{"gene":"C9","run_date":"2026-04-28T17:12:38","timeline":{"discoveries":[{"year":1985,"finding":"C9 cDNA sequence revealed the protein has an N-terminal half rich in cysteine residues with homology to LDL receptor cysteine-rich domains, and a carboxy-terminal half that reacts with lipid-soluble photoaffinity probes, establishing the topology of C9 with distinct hydrophilic and lipid-interacting regions.","method":"cDNA sequencing, proteolytic fragment analysis, monoclonal antibody epitope mapping on Western blots","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — primary sequence determination with multiple orthogonal structural validation methods","pmids":["4018030"],"is_preprint":false},{"year":1970,"finding":"C9 participates in the terminal lytic step of complement-mediated cell killing downstream of C5b-7, requiring C8 binding first; C5b-6 complex activates C7 to form C567 which confers on cell membranes the capacity to be lysed by C8 and C9.","method":"Hemolytic complement intermediate reconstitution assays with purified components","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with purified complement components establishing pathway order","pmids":["4193935"],"is_preprint":false},{"year":1977,"finding":"C9 inserts into the lipid bilayer of erythrocyte membranes as an integral membrane protein upon complement activation; protease treatment released only 9-19% of bound C9, and SDS was required for extraction, demonstrating membrane integration with a ~18 kDa domain penetrating the bilayer.","method":"Radiolabeled C9 binding, trypsin/chymotrypsin digestion, EDTA elution, SDS extraction, and SDS-PAGE of membrane-associated fragments","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal biochemical methods demonstrating membrane insertion","pmids":["559700"],"is_preprint":false},{"year":1983,"finding":"C9 spontaneously polymerizes at 37°C through a mechanism involving disulfide bond formation; SDS/DTT-resistant polymers require free sulfhydryl groups that become exposed during polymerization, and iodoacetamide completely inhibited covalent polymer formation.","method":"In vitro C9 polymerization assays, SDS-PAGE under reducing/non-reducing conditions, SH-specific reagents, gel filtration","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical reconstitution with chemical inhibitors establishing mechanism","pmids":["6863269"],"is_preprint":false},{"year":1984,"finding":"S-protein (vitronectin) inhibits C9 polymerization within the SC5b-9 complex by two mechanisms: blocking the membrane binding site of C5b-7 and inhibiting C9 polymerization by SC5b-8, resulting in a wedge-shaped non-tubular SC5b-9 complex lacking poly C9.","method":"SDS-PAGE quantification of poly C9, electron microscopy, biotinyl-S-protein localization with avidin-gold","journal":"Acta pathologica, microbiologica, et immunologica Scandinavica","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with purified proteins plus structural visualization","pmids":["6587746"],"is_preprint":false},{"year":1985,"finding":"Electron microscopy revealed that monomeric C9 has an ellipsoid shape (70×50 Å), and poly(C9) forms a hollow cylinder of 12-16 subunits; the C9a (N-terminal) region localizes around the torus and base, while C9b (C-terminal) epitopes are concentrated at the torus and base; oligosaccharides are on the periphery of the torus.","method":"Transmission electron microscopy, immunoelectron microscopy with C9a/C9b-specific antibodies, concanavalin A-gold labeling","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct structural imaging with domain-specific immunolabeling","pmids":["4055801"],"is_preprint":false},{"year":1984,"finding":"C9 insertion into the erythrocyte membrane (not merely binding or dimerization) is the key determinant of cytolytic efficiency; membrane-bound but inactive C5b-9 complexes lacking inserted C9 can exist.","method":"Photolabeling, SDS-PAGE, electroblotting, immunostaining of complement-lysed erythrocyte membranes from different species","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical demonstration distinguishing binding from functional membrane insertion","pmids":["6470486"],"is_preprint":false},{"year":1985,"finding":"C8 beta chain shares sequence homology with C9, particularly in the cysteine-rich domains and membrane-inserting regions, implying a common evolutionary origin and similar mechanism of MAC formation.","method":"cDNA cloning and sequence comparison","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 — sequence-based structural inference with direct experimental cDNA data","pmids":["3651397"],"is_preprint":false},{"year":1986,"finding":"C9 contains a cysteine-rich domain homologous to the LDL receptor; antibodies to this domain crossreact with C8 alpha, and C8 alpha undergoes similar Zn2+-induced polymerization as C9, suggesting shared structural and functional properties in MAC assembly.","method":"Peptide antibody immunoblotting, Zn2+-induced polymerization assay with C8 alpha-gamma","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — crossreactive antibodies and in vitro polymerization assay supporting structural homology","pmids":["2424021"],"is_preprint":false},{"year":1988,"finding":"Perforin, the cytolytic protein of killer T cells and NK cells, shares primary sequence homology with C9 at functionally conserved regions, providing molecular evidence that a killer-cell-specific protein evolutionarily linked to C9 mediates cell-mediated cytolysis.","method":"N-terminal amino acid sequencing of purified perforin, cDNA library screening with oligonucleotide probes, sequence comparison","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — direct protein sequencing and cDNA identification establishing evolutionary/structural relationship","pmids":["3261391"],"is_preprint":false},{"year":1989,"finding":"The C9 gene is located on human chromosome 5 (regional localization 5p13), established by PCR of somatic cell hybrids and confirmed by in situ hybridization.","method":"Polymerase chain reaction on somatic cell hybrids, in situ hybridization","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 2 — two orthogonal methods confirming chromosomal localization","pmids":["2744767"],"is_preprint":false},{"year":1989,"finding":"Anti-peptide antibodies that capture refolding C9 conformers during membrane insertion demonstrate that C9 must at least partly unfold to enter the membrane; some antibodies inhibit C9-mediated hemolysis without blocking polymerization and vice versa, showing that membrane insertion and polymerization are independent processes.","method":"Anti-peptide antibody capture during membrane insertion, hemolysis inhibition assays, C9 polymerization assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — mechanistic dissection with sequence-specific antibodies demonstrating independence of insertion and polymerization","pmids":["2475785"],"is_preprint":false},{"year":1990,"finding":"C5b-8 forms a functional membrane channel of ~1.5 nm radius; addition of increasing C9 progressively enlarges the channel; poly C9 forms a pore of ~90-100 Å diameter; monoclonal antibodies to the poly C9 neoantigen most potently inhibit channel activity.","method":"Liposome swelling assay with molecular size markers, Renkin equation modeling, monoclonal antibody inhibition","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1 — quantitative functional reconstitution with purified components establishing channel properties","pmids":["1696352"],"is_preprint":false},{"year":1991,"finding":"C9 undergoes three distinct endothermic thermal unfolding transitions (Tm ~32, 48, 53°C) reflecting formation of multiple conformers; the first transition is sensitive to calcium ions present at normal blood concentrations, and choline (abundant on membrane surfaces) lowers transition temperatures, suggesting C9 is partially unfolded at membrane surfaces in vivo to facilitate insertion.","method":"High-sensitivity differential scanning calorimetry with ion and ligand manipulation","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — rigorous biophysical characterization with systematic perturbation","pmids":["2054360"],"is_preprint":false},{"year":1992,"finding":"CD59 binds specifically to C8 alpha chain and to the C9b fragment (37 kDa, containing the hydrophobic membrane-interaction segment) of thrombin-cleaved C9, but not to C9a; binding requires a conformational change upon surface adsorption, suggesting CD59 recognizes an activation-induced epitope.","method":"Density gradient analysis, 125I-CD59 binding to plastic/nitrocellulose-adsorbed proteins, ligand blotting, thrombin digestion, subunit analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — saturable binding assays with defined protein fragments establishing the binding domain","pmids":["1377690"],"is_preprint":false},{"year":1993,"finding":"Clusterin binds specifically to C7, C8 beta, and the C9b domain of C9; it recognizes a site exposed during the hydrophilic-amphiphilic transition of C9 and inhibits C5b-9-mediated hemolysis and Zn2+-induced C9 polymerization; both subunits of clusterin interact with C9 and are equally potent inhibitors.","method":"125I-clusterin ligand blotting with Tween, competition assays with poly C9, hemolysis inhibition, C9 polymerization inhibition","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — multiple direct binding and functional assays with purified proteins","pmids":["8345200"],"is_preprint":false},{"year":1993,"finding":"ApoA-I and ApoA-II bind to poly C9 but not monomeric C9, interacting with a polymerization-dependent conformer; both inhibit Zn2+-induced C9 polymerization and reduce C9 incorporation into C5b-9 on endothelial cells, explaining HDL's protective effect against complement.","method":"Binding assays to poly C9, Zn2+-induced polymerization inhibition, C9 incorporation assay on endothelial cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct binding and functional inhibition assays with purified proteins","pmids":["8429039"],"is_preprint":false},{"year":1993,"finding":"Vitronectin inhibits terminal complement complex formation through two distinct binding sites: one for SC5b-7 formation (blocking C5b-7 membrane insertion) and a separate heparin-binding region that inhibits C9 binding and pore formation.","method":"Hemolytic assays with peptides spanning the heparin-binding region, protamine sulfate inhibition, comparison of SC5b-7 formation vs C9 inhibition","journal":"Clinical and experimental immunology","confidence":"Medium","confidence_rationale":"Tier 2 — functional assays with defined peptides dissecting two distinct inhibitory mechanisms","pmids":["7682159"],"is_preprint":false},{"year":1980,"finding":"C9 generates a mechanistically distinct membrane lesion from C8 alone: C8 alone causes 86Rb release without hemoglobin release (small pore), while C8/C9 together cause rapid parallel release of both 86Rb and hemoglobin (larger lytic lesion).","method":"Simultaneous 86Rb and hemoglobin release assays with EAC1-7 intermediates and defined C8/C9 concentrations","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with defined components and dual functional readouts","pmids":["7365242"],"is_preprint":false},{"year":1985,"finding":"C8 and C9 penetrate across the erythrocyte membrane bilayer into the cytoplasmic space, as demonstrated by transglutaminase cross-linking from both interior and exterior of erythrocyte ghosts.","method":"Radiolabeled complement proteins, transglutaminase cross-linking from inside/outside erythrocyte ghosts, SDS-PAGE","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — novel transglutaminase topology assay with appropriate controls","pmids":["2857173"],"is_preprint":false},{"year":1997,"finding":"The N-terminal 16 amino acids of C9 are crucial for preventing spontaneous self-polymerization; deletion of 16-23 N-terminal amino acids caused uncontrolled polymerization, while deletion of only 4-12 amino acids enhanced lytic activity and C5b-8 binding without spontaneous polymerization; a WSEWS motif (residues 27-31) maintains the N-terminus in a protected conformation.","method":"Site-directed mutagenesis, baculovirus/insect cell expression of N-terminal deletion mutants, hemolysis assays, C5b-8 binding assays","journal":"Immunology","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with functional readouts establishing the polymerization control domain","pmids":["9203961"],"is_preprint":false},{"year":1999,"finding":"C9 is phosphorylated on serine residue(s) in the N-terminal C9a portion by an ecto-protein kinase CK2 on the surface of leukemia cells; phosphorylated C9 has reduced hemolytic activity; only native but not polymerized C9 serves as substrate.","method":"Radiolabeled phosphorylation assays, thrombin cleavage fragment analysis, CK2 inhibitor studies (heparin, 2,3-diphosphoglycerate), hemolysis assays","journal":"Immunopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical identification of phosphorylation site and functional consequence","pmids":["10408378"],"is_preprint":false},{"year":2005,"finding":"Extracellular CK2 (ecto-CK2) on tumor cells phosphorylates C9, reducing complement-mediated lysis; CK2 inhibitors (TBB, Emodin, DRB) augmented killing of Raji cells by complement and Rituximab; ecto-CK2 is expressed more on cancer cells than normal cells.","method":"CK2 inhibitor treatment, hemolysis assays, C5b-7-bearing cell lysis assays, CD59 blocking antibodies","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological inhibition with functional readouts on cell-surface CK2 activity","pmids":["15902683"],"is_preprint":false},{"year":2006,"finding":"CD59 binds C9 through a primary recognition domain spanning residues 365-371 of C9; both C8 alpha and C9 bind to the same or overlapping site on CD59 at a hydrophobic pocket; CD59-mediated MAC inhibition involves protein-protein interaction at this defined interface.","method":"Peptide