetic and pharmacological inhibition of C5aR1 ameliorated lung immunopathology in SARS-CoV-2-infected K18-hACE2 transgenic mice, with NETs identified as the downstream effector mechanism.\",\n      \"method\": \"Genetic C5aR1 inhibition, pharmacological C5aR1 antagonism, NET quantification, in vivo SARS-CoV-2 infection model, lung histopathology\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological loss-of-function with defined mechanistic readout (NETs), single lab\",\n      \"pmids\": [\"37104043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In podocytes in lupus nephritis, C5a upregulates Drp1S616 phosphorylation via C5aR1 signaling, promoting mitochondrial fission, mitochondrial dysfunction, and podocyte injury. C5aR1 knockdown by siRNA substantially suppressed C5a-induced Drp1S616 phosphorylation and mitochondrial fission. C5aR1 inhibitor treatment of lupus-prone mice reduced Drp1S616 phosphorylation and podocyte damage.\",\n      \"method\": \"siRNA knockdown of C5aR1, Drp1 phosphorylation assay, mitochondrial morphology analysis, in vivo lupus-prone mouse model with C5aR1 inhibitor, proteinuria measurement\",\n      \"journal\": \"Molecular therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA and pharmacological inhibition with defined phosphorylation mechanistic readout, single lab\",\n      \"pmids\": [\"38449312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The C5a/C5aR pathway in gastric cancer promotes pathogenesis by activating PI3K/AKT signaling, which suppresses p21/p-p21 expression. C5aR antagonist and PI3K inhibitor both reversed C5a-induced p21 suppression, and C5aR antagonist reduced tumor growth in mice with elevated p21 expression.\",\n      \"method\": \"Western blotting (PI3K/AKT, p21), C5aR antagonist treatment, PI3K inhibitor treatment, in vitro C5a stimulation, in vivo tumor growth model\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway inhibition with two independent inhibitors and in vivo validation, single lab\",\n      \"pmids\": [\"29031586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"C5a/C5aR pathway in acute liver failure is essential for up-regulating SphK1 expression through p38-MAPK activation: C5a stimulation of macrophages increased p38-MAPK phosphorylation; p38-MAPK inhibitor (SB203580) reduced SphK1 production after C5a stimulation. C5aR blockade significantly downregulated p38-MAPK phosphorylation in vivo and in vitro.\",\n      \"method\": \"Western blotting (p38-MAPK, SphK1), C5aR antagonist treatment, p38-MAPK inhibitor SB203580, in vivo ALF mouse model, in vitro C5a stimulation of macrophages\",\n      \"journal\": \"World journal of gastroenterology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition at two pathway nodes with consistent in vitro/in vivo findings, single lab\",\n      \"pmids\": [\"28028363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"C5aR-mediated myocardial ischemia/reperfusion injury involves activation of protein kinase C delta (PKC-δ) and induction of PKC-mediated mitogen-activated protein kinase phosphatase-1 (MKP-1), leading to increased activity of the p42/p44 MAP kinase cascade. Blockade of C5aR also markedly decreased microvascular permeability and leukocyte adherence to coronary artery endothelium.\",\n      \"method\": \"Anti-C5aR antibody blockade in mice, PKC-δ and MKP-1 activity assays, p42/p44 MAPK assay, microvascular permeability measurement, leukocyte adherence assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo C5aR blockade with defined signaling cascade measurements, single lab\",\n      \"pmids\": [\"17416341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"C5a-induced G-CSF production in LPS-activated macrophages requires signaling through both C5aR (C5aR1) and C5L2; C5a did not enhance G-CSF production in macrophages from either C5aR- or C5L2-deficient mice. The effect was associated with activation of PI3K/Akt and MEK1/2 signaling pathways.\",\n      \"method\": \"C5aR−/− and C5L2−/− mouse peritoneal macrophages, G-CSF ELISA, PI3K/Akt and MEK1/2 signaling assays, cecal ligation and puncture sepsis model\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO of two receptors with defined pathway readouts, single lab\",\n      \"pmids\": [\"23575697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PMX-53, established as a potent CD88 (C5aR1) antagonist, also functions as a low-affinity agonist for MrgX2 at concentrations ≥30 nM. Tryptophan and arginine residues in PMX-53 are required for both CD88 antagonism (blocking C5a-induced Ca2+ mobilization in HMC-1) and MrgX2 agonism (degranulation in RBL-2H3/MrgX2 cells). C5a itself does not use MrgX1 or MrgX2 for mast cell degranulation.