Affinage

C9

Complement component C9 · UniProt P02748

Length
559 aa
Mass
63.2 kDa
Annotated
2026-04-28
100 papers in source corpus 38 papers cited in narrative 38 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

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).

Mechanistic history

Synthesis pass · year-by-year structured walk · 19 steps
  1. 1970 High

    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

    PMID:4193935

    Open questions at the time
    • Mechanism of C9-mediated lysis unknown
    • Stoichiometry undefined
    • Whether C9 acts enzymatically or structurally was unclear
  2. 1980 High

    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

    PMID:7365242

    Open questions at the time
    • Whether C9 inserts into the membrane or acts peripherally was unknown
    • Molecular structure of the lesion undefined
  3. 1977 High

    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

    PMID:559700

    Open questions at the time
    • Topology of transmembrane insertion unknown
    • Whether C9 spans both leaflets was unresolved
  4. 1983 High

    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

    PMID:6863269

    Open questions at the time
    • Stoichiometry of the polymer unknown
    • Relationship of polymerization to membrane insertion unclear
  5. 1984 High

    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]

    PMID:6470486 PMID:6587746

    Open questions at the time
    • Identity of membrane-inserting domain unknown
    • Whether insertion and polymerization are independent processes was unresolved
  6. 1985 High

    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]

    PMID:2857173 PMID:4018030 PMID:4055801

    Open questions at the time
    • Atomic-resolution structure unavailable
    • Exact stoichiometry debated (12–16 vs later 22 subunits)
    • Mechanism of conformational change during insertion unknown
  7. 1988 High

    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

    PMID:3261391

    Open questions at the time
    • Whether perforin and C9 polymerize by identical mechanisms unknown
    • Whether MACPF domain is sufficient for pore formation not tested
  8. 1989 High

    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

    PMID:2475785

    Open questions at the time
    • Which specific domains refold during insertion was not determined
    • Structural basis of the unfolded intermediate unknown
  9. 1990 High

    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

    PMID:1696352

    Open questions at the time
    • Exact stoichiometry per pore still debated
    • Dynamic behavior of partially assembled pores unknown
  10. 1991 High

    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

    PMID:2054360

    Open questions at the time
    • Which domain unfolds at each transition not mapped
    • In vivo relevance of choline-induced unfolding unconfirmed
  11. 1993 High

    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]

    PMID:1377690 PMID:7682159 PMID:8345200 PMID:8429039

    Open questions at the time
    • Structural basis of inhibitor-C9 interfaces unresolved
    • Relative contributions of each inhibitor in vivo unknown
    • Whether inhibitors act cooperatively or redundantly not tested
  12. 1997 High

    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

    PMID:9203961

    Open questions at the time
    • How C5b-8 binding relieves N-terminal autoinhibition unknown
    • Structural basis of WSEWS motif function not determined
  13. 1999 Medium

    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

    PMID:10408378

    Open questions at the time
    • 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
  14. 2002 High

    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]

    PMID:11970970 PMID:12463754

    Open questions at the time
    • Atomic-resolution structure of C8α–C9 interface unknown
    • Whether MAC contribution to neuroinflammation involves sublytic signaling or cell lysis unclear
  15. 2006 High

    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]

    PMID:16618117 PMID:16844690 PMID:17123534

    Open questions at the time
    • Crystal structure of CD59–C9 complex unavailable
    • Whether paramyosin mimics CD59's mechanism of inhibition unknown
  16. 2014 High

    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

    PMID:24719326

    Open questions at the time
    • Whether mortalin acts extracellularly or at the cell surface in vivo unclear
    • Structural basis of nucleotide-dependent C9 release unknown
  17. 2016 High

    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

    PMID:26841934

    Open questions at the time
    • Atomic-resolution structure of monomeric C9 and full MAC not yet available
    • Mechanism of conformational switch from monomer to β-hairpin not visualized
  18. 2018 High

    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

    PMID:29767720 PMID:33783477

    Open questions at the time
    • Mechanism by which altered polymerization leads to retinal pathology unknown
    • Whether variants affect MAC assembly on RPE cells specifically not tested
  19. 2021 High

    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

    PMID:34752492

    Open questions at the time
    • Whether polymerization is equally important for killing Gram-positive bacteria unknown
    • Mechanism by which O-antigen sterically or biochemically blocks polymerization not resolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • 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.
  • 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

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 5 GO:0008289 lipid binding 3
Localization
GO:0005576 extracellular region 4 GO:0005886 plasma membrane 3
Pathway
R-HSA-168256 Immune System 5
Partners
APOA1APOA2C8AC8BCD59CLUHSPA9VTN
Complex memberships
Membrane attack complex (MAC/C5b-9)