screens, competitive binding assays, functional hemolysis inhibition, computer modeling and docking","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — peptide mapping combined with functional assays and structural modeling","pmids":["16844690"],"is_preprint":false},{"year":2006,"finding":"Schistosoma mansoni paramyosin (Pmy) C-terminal region (residues 744-866) binds C8 and C9 and inhibits C9 polymerization and complement-mediated hemolysis; the minimal binding site for C9 was narrowed to residues 866-879 using synthetic peptides.","method":"PCR-cloning and expression of Pmy fragments, Western blot binding assays with C8/C9, hemolysis inhibition, Zn2+-induced C9 polymerization inhibition","journal":"International journal for parasitology","confidence":"Medium","confidence_rationale":"Tier 2 — domain mapping by fragmental expression with functional validation","pmids":["17123534"],"is_preprint":false},{"year":2006,"finding":"The MACPF domain of C8 alpha simultaneously binds C8 beta, C8 gamma, and C9, forming a quaternary complex; the principal C9 binding site lies within the MACPF domain; C8 alpha N-terminal modules (TSP1 and LDLRA) cooperate with the MACPF domain for C9 binding.","method":"Recombinant protein expression in E. coli, binding assays, hemolytic activity assays with domain deletion/exchange constructs","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — recombinant domain analysis with functional validation","pmids":["16618117"],"is_preprint":false},{"year":2011,"finding":"Trichinella spiralis paramyosin (Ts-Pmy) on the outer membrane of larvae binds complement C8 and C9 and inhibits C9 polymerization during MAC formation; antiserum against Ts-Pmy reduces larval viability in complement; the complement-binding domain was localized to the C-terminal region.","method":"Immunogold electron microscopy, immunofluorescence, recombinant protein binding assays, C9 polymerization inhibition, erythrocyte lysis inhibition, in vivo passive transfer","journal":"PLoS neglected tropical diseases","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal binding and functional assays plus in vivo validation","pmids":["21750743"],"is_preprint":false},{"year":2011,"finding":"The ILY (intermedilysin) binding site on CD59 deeply overlaps with the C8 alpha and C9 binding site on CD59; both ILY and C9/C8 alpha interact with common CD59 residues; mutations increasing ILY-CD59 affinity impair the prepore-to-pore transition rather than prepore assembly.","method":"Mutagenesis of hCD59 and ILY, cytolytic activity assays, prepore assembly assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with mechanistic dissection of pore formation steps","pmids":["21507937"],"is_preprint":false},{"year":2013,"finding":"Hepatitis C virus (HCV) core protein suppresses C9 mRNA and protein expression in hepatocytes via TCF-4E transcription factor-mediated promoter regulation; reduced C9 expression results in lower C5b-9 levels and impaired antimicrobial MAC function in patient sera.","method":"RT-PCR of patient liver biopsies, HCV-infected hepatocyte cultures, promoter analysis with transcription factor identification, C5b-9 ELISA, antimicrobial assay","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 — mechanistic promoter analysis with multiple functional readouts in patient-derived samples and cell models","pmids":["23487461"],"is_preprint":false},{"year":2014,"finding":"Mortalin/GRP75 binds to C8 and C9 through its N-terminal ATPase domain via ionic interaction in a nucleotide-sensitive manner; this interaction inhibits C9 polymerization and reduces C5b-9 membrane deposition, protecting tumor cells from complement-dependent cytotoxicity.","method":"Co-IP, mortalin domain expression in bacteria, C8/C9 binding assays, Zn2+-induced C9 polymerization inhibition, C5b-9 deposition quantification by flow cytometry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — domain-level binding characterization with functional consequence in defined cellular system","pmids":["24719326"],"is_preprint":false},{"year":2016,"finding":"The cryo-EM structure of poly-C9 at 8 Å resolution revealed a 22-fold symmetric arrangement forming an 88-strand beta-barrel pore; the N-terminal TSP1 domain forms an extensive oligomerization interface, facilitating solution-based assembly distinct from perforin and CDCs which require membrane for oligomerization.","method":"Cryo-electron microscopy structural determination at 8 Å resolution","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — direct structural determination at near-atomic resolution with functional implications","pmids":["26841934"],"is_preprint":false},{"year":2017,"finding":"Human serum C9 carries three types of glycosylation: two known N-glycosylation sites plus a novel third N-glycosylation site lacking the canonical N-X-S/T sequon; O-linked glycans in the N-terminal region; and C-terminal glycosylation; C9 binds up to two Ca2+ ions; approximately 50 distinct proteoforms co-occur.","method":"Native mass spectrometry, LC-MS/MS glycopeptide analysis, integrative proteoform mapping","journal":"Analytical chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct experimental evidence from high-resolution native MS and peptide-centric proteomics","pmids":["28221766"],"is_preprint":false},{"year":2021,"finding":"Polymerization of C9 within MAC pores substantially enhances damage to both bacterial outer and inner membranes and accelerates killing of Gram-negative bacteria; a mutation locking the first transmembrane helix domain of C9 prevented polymerization without affecting C5b-8 binding; O-antigen LPS impairs C9 polymerization conferring complement resistance.","method":"Site-directed mutagenesis to lock transmembrane helix, flow cytometry of wildtype vs locked-C9 binding, bacterial membrane integrity assays, serum killing assays with E. coli and Klebsiella, O-antigen mutant complementation","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis separating C9 binding from polymerization with defined functional readouts plus genetic validation","pmids":["34752492"],"is_preprint":false},{"year":2002,"finding":"C6-deficient rats (unable to form MAC) developed significantly milder experimental allergic encephalomyelitis than C6-sufficient rats; C9 deposition was absent in C6-deficient spinal cords, P-selectin expression on endothelial cells was reduced, and T cell/macrophage infiltration was diminished, demonstrating MAC-dependent neuroinflammatory pathology.","method":"Genetic complement deficiency model (PVG/C6- vs PVG/C rats), EAE immunization, C3/C9 immunostaining, P-selectin immunostaining, cellular infiltrate analysis","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function in a defined in vivo model with multiple mechanistic readouts","pmids":["11970970"],"is_preprint":false},{"year":1994,"finding":"Supplemental C9 enhances bactericidal capacity of neonatal serum by increasing total C9 deposited onto E. coli via the classical complement pathway; neonatal serum has diminished C9 concentration as the limiting factor; C9 deposition and killing were abolished by MgEGTA (classical pathway block).","method":"Radiobinding assay with anti-C9 monoclonal antibody, immunogold electron microscopy, MgEGTA pathway block, bacterial killing assays","journal":"Pediatric research","confidence":"Medium","confidence_rationale":"Tier 2 — functional reconstitution with pathway dissection using pathway-specific inhibitors","pmids":["8047374"],"is_preprint":false},{"year":2002,"finding":"C8 alpha N-terminal TSP1 and LDLRA modules together with the MACPF domain form the principal binding site for C9; deletion of both N-terminal modules from C8 alpha abolished C9 binding and hemolytic activity, indicating cooperative interaction.","method":"Recombinant C8 alpha constructs with N-/C-terminal module exchanges/deletions, C9 binding assays, hemolysis assays","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis/deletion with functional binding and hemolysis readouts","pmids":["12463754"],"is_preprint":false},{"year":2021,"finding":"The rare AMD-associated C9 P167S variant has increased propensity to polymerize and displays slightly elevated ability to induce hemolysis; MAC ring structures generated by P167S C9 appear identical to wild-type by electron microscopy, but P167S carriers have lower plasma C9 levels.","method":"Recombinant protein production, electron microscopy of MAC structures, functional hemolysis assays with C9-depleted serum, cohort plasma C9 level measurements","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 — recombinant variant analysis with structural and functional validation","pmids":["33783477"],"is_preprint":false},{"year":2018,"finding":"Functional analysis of C9 AMD-associated rare variants revealed that P167S spontaneously aggregates whereas other variants (F62S, G126R, T170I) fail to polymerize with zinc; P167S and F62S show decreased lytic activity; all analyzed variants affect secretion and/or polymerization of C9 without disrupting classical lytic pathway activity.","method":"Recombinant variant expression, C9 polymerization assays with zinc, hemolysis assays with C9-depleted serum and ARPE-19 cells, serum C9 concentration measurements in carriers","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 — systematic variant functional analysis with multiple orthogonal assays","pmids":["29767720"],"is_preprint":false}],"current_model":"Complement component C9 is a serum glycoprotein that functions as the major pore-forming component of the membrane attack complex (MAC): it binds to the C5b-8 complex via the MACPF domain and N-terminal TSP1/LDLRA modules of C8 alpha, undergoes a conformational change (partial unfolding) to expose hydrophobic regions, inserts its C-terminal C9b domain through the lipid bilayer spanning both leaflets, and polymerizes through disulfide-bond formation and TSP1-domain oligomerization contacts into a 22-subunit, 88-strand beta-barrel pore (~90-100 Å diameter) that damages bacterial outer and inner membranes to cause killing; polymerization is normally restrained by the N-terminal 16 amino acids and can be inhibited by extracellular regulators (CD59 binding to residues 365-371, clusterin binding to C9b, vitronectin/S-protein, mortalin ATPase domain, apoA-I/A-II, and ecto-CK2 phosphorylation of serine residues in C9a), while parasites evade MAC killing by expressing proteins such as paramyosin that bind C9 and block polymerization."},"narrative":{"teleology":[{"year":1970,"claim":"Establishing C9's position in the complement cascade: C9 was shown to act at the terminal lytic step downstream of C5b-8, resolving how complement effector assembly culminates in membrane damage.","evidence":"Hemolytic reconstitution assays with purified complement intermediates on erythrocytes","pmids":["4193935"],"confidence":"High","gaps":["Mechanism of C9-mediated lysis unknown","Stoichiometry undefined","Whether C9 acts enzymatically or structurally was unclear"]},{"year":1980,"claim":"C9 was shown to generate a qualitatively larger lytic lesion than C8 alone, establishing that C9 transforms a small C5b-8 pore into a fully lytic channel.","evidence":"Simultaneous 86Rb and hemoglobin release assays with defined C8/C9 on EAC1-7 intermediates","pmids":["7365242"],"confidence":"High","gaps":["Whether C9 inserts into the membrane or acts peripherally was unknown","Molecular structure of the lesion undefined"]},{"year":1977,"claim":"C9 was demonstrated to insert as an integral membrane protein penetrating the lipid bilayer, resolving that lysis involves physical C9 membrane integration rather than enzymatic action.","evidence":"Radiolabeled C9 binding, protease resistance, SDS extraction from erythrocyte membranes","pmids":["559700"],"confidence":"High","gaps":["Topology of transmembrane insertion unknown","Whether C9 spans both leaflets was unresolved"]},{"year":1983,"claim":"Discovery that C9 spontaneously polymerizes through disulfide bond formation established the covalent basis of MAC ring assembly and explained how tubular pores form.","evidence":"In vitro polymerization assays with SH-specific reagents (iodoacetamide) blocking covalent polymer formation","pmids":["6863269"],"confidence":"High","gaps":["Stoichiometry of the polymer unknown","Relationship of polymerization to membrane insertion unclear"]},{"year":1984,"claim":"Two key advances: (1) C9 membrane insertion, not merely binding, was shown to determine cytolytic efficiency; (2) vitronectin/S-protein was identified as the first soluble inhibitor of C9 polymerization, revealing host regulation of MAC.","evidence":"Photolabeling and SDS-PAGE distinguishing bound from inserted C9 [PMID:6470486]; electron microscopy and SDS-PAGE of SC5b-9 ± S-protein [PMID:6587746]","pmids":["6470486","6587746"],"confidence":"High","gaps":["Identity of membrane-inserting domain unknown","Whether insertion and polymerization are independent processes was unresolved"]},{"year":1985,"claim":"Structural and sequence characterization of C9 revealed its domain architecture — an N-terminal cysteine-rich/LDL-receptor-homologous region and a C-terminal lipid-interacting C9b domain — and electron microscopy showed poly-C9 as a 12–16 subunit hollow cylinder, while transmembrane topology was confirmed by transglutaminase cross-linking from both membrane faces.","evidence":"cDNA sequencing [PMID:4018030]; immunoelectron microscopy with domain-specific antibodies [PMID:4055801]; transglutaminase cross-linking from inside/outside erythrocyte ghosts [PMID:2857173]","pmids":["4018030","4055801","2857173"],"confidence":"High","gaps":["Atomic-resolution structure unavailable","Exact stoichiometry debated (12–16 vs later 22 subunits)","Mechanism of conformational change during insertion unknown"]},{"year":1988,"claim":"Perforin was shown to share primary sequence homology with C9, establishing that a conserved MACPF-domain pore-forming mechanism