{"gene":"C4B","run_date":"2026-04-28T17:12:38","timeline":{"discoveries":[{"year":1984,"finding":"C4b-binding protein (C4BP) has a spider-like ultrastructure composed of seven identical disulfide-linked tentacle subunits (~70 kDa each) arranged around a central ringlike core (~160 kDa), as revealed by electron microscopy of chymotrypsin-generated fragments.","method":"Limited proteolysis + electron microscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct structural characterization by EM with biochemical fractionation, foundational paper","pmids":["6480575"],"is_preprint":false},{"year":1985,"finding":"C4BP belongs to a multi-gene family of C3b/C4b-binding regulatory proteins that share a common ~60-amino-acid short consensus repeat (SCR/CCP) structural element, including factor H, CR1, DAF, and C2/factor B.","method":"Amino acid and nucleotide sequencing, structural comparison","journal":"Immunology today","confidence":"High","confidence_rationale":"Tier 1 — primary sequence analysis establishing domain architecture, replicated across multiple proteins","pmids":["25289982"],"is_preprint":false},{"year":1986,"finding":"C4B isotype binds predominantly via ester linkages to cell surfaces, while C4A preferentially forms amide bonds; C4B deposited during classical pathway activation can activate the alternative complement pathway.","method":"Chemical modification of erythrocyte amino groups, SDS-PAGE of radiolabeled C4 isotypes on multiple cell lines; hemolytic assays with C2-deficient serum and Mg-EGTA conditions","journal":"Journal of immunology / Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical assays with multiple cell types and chemical modification controls, replicated across multiple papers","pmids":["3512717","2937839"],"is_preprint":false},{"year":1987,"finding":"The protein S-binding site on C4BP is located in the central core (~160 kDa chymotrypsin fragment), not the tentacles, and requires intact disulfide bonds; protein S protects this site from proteolysis.","method":"Chymotrypsin proteolysis, immunoblotting with polyclonal antisera, direct binding assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution and proteolysis with functional binding readout","pmids":["2956264"],"is_preprint":false},{"year":1988,"finding":"A novel ~45 kDa beta-chain subunit in C4BP is directly involved in protein S binding; chymotrypsin cleavage of this subunit abolishes protein S binding, and protein S protects the beta-chain from proteolysis.","method":"SDS-PAGE, gel filtration in 6M guanidine HCl, chymotrypsin protection assay, N-terminal sequencing","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution with proteolysis protection assay identifying specific subunit","pmids":["2970465"],"is_preprint":false},{"year":1988,"finding":"The protein S-binding site on C4BP maps to a peptide near the C-terminus of the alpha-chain core (residues Ser447–Tyr467), identified by monoclonal antibody MFbp16 affinity chromatography and competition binding with protein S.","method":"Chymotrypsin digestion, affinity chromatography on MFbp16-Sepharose, competition binding assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical mapping with monoclonal antibody and competition, single lab","pmids":["2460456"],"is_preprint":false},{"year":1988,"finding":"C4A3 binds immunoglobulins (IgG, IgM, IgA) in the fluid phase approximately 3–4 times more efficiently than C4B1, with C4A forming predominantly amide linkages and C4B1 forming both amide and ester bonds.","method":"Fluid-phase binding assay with purified C4, C1s and antibody; covalent bond characterization","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with purified components and bond-type characterization","pmids":["3264881"],"is_preprint":false},{"year":1989,"finding":"C4BP circulates in plasma as two subpopulations: a major form (seven alpha-chains + one beta-chain) that binds protein S, and a minor form lacking the beta-chain that cannot bind protein S, establishing the beta-chain as the sole protein S binding subunit.","method":"Subpopulation isolation, SDS-PAGE, direct protein S binding assay","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — biochemical fractionation with direct functional binding confirmation","pmids":["2532155"],"is_preprint":false},{"year":1989,"finding":"C4BP synthesis and secretion is induced by IL-6 and TNF-α in the HepG2 hepatoma cell line, and plasma C4BP levels are elevated in acute pneumonia patients, establishing C4BP as an acute phase protein.","method":"Cell culture with cytokine stimulation, plasma measurements in pneumonia patients","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — cell-based assay plus clinical correlation, single lab","pmids":["2480119"],"is_preprint":false},{"year":1990,"finding":"Nascent C3b covalently attaches to C4b, and C3b in C4b–C3b complexes is protected from inactivation by factors H and I, providing a mechanism by which classical pathway activation recruits and amplifies the alternative pathway.","method":"In vitro reconstitution with purified complement components, kinetic protection assays, surface plasmon resonance-type binding","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with purified components, quantitative protection assays","pmids":["2148521"],"is_preprint":false},{"year":1990,"finding":"C4b deposited on cell surfaces activates the alternative pathway by binding the C3 convertase C3bBbP through a C3b interaction, amplifying C3b deposition; this requires C3b, properdin, factor B, and factor D but does not involve direct C4bBb formation.","method":"Hemolytic assays, radiolabeled component binding studies, C5-deficient serum experiments","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with defined purified components and genetic-deficiency controls","pmids":["2247091"],"is_preprint":false},{"year":1990,"finding":"C4A is more effective than C4B in enhancing CR1-mediated binding of immune complexes to erythrocytes, whereas C4B is only modestly less efficient at inhibiting immunoprecipitation; the major functional difference between the isotypes is at the level of CR1 binding.","method":"CR1 binding assay with purified C4A and C4B, immune precipitation inhibition assay","journal":"Clinical and experimental immunology","confidence":"High","confidence_rationale":"Tier 1 — comparative in vitro functional assay with purified isotypes","pmids":["2138067"],"is_preprint":false},{"year":1991,"finding":"The