\",\n      \"method\": \"Ca2+ mobilization assay in HMC-1 (CD88 antagonism), degranulation assay in RBL-2H3 stably expressing MrgX1 or MrgX2, Ala/dArg substitution mutagenesis of PMX-53\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection with mutagenesis of ligand and multiple cell systems, single lab\",\n      \"pmids\": [\"21441599\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"C5a caused RalA-mediated exocytosis of von Willebrand factor (vWF) and P-selectin from Weibel-Palade bodies in microvascular endothelial cells via C5aR1, which favored further vWF binding on the endothelium and platelet adhesion and aggregation, demonstrating the C5a/C5aR1 axis as a direct mediator of endothelial prothrombotic activation.\",\n      \"method\": \"In vitro and ex vivo endothelial cell assays with C5a/aHUS serum, RalA activation assay, vWF and P-selectin exocytosis assay, platelet adhesion/aggregation assay, microfluidic chamber\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic dissection of RalA-mediated exocytosis with multiple vascular functional readouts, single lab\",\n      \"pmids\": [\"34852172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Blocking the C5a-C5aR pathway on platelets (using antibody-mediated neutralization, IgG depletion, or the Syk inhibitor fostamatinib) reversed COVID-19 plasma-induced platelet hyperactivation and prevented platelet aggregation in endothelial microfluidic chamber conditions, identifying C5a-C5aR as a direct activating pathway on platelets.\",\n      \"method\": \"Antibody-mediated neutralization, IgG depletion, Syk inhibitor (fostamatinib), platelet activation assay (P-selectin expression), endothelial microfluidic aggregation assay\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection using three orthogonal interventions, single study\",\n      \"pmids\": [\"35309299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"C5aR1 activation mediates an evolutionarily conserved response that promotes cardiomyocyte proliferation after cardiac injury. Pharmacological inhibition of C5aR1 significantly attenuated the cardiomyocyte proliferative response in zebrafish, axolotl, and mice; genetic deletion of C5aR1 in mice also diminished the proliferative response after left ventricular apical resection.\",\n      \"method\": \"Cross-species transcriptomic screen, C5aR1 genetic deletion (mice), pharmacological C5aR1 inhibition (three species), cardiomyocyte proliferation assay after apical resection\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological loss-of-function across three species with defined cellular phenotype (cardiomyocyte proliferation), single lab\",\n      \"pmids\": [\"29348261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In Schwann cells, C5aR1 activation by C5a activates the NLRP1 inflammasome and triggers subsequent IL-1β release. The released IL-1β recruits macrophages to sciatic/trigeminal nerves, increasing oxidative stress that activates the proalgesic TRPA1 pathway, resulting in widespread pain in a mouse model of endometriosis. Silencing C5aR1 in Schwann cells blocked this cascade.\",\n      \"method\": \"Schwann cell-specific C5aR1 silencing, NLRP1 inflammasome activation assay, IL-1β measurement, macrophage recruitment assay, oxidative stress assay, TRPA1 pathway assay, in vivo endometriosis pain model\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-specific silencing with defined multi-step mechanistic cascade, single lab\",\n      \"pmids\": [\"39587068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"C5a-C5aR1 induces endoplasmic reticulum stress and activates the PERK-eIF2α-ATF4 pathway in vascular smooth muscle cells (VSMCs), promoting osteogenic transdifferentiation. CREB3L1 was identified as a key downstream mediator of this pathway, promoting COL1α1 expression and accelerating vascular calcification.