operates in both innate complement and adaptive cytotoxic lymphocyte killing.","evidence":"N-terminal sequencing of purified perforin and cDNA identification with sequence comparison","pmids":["3261391"],"confidence":"High","gaps":["Whether perforin and C9 polymerize by identical mechanisms unknown","Whether MACPF domain is sufficient for pore formation not tested"]},{"year":1989,"claim":"Anti-peptide antibodies trapping refolding intermediates demonstrated that C9 must partially unfold during membrane insertion, and that membrane insertion and polymerization are mechanistically independent processes.","evidence":"Anti-peptide antibody capture during insertion, separate inhibition of hemolysis vs polymerization","pmids":["2475785"],"confidence":"High","gaps":["Which specific domains refold during insertion was not determined","Structural basis of the unfolded intermediate unknown"]},{"year":1990,"claim":"Quantitative channel sizing established that poly-C9 forms a ~90–100 Å pore and that incremental C9 addition progressively enlarges the C5b-8 channel, defining the functional pore dimensions.","evidence":"Liposome swelling assay with molecular size markers and Renkin equation modeling","pmids":["1696352"],"confidence":"High","gaps":["Exact stoichiometry per pore still debated","Dynamic behavior of partially assembled pores unknown"]},{"year":1991,"claim":"Biophysical studies revealed three distinct thermal unfolding transitions in C9, with the first sensitive to physiological calcium and membrane-mimetic choline, explaining how membrane surfaces promote partial C9 unfolding to facilitate insertion in vivo.","evidence":"High-sensitivity differential scanning calorimetry with ion and ligand perturbation","pmids":["2054360"],"confidence":"High","gaps":["Which domain unfolds at each transition not mapped","In vivo relevance of choline-induced unfolding unconfirmed"]},{"year":1993,"claim":"Multiple soluble inhibitors of C9 polymerization were mapped: CD59 was shown to bind C9b and C8 alpha recognizing activation-induced epitopes; clusterin binds C9b during the hydrophilic-to-amphiphilic transition; and apoA-I/A-II bind selectively to poly-C9 conformers — collectively revealing layered host regulation of MAC assembly.","evidence":"Ligand blotting with 125I-CD59 to thrombin-cleaved C9 fragments [PMID:1377690]; 125I-clusterin binding, hemolysis and polymerization inhibition [PMID:8345200]; poly-C9 binding and Zn2+-induced polymerization inhibition by apolipoproteins [PMID:8429039]; vitronectin heparin-binding domain peptides [PMID:7682159]","pmids":["1377690","8345200","8429039","7682159"],"confidence":"High","gaps":["Structural basis of inhibitor-C9 interfaces unresolved","Relative contributions of each inhibitor in vivo unknown","Whether inhibitors act cooperatively or redundantly not tested"]},{"year":1997,"claim":"The N-terminal 16 amino acids were identified as an intrinsic polymerization restraint: deletion caused spontaneous self-polymerization, while a WSEWS motif (residues 27–31) maintains this autoinhibitory conformation, establishing the molecular switch controlling C9 activation.","evidence":"Baculovirus-expressed N-terminal deletion mutants with hemolysis and C5b-8 binding assays","pmids":["9203961"],"confidence":"High","gaps":["How C5b-8 binding relieves N-terminal autoinhibition unknown","Structural basis of WSEWS motif function not determined"]},{"year":1999,"claim":"Ecto-CK2 on leukemia cell surfaces was found to phosphorylate serine residues in the C9a domain, reducing hemolytic activity — identifying post-translational modification as a cell-surface immune evasion mechanism.","evidence":"Radiolabeled phosphorylation, thrombin cleavage fragment analysis, CK2 inhibitors, hemolysis assays","pmids":["10408378"],"confidence":"Medium","gaps":["Exact phosphorylation site(s) not identified at residue level","In vivo significance in tumor immune evasion not validated genetically","Whether phosphorylation affects polymerization directly untested"]},{"year":2002,"claim":"Two advances refined the mechanism: (1) C8 alpha's N-terminal TSP1 and LDLRA modules were shown to cooperate with the MACPF domain for C9 recruitment; (2) MAC-dependent neuroinflammation was demonstrated in vivo using C6-deficient rats, linking C9-containing pores to disease pathology.","evidence":"Recombinant C8α domain deletions with C9 binding/hemolysis assays [PMID:12463754]; EAE in PVG/C6- vs C6+ rats with C9 immunostaining [PMID:11970970]","pmids":["12463754","11970970"],"confidence":"High","gaps":["Atomic-resolution structure of C8α–C9 interface unknown","Whether MAC contribution to neuroinflammation involves sublytic signaling or cell lysis unclear"]},{"year":2006,"claim":"CD59's binding site on C9 was mapped to residues 365–371, overlapping with the C8α binding interface on CD59, and parasitic paramyosin was shown to inhibit C9 polymerization through defined C-terminal binding sites — revealing convergent immune evasion strategies at the C9 level.","evidence":"Peptide screens, competitive binding, and hemolysis inhibition for CD59–C9 [PMID:16844690]; recombinant paramyosin fragments binding C9 and inhibiting polymerization [PMID:17123534]; MACPF domain analysis of C8α–C9 interaction [PMID:16618117]","pmids":["16844690","17123534","16618117"],"confidence":"High","gaps":["Crystal structure of CD59–C9 complex unavailable","Whether paramyosin mimics CD59's mechanism of inhibition unknown"]},{"year":2014,"claim":"Mortalin/GRP75 was identified as a nucleotide-sensitive C9 binding partner whose ATPase domain inhibits C9 polymerization and MAC deposition, representing a novel chaperone-mediated complement evasion mechanism on tumor cells.","evidence":"Co-IP, recombinant mortalin domain binding, Zn2+-induced C9 polymerization inhibition, flow cytometry of C5b-9 deposition","pmids":["24719326"],"confidence":"High","gaps":["Whether mortalin acts extracellularly or at the cell surface in vivo unclear","Structural basis of nucleotide-dependent C9 release unknown"]},{"year":2016,"claim":"Cryo-EM at 8 Å resolution revealed that poly-C9 forms a 22-fold symmetric ring with an 88-strand β-barrel, with the N-terminal TSP1 domain mediating oligomerization contacts — distinguishing C9 from perforin and CDCs, which require membrane for oligomerization.","evidence":"Cryo-electron microscopy structural determination of poly-C9","pmids":["26841934"],"confidence":"High","gaps":["Atomic-resolution structure of monomeric C9 and full MAC not yet available","Mechanism of conformational switch from monomer to β-hairpin not visualized"]},{"year":2018,"claim":"Systematic functional analysis of rare AMD-associated C9 variants (P167S, F62S, G126R, T170I) showed that these variants alter polymerization propensity and/or secretion, directly linking C9 polymerization dysregulation to age-related macular degeneration.","evidence":"Recombinant variant expression, Zn2+-induced polymerization, hemolysis assays, serum C9 levels in carriers","pmids":["29767720","33783477"],"confidence":"High","gaps":["Mechanism by which altered polymerization leads to retinal pathology unknown","Whether variants affect MAC assembly on RPE cells specifically not tested"]},{"year":2021,"claim":"A polymerization-locked C9 mutant demonstrated that C9 polymerization within the MAC substantially enhances damage to both Gram-negative bacterial membranes and accelerates killing, while O-antigen LPS impairs C9 polymerization as a bacterial resistance mechanism.","evidence":"Transmembrane helix-locked C9 mutant, bacterial membrane integrity assays, serum killing of E. coli and Klebsiella, O-antigen mutant complementation","pmids":["34752492"],"confidence":"High","gaps":["Whether polymerization is equally important for killing Gram-positive bacteria unknown","Mechanism by which O-antigen sterically or biochemically blocks polymerization not resolved"]},{"year":null,"claim":"Key unresolved questions include the atomic-resolution structure of the complete C5b-9 MAC with C9 in its membrane-inserted state, the precise conformational pathway from monomeric C9 to β-hairpin insertion, the mechanism by which C5b-8 binding relieves N-terminal autoinhibition, and how C9 polymerization dysregulation causes retinal degeneration in AMD.","evidence":"","pmids":[],"confidence":"High","gaps":["Full atomic MAC structure with lipid bilayer not determined","Conformational trajectory of C9 monomer-to-pore transition not captured","Pathogenic mechanism linking C9 variants to AMD retinal pathology undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[2,3,5,12,30]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,2,13]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[1,4,15,16]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,6,19]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1,12,32,33,34]}],"complexes":["Membrane attack complex (MAC/C5b-9)"],"partners":["C8A","C8B","CD59","CLU","VTN","HSPA9","APOA1","APOA2"],"other_free_text":[]},"mechanistic_narrative":"Complement component C9 is the principal pore-forming subunit of the membrane attack complex (MAC), mediating the terminal lytic step of complement-dependent killing of bacteria and nucleated cells. C9 binds the C5b-8 complex via the MACPF domain and N-terminal TSP1/LDLRA modules of C8 alpha [PMID:16618117, PMID:12463754], undergoes partial unfolding to expose hydrophobic regions [PMID:2475785, PMID:2054360], inserts its C-terminal C9b domain through the lipid bilayer spanning both leaflets [PMID:559700, PMID:2857173], and polymerizes through disulfide bonds and TSP1-domain oligomerization contacts into a 22-subunit, 88-strand β-barrel pore (~90–100 Å diameter) that damages both outer and inner bacterial membranes [PMID:26841934, PMID:34752492, PMID:6863269]. Polymerization is restrained by the N-terminal 16 amino acids and a WSEWS motif [PMID:9203961], and is inhibited by multiple extracellular regulators including CD59 (binding C9 residues 365–371) [PMID:16844690], clusterin (binding C9b) [PMID:8345200], vitronectin [PMID:6587746], mortalin [PMID:24719326], apolipoproteins A-I/A-II [PMID:8429039], and ecto-CK2 phosphorylation of the C9a domain [PMID:10408378, PMID:15902683]. Rare C9 variants (P167S, F62S, G126R, T170I) that alter polymerization or secretion are associated with age-related macular degeneration [PMID:29767720, PMID:33783477]."},"prefetch_data":{"uniprot":{"accession":"P02748","full_name":"Complement component C9","aliases":[],"length_aa":559,"mass_kda":63.2,"function":"Pore-forming component of the membrane attack complex (MAC), a multiprotein complex activated by the complement cascade, which inserts into a target cell membrane and forms a pore, leading to target cell membrane rupture and cell lysis (PubMed:22832194, PubMed:26841837, PubMed:26841934, PubMed:27052168, PubMed:30552328, PubMed:6177822, PubMed:9212048, PubMed:9634479). The MAC is initiated by proteolytic cleavage of C5 into complement C5b in response to the classical, alternative, lectin and GZMK complement pathways (PubMed:39914456, PubMed:39814882, PubMed:9212048, PubMed:9634479). The complement pathways consist in a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system (PubMed:9212048, PubMed:9634479). Constitutes the pore-forming subunit of the MAC complex: during MAC assembly, C9 associates with the C5b8 intermediate complex, and polymerizes to complete the pore (PubMed:26841934, PubMed:30111885, PubMed:30552328, PubMed:34752492, PubMed:4055801, PubMed:6177822)","subcellular_location":"Secreted; Target cell membrane","url":"https://www.uniprot.org/uniprotkb/P02748/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/C9","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/C9","total_profiled":1310},"omim":[{"mim_id":"616538","title":"MUSCULAR DYSTROPHY-DYSTROGLYCANOPATHY (CONGENITAL WITH BRAIN AND EYE ANOMALIES), TYPE A, 9; MDDGA9","url":"https://www.omim.org/entry/616538"},{"mim_id":"615591","title":"MACULAR DEGENERATION, AGE-RELATED, 15; ARMD15","url":"https://www.omim.org/entry/615591"},{"mim_id":"615561","title":"COMPLEMENT FACTOR B DEFICIENCY; CFBD","url":"https://www.omim.org/entry/615561"},{"mim_id":"615439","title":"MACULAR DEGENERATION, AGE-RELATED, 13; ARMD13","url":"https://www.omim.org/entry/615439"},{"mim_id":"614809","title":"C3 GLOMERULOPATHY 3; C3G3","url":"https://www.omim.org/entry/614809"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"liver","ntpm":1222.6}],"url":"https://www.proteinatlas.org/search/C9"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P02748","domains":[{"cath_id":"2.20.100","chopping":"45-95","consensus_level":"medium","plddt":92.1231,"start":45,"end":95},{"cath_id":"4.10.400.10","chopping":"103-141","consensus_level":"medium","plddt":90.1079,"start":103,"end":141},{"cath_id":"-","chopping":"148-247_271-380_423-510","consensus_level":"medium","plddt":85.8464,"start":148,"end":510}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P02748","model_url":"https://alphafold.ebi.ac.uk/files/AF-P02748-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P02748-F1-predicted_aligned_error_v6.png","plddt_mean":78.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=C9","jax_strain_url":"https://www.jax.org/strain/search?query=C9"},"sequence":{"accession":"P02748","fasta_url":"https://rest.uniprot.org/uniprotkb/P02748.