C4BP alpha-chain gene spans >40 kb, is organized into 12 exons with each of the eight SCR repeats encoded by individual exons (except SCR2 which is split), and contains acute phase and liver-specific regulatory elements in its promoter region.","method":"Genomic cloning, exon mapping, sequence analysis, comparison with mouse C4BP alpha transcript","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 — complete gene structure determination","pmids":["2022920"],"is_preprint":false},{"year":1991,"finding":"C4BP beta-chain gene spans >10 kb, encodes three SCR domains plus a C-terminal non-repeat region, and produces two distinct mRNA classes from different transcription start sites; the alpha- and beta-chain genes are closely linked at chromosome 1q32.","method":"Genomic cloning, Northern blot, primer extension, S1 nuclease protection, cDNA isolation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — complete gene structure determination with multiple methods","pmids":["8325877"],"is_preprint":false},{"year":1993,"finding":"Protein S residues 413–434 (particularly the PSP-420 peptide, residues 420–434) are essential for binding to C4BP; a monoclonal antibody (LJ-56) against this region blocks complex formation and specifically recognizes free protein S but not the protein S:C4BP complex.","method":"Synthetic peptide inhibition assay, ELISA, polyclonal and monoclonal antibody inhibition studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — peptide mapping and antibody epitope confirmation, multiple orthogonal approaches","pmids":["7688369"],"is_preprint":false},{"year":1994,"finding":"Beta-chain residues 31–45 of C4BP (with the sequence YxLVG being critical) provide a protein S-binding site; peptide beta(31-45) inhibits the protein S:C4BP interaction and blocks protein S APC-cofactor activity.","method":"Synthetic peptide inhibition assays, surface plasmon resonance binding, coagulation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — peptide mapping with functional coagulation readout, multiple methods","pmids":["8300581"],"is_preprint":false},{"year":1994,"finding":"Complement receptor CR1 (CD35) has two functional sites: site 1 (SCR1–2) binds C4b and serves as cofactor for C4b cleavage; site 2 (SCR8–9) binds primarily C3b but also C4b with greater cofactor activity for C4b cleavage than site 1.","method":"Substitution mutagenesis of CR1 constructs, binding assays, cofactor activity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with functional binding and cofactor assays","pmids":["8175757"],"is_preprint":false},{"year":1994,"finding":"Murine C4BPB gene has become a pseudogene due to two in-frame stop codons, while the human gene is functional; this explains the absence of protein S binding by murine C4BP and reveals an evolutionary difference in the coagulation–complement interface.","method":"Genomic cloning, sequence analysis of multiple mouse strains, Southern blotting","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 1 — direct sequence determination across multiple strains demonstrating stop codons","pmids":["7959726"],"is_preprint":false},{"year":1995,"finding":"Serum amyloid P component (SAP) binds to the central core of C4BP (not the tentacles) with high affinity (Kd ~30 nM) in a calcium-dependent, carbohydrate-dependent manner; the C4BP beta-chain is not required for SAP binding.","method":"SAP-Sepharose affinity chromatography, quantitative affinity chromatography, recombinant C4BP constructs","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — affinity chromatography with recombinant deletion constructs and quantitative binding constants","pmids":["7592941"],"is_preprint":false},{"year":1995,"finding":"IL-6, IL-1β, and IFN-γ differentially upregulate C4BPA and C4BPB gene expression in Hep3B cells; TNF-α downregulates both; IFN-γ combined with TNF-α produces a synergistic 10-fold induction of C4BP alpha-mRNA with minimal C4BP beta-mRNA increase, providing a mechanism to maintain C4BP beta homeostasis during acute phase response.","method":"Cytokine stimulation of Hep3B cells, Northern blot analysis of C4BPA and C4BPB mRNAs, analysis of C4BP isoforms in acute phase patient samples","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — cell-based gene expression with clinical correlation, multiple cytokines tested","pmids":["7561114"],"is_preprint":false},{"year":1996,"finding":"The entire protein S-binding site on C4BP resides within SCR-1 of the beta-chain; alpha/beta-chain chimeras replacing only SCR-1 of the alpha-chain with beta-chain SCR-1 confer full protein S binding affinity (Ka ~2.3×10⁸ M⁻¹).","method":"Recombinant alpha/beta chain chimera expression in eukaryotic cells, protein S binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — domain-swap chimeras with quantitative binding measurements","pmids":["8702842"],"is_preprint":false},{"year":1998,"finding":"The C4BP beta-chain SCR-1 interaction with protein S is primarily hydrophobic in nature, mediated by a solvent-exposed hydrophobic cluster; ionic interactions contribute minimally.","method":"Homology modeling, inter-species sequence comparison, binding studies with salt and detergent","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2/3 — experimental binding with computational modeling, single lab","pmids":["9774728"],"is_preprint":false},{"year":1998,"finding":"Modeling of C4BP alpha-chain 8 CCP modules identified a cluster of positively charged residues at the CCP1–CCP2 interface as the principal binding site for C4b, heparin, and bacterial Arp/Sir proteins.","method":"Computer modeling combined with monoclonal antibody mapping and heparin binding experiments","journal":"Proteins","confidence":"Medium","confidence_rationale":"Tier 3 — computational modeling with experimental antibody and heparin binding support, single lab","pmids":["9626699"],"is_preprint":false},{"year":1999,"finding":"Both G domains (G1 and G2) of the sex-hormone-binding globulin-like region of protein S contribute to C4BP binding; full-affinity binding requires both domains, with G1 contributing more than G2.","method":"Recombinant protein S/Gas6 chimeras, surface plasmon resonance, microtiter plate binding assays","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — domain-swap chimeras with quantitative SPR measurements","pmids":["10583388"],"is_preprint":false},{"year":1999,"finding":"CR1 has a single C1q binding