Evidence

Reading pass · 38 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1985 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. cDNA sequencing, proteolytic fragment analysis, monoclonal antibody epitope mapping on Western blots The EMBO journal High 4018030
1970 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. Hemolytic complement intermediate reconstitution assays with purified components The Journal of experimental medicine High 4193935
1977 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. Radiolabeled C9 binding, trypsin/chymotrypsin digestion, EDTA elution, SDS extraction, and SDS-PAGE of membrane-associated fragments Journal of immunology High 559700
1983 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. In vitro C9 polymerization assays, SDS-PAGE under reducing/non-reducing conditions, SH-specific reagents, gel filtration The Journal of biological chemistry High 6863269
1984 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. SDS-PAGE quantification of poly C9, electron microscopy, biotinyl-S-protein localization with avidin-gold Acta pathologica, microbiologica, et immunologica Scandinavica High 6587746
1985 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. Transmission electron microscopy, immunoelectron microscopy with C9a/C9b-specific antibodies, concanavalin A-gold labeling The Journal of biological chemistry High 4055801
1984 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. Photolabeling, SDS-PAGE, electroblotting, immunostaining of complement-lysed erythrocyte membranes from different species Journal of immunology High 6470486
1985 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. cDNA cloning and sequence comparison Biochemistry Medium 3651397
1986 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. Peptide antibody immunoblotting, Zn2+-induced polymerization assay with C8 alpha-gamma Proceedings of the National Academy of Sciences of the United States of America Medium 2424021
1988 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-terminal amino acid sequencing of purified perforin, cDNA library screening with oligonucleotide probes, sequence comparison Nature High 3261391
1989 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. Polymerase chain reaction on somatic cell hybrids, in situ hybridization Genomics High 2744767
1989 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. Anti-peptide antibody capture during membrane insertion, hemolysis inhibition assays, C9 polymerization assays Nature High 2475785
1990 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. Liposome swelling assay with molecular size markers, Renkin equation modeling, monoclonal antibody inhibition Molecular immunology High 1696352
1991 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. High-sensitivity differential scanning calorimetry with ion and ligand manipulation Biochemistry High 2054360
1992 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. Density gradient analysis, 125I-CD59 binding to plastic/nitrocellulose-adsorbed proteins, ligand blotting, thrombin digestion, subunit analysis The Journal of biological chemistry High 1377690
1993 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. 125I-clusterin ligand blotting with Tween, competition assays with poly C9, hemolysis inhibition, C9 polymerization inhibition Journal of immunology High 8345200
1993 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. Binding assays to poly C9, Zn2+-induced polymerization inhibition, C9 incorporation assay on endothelial cells The Journal of biological chemistry High 8429039
1993 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. Hemolytic assays with peptides spanning the heparin-binding region, protamine sulfate inhibition, comparison of SC5b-7 formation vs C9 inhibition Clinical and experimental immunology Medium 7682159
1980 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). Simultaneous 86Rb and hemoglobin release assays with EAC1-7 intermediates and defined C8/C9 concentrations Journal of immunology High 7365242
1985 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. Radiolabeled complement proteins, transglutaminase cross-linking from inside/outside erythrocyte ghosts, SDS-PAGE The Journal of biological chemistry High 2857173
1997 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. Site-directed mutagenesis, baculovirus/insect cell expression of N-terminal deletion mutants, hemolysis assays, C5b-8 binding assays Immunology High 9203961
1999 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. Radiolabeled phosphorylation assays, thrombin cleavage fragment analysis, CK2 inhibitor studies (heparin, 2,3-diphosphoglycerate), hemolysis assays Immunopharmacology Medium 10408378
2005 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. CK2 inhibitor treatment, hemolysis assays, C5b-7-bearing cell lysis assays, CD59 blocking antibodies European journal of immunology Medium 15902683
2006 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. Peptide screens, competitive binding assays, functional hemolysis inhibition, computer modeling and docking The Journal of biological chemistry High 16844690
2006 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. PCR-cloning and expression of Pmy fragments, Western blot binding assays with C8/C9, hemolysis inhibition, Zn2+-induced C9 polymerization inhibition International journal for parasitology Medium 17123534
2006 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. Recombinant protein expression in E. coli, binding assays, hemolytic activity assays with domain deletion/exchange constructs Biochemistry High 16618117
2011 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. Immunogold electron microscopy, immunofluorescence, recombinant protein binding assays, C9 polymerization inhibition, erythrocyte lysis inhibition, in vivo passive transfer PLoS neglected tropical diseases High 21750743
2011 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. Mutagenesis of hCD59 and ILY, cytolytic activity assays, prepore assembly assays The Journal of biological chemistry High 21507937
2013 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. RT-PCR of patient liver biopsies, HCV-infected hepatocyte cultures, promoter analysis with transcription factor identification, C5b-9 ELISA, antimicrobial assay Journal of virology High 23487461
2014 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. Co-IP, mortalin domain expression in bacteria, C8/C9 binding assays, Zn2+-induced C9 polymerization inhibition, C5b-9 deposition quantification by flow cytometry The Journal of biological chemistry High 24719326
2016 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. Cryo-electron microscopy structural determination at 8 Å resolution Nature communications High 26841934
2017 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. Native mass spectrometry, LC-MS/MS glycopeptide analysis, integrative proteoform mapping Analytical chemistry High 28221766
2021 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. 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 PLoS pathogens High 34752492
2002 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. Genetic complement deficiency model (PVG/C6- vs PVG/C rats), EAE immunization, C3/C9 immunostaining, P-selectin immunostaining, cellular infiltrate analysis Journal of immunology High 11970970
1994 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). Radiobinding assay with anti-C9 monoclonal antibody, immunogold electron microscopy, MgEGTA pathway block, bacterial killing assays Pediatric research Medium 8047374
2002 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. Recombinant C8 alpha constructs with N-/C-terminal module exchanges/deletions, C9 binding assays, hemolysis assays Biochemistry High 12463754
2021 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. Recombinant protein production, electron microscopy of MAC structures, functional hemolysis assays with C9-depleted serum, cohort plasma C9 level measurements Human molecular genetics High 33783477
2018 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. Recombinant variant expression, C9 polymerization assays with zinc, hemolysis assays with C9-depleted serum and ARPE-19 cells, serum C9 concentration measurements in carriers Human molecular genetics High 29767720