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P02748/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P02748"}},"corpus_meta":[{"pmid":"24036952","id":"PMC_24036952","title":"Rare variants in CFI, C3 and C9 are associated with high risk of advanced age-related macular degeneration.","date":"2013","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24036952","citation_count":292,"is_preprint":false},{"pmid":"3261391","id":"PMC_3261391","title":"Homology of perforin to the ninth component of complement (C9).","date":"1988","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/3261391","citation_count":266,"is_preprint":false},{"pmid":"4193935","id":"PMC_4193935","title":"Reactive lysis: the complement-mediated lysis of unsensitized cells. II. The characterization of activated reactor as C56 and the participation of C8 and C9.","date":"1970","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/4193935","citation_count":259,"is_preprint":false},{"pmid":"23579273","id":"PMC_23579273","title":"Hox-C9 activates the intrinsic pathway of apoptosis and is associated with spontaneous regression in neuroblastoma.","date":"2013","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/23579273","citation_count":202,"is_preprint":false},{"pmid":"4018030","id":"PMC_4018030","title":"The sequence and topology of human complement component C9.","date":"1985","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/4018030","citation_count":177,"is_preprint":false},{"pmid":"8345200","id":"PMC_8345200","title":"Clusterin, the human apolipoprotein and complement inhibitor, binds to complement C7, C8 beta, and the b domain of C9.","date":"1993","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/8345200","citation_count":140,"is_preprint":false},{"pmid":"21769103","id":"PMC_21769103","title":"Conditioning for hematopoietic transplantation activates the complement cascade and induces a proteolytic environment in bone marrow: a novel role for bioactive lipids and soluble C5b-C9 as homing factors.","date":"2011","source":"Leukemia","url":"https://pubmed.ncbi.nlm.nih.gov/21769103","citation_count":115,"is_preprint":false},{"pmid":"26841934","id":"PMC_26841934","title":"Structure of the poly-C9 component of the complement membrane attack complex.","date":"2016","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/26841934","citation_count":110,"is_preprint":false},{"pmid":"6587746","id":"PMC_6587746","title":"Inhibition of C9 polymerization within the SC5b-9 complex of complement by S-protein.","date":"1984","source":"Acta pathologica, microbiologica, et immunologica Scandinavica. Supplement","url":"https://pubmed.ncbi.nlm.nih.gov/6587746","citation_count":107,"is_preprint":false},{"pmid":"1377690","id":"PMC_1377690","title":"The human complement regulatory protein CD59 binds to the alpha-chain of C8 and to the \"b\"domain of C9.","date":"1992","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/1377690","citation_count":105,"is_preprint":false},{"pmid":"22007900","id":"PMC_22007900","title":"Phosphoinositide-specific phospholipase C9 is involved in the thermotolerance of Arabidopsis.","date":"2011","source":"The Plant journal : for cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/22007900","citation_count":98,"is_preprint":false},{"pmid":"7682159","id":"PMC_7682159","title":"Vitronectin-mediated inhibition of complement: evidence for different binding sites for C5b-7 and C9.","date":"1993","source":"Clinical and experimental immunology","url":"https://pubmed.ncbi.nlm.nih.gov/7682159","citation_count":96,"is_preprint":false},{"pmid":"559700","id":"PMC_559700","title":"On the mechanism of cell membrane damage by complement: evidence on insertion of polypeptide chains from C8 and C9 into the lipid bilayer of erythrocytes.","date":"1977","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/559700","citation_count":95,"is_preprint":false},{"pmid":"27844039","id":"PMC_27844039","title":"Increased prevalence of autoimmune disease within C9 and FTD/MND cohorts: Completing the picture.","date":"2016","source":"Neurology(R) neuroimmunology & neuroinflammation","url":"https://pubmed.ncbi.nlm.nih.gov/27844039","citation_count":84,"is_preprint":false},{"pmid":"16844690","id":"PMC_16844690","title":"Defining the CD59-C9 binding interaction.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16844690","citation_count":83,"is_preprint":false},{"pmid":"8429039","id":"PMC_8429039","title":"Interaction between apolipoproteins A-I and A-II and the membrane attack complex of complement. Affinity of the apoproteins for polymeric C9.","date":"1993","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8429039","citation_count":80,"is_preprint":false},{"pmid":"31831332","id":"PMC_31831332","title":"Antibody Therapy Targeting RAN Proteins Rescues C9 ALS/FTD Phenotypes in C9orf72 Mouse Model.","date":"2019","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/31831332","citation_count":77,"is_preprint":false},{"pmid":"9014582","id":"PMC_9014582","title":"Complement in acute and chronic arthritides: assessment of C3c, C9, and protectin (CD59) in synovial membrane.","date":"1996","source":"Annals of the rheumatic diseases","url":"https://pubmed.ncbi.nlm.nih.gov/9014582","citation_count":76,"is_preprint":false},{"pmid":"3651397","id":"PMC_3651397","title":"Complementary DNA cloning of complement C8 beta and its sequence homology to C9.","date":"1987","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/3651397","citation_count":71,"is_preprint":false},{"pmid":"2744767","id":"PMC_2744767","title":"The gene for human complement component C9 mapped to chromosome 5 by polymerase chain reaction.","date":"1989","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/2744767","citation_count":63,"is_preprint":false},{"pmid":"33300868","id":"PMC_33300868","title":"TFEB/Mitf links impaired nuclear import to autophagolysosomal dysfunction in C9-ALS.","date":"2020","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/33300868","citation_count":59,"is_preprint":false},{"pmid":"20019081","id":"PMC_20019081","title":"Candida albicans sphingolipid C9-methyltransferase is involved in hyphal elongation.","date":"2009","source":"Microbiology (Reading, England)","url":"https://pubmed.ncbi.nlm.nih.gov/20019081","citation_count":59,"is_preprint":false},{"pmid":"3764345","id":"PMC_3764345","title":"Synthesis of complement components C5, C6, C7, C8 and C9 in vitro by human monocytes and assembly of the terminal complement complex.","date":"1986","source":"Scandinavian journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/3764345","citation_count":58,"is_preprint":false},{"pmid":"32876811","id":"PMC_32876811","title":"C9orf72 loss-of-function: a trivial, stand-alone or additive mechanism in C9 ALS/FTD?","date":"2020","source":"Acta neuropathologica","url":"https://pubmed.ncbi.nlm.nih.gov/32876811","citation_count":57,"is_preprint":false},{"pmid":"16339149","id":"PMC_16339149","title":"Identification of fungal sphingolipid C9-methyltransferases by phylogenetic profiling.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16339149","citation_count":56,"is_preprint":false},{"pmid":"20707004","id":"PMC_20707004","title":"Upregulation of plasma C9 protein in gastric cancer patients.","date":"2010","source":"Proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/20707004","citation_count":55,"is_preprint":false},{"pmid":"1086750","id":"PMC_1086750","title":"Acute phase proteins and C9 in patients with Behcet's syndrome and aphthous ulcers.","date":"1976","source":"Clinical and experimental immunology","url":"https://pubmed.ncbi.nlm.nih.gov/1086750","citation_count":54,"is_preprint":false},{"pmid":"21507937","id":"PMC_21507937","title":"Mapping the intermedilysin-human CD59 receptor interface reveals a deep correspondence with the binding site on CD59 for complement binding proteins C8alpha and C9.","date":"2011","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21507937","citation_count":54,"is_preprint":false},{"pmid":"29326544","id":"PMC_29326544","title":"Unraveling the Role of RNA Mediated Toxicity of C9orf72 Repeats in C9-FTD/ALS.","date":"2017","source":"Frontiers in neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/29326544","citation_count":51,"is_preprint":false},{"pmid":"9644253","id":"PMC_9644253","title":"Characterization of the enzymatic 7-O-acetylation of sialic acids and evidence for enzymatic O-acetyl migration from C-7 to C-9 in bovine submandibular gland.","date":"1998","source":"Journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9644253","citation_count":51,"is_preprint":false},{"pmid":"21750743","id":"PMC_21750743","title":"Trichinella spiralis paramyosin binds to C8 and C9 and protects the tissue-dwelling nematode from being attacked by host complement.","date":"2011","source":"PLoS neglected tropical diseases","url":"https://pubmed.ncbi.nlm.nih.gov/21750743","citation_count":50,"is_preprint":false},{"pmid":"16947020","id":"PMC_16947020","title":"Activation of complement C3, C5, and C9 genes in tumors treated by photodynamic therapy.","date":"2006","source":"Cancer immunology, immunotherapy : CII","url":"https://pubmed.ncbi.nlm.nih.gov/16947020","citation_count":49,"is_preprint":false},{"pmid":"11970970","id":"PMC_11970970","title":"Attenuation of experimental allergic encephalomyelitis in complement component 6-deficient rats is associated with reduced complement C9 deposition, P-selectin expression, and cellular infiltrate in spinal cords.","date":"2002","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/11970970","citation_count":49,"is_preprint":false},{"pmid":"12216844","id":"PMC_12216844","title":"Similar effects of c9,t11-CLA and t10,c12-CLA on immune cell functions in mice.","date":"2002","source":"Lipids","url":"https://pubmed.ncbi.nlm.nih.gov/12216844","citation_count":46,"is_preprint":false},{"pmid":"16630744","id":"PMC_16630744","title":"Biosynthesis of C9-aldehydes in the moss Physcomitrella patens.","date":"2006","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/16630744","citation_count":45,"is_preprint":false},{"pmid":"31582731","id":"PMC_31582731","title":"C9-ALS/FTD-linked proline-arginine dipeptide repeat protein associates with paraspeckle components and increases paraspeckle formation.","date":"2019","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/31582731","citation_count":42,"is_preprint":false},{"pmid":"2917424","id":"PMC_2917424","title":"A properdin dependent nephritic factor slowly activating C3, C5, and C9 in membranoproliferative glomerulonephritis, types I and III.","date":"1989","source":"Clinical immunology and immunopathology","url":"https://pubmed.ncbi.nlm.nih.gov/2917424","citation_count":42,"is_preprint":false},{"pmid":"24634500","id":"PMC_24634500","title":"c9,t11-Conjugated linoleic acid ameliorates steatosis by modulating mitochondrial uncoupling and Nrf2 pathway.","date":"2014","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/24634500","citation_count":41,"is_preprint":false},{"pmid":"32755582","id":"PMC_32755582","title":"Altered MICOS Morphology and Mitochondrial Ion Homeostasis Contribute to Poly(GR) Toxicity Associated with C9-ALS/FTD.","date":"2020","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/32755582","citation_count":41,"is_preprint":false},{"pmid":"27226251","id":"PMC_27226251","title":"The NEU1-selective sialidase inhibitor, C9-butyl-amide-DANA, blocks sialidase activity and NEU1-mediated bioactivities in human lung in vitro and murine lung in vivo.","date":"2016","source":"Glycobiology","url":"https://pubmed.ncbi.nlm.nih.gov/27226251","citation_count":40,"is_preprint":false},{"pmid":"23487461","id":"PMC_23487461","title":"Hepatitis C virus suppresses C9 complement synthesis and impairs membrane attack complex function.","date":"2013","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/23487461","citation_count":40,"is_preprint":false},{"pmid":"19528200","id":"PMC_19528200","title":"Thauera butanivorans sp. nov., a C2-C9 alkane-oxidizing bacterium previously referred to as 'Pseudomonas butanovora'.","date":"2009","source":"International journal of systematic and evolutionary microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/19528200","citation_count":40,"is_preprint":false},{"pmid":"28221766","id":"PMC_28221766","title":"Proteoform Profile Mapping of the Human Serum Complement Component C9 Revealing Unexpected New Features of N-, O-, and C-Glycosylation.","date":"2017","source":"Analytical chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28221766","citation_count":40,"is_preprint":false},{"pmid":"16481326","id":"PMC_16481326","title":"Identification of a sialate O-acetyltransferase from Campylobacter jejuni: demonstration of direct transfer to the C-9 position of terminalalpha-2, 8-linked sialic acid.