site on LHR-D; C1q and C4b bind CR1 independently and additively support erythrocyte adhesion, confirming CR1 as the receptor for all major complement opsonic ligands.","method":"BIAcore binding analysis, erythrocyte adhesion assay, anti-CR1 Fab inhibition","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — SPR with independent binding confirmation and cellular adhesion assay","pmids":["10528211"],"is_preprint":false},{"year":2001,"finding":"Type IV pili of N. gonorrhoeae bind C4BP via the N-terminal part of PilC at CCP1 and CCP2 of the C4BP alpha-chain through ionic interactions; this binding overlaps only partially with the MCP (CD46) binding site on pili.","method":"Direct binding assay with isolated pili, C4BP mutants lacking individual CCPs, competition assays with C4b and NaCl titration","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — binding with deletion mutants and competition assays defining molecular interface","pmids":["11359834"],"is_preprint":false},{"year":2002,"finding":"Membrane cofactor protein (MCP/CD46) is the primary cofactor mediating C4b cleavage on MCP-expressing cells; fluid-phase C4BP does not significantly cleave cell-surface C4b in this model. For C3b deposited via the classical pathway, factor H is the primary cofactor.","method":"FACS and Western blotting on MCP-transfected cells, function-blocking monoclonal antibody, Mg-EGTA pathway-specific conditions","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — cell-based experiments with transfection, specific mAb blockade, and pathway-selective conditions","pmids":["12055245"],"is_preprint":false},{"year":2002,"finding":"OmpA of E. coli K1 binds the alpha-chain CCP3 of C4BP through hydrophobic interactions (not inhibited by C4b, heparin, or salt), recruiting C4BP to the bacterial surface and conferring serum resistance.","method":"Flow cytometry, CCP deletion mutants of recombinant C4BP, competition with synthetic CCP3 peptides, serum bactericidal assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — recombinant deletion mutant mapping with functional bactericidal assay","pmids":["12444142"],"is_preprint":false},{"year":2002,"finding":"Protein S mediates binding of C4BP to apoptotic cells by binding phosphatidylserine exposed on the apoptotic cell surface; this binding is calcium-dependent and blockable by annexin V, localizing complement regulatory activity to apoptotic cells.","method":"Binding assays with Jurkat apoptosis model, blocking with anti-PS Gla domain antibodies and annexin V, C4b interaction confirmation","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — cell-based assay with specific blocking antibodies and functional complement readout","pmids":["12193728"],"is_preprint":false},{"year":2002,"finding":"The C4b-binding site on C4BP requires CCP1–3 of the alpha-chain and is mediated by a cluster of positively charged amino acids at the CCP1–CCP2 interface; loss of C4b binding abolishes all classical pathway inhibitory activity of C4BP.","method":"Homology-based modeling, recombinant mutagenesis, complement functional assays","journal":"Biochemical Society transactions","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with functional complement assay readout","pmids":["12440957"],"is_preprint":false},{"year":2002,"finding":"Protein S binding to C4BP is mediated by a cluster of surface-exposed hydrophobic amino acids on CCP1 of the beta-chain; heparin binding requires CCP1–3 of the alpha-chain with CCP2 being most important.","method":"Homology-based computer modeling, recombinant mutagenesis, binding assays","journal":"Biochemical Society transactions","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with binding assays identifying specific residues","pmids":["12440957"],"is_preprint":false},{"year":2003,"finding":"The alpha-chain of C4BP binds directly to CD40 on human B cells at a site distinct from CD40L, inducing B-cell proliferation, upregulation of CD54 and CD86, and IL-4-dependent IgE isotype switching; this effect requires CD40 and IKKγ/NEMO signaling.","method":"Direct binding assays, B-cell proliferation and differentiation assays, experiments with B cells from CD40- and IKKγ/NEMO-deficient patients, colocalization in germinal centers","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — direct binding plus functional cellular readout validated with genetic-deficiency patient cells and tissue colocalization","pmids":["12818164"],"is_preprint":false},{"year":2003,"finding":"Zinc at micromolar concentrations enhances C4BP cofactor activity toward C4b/C3b by increasing affinity between C4b/C3b and cofactor proteins; millimolar zinc concentrations inhibit cofactor activity by aggregating C4b/C3b.","method":"Cofactor activity assays, 65Zn binding studies, fluorescent chelator Kd measurements, surface plasmon resonance","journal":"Archives of biochemistry and biophysics","confidence":"High","confidence_rationale":"Tier 1 — quantitative binding and activity measurements with multiple methods","pmids":["14522582"],"is_preprint":false},{"year":2004,"finding":"M. catarrhalis UspA2 and UspA1 bind C4BP alpha-chain at CCP2, CCP5, and CCP7; surface-bound C4BP retains cofactor activity for C4b degradation, conferring serum resistance.","method":"Flow cytometry, RIA, recombinant UspA binding assays with C4BP deletion mutants, cofactor activity assay for C4b degradation","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — domain mapping with deletion mutants and functional complement assay","pmids":["15383594"],"is_preprint":false},{"year":2004,"finding":"C. albicans hyphal and yeast forms bind C4BP at CCP1–2 of the alpha-chain; surface-bound C4BP retains cofactor activity for C4b inactivation and mediates adhesion of C. albicans to host endothelial cells.","method":"Confocal microscopy, flow cytometry, ELISA, absorption from human serum, recombinant deletion constructs, monoclonal antibodies","journal":"Infection and immunity","confidence":"High","confidence_rationale":"Tier 2 — multiple binding methods with domain mapping and functional complement and adhesion assays","pmids":["15501796"],"is_preprint":false},{"year":2004,"finding":"The C4BP–protein S complex inhibits phagocytosis of apoptotic cells by macrophages; free protein S enhances phagocytosis, but when complexed to C4BP, the protein S proengulfment activity is blocked while C4BP localizes to apoptotic cell surfaces via protein S.","method":"Phagocytosis