Source papers

Stage 0 corpus · 100 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2013 Rare variants in CFI, C3 and C9 are associated with high risk of advanced age-related macular degeneration. Nature genetics 292 24036952
1988 Homology of perforin to the ninth component of complement (C9). Nature 266 3261391
1970 Reactive lysis: the complement-mediated lysis of unsensitized cells. II. The characterization of activated reactor as C56 and the participation of C8 and C9. The Journal of experimental medicine 259 4193935
2013 Hox-C9 activates the intrinsic pathway of apoptosis and is associated with spontaneous regression in neuroblastoma. Cell death & disease 202 23579273
1985 The sequence and topology of human complement component C9. The EMBO journal 177 4018030
1993 Clusterin, the human apolipoprotein and complement inhibitor, binds to complement C7, C8 beta, and the b domain of C9. Journal of immunology (Baltimore, Md. : 1950) 140 8345200
2011 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. Leukemia 115 21769103
2016 Structure of the poly-C9 component of the complement membrane attack complex. Nature communications 110 26841934
1984 Inhibition of C9 polymerization within the SC5b-9 complex of complement by S-protein. Acta pathologica, microbiologica, et immunologica Scandinavica. Supplement 107 6587746
1992 The human complement regulatory protein CD59 binds to the alpha-chain of C8 and to the "b"domain of C9. The Journal of biological chemistry 105 1377690
2011 Phosphoinositide-specific phospholipase C9 is involved in the thermotolerance of Arabidopsis. The Plant journal : for cell and molecular biology 98 22007900
1993 Vitronectin-mediated inhibition of complement: evidence for different binding sites for C5b-7 and C9. Clinical and experimental immunology 96 7682159
1977 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. Journal of immunology (Baltimore, Md. : 1950) 95 559700
2016 Increased prevalence of autoimmune disease within C9 and FTD/MND cohorts: Completing the picture. Neurology(R) neuroimmunology & neuroinflammation 84 27844039
2006 Defining the CD59-C9 binding interaction. The Journal of biological chemistry 83 16844690
1993 Interaction between apolipoproteins A-I and A-II and the membrane attack complex of complement. Affinity of the apoproteins for polymeric C9. The Journal of biological chemistry 80 8429039
2019 Antibody Therapy Targeting RAN Proteins Rescues C9 ALS/FTD Phenotypes in C9orf72 Mouse Model. Neuron 77 31831332
1996 Complement in acute and chronic arthritides: assessment of C3c, C9, and protectin (CD59) in synovial membrane. Annals of the rheumatic diseases 76 9014582
1987 Complementary DNA cloning of complement C8 beta and its sequence homology to C9. Biochemistry 71 3651397
1989 The gene for human complement component C9 mapped to chromosome 5 by polymerase chain reaction. Genomics 63 2744767
2020 TFEB/Mitf links impaired nuclear import to autophagolysosomal dysfunction in C9-ALS. eLife 59 33300868
2009 Candida albicans sphingolipid C9-methyltransferase is involved in hyphal elongation. Microbiology (Reading, England) 59 20019081
1986 Synthesis of complement components C5, C6, C7, C8 and C9 in vitro by human monocytes and assembly of the terminal complement complex. Scandinavian journal of immunology 58 3764345
2020 C9orf72 loss-of-function: a trivial, stand-alone or additive mechanism in C9 ALS/FTD? Acta neuropathologica 57 32876811
2005 Identification of fungal sphingolipid C9-methyltransferases by phylogenetic profiling. The Journal of biological chemistry 56 16339149
2010 Upregulation of plasma C9 protein in gastric cancer patients. Proteomics 55 20707004
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