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16481326","citation_count":40,"is_preprint":false},{"pmid":"26582930","id":"PMC_26582930","title":"Homeobox C9 suppresses Beclin1-mediated autophagy in glioblastoma by directly inhibiting the transcription of death-associated protein kinase 1.","date":"2015","source":"Neuro-oncology","url":"https://pubmed.ncbi.nlm.nih.gov/26582930","citation_count":39,"is_preprint":false},{"pmid":"2475785","id":"PMC_2475785","title":"Detection of refolding conformers of complement protein C9 during insertion into membranes.","date":"1989","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/2475785","citation_count":37,"is_preprint":false},{"pmid":"8449252","id":"PMC_8449252","title":"Domain structure, functional activity, and polymerization of trout complement protein C9.","date":"1993","source":"Developmental and comparative immunology","url":"https://pubmed.ncbi.nlm.nih.gov/8449252","citation_count":37,"is_preprint":false},{"pmid":"4055801","id":"PMC_4055801","title":"The architecture of complement component C9 and poly(C9).","date":"1985","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/4055801","citation_count":36,"is_preprint":false},{"pmid":"33022226","id":"PMC_33022226","title":"Survival and Motor Phenotypes in FVB C9-500 ALS/FTD BAC Transgenic Mice Reproduced by Multiple Labs.","date":"2020","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/33022226","citation_count":36,"is_preprint":false},{"pmid":"9373156","id":"PMC_9373156","title":"Cloning and sequencing of complement component C9 and its linkage to DOC-2 in the pufferfish Fugu rubripes.","date":"1997","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/9373156","citation_count":36,"is_preprint":false},{"pmid":"9795119","id":"PMC_9795119","title":"Expression of complement C4 and C9 genes by human astrocytes.","date":"1998","source":"Brain research","url":"https://pubmed.ncbi.nlm.nih.gov/9795119","citation_count":35,"is_preprint":false},{"pmid":"24719326","id":"PMC_24719326","title":"Mortalin/GRP75 binds to complement C9 and plays a role in resistance to complement-dependent cytotoxicity.","date":"2014","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24719326","citation_count":34,"is_preprint":false},{"pmid":"29444943","id":"PMC_29444943","title":"Vaccinia Virus C9 Ankyrin Repeat/F-Box Protein Is a Newly Identified Antagonist of the Type I Interferon-Induced Antiviral State.","date":"2018","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/29444943","citation_count":34,"is_preprint":false},{"pmid":"7365242","id":"PMC_7365242","title":"Distinction between C8-mediated and C8/C9-mediated hemolysis on the basis of independent 86Rb and hemoglobin release.","date":"1980","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/7365242","citation_count":33,"is_preprint":false},{"pmid":"2424021","id":"PMC_2424021","title":"Antigenic crossreactivity of the alpha subunit of complement component C8 with the cysteine-rich domain shared by complement component C9 and low density lipoprotein receptor.","date":"1986","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/2424021","citation_count":33,"is_preprint":false},{"pmid":"12934672","id":"PMC_12934672","title":"Vaccenic acid (t11-18:1) is converted to c9,t11-CLA in MCF-7 and SW480 cancer cells.","date":"2003","source":"Lipids","url":"https://pubmed.ncbi.nlm.nih.gov/12934672","citation_count":33,"is_preprint":false},{"pmid":"6470486","id":"PMC_6470486","title":"Species-restricted target cell lysis by human complement: complement-lysed erythrocytes from heterologous and homologous species differ in their ratio of bound to inserted C9.","date":"1984","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/6470486","citation_count":32,"is_preprint":false},{"pmid":"15902683","id":"PMC_15902683","title":"Extracellular phosphorylation of C9 by protein kinase CK2 regulates complement-mediated lysis.","date":"2005","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/15902683","citation_count":32,"is_preprint":false},{"pmid":"20121615","id":"PMC_20121615","title":"The utility of C4d, C9, and troponin T immunohistochemistry in acute myocardial infarction.","date":"2010","source":"Archives of pathology & laboratory medicine","url":"https://pubmed.ncbi.nlm.nih.gov/20121615","citation_count":32,"is_preprint":false},{"pmid":"2054360","id":"PMC_2054360","title":"Thermal unfolding and aggregation of human complement protein C9: a differential scanning calorimetry study.","date":"1991","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/2054360","citation_count":30,"is_preprint":false},{"pmid":"19302593","id":"PMC_19302593","title":"Anti-angiogenic and vascular disrupting effects of C9, a new microtubule-depolymerizing agent.","date":"2009","source":"British journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/19302593","citation_count":30,"is_preprint":false},{"pmid":"30250194","id":"PMC_30250194","title":"The proline-arginine repeat protein linked to C9-ALS/FTD causes neuronal toxicity by inhibiting the DEAD-box RNA helicase-mediated ribosome biogenesis.","date":"2018","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/30250194","citation_count":29,"is_preprint":false},{"pmid":"24658352","id":"PMC_24658352","title":"Chemerin C9 peptide induces receptor internalization through a clathrin-independent pathway.","date":"2014","source":"Acta pharmacologica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/24658352","citation_count":28,"is_preprint":false},{"pmid":"32639008","id":"PMC_32639008","title":"Arginine-rich dipeptide-repeat proteins as phase disruptors in C9-ALS/FTD.","date":"2020","source":"Emerging topics in life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/32639008","citation_count":28,"is_preprint":false},{"pmid":"10408378","id":"PMC_10408378","title":"Phosphorylation of the complement component, C9, by an ecto-protein kinase of human leukemic cells.","date":"1999","source":"Immunopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/10408378","citation_count":28,"is_preprint":false},{"pmid":"8620918","id":"PMC_8620918","title":"Perforant path transection induces complement C9 deposition in hippocampus.","date":"1996","source":"Experimental neurology","url":"https://pubmed.ncbi.nlm.nih.gov/8620918","citation_count":28,"is_preprint":false},{"pmid":"32125157","id":"PMC_32125157","title":"c9, t11, c15-CLNA and t9, t11, c15-CLNA from Lactobacillus plantarum ZS2058 Ameliorate Dextran Sodium Sulfate-Induced Colitis in Mice.","date":"2020","source":"Journal of agricultural and food chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/32125157","citation_count":28,"is_preprint":false},{"pmid":"17123534","id":"PMC_17123534","title":"Mapping of the complement C9 binding domain in paramyosin of the blood fluke Schistosoma mansoni.","date":"2006","source":"International journal for parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/17123534","citation_count":28,"is_preprint":false},{"pmid":"6863269","id":"PMC_6863269","title":"Mechanisms for the spontaneous formation of covalently linked polymers of the terminal membranolytic complement protein (C9).","date":"1983","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/6863269","citation_count":26,"is_preprint":false},{"pmid":"3494251","id":"PMC_3494251","title":"The cytolytic protein of human lymphocytes related to the ninth component (C9) of human complement: isolation from anti-CD3-activated peripheral blood mononuclear cells.","date":"1987","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/3494251","citation_count":26,"is_preprint":false},{"pmid":"28075566","id":"PMC_28075566","title":"Chilling Stress Upregulates α-Linolenic Acid-Oxidation Pathway and Induces Volatiles of C6 and C9 Aldehydes in Mango Fruit.","date":"2017","source":"Journal of agricultural and food chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28075566","citation_count":25,"is_preprint":false},{"pmid":"32971853","id":"PMC_32971853","title":"Glycoproteomic Analysis Reveals Aberrant Expression of Complement C9 and Fibronectin in the Plasma of Patients with Colorectal Cancer.","date":"2020","source":"Proteomes","url":"https://pubmed.ncbi.nlm.nih.gov/32971853","citation_count":24,"is_preprint":false},{"pmid":"1696352","id":"PMC_1696352","title":"Comparison of channels formed by poly C9, C5b-8 and the membrane attack complex of complement.","date":"1990","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/1696352","citation_count":24,"is_preprint":false},{"pmid":"26070565","id":"PMC_26070565","title":"Compartmentation of Metabolism of the C12-, C9-, and C5-n-dicarboxylates in Rat Liver, Investigated by Mass Isotopomer Analysis: ANAPLEROSIS FROM DODECANEDIOATE.","date":"2015","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/26070565","citation_count":23,"is_preprint":false},{"pmid":"34752492","id":"PMC_34752492","title":"Polymerization of C9 enhances bacterial cell envelope damage and killing by membrane attack complex pores.","date":"2021","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/34752492","citation_count":23,"is_preprint":false},{"pmid":"1453611","id":"PMC_1453611","title":"IgA nephropathy in patients with congenital C9 deficiency.","date":"1992","source":"Kidney international","url":"https://pubmed.ncbi.nlm.nih.gov/1453611","citation_count":23,"is_preprint":false},{"pmid":"6665822","id":"PMC_6665822","title":"Structure-activity relationships of estrogens. Effects of 14-dehydrogenation and axial methyl groups at C-7, C-9 and C-11.","date":"1983","source":"Steroids","url":"https://pubmed.ncbi.nlm.nih.gov/6665822","citation_count":22,"is_preprint":false},{"pmid":"9203961","id":"PMC_9203961","title":"Mutation of recombinant complement component C9 reveals the significance of the N-terminal region for polymerization.","date":"1997","source":"Immunology","url":"https://pubmed.ncbi.nlm.nih.gov/9203961","citation_count":22,"is_preprint":false},{"pmid":"16618117","id":"PMC_16618117","title":"Functional studies of the MACPF domain of human complement protein C8alpha reveal sites for simultaneous binding of C8beta, C8gamma, and C9.","date":"2006","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16618117","citation_count":21,"is_preprint":false},{"pmid":"10072638","id":"PMC_10072638","title":"Reference typing report for complement components C6, C7 and C9 including mutations leading to deficiencies.","date":"1998","source":"Experimental and clinical immunogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/10072638","citation_count":21,"is_preprint":false},{"pmid":"24564979","id":"PMC_24564979","title":"Mapping of the complement C9 binding domain on Trichinella spiralis paramyosin.","date":"2014","source":"Parasites & vectors","url":"https://pubmed.ncbi.nlm.nih.gov/24564979","citation_count":20,"is_preprint":false},{"pmid":"12596049","id":"PMC_12596049","title":"Founder effect of the C9 R95X mutation in Orientals.","date":"2003","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/12596049","citation_count":20,"is_preprint":false},{"pmid":"10441679","id":"PMC_10441679","title":"Phylogenetic analysis of the homologous proteins of the terminal complement complex supports the emergence of C6 and C7 followed by C8 and C9.","date":"1999","source":"Journal of molecular evolution","url":"https://pubmed.ncbi.nlm.nih.gov/10441679","citation_count":20,"is_preprint":false},{"pmid":"18343507","id":"PMC_18343507","title":"Association between activation of phase 2 enzymes and down-regulation of dendritic cell maturation by c9,t11-conjugated linoleic acid.","date":"2008","source":"Immunology letters","url":"https://pubmed.ncbi.nlm.nih.gov/18343507","citation_count":20,"is_preprint":false},{"pmid":"2828929","id":"PMC_2828929","title":"Role of complement C9 and calcium in the generation of arachidonic acid and its metabolites from rat polymorphonuclear leukocytes.","date":"1987","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/2828929","citation_count":19,"is_preprint":false},{"pmid":"2857173","id":"PMC_2857173","title":"Penetration of C8 and C9 in the C5b-9 complex across the erythrocyte membrane into the cytoplasmic space.","date":"1985","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/2857173","citation_count":19,"is_preprint":false},{"pmid":"32030801","id":"PMC_32030801","title":"The dietary c9,t11-conjugated linoleic acid enriched from butter reduces breast cancer progression in vivo.","date":"2020","source":"Journal of food biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/32030801","citation_count":17,"is_preprint":false},{"pmid":"36130523","id":"PMC_36130523","title":"Nucleoporins are degraded via upregulation of ESCRT-III/Vps4 complex in Drosophila models of C9-ALS/FTD.","date":"2022","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/36130523","citation_count":17,"is_preprint":false},{"pmid":"820858","id":"PMC_820858","title":"Folate analogues altered in the C9-N10 bridge region. 10-Oxafolic acid and 10-oxaaminopterin.","date":"1976","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/820858","citation_count":16,"is_preprint":false},{"pmid":"33783477","id":"PMC_33783477","title":"The rare C9 P167S risk variant for age-related macular degeneration increases polymerization of the terminal component of the complement cascade.","date":"2021","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33783477","citation_count":16,"is_preprint":false},{"pmid":"2474318","id":"PMC_2474318","title":"Vitronectin colocalizes with Ig deposits and C9 neoantigen in discoid lupus erythematosus and dermatitis herpetiformis, but not in bullous pemphigoid.","date":"1989","source":"The British journal of dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/2474318","citation_count":16,"is_preprint":false},{"pmid":"2767685","id":"PMC_2767685","title":"The gene for human complement C9 is on chromosome 5.","date":"1989","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/2767685","citation_count":16,"is_preprint":false},{"pmid":"30953778","id":"PMC_30953778","title":"Multi-level engineering of Baeyer-Villiger monooxygenase-based Escherichia coli biocatalysts for the production of C9 chemicals from oleic acid.","date":"2019","source":"Metabolic engineering","url":"https://pubmed.ncbi.nlm.nih.gov/30953778","citation_count":16,"is_preprint":false},{"pmid":"29767720","id":"PMC_29767720","title":"Functional analyses of rare genetic variants in complement component C9 identified in patients with age-related macular degeneration.","date":"2018","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29767720","citation_count":16,"is_preprint":false},{"pmid":"8047374","id":"PMC_8047374","title":"Supplemental complement component C9 enhances the capacity of neonatal serum to kill multiple isolates of pathogenic Escherichia coli.","date":"1994","source":"Pediatric research","url":"https://pubmed.ncbi.nlm.nih.gov/8047374","citation_count":16,"is_preprint":false},{"pmid":"34355237","id":"PMC_34355237","title":"Evaluation of the immunomodulatory effects of C9-13-CPs in macrophages.","date":"2021","source":"Acta biochimica et biophysica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/34355237","citation_count":15,"is_preprint":false},{"pmid":"7697921","id":"PMC_7697921","title":"The kinetics and distribution of C9 and SC5b-9 in vivo: effects of complement activation.","date":"1995","source":"Clinical and experimental immunology","url":"https://pubmed.ncbi.nlm.nih.gov/7697921","citation_count":15,"is_preprint":false},{"pmid":"19879250","id":"PMC_19879250","title":"Angiotensin-induced EGF receptor transactivation inhibits insulin signaling in C9 hepatic cells.","date":"2009","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/19879250","citation_count":15,"is_preprint":false},{"pmid":"12463754","id":"PMC_12463754","title":"Binding of human complement C8 to C9: role of the N-terminal modules in the C8 alpha subunit.","date":"2002","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12463754","citation_count":15,"is_preprint":false},{"pmid":"29981471","id":"PMC_29981471","title":"Membrane attack complex-associated molecules from redlip mullet (Liza haematocheila): Molecular characterization and transcriptional evidence of C6, C7, C8β, and C9 in innate immunity.","date":"2018","source":"Fish & shellfish immunology","url":"https://pubmed.ncbi.nlm.nih.gov/29981471","citation_count":13,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":48005,"output_tokens":8133,"usd":0.133005},"stage2":{"model":"claude-opus-4-6","input_tokens":11976,"output_tokens":4552,"usd":0.26052},"total_usd":0.393525,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1985,\n      \"finding\": \"C9 cDNA sequence revealed the protein has an N-terminal half rich in cysteine residues with homology to LDL receptor cysteine-rich domains, and a carboxy-terminal half that reacts with lipid-soluble photoaffinity probes, establishing the topology of C9 with distinct hydrophilic and lipid-interacting regions.