\",\n      \"method\": \"In vitro VSMC calcification model, C5aR1 antagonist PMX53 (in vitro and in vivo), ER stress pathway analysis (PERK/eIF2α/ATF4), CREB3L1 knockdown, calcium deposition assay, osteogenic marker expression\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition with defined signaling cascade and downstream mediator, single lab\",\n      \"pmids\": [\"37603848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Intracellular C5aR1 in glioblastoma suppresses ferroptosis by stabilizing GPX4 expression via METTL3-dependent m6A methylation. ERK1/2 signaling activation by C5aR1 increases METTL3 protein abundance, which enhances m6A stability of GPX4 mRNA, preventing lipid peroxide accumulation and ferroptosis. C5aR1 knockdown induced ferroptosis.\",\n      \"method\": \"C5aR1 knockdown, ERK1/2 signaling assay, METTL3 m6A methylation assay, GPX4 mRNA stability assay, lipid peroxide accumulation measurement, intracranial xenograft mouse model with PMX205\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway from C5aR1 to m6A modification with in vivo validation, single lab\",\n      \"pmids\": [\"39368999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"VEGFR2 survival and mitotic signaling in endothelial cells requires concurrent C3aR/C5aR1 and IL-6R-gp130 co-signaling. Blockade of C3aR/C5aR1 totally abolished VEGFR2 auto-phosphorylation and downstream Src, ERK, AKT, mTOR, and STAT3 activation. Co-immunoprecipitation, confocal microscopy, ligand pulldown, and BRET assays indicated physical interaction among the four receptors.\",\n      \"method\": \"Co-immunoprecipitation, confocal microscopy, ligand pulldown, BRET assay, VEGFR2 phosphorylation assay, cell cycle analysis, in vivo retina angiogenesis model\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple physical interaction methods plus functional cascade, single lab\",\n      \"pmids\": [\"30765465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"C5L2 and C5aR form homo- and heterodimers (demonstrated by BRET in transfected HEK 293 cells), stable in the presence of ligand. In adipocytes, C5a stimulation caused C5L2 internalization with perinuclear co-localization with C5aR by confocal microscopy. C5a completely blocked ASP signaling through C5L2 in both C5aRKO and wild-type adipocytes, indicating receptor cross-talk.\",\n      \"method\": \"BRET (bioluminescence resonance energy transfer), confocal microscopy, C5aRKO adipocytes, Akt/NFκB phosphorylation assay, triglyceride synthesis assay\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — BRET and confocal evidence for dimerization with functional cross-talk, single lab\",\n      \"pmids\": [\"23268185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CD88 (C5aR1) is expressed on presynaptic terminals of hippocampal mossy fibres in the CA3 region of rat brain; confocal immunolabelling showed high co-localization with presynaptic proteins (synaptophysin, synapsin-1) but not with astrocytes or microglia; electron microscopy confirmed localization to large presynaptic terminals within the stratum lucidum.\",\n      \"method\": \"Dual-immunolabelling (confocal microscopy), electron microscopy, comparison with astrocyte (GFAP), microglia (IBA1), and presynaptic protein markers\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — confocal and electron microscopy providing definitive subcellular localization, single lab; no direct functional consequence established\",\n      \"pmids\": [\"19917081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"C5aR1 is required for a normal host immune response to Listeria monocytogenes by suppressing type 1 IFN expression; C5aR1−/− mice had elevated serum IFN-α and IFN-β, elevated TRAIL in NK cells, and increased splenocyte apoptosis (elevated caspase-3/TUNEL). Blocking type 1 IFNR in C5aR1−/− mice resulted in near-complete rescue of L. monocytogenes-induced mortality.\",\n      \"method\": \"C5aR1−/− mice, serum IFN-α/β ELISA, TRAIL expression in NK cells, TUNEL/caspase-3 staining, anti-type 1 IFNR antibody rescue experiment, bacterial burden quantification\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with mechanistic rescue experiment placing type 1 IFN suppression downstream of C5aR1, single lab\",\n      \"pmids\": [\"25297874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"C5aR1 signaling in macrophages promotes C5a production and modulates their immunosuppressive function in colorectal cancer: C5a/C5aR1 signaling recruited MDSCs into the inflamed colorectum to impair CD8+ T cells. Bone marrow transplantation revealed that C5aR1 expression by immune cells was critical for colorectal tumorigenesis.