assay with primary human macrophages and THP-1 cells, complement-depleted serum reconstitution, anti-Gla domain antibody blocking","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — functional cellular assay with serum reconstitution and specific blocking antibody","pmids":["15096498"],"is_preprint":false},{"year":2005,"finding":"N. gonorrhoeae porin (Por) binds human C4BP in a species-specific manner to evade complement; Por1B-bearing strains bind chimpanzee C4BP but not rodent/lagomorph C4BP, explaining the host restriction of gonorrhea.","method":"Serum bactericidal assays with species-specific sera, C4BP binding studies, C4BP reconstitution in heterologous sera","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 2 — functional bactericidal assay with species comparison and reconstitution experiment","pmids":["16275906"],"is_preprint":false},{"year":2006,"finding":"CRP binds C4BP, with the binding site localized to the central core of C4BP; C4BP lacking beta-chain and protein S (an acute-phase form) binds CRP with higher affinity; C4BP–CRP complexes exist in patient serum and C4BP retains full complement regulatory activity in the presence of CRP.","method":"ELISA with recombinant CRP and phosphorylcholine-CRP, proteolytic C4BP fragment binding, ionic strength titration, patient serum analysis, complement activation assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple binding methods with domain localization and functional complement readout, patient serum confirmation","pmids":["16751408"],"is_preprint":false},{"year":2007,"finding":"Y. enterocolitica uses both YadA and Ail outer membrane proteins as C4BP receptors; Ail-mediated C4BP binding is blocked by O-antigen and outer core LPS. Surface-bound C4BP retains factor I-mediated C4b degradation activity.","method":"C4BP binding assays with LPS/protein mutant panel, flow cytometry, cofactor activity assay","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 — systematic mutant analysis with functional complement assay","pmids":["18769718"],"is_preprint":false},{"year":2007,"finding":"N. gonorrhoeae Por1B selectively binds C4b via amide linkages (at loops 4–5) and C3b via ester linkages; all Opa proteins (A,B,C,D,E,F,I) bind both C4b and C3b; C4Ab preferentially forms monomers/heterodimers while C4Bb participates in C5 convertase heterodimer formation.","method":"Hybrid Por1A/1B molecule analysis, serum with only C4A isoform, Opa-specific variant strains, bond-type characterization","journal":"Infection and immunity","confidence":"High","confidence_rationale":"Tier 2 — systematic mutant and isoform-specific analysis with bond-type characterization","pmids":["17984207"],"is_preprint":false},{"year":2008,"finding":"C4BP binds Aβ1-42 peptide directly via the C4BP alpha-chain and localizes to amyloid plaques and apoptotic cells in Alzheimer's disease brain, limiting complement activation on these targets in vitro.","method":"Immunohistochemistry, in vitro binding assay with dead brain cells and Aβ1-42, complement activation assay","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding assay with functional complement readout, single lab","pmids":["18556068"],"is_preprint":false},{"year":2009,"finding":"C4BP binds directly to small leucine-rich repeat proteins (SLRPs: osteoadherin, chondroadherin, fibromodulin, PRELP) predominantly via its central core; C4BP binding does not impair complement inhibitory activity but limits C9 deposition activated by SLRPs in serum.","method":"Direct binding assays with C4BP fragments/mutants, electron microscopy, C9 deposition assay with C4BP-depleted serum","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — domain mapping with multiple deletion mutants, EM, and functional complement assay","pmids":["19155499"],"is_preprint":false},{"year":2009,"finding":"C4BP regulates the lectin pathway C3/C5 convertase with ~7–13-fold greater affinity for C4b deposited via the lectin pathway than the classical pathway; at high C4b density, all seven alpha-chains of C4BP can simultaneously engage C4b.","method":"Reconstituted complement assays on zymosan and E(Man), stoichiometric analysis of C4b per C4BP","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1 — quantitative in vitro reconstitution establishing pathway-specific affinities","pmids":["19660812"],"is_preprint":false},{"year":2011,"finding":"Dengue, West Nile, and yellow fever virus NS1 directly binds C4BP with binding sites on NS1 that partially overlap the C4b-binding sites; soluble NS1 recruits C4BP to inactivate C4b in solution and on plasma membranes, representing a second complement-evasion mechanism.","method":"Direct binding assays, mapping studies with C4BP mutants, C4b inactivation assays on plasma membrane","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — binding domain mapping with functional C4b inactivation assay, tested for three flaviviruses","pmids":["21642539"],"is_preprint":false},{"year":2011,"finding":"PTX3 binds C4BP at SCR1–3 of the C4BP alpha-chain; PTX3 does not compete with factor H for C4BP binding but is inhibited by C1q and L-ficolin; C4BP recruited by PTX3 on extracellular matrix or late apoptotic cells retains complement regulatory activity and reduces C5b-9 deposition.","method":"ELISA, competition binding assays, complement deposition assays on ECM and apoptotic cells","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — domain mapping with multiple competition assays and functional complement readout","pmids":["21915248"],"is_preprint":false},{"year":2011,"finding":"Candida Pra1 is the first fungal C4BP-binding protein; Pra1 binds C4BP at CCP4, CCP7, and CCP8 of the alpha-chain through ionic interactions; C4BP and factor H bind simultaneously to Pra1; surface-bound C4BP inhibits C4b and C3b deposition.","method":"ELISA, isothermal titration calorimetry, recombinant C4BP CCP deletion mutants, C4BP/factor H co-binding assays, C4b/C3b surface deposition assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — ITC for affinity measurement plus domain mapping and functional complement assay","pmids":["21212281"],"is_preprint":false},{"year":2012,"finding":"Pneumococcal enolase binds C4BP at CCP1/CCP2 and CCP8 of the C4BP alpha-chain; C4BP and plasminogen bind distinct sites on enolase without competition; enolase-bound C4BP retains cofactor activity for C4b degradation.","method":"Dose-dependent binding assays, ionic strength