\",\n      \"method\": \"cDNA sequencing, proteolytic fragment analysis, monoclonal antibody epitope mapping on Western blots\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — primary sequence determination with multiple orthogonal structural validation methods\",\n      \"pmids\": [\"4018030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1970,\n      \"finding\": \"C9 participates in the terminal lytic step of complement-mediated cell killing downstream of C5b-7, requiring C8 binding first; C5b-6 complex activates C7 to form C567 which confers on cell membranes the capacity to be lysed by C8 and C9.\",\n      \"method\": \"Hemolytic complement intermediate reconstitution assays with purified components\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with purified complement components establishing pathway order\",\n      \"pmids\": [\"4193935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1977,\n      \"finding\": \"C9 inserts into the lipid bilayer of erythrocyte membranes as an integral membrane protein upon complement activation; protease treatment released only 9-19% of bound C9, and SDS was required for extraction, demonstrating membrane integration with a ~18 kDa domain penetrating the bilayer.\",\n      \"method\": \"Radiolabeled C9 binding, trypsin/chymotrypsin digestion, EDTA elution, SDS extraction, and SDS-PAGE of membrane-associated fragments\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal biochemical methods demonstrating membrane insertion\",\n      \"pmids\": [\"559700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1983,\n      \"finding\": \"C9 spontaneously polymerizes at 37°C through a mechanism involving disulfide bond formation; SDS/DTT-resistant polymers require free sulfhydryl groups that become exposed during polymerization, and iodoacetamide completely inhibited covalent polymer formation.\",\n      \"method\": \"In vitro C9 polymerization assays, SDS-PAGE under reducing/non-reducing conditions, SH-specific reagents, gel filtration\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical reconstitution with chemical inhibitors establishing mechanism\",\n      \"pmids\": [\"6863269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"S-protein (vitronectin) inhibits C9 polymerization within the SC5b-9 complex by two mechanisms: blocking the membrane binding site of C5b-7 and inhibiting C9 polymerization by SC5b-8, resulting in a wedge-shaped non-tubular SC5b-9 complex lacking poly C9.\",\n      \"method\": \"SDS-PAGE quantification of poly C9, electron microscopy, biotinyl-S-protein localization with avidin-gold\",\n      \"journal\": \"Acta pathologica, microbiologica, et immunologica Scandinavica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with purified proteins plus structural visualization\",\n      \"pmids\": [\"6587746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"Electron microscopy revealed that monomeric C9 has an ellipsoid shape (70×50 Å), and poly(C9) forms a hollow cylinder of 12-16 subunits; the C9a (N-terminal) region localizes around the torus and base, while C9b (C-terminal) epitopes are concentrated at the torus and base; oligosaccharides are on the periphery of the torus.\",\n      \"method\": \"Transmission electron microscopy, immunoelectron microscopy with C9a/C9b-specific antibodies, concanavalin A-gold labeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural imaging with domain-specific immunolabeling\",\n      \"pmids\": [\"4055801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"C9 insertion into the erythrocyte membrane (not merely binding or dimerization) is the key determinant of cytolytic efficiency; membrane-bound but inactive C5b-9 complexes lacking inserted C9 can exist.\",\n      \"method\": \"Photolabeling, SDS-PAGE, electroblotting, immunostaining of complement-lysed erythrocyte membranes from different species\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical demonstration distinguishing binding from functional membrane insertion\",\n      \"pmids\": [\"6470486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"C8 beta chain shares sequence homology with C9, particularly in the cysteine-rich domains and membrane-inserting regions, implying a common evolutionary origin and similar mechanism of MAC formation.\",\n      \"method\": \"cDNA cloning and sequence comparison\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — sequence-based structural inference with direct experimental cDNA data\",\n      \"pmids\": [\"3651397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"C9 contains a cysteine-rich domain homologous to the LDL receptor; antibodies to this domain crossreact with C8 alpha, and C8 alpha undergoes similar Zn2+-induced polymerization as C9, suggesting shared structural and functional properties in MAC assembly.\",\n      \"method\": \"Peptide antibody immunoblotting, Zn2+-induced polymerization assay with C8 alpha-gamma\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — crossreactive antibodies and in vitro polymerization assay supporting structural homology\",\n      \"pmids\": [\"2424021\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Perforin, the cytolytic protein of killer T cells and NK cells, shares primary sequence homology with C9 at functionally conserved regions, providing molecular evidence that a killer-cell-specific protein evolutionarily linked to C9 mediates cell-mediated cytolysis.\",\n      \"method\": \"N-terminal amino acid sequencing of purified perforin, cDNA library screening with oligonucleotide probes, sequence comparison\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct protein sequencing and cDNA identification establishing evolutionary/structural relationship\",\n      \"pmids\": [\"3261391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"The C9 gene is located on human chromosome 5 (regional localization 5p13), established by PCR of somatic cell hybrids and confirmed by in situ hybridization.\",\n      \"method\": \"Polymerase chain reaction on somatic cell hybrids, in situ hybridization\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two orthogonal methods confirming chromosomal localization\",\n      \"pmids\": [\"2744767\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"Anti-peptide antibodies that capture refolding C9 conformers during membrane insertion demonstrate that C9 must at least partly unfold to enter the membrane; some antibodies inhibit C9-mediated hemolysis without blocking polymerization and vice versa, showing that membrane insertion and polymerization are independent processes.\",\n      \"method\": \"Anti-peptide antibody capture during membrane insertion, hemolysis inhibition assays, C9 polymerization assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mechanistic dissection with sequence-specific antibodies demonstrating independence of insertion and polymerization\",\n      \"pmids\": [\"2475785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"C5b-8 forms a functional membrane channel of ~1.5 nm radius; addition of increasing C9 progressively enlarges the channel; poly C9 forms a pore of ~90-100 Å diameter; monoclonal antibodies to the poly C9 neoantigen most potently inhibit channel activity.\",\n      \"method\": \"Liposome swelling assay with molecular size markers, Renkin equation modeling, monoclonal antibody inhibition\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative functional reconstitution with purified components establishing channel properties\",\n      \"pmids\": [\"1696352\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"C9 undergoes three distinct endothermic thermal unfolding transitions (Tm ~32, 48, 53°C) reflecting formation of multiple conformers; the first transition is sensitive to calcium ions present at normal blood concentrations, and choline (abundant on membrane surfaces) lowers transition temperatures, suggesting C9 is partially unfolded at membrane surfaces in vivo to facilitate insertion.\",\n      \"method\": \"High-sensitivity differential scanning calorimetry with ion and ligand manipulation\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous biophysical characterization with systematic perturbation\",\n      \"pmids\": [\"2054360\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"CD59 binds specifically to C8 alpha chain and to the C9b fragment (37 kDa, containing the hydrophobic membrane-interaction segment) of thrombin-cleaved C9, but not to C9a; binding requires a conformational change upon surface adsorption, suggesting CD59 recognizes an activation-induced epitope.\",\n      \"method\": \"Density gradient analysis, 125I-CD59 binding to plastic/nitrocellulose-adsorbed proteins, ligand blotting, thrombin digestion, subunit analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — saturable binding assays with defined protein fragments establishing the binding domain\",\n      \"pmids\": [\"1377690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Clusterin binds specifically to C7, C8 beta, and the C9b domain of C9; it recognizes a site exposed during the hydrophilic-amphiphilic transition of C9 and inhibits C5b-9-mediated hemolysis and Zn2+-induced C9 polymerization; both subunits of clusterin interact with C9 and are equally potent inhibitors.\",\n      \"method\": \"125I-clusterin ligand blotting with Tween, competition assays with poly C9, hemolysis inhibition, C9 polymerization inhibition\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple direct binding and functional assays with purified proteins\",\n      \"pmids\": [\"8345200\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"ApoA-I and ApoA-II bind to poly C9 but not monomeric C9, interacting with a polymerization-dependent conformer; both inhibit Zn2+-induced C9 polymerization and reduce C9 incorporation into C5b-9 on endothelial cells, explaining HDL's protective effect against complement.\",\n      \"method\": \"Binding assays to poly C9, Zn2+-induced polymerization inhibition, C9 incorporation assay on endothelial cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct binding and functional inhibition assays with purified proteins\",\n      \"pmids\": [\"8429039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Vitronectin inhibits terminal complement complex formation through two distinct binding sites: one for SC5b-7 formation (blocking C5b-7 membrane insertion) and a separate heparin-binding region that inhibits C9 binding and pore formation.\",\n      \"method\": \"Hemolytic assays with peptides spanning the heparin-binding region, protamine sulfate inhibition, comparison of SC5b-7 formation vs C9 inhibition\",\n      \"journal\": \"Clinical and experimental immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional assays with defined peptides dissecting two distinct inhibitory mechanisms\",\n      \"pmids\": [\"7682159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1980,\n      \"finding\": \"C9 generates a mechanistically distinct membrane lesion from C8 alone: C8 alone causes 86Rb release without hemoglobin release (small pore), while C8/C9 together cause rapid parallel release of both 86Rb and hemoglobin (larger lytic lesion).\",\n      \"method\": \"Simultaneous 86Rb and hemoglobin release assays with EAC1-7 intermediates and defined C8/C9 concentrations\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with defined components and dual functional readouts\",\n      \"pmids\": [\"7365242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"C8 and C9 penetrate across the erythrocyte membrane bilayer into the cytoplasmic space, as demonstrated by transglutaminase cross-linking from both interior and exterior of erythrocyte ghosts.\",\n      \"method\": \"Radiolabeled complement proteins, transglutaminase cross-linking from inside/outside erythrocyte ghosts, SDS-PAGE\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — novel transglutaminase topology assay with appropriate controls\",\n      \"pmids\": [\"2857173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The N-terminal 16 amino acids of C9 are crucial for preventing spontaneous self-polymerization; deletion of 16-23 N-terminal amino acids caused uncontrolled polymerization, while deletion of only 4-12 amino acids enhanced lytic activity and C5b-8 binding without spontaneous polymerization; a WSEWS motif (residues 27-31) maintains the N-terminus in a protected conformation.\",\n      \"method\": \"Site-directed mutagenesis, baculovirus/insect cell expression of N-terminal deletion mutants, hemolysis assays, C5b-8 binding assays\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with functional readouts establishing the polymerization control domain\",\n      \"pmids\": [\"9203961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"C9 is phosphorylated on serine residue(s) in the N-terminal C9a portion by an ecto-protein kinase CK2 on the surface of leukemia cells; phosphorylated C9 has reduced hemolytic activity; only native but not polymerized C9 serves as substrate.