\",\n      \"method\": \"C5ar1-deficient mice in AOM/DSS colorectal cancer model, flow cytometry, immunohistochemistry, bone marrow transplantation, cytokine/chemokine multiplex assay, C5aR1 antagonist PMX205\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO, bone marrow transplantation, and pharmacological validation, single lab\",\n      \"pmids\": [\"32754267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Paclitaxel can directly bind and activate C5aR1 (predicted by molecular docking and confirmed by competitive binding assay in vitro), triggering the NFκB/P38 pathway and c-Fos. C5aR1 inhibition or knockout protected from paclitaxel-induced peripheral neuropathy (cold and mechanical allodynia) and reduced hypersensitivity reactions in mice.\",\n      \"method\": \"Molecular docking, competitive binding assay, NFκB/P38 assay, c-Fos assay, C5aR1 knockout mice, C5aR1 pharmacological inhibition, in vivo CIPN model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — molecular docking plus competitive binding (without full reconstitution), in vivo phenotype; direct binding not fully reconstituted biochemically\",\n      \"pmids\": [\"35614037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"C5aR (CD88) is expressed on mast cells in a tissue-specific manner: skin mast cells and a subset of cardiac mast cells expressed CD88, whereas lung, uterine, and tonsillar mast cells did not. C5a-induced histamine release from skin mast cells and basophils was inhibited by the anti-CD88 blocking antibody S5/1, demonstrating CD88-mediated signaling in these cells.\",\n      \"method\": \"Monoclonal antibody immunofluorescence staining, double immunoperoxidase staining (tryptase vs CD88), histamine release assay with anti-CD88 blocking antibody\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional blocking antibody demonstrating CD88-dependent histamine release in primary skin mast cells, replicated across organs\",\n      \"pmids\": [\"7673728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"C5aR is expressed on hepatocytes, lung bronchial and alveolar epithelial cells, and lung vascular smooth muscle and endothelial cells (non-myeloid cells), as demonstrated by immunohistochemistry and ligand-binding studies, expanding known C5aR expression beyond myeloid blood cells.\",\n      \"method\": \"Immunohistochemistry, radioligand binding studies\",\n      \"journal\": \"Immunology letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — localization by two methods but no direct functional consequence demonstrated in non-myeloid cells\",\n      \"pmids\": [\"7797249\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"IFN-γ up-regulates C5aR (CD88) in immature myeloblastic U937, HL-60, and MonoMac6 cells, inducing functional receptor coupling. The induced C5a responsiveness is completely pertussis toxin-sensitive, implicating Gαi. An additional pertussis toxin-resistant pathway exists in U937 after dibutyryl cAMP induction. PMA increases C5aR expression and acts synergistically with IFN-γ.\",\n      \"method\": \"Radioligand binding, Ca2+ mobilization assay, pertussis toxin treatment, protein kinase C inhibitor (staurosporine), N-acetyl-β-D-glucosaminidase release assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays with pharmacological dissection, single lab; replicated across three cell lines\",\n      \"pmids\": [\"7594603\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"C5aR1 (CD88) is a Gαi-coupled seven-transmembrane receptor for the complement anaphylatoxin C5a whose cryo-EM structures reveal a two-site ligand-engagement mechanism (N-terminal extracellular domain for high-affinity native C5a binding; transmembrane core for peptide agonists), position-69 of C5a as the agonist/antagonist switch, and biased signaling through G protein versus β-arrestin pathways controlled by distinct TM7/H8 conformational changes; agonist-induced receptor desensitization is mediated by phosphorylation of Ser334/Ser338 on the C-terminal tail, while C-terminal phosphorylation is dispensable for sequestration; C5aR1 signals through Gαi (pertussis toxin-sensitive) to activate RhoA-dependent cytoskeletal rearrangement and