titration, recombinant C4BP mutants lacking individual CCPs, C3b deposition assay, cofactor activity assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — systematic CCP domain mapping with functional complement assay, two independent binding sites identified","pmids":["22925928"],"is_preprint":false},{"year":2013,"finding":"Mutations in C4BPA (R120H, I126T, G423T) found in women with recurrent miscarriage affect the expression level and/or factor I cofactor activity of C4BP, while a CD46 variant (N213I) causes deficient protein processing and impaired cofactor activity for both C4b and C3b.","method":"Sequencing, recombinant protein expression, cofactor activity assay for factor I","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — recombinant mutagenesis with functional assay, clinical association context","pmids":["23508668"],"is_preprint":false},{"year":2016,"finding":"C4BP uses a conserved 'reading head' in CCP1–3 to detect hidden conserved sequence patterns within the hypervariable M protein regions of Group A Streptococcus, enabling broad (~90% M type) recognition; crystal structures of four M proteins in complex with C4BP revealed a uniform binding mechanism.","method":"Crystal structure determination of four M protein–C4BP complexes, functional binding validation","journal":"Nature microbiology","confidence":"High","confidence_rationale":"Tier 1 — multiple crystal structures with functional validation, mechanism established at atomic resolution","pmids":["27595425"],"is_preprint":false},{"year":2017,"finding":"B. burgdorferi OspC directly binds complement component C4b and competes with complement protein C2 for C4b binding, thereby inhibiting classical and lectin pathway activation; this confers bloodstream survival in vivo.","method":"Direct binding assays, C2 competition assay, in vivo mouse bloodstream survival experiments","journal":"Cellular microbiology","confidence":"High","confidence_rationale":"Tier 2 — direct binding with competition assay and in vivo validation","pmids":["28873507"],"is_preprint":false},{"year":2018,"finding":"Pneumococcal PspA and PspC both bind serum C4BP; deletion of PspA or PspC reduces C4BP deposition on bacteria, increases C4b and iC4b deposition, and reduces C4dg, establishing that PspA and PspC sequester C4BP to inactivate C4b and evade complement.","method":"Targeted gene deletion, serum opsonization assays, recombinant PspA/PspC binding assays, mouse infection experiments","journal":"Infection and immunity","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with functional complement deposition assay and in vivo virulence confirmation","pmids":["30323030"],"is_preprint":false},{"year":2023,"finding":"CryoEM structures show that IgG3 forms elevated hexameric Fc platforms; mass spectrometry reveals that C1 (activated by IgG3) deposits C4b directly onto specific IgG3 residues proximal to the Fab domains, a consequence of the elevated height of the C1-IgG3 complex.","method":"CryoEM structure determination of IgG3-antigen-C1 complexes, mass spectrometry identification of C4b deposition sites","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structural determination combined with MS identification of C4b attachment sites","pmids":["37419978"],"is_preprint":false}],"current_model":"C4B (complement component 4B) is cleaved by activated C1 to generate C4b, which covalently attaches to targets preferentially via ester linkages (unlike C4A which forms amide bonds), initiates classical/lectin pathway C3 convertase assembly, can recruit the alternative pathway by protecting nascent C3b from inactivation, and is regulated by the soluble inhibitor C4BP—a spider-like multimer of seven alpha-chains (each bearing a C4b-binding site in CCP1-3) plus one beta-chain (bearing the protein S-binding site in CCP1-SCR1)—which acts as cofactor for factor I-mediated cleavage of C4b, with the C4BP–protein S complex additionally localizing complement regulation to apoptotic cell surfaces; numerous pathogens (N. gonorrhoeae, S. pyogenes, S. pneumoniae, C. albicans, E. coli, Borrelia, etc.) exploit C4BP by binding its alpha-chain CCPs to evade complement-mediated killing."},"narrative":{"teleology":[{"year":1984,"claim":"Determining the ultrastructure of C4BP revealed how a multivalent regulator could simultaneously engage multiple C4b molecules, establishing the physical basis for its potent complement-inhibitory activity.","evidence":"Limited proteolysis and electron microscopy of purified C4BP showing seven tentacle subunits around a central core","pmids":["6480575"],"confidence":"High","gaps":["Stoichiometry of simultaneous C4b engagement was not measured","No atomic-resolution structure of the full complex"]},{"year":1986,"claim":"Distinguishing the bond chemistry of C4A versus C4B isotypes explained their divergent biological roles: C4B's preference for ester linkages promotes efficient surface opsonization, while C4A's amide bonds favor immune complex handling.","evidence":"Chemical modification of erythrocyte amino groups, SDS-PAGE of radiolabeled C4 isotypes, and hemolytic assays with C2-deficient serum","pmids":["3512717","2937839"],"confidence":"High","gaps":["Structural basis for the thioester reactivity difference between isotypes was not resolved","In vivo relevance of differential bond formation not directly tested"]},{"year":1988,"claim":"Identification of the C4BP beta-chain as the sole protein S–binding subunit resolved how C4BP bridges complement regulation and coagulation, and explained why beta-chain-lacking C4BP isoforms cannot sequester protein S.","evidence":"SDS-PAGE, gel filtration, chymotrypsin protection assays, and direct binding with subpopulation fractionation","pmids":["2970465","2532155"],"confidence":"High","gaps":["Atomic contacts between beta-chain and protein S were unknown","Physiological regulation of beta-chain expression not yet addressed"]},{"year":1990,"claim":"Demonstrating that surface-deposited C4b protects nascent C3b from inactivation and recruits the alternative pathway convertase C3bBbP established the mechanism by which classical pathway activation amplifies through the alternative loop.","evidence":"In vitro reconstitution with purified complement components and hemolytic assays with defined component additions","pmids":["2148521","2247091"],"confidence":"High","gaps":["Structural basis of C4b–C3b protective interaction not resolved","Relative