\",\n      \"method\": \"Radiolabeled phosphorylation assays, thrombin cleavage fragment analysis, CK2 inhibitor studies (heparin, 2,3-diphosphoglycerate), hemolysis assays\",\n      \"journal\": \"Immunopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical identification of phosphorylation site and functional consequence\",\n      \"pmids\": [\"10408378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Extracellular CK2 (ecto-CK2) on tumor cells phosphorylates C9, reducing complement-mediated lysis; CK2 inhibitors (TBB, Emodin, DRB) augmented killing of Raji cells by complement and Rituximab; ecto-CK2 is expressed more on cancer cells than normal cells.\",\n      \"method\": \"CK2 inhibitor treatment, hemolysis assays, C5b-7-bearing cell lysis assays, CD59 blocking antibodies\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological inhibition with functional readouts on cell-surface CK2 activity\",\n      \"pmids\": [\"15902683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CD59 binds C9 through a primary recognition domain spanning residues 365-371 of C9; both C8 alpha and C9 bind to the same or overlapping site on CD59 at a hydrophobic pocket; CD59-mediated MAC inhibition involves protein-protein interaction at this defined interface.\",\n      \"method\": \"Peptide screens, competitive binding assays, functional hemolysis inhibition, computer modeling and docking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — peptide mapping combined with functional assays and structural modeling\",\n      \"pmids\": [\"16844690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Schistosoma mansoni paramyosin (Pmy) C-terminal region (residues 744-866) binds C8 and C9 and inhibits C9 polymerization and complement-mediated hemolysis; the minimal binding site for C9 was narrowed to residues 866-879 using synthetic peptides.\",\n      \"method\": \"PCR-cloning and expression of Pmy fragments, Western blot binding assays with C8/C9, hemolysis inhibition, Zn2+-induced C9 polymerization inhibition\",\n      \"journal\": \"International journal for parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping by fragmental expression with functional validation\",\n      \"pmids\": [\"17123534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The MACPF domain of C8 alpha simultaneously binds C8 beta, C8 gamma, and C9, forming a quaternary complex; the principal C9 binding site lies within the MACPF domain; C8 alpha N-terminal modules (TSP1 and LDLRA) cooperate with the MACPF domain for C9 binding.\",\n      \"method\": \"Recombinant protein expression in E. coli, binding assays, hemolytic activity assays with domain deletion/exchange constructs\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — recombinant domain analysis with functional validation\",\n      \"pmids\": [\"16618117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Trichinella spiralis paramyosin (Ts-Pmy) on the outer membrane of larvae binds complement C8 and C9 and inhibits C9 polymerization during MAC formation; antiserum against Ts-Pmy reduces larval viability in complement; the complement-binding domain was localized to the C-terminal region.\",\n      \"method\": \"Immunogold electron microscopy, immunofluorescence, recombinant protein binding assays, C9 polymerization inhibition, erythrocyte lysis inhibition, in vivo passive transfer\",\n      \"journal\": \"PLoS neglected tropical diseases\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal binding and functional assays plus in vivo validation\",\n      \"pmids\": [\"21750743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The ILY (intermedilysin) binding site on CD59 deeply overlaps with the C8 alpha and C9 binding site on CD59; both ILY and C9/C8 alpha interact with common CD59 residues; mutations increasing ILY-CD59 affinity impair the prepore-to-pore transition rather than prepore assembly.\",\n      \"method\": \"Mutagenesis of hCD59 and ILY, cytolytic activity assays, prepore assembly assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with mechanistic dissection of pore formation steps\",\n      \"pmids\": [\"21507937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Hepatitis C virus (HCV) core protein suppresses C9 mRNA and protein expression in hepatocytes via TCF-4E transcription factor-mediated promoter regulation; reduced C9 expression results in lower C5b-9 levels and impaired antimicrobial MAC function in patient sera.\",\n      \"method\": \"RT-PCR of patient liver biopsies, HCV-infected hepatocyte cultures, promoter analysis with transcription factor identification, C5b-9 ELISA, antimicrobial assay\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic promoter analysis with multiple functional readouts in patient-derived samples and cell models\",\n      \"pmids\": [\"23487461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Mortalin/GRP75 binds to C8 and C9 through its N-terminal ATPase domain via ionic interaction in a nucleotide-sensitive manner; this interaction inhibits C9 polymerization and reduces C5b-9 membrane deposition, protecting tumor cells from complement-dependent cytotoxicity.\",\n      \"method\": \"Co-IP, mortalin domain expression in bacteria, C8/C9 binding assays, Zn2+-induced C9 polymerization inhibition, C5b-9 deposition quantification by flow cytometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — domain-level binding characterization with functional consequence in defined cellular system\",\n      \"pmids\": [\"24719326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The cryo-EM structure of poly-C9 at 8 Å resolution revealed a 22-fold symmetric arrangement forming an 88-strand beta-barrel pore; the N-terminal TSP1 domain forms an extensive oligomerization interface, facilitating solution-based assembly distinct from perforin and CDCs which require membrane for oligomerization.\",\n      \"method\": \"Cryo-electron microscopy structural determination at 8 Å resolution\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural determination at near-atomic resolution with functional implications\",\n      \"pmids\": [\"26841934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Human serum C9 carries three types of glycosylation: two known N-glycosylation sites plus a novel third N-glycosylation site lacking the canonical N-X-S/T sequon; O-linked glycans in the N-terminal region; and C-terminal glycosylation; C9 binds up to two Ca2+ ions; approximately 50 distinct proteoforms co-occur.\",\n      \"method\": \"Native mass spectrometry, LC-MS/MS glycopeptide analysis, integrative proteoform mapping\",\n      \"journal\": \"Analytical chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct experimental evidence from high-resolution native MS and peptide-centric proteomics\",\n      \"pmids\": [\"28221766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Polymerization of C9 within MAC pores substantially enhances damage to both bacterial outer and inner membranes and accelerates killing of Gram-negative bacteria; a mutation locking the first transmembrane helix domain of C9 prevented polymerization without affecting C5b-8 binding; O-antigen LPS impairs C9 polymerization conferring complement resistance.\",\n      \"method\": \"Site-directed mutagenesis to lock transmembrane helix, flow cytometry of wildtype vs locked-C9 binding, bacterial membrane integrity assays, serum killing assays with E. coli and Klebsiella, O-antigen mutant complementation\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis separating C9 binding from polymerization with defined functional readouts plus genetic validation\",\n      \"pmids\": [\"34752492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"C6-deficient rats (unable to form MAC) developed significantly milder experimental allergic encephalomyelitis than C6-sufficient rats; C9 deposition was absent in C6-deficient spinal cords, P-selectin expression on endothelial cells was reduced, and T cell/macrophage infiltration was diminished, demonstrating MAC-dependent neuroinflammatory pathology.\",\n      \"method\": \"Genetic complement deficiency model (PVG/C6- vs PVG/C rats), EAE immunization, C3/C9 immunostaining, P-selectin immunostaining, cellular infiltrate analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function in a defined in vivo model with multiple mechanistic readouts\",\n      \"pmids\": [\"11970970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Supplemental C9 enhances bactericidal capacity of neonatal serum by increasing total C9 deposited onto E. coli via the classical complement pathway; neonatal serum has diminished C9 concentration as the limiting factor; C9 deposition and killing were abolished by MgEGTA (classical pathway block).\",\n      \"method\": \"Radiobinding assay with anti-C9 monoclonal antibody, immunogold electron microscopy, MgEGTA pathway block, bacterial killing assays\",\n      \"journal\": \"Pediatric research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional reconstitution with pathway dissection using pathway-specific inhibitors\",\n      \"pmids\": [\"8047374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"C8 alpha N-terminal TSP1 and LDLRA modules together with the MACPF domain form the principal binding site for C9; deletion of both N-terminal modules from C8 alpha abolished C9 binding and hemolytic activity, indicating cooperative interaction.\",\n      \"method\": \"Recombinant C8 alpha constructs with N-/C-terminal module exchanges/deletions, C9 binding assays, hemolysis assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis/deletion with functional binding and hemolysis readouts\",\n      \"pmids\": [\"12463754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The rare AMD-associated C9 P167S variant has increased propensity to polymerize and displays slightly elevated ability to induce hemolysis; MAC ring structures generated by P167S C9 appear identical to wild-type by electron microscopy, but P167S carriers have lower plasma C9 levels.\",\n      \"method\": \"Recombinant protein production, electron microscopy of MAC structures, functional hemolysis assays with C9-depleted serum, cohort plasma C9 level measurements\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — recombinant variant analysis with structural and functional validation\",\n      \"pmids\": [\"33783477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Functional analysis of C9 AMD-associated rare variants revealed that P167S spontaneously aggregates whereas other variants (F62S, G126R, T170I) fail to polymerize with zinc; P167S and F62S show decreased lytic activity; all analyzed variants affect secretion and/or polymerization of C9 without disrupting classical lytic pathway activity.\",\n      \"method\": \"Recombinant variant expression, C9 polymerization assays with zinc, hemolysis assays with C9-depleted serum and ARPE-19 cells, serum C9 concentration measurements in carriers\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic variant functional analysis with multiple orthogonal assays\",\n      \"pmids\": [\"29767720\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Complement component C9 is a serum glycoprotein that functions as the major pore-forming component of the membrane attack complex (MAC): it binds to the C5b-8 complex via the MACPF domain and N-terminal TSP1/LDLRA modules of C8 alpha, undergoes a conformational change (partial unfolding) to expose hydrophobic regions, inserts its C-terminal C9b domain through the lipid bilayer spanning both leaflets, and polymerizes through disulfide-bond formation and TSP1-domain oligomerization contacts into a 22-subunit, 88-strand beta-barrel pore (~90-100 Å diameter) that damages bacterial outer and inner membranes to cause killing; polymerization is normally restrained by the N-terminal 16 amino acids and can be inhibited by extracellular regulators (CD59 binding to residues 365-371, clusterin binding to C9b, vitronectin/S-protein, mortalin ATPase domain, apoA-I/A-II, and ecto-CK2 phosphorylation of serine residues in C9a), while parasites evade MAC killing by expressing proteins such as paramyosin that bind C9 and block polymerization.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"Complement component C9 is the principal pore-forming subunit of the membrane attack complex (MAC), mediating the terminal lytic step of complement-dependent killing of bacteria and nucleated cells. C9 binds the C5b-8 complex via the MACPF domain and N-terminal TSP1/LDLRA modules of C8 alpha [PMID:16618117, PMID:12463754], undergoes partial unfolding to expose hydrophobic regions [PMID:2475785, PMID:2054360], inserts its C-terminal C9b domain through the lipid bilayer spanning both leaflets [PMID:559700, PMID:2857173], and polymerizes through disulfide bonds and TSP1-domain oligomerization contacts into a 22-subunit, 88-strand β-barrel pore (~90–100 Å diameter) that damages both outer and inner bacterial membranes [PMID:26841934, PMID:34752492, PMID:6863269]. Polymerization is restrained by the N-terminal 16 amino acids and a WSEWS motif [PMID:9203961], and is inhibited by multiple extracellular regulators including CD59 (binding C9 residues 365–371) [PMID:16844690], clusterin (binding C9b) [PMID:8345200], vitronectin [PMID:6587746], mortalin [PMID:24719326], apolipoproteins A-I/A-II [PMID:8429039], and ecto-CK2 phosphorylation of the C9a domain [PMID:10408378, PMID:15902683]. Rare C9 variants (P167S, F62S, G126R, T170I) that alter polymerization or secretion are associated with age-related macular degeneration [PMID:29767720, PMID:33783477].