cell invasion, PI3K/AKT, p38-MAPK, ERK1/2, NF-κB, and mTOR pathways in diverse cell types; intracellularly, autocrine C5a generated by a lysosomal C5 convertase (CTSD) engages C5aR1 on mitochondrial membranes of macrophages to drive reverse electron chain ROS and IL-1β production, and on lysosomes of tumor cells to stabilize β-catenin via a K48→K63 ubiquitin switch through a KCTD5/cullin3/Roc-1 complex; C5L2 negatively modulates C5aR1 β-arrestin signaling by forming heterodimers with C5aR1 and acting as an obligate decoy for the β-arrestin pathway, while both receptors are required for G-CSF production; C5aR1 also physically associates with TLR2 in osteoblasts and requires co-signaling from C3aR/C5aR1 and IL-6R-gp130 for VEGFR2-driven endothelial mitogenesis; in Schwann cells, C5aR1 activates the NLRP1 inflammasome/IL-1β/TRPA1 pain axis, and in podocytes it promotes Drp1S616-dependent mitochondrial fission underlying lupus nephritis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"C5aR1 (CD88) is a Gαi-coupled seven-transmembrane receptor for the complement anaphylatoxin C5a that transduces inflammatory, chemotactic, and proliferative signals across myeloid and non-myeloid cell types [#9, #37]. Cryo-EM structures of the C5a–C5aR1–Gi complex define a two-site engagement mechanism in which the receptor N-terminus mediates high-affinity binding of native C5a while the transmembrane core accommodates peptide agonists, with distinct conformational changes in the intracellular end of TM7 and helix 8 governing agonist recognition and biased signaling [#0, #1]; this structural framework is corroborated by chimeric-receptor mapping showing that the C5aR1 N-terminus is required for native C5a binding but dispensable for analogue peptides, and by identification of position-69 of C5a as the agonist/antagonist switch [#4, #5]. Signaling is pertussis toxin-sensitive through Gαi, and individual agonists display bias between G protein coupling and β-arrestin recruitment [#9]; agonist-induced desensitization requires phosphorylation of Ser334/Ser338 on the C-terminal tail, whereas receptor sequestration proceeds through a distinct, phosphorylation-independent route [#2, #3]. Downstream, C5aR1 engages RhoA-dependent cytoskeletal rearrangement and MMP release to drive cell invasion, and PI3K/AKT, p38-MAPK, ERK1/2, NF-κB, and mTOR cascades in diverse contexts [#11, #18, #10]. Beyond the plasma membrane, autocrine C5a generated by intracellular convertases engages C5aR1 on intracellular membranes — on macrophage mitochondria to drive reverse-electron-chain ROS and IL-1β production, and on tumor-cell lysosomes/endosomes (via cathepsin D) where it assembles a KCTD5/cullin3/Roc-1 complex that switches β-catenin polyubiquitination from K48 to K63 to stabilize β-catenin and promote tumorigenesis [#7, #8]. Receptor function is modulated by the decoy receptor C5L2, which heterodimerizes with C5aR1 and negatively regulates the β-arrestin pathway, with both receptors required for G-CSF production [#6, #30, #21]. C5aR1 additionally physically associates with TLR2 in osteoblasts and participates in C3aR/C5aR1–IL-6R–gp130 co-signaling required for VEGFR2-driven endothelial mitogenesis [#13, #29]. Through these activities C5aR1 contributes to neutrophil chemotaxis, mast-cell histamine release, thrombotic endothelial activation, inflammasome-driven pain, mitochondrial fission in podocytes, and tissue-injury and tumor pathologies [#35, #23, #26, #17].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Establishing that C5aR is expressed and functional beyond myeloid blood cells defined the breadth of tissues that respond directly to C5a.\",\n      \"evidence\": \"Immunohistochemistry, radioligand binding, and anti-CD88 blocking-antibody histamine-release assays in mast cells, hepatocytes, and lung epithelium/endothelium\",\n      \"pmids\": [\"7673728\", \"7797249\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequences of non-myeloid expression not established in most tissues at the time\", \"Signaling mechanism in these cells not yet defined\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Identifying IFN-γ-inducible, pertussis toxin-sensitive coupling answered how C5a responsiveness is acquired and which G protein transduces it.