contribution in vivo versus lectin pathway-deposited C4b unknown"]},{"year":1996,"claim":"Domain-swap chimeras localized the protein S–binding site to SCR-1 (CCP1) of the C4BP beta-chain, while mutagenesis mapped the C4b-binding site to positively charged residues at the CCP1–2 interface of the alpha-chain, defining the two principal functional surfaces of C4BP.","evidence":"Recombinant alpha/beta-chain chimeras with quantitative binding assays, and site-directed mutagenesis with complement functional assays","pmids":["8702842","12440957"],"confidence":"High","gaps":["High-resolution co-crystal of C4BP–C4b complex not available","Role of CCP3 in C4b binding mechanism unclear"]},{"year":2002,"claim":"Discovery that protein S targets the C4BP–protein S complex to phosphatidylserine on apoptotic cells revealed a mechanism for localizing complement regulation to dying cells, preventing inflammatory complement activation during apoptotic clearance.","evidence":"Binding assays on apoptotic Jurkat cells blocked by annexin V and anti-Gla domain antibodies","pmids":["12193728"],"confidence":"High","gaps":["Whether this mechanism is sufficient to prevent autoimmunity in vivo was not tested","Contribution relative to other apoptotic complement regulators (e.g., MCP) unresolved"]},{"year":2003,"claim":"The unexpected finding that C4BP alpha-chain binds CD40 on B cells and induces proliferation, costimulatory molecule upregulation, and IgE class switching revealed a non-complement immune-modulatory function of C4BP.","evidence":"Direct binding assays, B-cell proliferation/differentiation assays with CD40-deficient and NEMO-deficient patient cells, germinal center colocalization","pmids":["12818164"],"confidence":"High","gaps":["Structural basis of C4BP–CD40 interaction unknown","In vivo contribution to B-cell responses not tested","Whether this function is altered during acute phase response when alpha-chain-only C4BP rises"]},{"year":2001,"claim":"Systematic mapping of pathogen exploitation of C4BP established that diverse bacteria and fungi bind distinct CCP modules of the alpha-chain (CCP1–2 for N. gonorrhoeae pili and C. albicans; CCP3 for E. coli OmpA; CCP2/5/7 for M. catarrhalis) to recruit functional C4BP and evade complement killing.","evidence":"Flow cytometry, recombinant C4BP CCP deletion mutants, competition assays, and serum bactericidal assays across multiple pathogen systems","pmids":["11359834","12444142","15383594","15501796"],"confidence":"High","gaps":["Whether therapeutic blockade of specific CCPs could prevent immune evasion without disabling complement regulation","Evolutionary arms race dynamics between pathogen ligands and C4BP polymorphisms not characterized"]},{"year":2016,"claim":"Crystal structures of Group A Streptococcus M proteins bound to C4BP CCP1–3 revealed a conserved 'reading head' mechanism by which C4BP recognizes hidden sequence patterns in hypervariable M protein regions, explaining how ~90% of M types exploit C4BP.","evidence":"Crystal structures of four M protein–C4BP complexes with functional binding validation","pmids":["27595425"],"confidence":"High","gaps":["Whether this reading head is also exploited by non-streptococcal pathogens","No structure of full-length heptameric C4BP bound to M protein"]},{"year":2023,"claim":"CryoEM visualization of C1-activated IgG3 hexameric platforms combined with mass spectrometry identification of C4b deposition sites on IgG3 Fab-proximal residues established the spatial geometry of nascent C4b covalent attachment during classical pathway initiation.","evidence":"CryoEM structure of IgG3-antigen-C1 complexes and MS identification of C4b attachment sites","pmids":["37419978"],"confidence":"High","gaps":["Whether the same attachment geometry applies to IgG1/IgG2-initiated activation","Structural basis for C4b transition to C3 convertase on the antibody platform not resolved"]},{"year":null,"claim":"A complete atomic-resolution structure of the full heptameric C4BP in complex with C4b, and the structural basis for how C4BP serves simultaneously as factor I cofactor and alternative pathway regulator, remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No full-length cryo-EM or crystal structure of heptameric C4BP–C4b complex","Mechanism by which C4BP discriminates lectin vs. classical pathway-deposited C4b at the structural level is unknown","In vivo validation of C4BPA mutations (R120H, I126T, G423T) as causative for recurrent miscarriage awaits larger cohorts and animal models"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[29,32,42,44]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[28]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[28,35]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,7,37,42]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[28,43]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2,9,10,29,42,48]},{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[15,28]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[36,50,43]}],"complexes":["C4b-binding protein (C4BP) complex","C4BP–protein S complex","Classical pathway C3 convertase (C4b2a)"],"partners":["C4BPA","C4BPB","PROS1","C2","C3","CR1","CFI","CD40"],"other_free_text":[]},"mechanistic_narrative":"C4B encodes the C4B isotype of complement component 4, a central effector of the classical and lectin complement pathways that, upon cleavage by activated C1, generates the opsonin C4b which covalently attaches to target surfaces preferentially via ester linkages—in contrast to C4A, which forms amide bonds and binds immune complexes more efficiently [PMID:3512717, PMID:3264881]. Surface-deposited C4b nucleates C3 convertase assembly and recruits the alternative pathway by protecting nascent C3b from factor H/I–mediated inactivation, thereby amplifying complement activation [PMID:2148521, PMID:2247091]. C4b activity is regulated by soluble C4b-binding protein (C4BP), a spider-shaped heptameric complex of alpha-chains (each bearing C4b-binding sites in CCP1–3) and one beta-chain (whose CCP1 binds protein S), which serves as cofactor for factor I–mediated cleavage of C4b; the C4BP–protein S complex additionally localizes complement regulation to apoptotic cell surfaces through protein S binding to phosphatidylserine [PMID:6480575, PMID:12440957, PMID:8702842, PMID:12193728]. Numerous bacterial and viral pathogens—including N. gonorrhoeae, S. pyogenes, E. coli K1, C. albicans, S. pneumoniae, and flavivirus NS1—exploit C4BP by engaging distinct alpha-chain CCP modules to recruit its cofactor activity and evade complement-mediated killing [PMID:27595425, PMID:12444142, PMID:21642539, PMID:30323030]."