\",\n  \"teleology\": [\n    {\n      \"year\": 1970,\n      \"claim\": \"Establishing C9's position in the complement cascade: C9 was shown to act at the terminal lytic step downstream of C5b-8, resolving how complement effector assembly culminates in membrane damage.\",\n      \"evidence\": \"Hemolytic reconstitution assays with purified complement intermediates on erythrocytes\",\n      \"pmids\": [\"4193935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of C9-mediated lysis unknown\", \"Stoichiometry undefined\", \"Whether C9 acts enzymatically or structurally was unclear\"]\n    },\n    {\n      \"year\": 1980,\n      \"claim\": \"C9 was shown to generate a qualitatively larger lytic lesion than C8 alone, establishing that C9 transforms a small C5b-8 pore into a fully lytic channel.\",\n      \"evidence\": \"Simultaneous 86Rb and hemoglobin release assays with defined C8/C9 on EAC1-7 intermediates\",\n      \"pmids\": [\"7365242\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether C9 inserts into the membrane or acts peripherally was unknown\", \"Molecular structure of the lesion undefined\"]\n    },\n    {\n      \"year\": 1977,\n      \"claim\": \"C9 was demonstrated to insert as an integral membrane protein penetrating the lipid bilayer, resolving that lysis involves physical C9 membrane integration rather than enzymatic action.\",\n      \"evidence\": \"Radiolabeled C9 binding, protease resistance, SDS extraction from erythrocyte membranes\",\n      \"pmids\": [\"559700\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Topology of transmembrane insertion unknown\", \"Whether C9 spans both leaflets was unresolved\"]\n    },\n    {\n      \"year\": 1983,\n      \"claim\": \"Discovery that C9 spontaneously polymerizes through disulfide bond formation established the covalent basis of MAC ring assembly and explained how tubular pores form.\",\n      \"evidence\": \"In vitro polymerization assays with SH-specific reagents (iodoacetamide) blocking covalent polymer formation\",\n      \"pmids\": [\"6863269\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the polymer unknown\", \"Relationship of polymerization to membrane insertion unclear\"]\n    },\n    {\n      \"year\": 1984,\n      \"claim\": \"Two key advances: (1) C9 membrane insertion, not merely binding, was shown to determine cytolytic efficiency; (2) vitronectin/S-protein was identified as the first soluble inhibitor of C9 polymerization, revealing host regulation of MAC.\",\n      \"evidence\": \"Photolabeling and SDS-PAGE distinguishing bound from inserted C9 [PMID:6470486]; electron microscopy and SDS-PAGE of SC5b-9 ± S-protein [PMID:6587746]\",\n      \"pmids\": [\"6470486\", \"6587746\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of membrane-inserting domain unknown\", \"Whether insertion and polymerization are independent processes was unresolved\"]\n    },\n    {\n      \"year\": 1985,\n      \"claim\": \"Structural and sequence characterization of C9 revealed its domain architecture — an N-terminal cysteine-rich/LDL-receptor-homologous region and a C-terminal lipid-interacting C9b domain — and electron microscopy showed poly-C9 as a 12–16 subunit hollow cylinder, while transmembrane topology was confirmed by transglutaminase cross-linking from both membrane faces.\",\n      \"evidence\": \"cDNA sequencing [PMID:4018030]; immunoelectron microscopy with domain-specific antibodies [PMID:4055801]; transglutaminase cross-linking from inside/outside erythrocyte ghosts [PMID:2857173]\",\n      \"pmids\": [\"4018030\", \"4055801\", \"2857173\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution structure unavailable\", \"Exact stoichiometry debated (12–16 vs later 22 subunits)\", \"Mechanism of conformational change during insertion unknown\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"Perforin was shown to share primary sequence homology with C9, establishing that a conserved MACPF-domain pore-forming mechanism operates in both innate complement and adaptive cytotoxic lymphocyte killing.\",\n      \"evidence\": \"N-terminal sequencing of purified perforin and cDNA identification with sequence comparison\",\n      \"pmids\": [\"3261391\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether perforin and C9 polymerize by identical mechanisms unknown\", \"Whether MACPF domain is sufficient for pore formation not tested\"]\n    },\n    {\n      \"year\": 1989,\n      \"claim\": \"Anti-peptide antibodies trapping refolding intermediates demonstrated that C9 must partially unfold during membrane insertion, and that membrane insertion and polymerization are mechanistically independent processes.\",\n      \"evidence\": \"Anti-peptide antibody capture during insertion, separate inhibition of hemolysis vs polymerization\",\n      \"pmids\": [\"2475785\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific domains refold during insertion was not determined\", \"Structural basis of the unfolded intermediate unknown\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Quantitative channel sizing established that poly-C9 forms a ~90–100 Å pore and that incremental C9 addition progressively enlarges the C5b-8 channel, defining the functional pore dimensions.\",\n      \"evidence\": \"Liposome swelling assay with molecular size markers and Renkin equation modeling\",\n      \"pmids\": [\"1696352\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact stoichiometry per pore still debated\", \"Dynamic behavior of partially assembled pores unknown\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Biophysical studies revealed three distinct thermal unfolding transitions in C9, with the first sensitive to physiological calcium and membrane-mimetic choline, explaining how membrane surfaces promote partial C9 unfolding to facilitate insertion in vivo.\",\n      \"evidence\": \"High-sensitivity differential scanning calorimetry with ion and ligand perturbation\",\n      \"pmids\": [\"2054360\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which domain unfolds at each transition not mapped\", \"In vivo relevance of choline-induced unfolding unconfirmed\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Multiple soluble inhibitors of C9 polymerization were mapped: CD59 was shown to bind C9b and C8 alpha recognizing activation-induced epitopes; clusterin binds C9b during the hydrophilic-to-amphiphilic transition; and apoA-I/A-II bind selectively to poly-C9 conformers — collectively revealing layered host regulation of MAC assembly.\",\n      \"evidence\": \"Ligand blotting with 125I-CD59 to thrombin-cleaved C9 fragments [PMID:1377690]; 125I-clusterin binding, hemolysis and polymerization inhibition [PMID:8345200]; poly-C9 binding and Zn2+-induced polymerization inhibition by apolipoproteins [PMID:8429039]; vitronectin heparin-binding domain peptides [PMID:7682159]\",\n      \"pmids\": [\"1377690\", \"8345200\", \"8429039\", \"7682159\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of inhibitor-C9 interfaces unresolved\", \"Relative contributions of each inhibitor in vivo unknown\", \"Whether inhibitors act cooperatively or redundantly not tested\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"The N-terminal 16 amino acids were identified as an intrinsic polymerization restraint: deletion caused spontaneous self-polymerization, while a WSEWS motif (residues 27–31) maintains this autoinhibitory conformation, establishing the molecular switch controlling C9 activation.\",\n      \"evidence\": \"Baculovirus-expressed N-terminal deletion mutants with hemolysis and C5b-8 binding assays\",\n      \"pmids\": [\"9203961\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How C5b-8 binding relieves N-terminal autoinhibition unknown\", \"Structural basis of WSEWS motif function not determined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Ecto-CK2 on leukemia cell surfaces was found to phosphorylate serine residues in the C9a domain, reducing hemolytic activity — identifying post-translational modification as a cell-surface immune evasion mechanism.\",\n      \"evidence\": \"Radiolabeled phosphorylation, thrombin cleavage fragment analysis, CK2 inhibitors, hemolysis assays\",\n      \"pmids\": [\"10408378\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Exact phosphorylation site(s) not identified at residue level\", \"In vivo significance in tumor immune evasion not validated genetically\", \"Whether phosphorylation affects polymerization directly untested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Two advances refined the mechanism: (1) C8 alpha's N-terminal TSP1 and LDLRA modules were shown to cooperate with the MACPF domain for C9 recruitment; (2) MAC-dependent neuroinflammation was demonstrated in vivo using C6-deficient rats, linking C9-containing pores to disease pathology.\",\n      \"evidence\": \"Recombinant C8α domain deletions with C9 binding/hemolysis assays [PMID:12463754]; EAE in PVG/C6- vs C6+ rats with C9 immunostaining [PMID:11970970]\",\n      \"pmids\": [\"12463754\", \"11970970\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution structure of C8α–C9 interface unknown\", \"Whether MAC contribution to neuroinflammation involves sublytic signaling or cell lysis unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"CD59's binding site on C9 was mapped to residues 365–371, overlapping with the C8α binding interface on CD59, and parasitic paramyosin was shown to inhibit C9 polymerization through defined C-terminal binding sites — revealing convergent immune evasion strategies at the C9 level.\",\n      \"evidence\": \"Peptide screens, competitive binding, and hemolysis inhibition for CD59–C9 [PMID:16844690]; recombinant paramyosin fragments binding C9 and inhibiting polymerization [PMID:17123534]; MACPF domain analysis of C8α–C9 interaction [PMID:16618117]\",\n      \"pmids\": [\"16844690\", \"17123534\", \"16618117\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure of CD59–C9 complex unavailable\", \"Whether paramyosin mimics CD59's mechanism of inhibition unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mortalin/GRP75 was identified as a nucleotide-sensitive C9 binding partner whose ATPase domain inhibits C9 polymerization and MAC deposition, representing a novel chaperone-mediated complement evasion mechanism on tumor cells.\",\n      \"evidence\": \"Co-IP, recombinant mortalin domain binding, Zn2+-induced C9 polymerization inhibition, flow cytometry of C5b-9 deposition\",\n      \"pmids\": [\"24719326\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mortalin acts extracellularly or at the cell surface in vivo unclear\", \"Structural basis of nucleotide-dependent C9 release unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Cryo-EM at 8 Å resolution revealed that poly-C9 forms a 22-fold symmetric ring with an 88-strand β-barrel, with the N-terminal TSP1 domain mediating oligomerization contacts — distinguishing C9 from perforin and CDCs, which require membrane for oligomerization.\",\n      \"evidence\": \"Cryo-electron microscopy structural determination of poly-C9\",\n      \"pmids\": [\"26841934\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution structure of monomeric C9 and full MAC not yet available\", \"Mechanism of conformational switch from monomer to β-hairpin not visualized\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Systematic functional analysis of rare AMD-associated C9 variants (P167S, F62S, G126R, T170I) showed that these variants alter polymerization propensity and/or secretion, directly linking C9 polymerization dysregulation to age-related macular degeneration.\",\n      \"evidence\": \"Recombinant variant expression, Zn2+-induced polymerization, hemolysis assays, serum C9 levels in carriers\",\n      \"pmids\": [\"29767720\", \"33783477\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which altered polymerization leads to retinal pathology unknown\", \"Whether variants affect MAC assembly on RPE cells specifically not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A polymerization-locked C9 mutant demonstrated that C9 polymerization within the MAC substantially enhances damage to both Gram-negative bacterial membranes and accelerates killing, while O-antigen LPS impairs C9 polymerization as a bacterial resistance mechanism.\",\n      \"evidence\": \"Transmembrane helix-locked C9 mutant, bacterial membrane integrity assays, serum killing of E. coli and Klebsiella, O-antigen mutant complementation\",\n      \"pmids\": [\"34752492\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether polymerization is equally important for killing Gram-positive bacteria unknown\", \"Mechanism by which O-antigen sterically or biochemically blocks polymerization not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the atomic-resolution structure of the complete C5b-9 MAC with C9 in its membrane-inserted state, the precise conformational pathway from monomeric C9 to β-hairpin insertion, the mechanism by which C5b-8 binding relieves N-terminal autoinhibition, and how C9 polymerization dysregulation causes retinal degeneration in AMD.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full atomic MAC structure with lipid bilayer not determined\", \"Conformational trajectory of C9 monomer-to-pore transition not captured\", \"Pathogenic mechanism linking C9 variants to AMD retinal pathology undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2, 3, 5, 12, 30]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 2, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [1, 4, 15, 16]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 6, 19]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 12, 32, 33, 34]}\n    ],\n    \"complexes\": [\n      \"Membrane attack complex (MAC/C5b-9)\"\n    ],\n    \"partners\": [\n      \"C8A\",\n      \"C8B\",\n      \"CD59\",\n      \"CLU\",\n      \"VTN\",\n      \"HSPA9\",\n      \"APOA1\",\n      \"APOA2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}