\",\n      \"evidence\": \"Radioligand binding, calcium mobilization, and pertussis toxin treatment in myeloblastic U937/HL-60/MonoMac6 cells\",\n      \"pmids\": [\"7594603\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the pertussis-toxin-resistant pathway not resolved\", \"Downstream effectors of Gαi not yet mapped\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Defining the C-terminal tail and a third-loop PKC motif as required for internalization separated the structural determinants of receptor trafficking from those of signaling.\",\n      \"evidence\": \"C-terminal truncation/point-mutant C5aR stably expressed in RBL-2H3 and HEK293 with internalization assays plus pertussis toxin and staurosporine controls\",\n      \"pmids\": [\"9209506\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the specific phosphorylated residues\", \"PMA-induced internalization mechanism left indirect\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Chimeric-receptor mapping resolved the two-binding-site model, showing the N-terminus is required for native C5a but not peptide agonist binding.\",\n      \"evidence\": \"C3aR/C5aR domain-swap constructs in HEK293 with radioligand binding and calcium mobilization\",\n      \"pmids\": [\"10085065\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution view of the binding sites not yet available\", \"Did not address biased signaling\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Pinpointing Ser334/Ser338 phosphorylation as the desensitization signal — distinct from sequestration — clarified how agonist-induced receptor shutoff is controlled.\",\n      \"evidence\": \"Site-directed mutagenesis in HL-60/COS-7 with calcium, ERK2, superoxide, and internalization readouts\",\n      \"pmids\": [\"10636859\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinases responsible for these phosphorylations not identified\", \"Link between phosphorylation and β-arrestin recruitment not established here\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identifying position-69 of C5a as the agonism switch and dissecting differential binding to CD88 versus C5L2 defined the ligand determinants of receptor selectivity.\",\n      \"evidence\": \"Site-directed mutagenesis of C5a with radioligand competition binding at CD88 and C5L2 on monocytes/HMC-1\",\n      \"pmids\": [\"14570896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the switch not yet visualized\", \"Downstream signaling consequences of the switch not characterized\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrating that C5L2 negatively modulates the β-arrestin pathway and resides largely intracellularly explained how a second receptor tunes C5a output without affecting calcium signaling.\",\n      \"evidence\": \"Flow cytometry, confocal, antibody blockade, ERK1/2 and calcium assays, and reciprocal Co-IP in primary human neutrophils\",\n      \"pmids\": [\"20044484\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of C5aR1–C5L2 heterodimers not quantified\", \"Mechanism by which C5L2 sequesters β-arrestin not resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showing C5L2–C5aR homo/heterodimerization and ligand-induced cross-talk established a physical basis for the decoy/modulatory relationship.\",\n      \"evidence\": \"BRET and confocal microscopy in HEK293 and C5aRKO adipocytes with Akt/NF-κB and triglyceride readouts\",\n      \"pmids\": [\"23268185\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"BRET dimerization not confirmed at endogenous expression\", \"Functional dimer interface not mapped\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Genetic dissection established that both C5aR1 and C5L2 are required together for C5a-driven G-CSF production, and that C5aR1 drives RhoA-dependent invasion.\",\n      \"evidence\": \"C5aR−/− and C5L2−/− macrophages with G-CSF ELISA and PI3K/Akt/MEK assays; RhoA-GTP pull-down and invasion assays in cancer cells\",\n      \"pmids\": [\"23575697\", \"23287562\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of the C5aR1/C5L2 co-requirement not defined\", \"Invasion findings from single labs without independent replication\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Quantitative bias profiling and identification of receptor co-signaling requirements clarified how distinct agonists and partner receptors shape C5aR1 output.