},"prefetch_data":{"uniprot":{"accession":"P0C0L5","full_name":"Complement C4-B","aliases":["Basic complement C4","C3 and PZP-like alpha-2-macroglobulin domain-containing protein 3"],"length_aa":1744,"mass_kda":192.8,"function":"Precursor of non-enzymatic components of the classical, lectin and GZMK complement pathways, which consist in a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system Non-enzymatic component of C3 and C5 convertases (By similarity). Generated following cleavage by complement proteases (C1S, MASP2 or GZMK, depending on the complement pathway), it covalently attaches to the surface of pathogens, where it acts as an opsonin that marks the surface of antigens for removal (By similarity). It then recruits the serine protease complement C2b to form the C3 and C5 convertases, which cleave and activate C3 and C5, respectively, the next components of the complement pathways (PubMed:8538770). Complement C4b-B isotype catalyzes the transacylation of the thioester carbonyl group to form ester bonds with carbohydrate antigens, while C4b-A isotype is responsible for effective binding to form amide bonds with immune aggregates or protein antigens (PubMed:8538770) Putative humoral mediator released following cleavage by complement proteases (C1S, MASP2 or GZMK, depending on the complement pathway). While it is strongly similar to anaphylatoxins, its role is unclear. Was reported to act as a mediator of local inflammatory process; however these effects were probably due to contamination with C3a and/C5a anaphylatoxins in biological assays","subcellular_location":"Secreted; Cell surface","url":"https://www.uniprot.org/uniprotkb/P0C0L5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/C4B","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":316,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/C4B","total_profiled":1310},"omim":[{"mim_id":"614380","title":"COMPLEMENT COMPONENT 4A DEFICIENCY; C4AD","url":"https://www.omim.org/entry/614380"},{"mim_id":"614379","title":"COMPLEMENT COMPONENT 4B DEFICIENCY; C4BD","url":"https://www.omim.org/entry/614379"},{"mim_id":"614374","title":"BLOOD GROUP, CHIDO/RODGERS SYSTEM","url":"https://www.omim.org/entry/614374"},{"mim_id":"613815","title":"CYTOCHROME P450, FAMILY 21, SUBFAMILY A, POLYPEPTIDE 2; CYP21A2","url":"https://www.omim.org/entry/613815"},{"mim_id":"612336","title":"THROMBOPHILIA DUE TO PROTEIN S DEFICIENCY, AUTOSOMAL DOMINANT; THPH5","url":"https://www.omim.org/entry/612336"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"adrenal gland","ntpm":174.9},{"tissue":"liver","ntpm":262.1}],"url":"https://www.proteinatlas.org/search/C4B"},"hgnc":{"alias_symbol":["CPAMD3","C4F","CO4","C4B1","C4B3","CH"],"prev_symbol":[]},"alphafold":{"accession":"P0C0L5","domains":[{"cath_id":"2.60.40.1930","chopping":"20-136","consensus_level":"high","plddt":91.811,"start":20,"end":136},{"cath_id":"2.60.40.1930","chopping":"141-237","consensus_level":"medium","plddt":91.4937,"start":141,"end":237},{"cath_id":"2.60.40.1940","chopping":"251-364","consensus_level":"high","plddt":88.6376,"start":251,"end":364},{"cath_id":"2.60.40.1930","chopping":"381-565","consensus_level":"medium","plddt":89.2315,"start":381,"end":565},{"cath_id":"1.20.91.20","chopping":"692-736","consensus_level":"medium","plddt":72.6869,"start":692,"end":736},{"cath_id":"2.60.40.10","chopping":"833-935","consensus_level":"high","plddt":88.7997,"start":833,"end":935},{"cath_id":"2.60.120.1540","chopping":"954-985_1325-1376","consensus_level":"high","plddt":80.4469,"start":954,"end":1376},{"cath_id":"1.50.10.20","chopping":"1006-1189","consensus_level":"medium","plddt":90.5868,"start":1006,"end":1189},{"cath_id":"2.60.40.690","chopping":"1398-1411_1464-1571","consensus_level":"high","plddt":82.3039,"start":1398,"end":1571},{"cath_id":"2.40.50.120","chopping":"1581-1744","consensus_level":"medium","plddt":85.9655,"start":1581,"end":1744}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P0C0L5","model_url":"https://alphafold.ebi.ac.uk/files/AF-P0C0L5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P0C0L5-F1-predicted_aligned_error_v6.png","plddt_mean":83.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=C4B","jax_strain_url":"https://www.jax.org/strain/search?query=C4B"},"sequence":{"accession":"P0C0L5","fasta_url":"https://rest.uniprot.org/uniprotkb/P0C0L5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P0C0L5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P0C0L5"}},"corpus_meta":[{"pmid":"21642539","id":"PMC_21642539","title":"Binding of flavivirus nonstructural protein NS1 to C4b binding protein modulates complement activation.","date":"2011","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/21642539","citation_count":160,"is_preprint":false},{"pmid":"15072852","id":"PMC_15072852","title":"Complement inhibitor C4b-binding protein-friend or foe in the innate immune system?","date":"2004","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/15072852","citation_count":155,"is_preprint":false},{"pmid":"10859342","id":"PMC_10859342","title":"Deficiencies of human complement component C4A and C4B and heterozygosity in length variants of RP-C4-CYP21-TNX (RCCX) modules in caucasians. The load of RCCX genetic diversity on major histocompatibility complex-associated disease.","date":"2000","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/10859342","citation_count":154,"is_preprint":false},{"pmid":"2970465","id":"PMC_2970465","title":"Novel subunit in C4b-binding protein required for protein S binding.","date":"1988","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/2970465","citation_count":144,"is_preprint":false},{"pmid":"12444142","id":"PMC_12444142","title":"A novel interaction of outer membrane protein A with C4b binding protein mediates serum resistance of Escherichia coli K1.","date":"2002","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/12444142","citation_count":136,"is_preprint":false},{"pmid":"12055245","id":"PMC_12055245","title":"Role of membrane cofactor protein (CD46) in regulation of C4b and C3b deposited on cells.","date":"2002","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/12055245","citation_count":119,"is_preprint":false},{"pmid":"3007562","id":"PMC_3007562","title":"Gene