\",\n      \"evidence\": \"cAMP, ERK, β-arrestin, and endocytosis assays with C5apep; Co-IP, BRET, and VEGFR2 phosphorylation for C3aR/C5aR1–IL-6R–gp130 co-signaling\",\n      \"pmids\": [\"31036565\", \"30765465\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of bias not yet linked to receptor conformation\", \"Direct versus indirect nature of the four-receptor association not fully separated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery of intracellular autocrine C5a acting on mitochondrial C5aR1 redefined the receptor as an organelle-localized signaling hub controlling macrophage metabolism and IL-1β.\",\n      \"evidence\": \"Intracellular convertase characterization, mitochondrial fractionation, metabolic/ROS assays, cell-permeable antagonist, macrophage-specific C5ar1 KO, and atherosclerosis model\",\n      \"pmids\": [\"34932384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of C5aR1 trafficking to mitochondria not defined\", \"How mitochondrial C5aR1 couples to ROS machinery not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defining a lysosomal CTSD-generated C5a–C5aR1–KCTD5/cullin3/Roc-1 axis that switches β-catenin ubiquitination established a non-canonical intracellular signaling output driving tumorigenesis.\",\n      \"evidence\": \"Genetic loss-of-function, pharmacological blockade, Co-IP of the multiprotein complex, ubiquitination assays, and in vivo colorectal tumor model\",\n      \"pmids\": [\"35649359\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Determinants of C5aR1 lysosomal localization not defined\", \"Generality across other Wnt-driven tumors not established\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Cryo-EM structures of the C5a–C5aR1–Gi complex with multiple agonists and a converting mutant provided the atomic framework for orthosteric ligand recognition, activation, and biased signaling.\",\n      \"evidence\": \"Cryo-EM of wild-type and I116A-mutant C5aR1–Gi complexes with C5a, C5apep, and BM213, plus site-directed mutagenesis and pharmacological assays\",\n      \"pmids\": [\"36806352\", \"37169960\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"β-arrestin-coupled structure not resolved\", \"Conformational basis of receptor-tail phosphorylation not visualized\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linking C5aR1 to mitochondrial fission, inflammasome-driven pain, and m6A-dependent ferroptosis suppression extended the receptor into organelle-level and disease-specific effector mechanisms.\",\n      \"evidence\": \"siRNA/pharmacological inhibition with Drp1S616, NLRP1/IL-1β/TRPA1, and ERK1/2–METTL3–GPX4 readouts in podocyte, Schwann-cell, and glioblastoma models\",\n      \"pmids\": [\"38449312\", \"39587068\", \"39368999\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Each mechanism shown in a single disease context by one lab\", \"Connection between receptor activation and these distinct downstream nodes not unified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single receptor selects among plasma-membrane Gαi/β-arrestin signaling versus its distinct mitochondrial and lysosomal intracellular programs remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trafficking determinants directing C5aR1 to mitochondria versus lysosomes unknown\", \"No structural model for intracellular complex assembly (e.g., with KCTD5/cullin3)\", \"How biased agonism integrates with organelle-specific outputs unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [0, 1, 4, 5]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 9, 37]},\n      {\"term_id\": \"GO:0004930\", \"supporting_discovery_ids\": [0, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [6, 31, 35]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [7, 21, 32, 33]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 9, 11, 18, 29]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [8, 16, 17, 27, 28]},\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [23, 24]}\n    ],\n    \"complexes\": [\n      \"C5aR1–C5L2 heterodimer\",\n      \"intracellular C5aR1–KCTD5/cullin3/Roc-1–β-catenin complex\",\n      \"C5aR1–TLR2\",\n      \"C3aR/C5aR1–IL-6R–gp130–VEGFR2 co-signaling cluster\"\n    ],\n    \"partners\": [\n      \"C5L2\",\n      \"ARRB\",\n      \"TLR2\",\n      \"KCTD5\",\n      \"CUL3\",\n      \"CTNNB1\",\n      \"VEGFR2\",\n      \"IL6R\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}