conversion in salt-losing congenital adrenal hyperplasia with absent complement C4B protein.","date":"1986","source":"The Journal of clinical endocrinology and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/3007562","citation_count":119,"is_preprint":false},{"pmid":"26658464","id":"PMC_26658464","title":"C4b-binding protein: The good, the bad and the deadly. Novel functions of an old friend.","date":"2015","source":"Immunology letters","url":"https://pubmed.ncbi.nlm.nih.gov/26658464","citation_count":113,"is_preprint":false},{"pmid":"25289982","id":"PMC_25289982","title":"Human C3b- and C4b-regulatory proteins: a new multi-gene family.","date":"1985","source":"Immunology today","url":"https://pubmed.ncbi.nlm.nih.gov/25289982","citation_count":110,"is_preprint":false},{"pmid":"12818164","id":"PMC_12818164","title":"C4b-binding protein (C4BP) activates B cells through the CD40 receptor.","date":"2003","source":"Immunity","url":"https://pubmed.ncbi.nlm.nih.gov/12818164","citation_count":106,"is_preprint":false},{"pmid":"37222657","id":"PMC_37222657","title":"Construction of Co4 Atomic Clusters to Enable Fe-N4 Motifs with Highly Active and Durable Oxygen Reduction Performance.","date":"2023","source":"Angewandte Chemie (International ed. in English)","url":"https://pubmed.ncbi.nlm.nih.gov/37222657","citation_count":105,"is_preprint":false},{"pmid":"15383594","id":"PMC_15383594","title":"The emerging pathogen Moraxella catarrhalis interacts with complement inhibitor C4b binding protein through ubiquitous surface proteins A1 and A2.","date":"2004","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/15383594","citation_count":103,"is_preprint":false},{"pmid":"12193728","id":"PMC_12193728","title":"Vitamin K-dependent protein S localizing complement regulator C4b-binding protein to the surface of apoptotic cells.","date":"2002","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/12193728","citation_count":96,"is_preprint":false},{"pmid":"18769718","id":"PMC_18769718","title":"Yersinia enterocolitica serum resistance proteins YadA and ail bind the complement regulator C4b-binding protein.","date":"2008","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/18769718","citation_count":96,"is_preprint":false},{"pmid":"2532155","id":"PMC_2532155","title":"Protein S binding in relation to the subunit composition of human C4b-binding protein.","date":"1989","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/2532155","citation_count":95,"is_preprint":false},{"pmid":"8175757","id":"PMC_8175757","title":"Analysis of the functional domains of complement receptor type 1 (C3b/C4b receptor; CD35) by substitution mutagenesis.","date":"1994","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8175757","citation_count":89,"is_preprint":false},{"pmid":"16751408","id":"PMC_16751408","title":"Regulation of complement activation by C-reactive protein: targeting of the inhibitory activity of C4b-binding protein.","date":"2006","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/16751408","citation_count":86,"is_preprint":false},{"pmid":"15501796","id":"PMC_15501796","title":"The hyphal and yeast forms of Candida albicans bind the complement regulator C4b-binding protein.","date":"2004","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/15501796","citation_count":86,"is_preprint":false},{"pmid":"28873507","id":"PMC_28873507","title":"Borrelia burgdorferi outer surface protein C (OspC) binds complement component C4b and confers bloodstream survival.","date":"2017","source":"Cellular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/28873507","citation_count":85,"is_preprint":false},{"pmid":"22826097","id":"PMC_22826097","title":"Effect of early syphilis infection on plasma viral load and CD4 cell count in human immunodeficiency virus-infected men: results from the FHDH-ANRS CO4 cohort.","date":"2012","source":"Archives of internal medicine","url":"https://pubmed.ncbi.nlm.nih.gov/22826097","citation_count":82,"is_preprint":false},{"pmid":"1708809","id":"PMC_1708809","title":"The C3b/C4b receptor is recognized by the Knops, McCoy, Swain-langley, and York blood group antisera.","date":"1991","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/1708809","citation_count":79,"is_preprint":false},{"pmid":"2952524","id":"PMC_2952524","title":"The superfamily of C3b/C4b-binding proteins.","date":"1987","source":"Federation proceedings","url":"https://pubmed.ncbi.nlm.nih.gov/2952524","citation_count":78,"is_preprint":false},{"pmid":"22925928","id":"PMC_22925928","title":"Enolase of Streptococcus pneumoniae binds human complement inhibitor C4b-binding protein and contributes to complement evasion.","date":"2012","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/22925928","citation_count":78,"is_preprint":false},{"pmid":"2295875","id":"PMC_2295875","title":"Null alleles of human complement C4. Evidence for pseudogenes at the C4A locus and for gene conversion at the C4B locus.","date":"1990","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/2295875","citation_count":76,"is_preprint":false},{"pmid":"16275906","id":"PMC_16275906","title":"Human C4b-binding protein selectively interacts with Neisseria gonorrhoeae and results in species-specific infection.","date":"2005","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/16275906","citation_count":71,"is_preprint":false},{"pmid":"15096498","id":"PMC_15096498","title":"The C4b-binding protein-protein S complex inhibits the phagocytosis of apoptotic cells.","date":"2004","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15096498","citation_count":69,"is_preprint":false},{"pmid":"6607672","id":"PMC_6607672","title":"Human C4 haplotypes with duplicated C4A or C4B.","date":"1984","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/6607672","citation_count":69,"is_preprint":false},{"pmid":"2952731","id":"PMC_2952731","title":"Monoclonal antibodies to the human C3b/C4b receptor (CR1) enhance specific B cell differentiation.","date":"1987","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/2952731","citation_count":65,"is_preprint":false},{"pmid":"12226794","id":"PMC_12226794","title":"Genetic sophistication of human complement components C4A and C4B and RP-C4-CYP21-TNX (RCCX) modules in the major histocompatibility complex.","date":"2002","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/12226794","citation_count":63,"is_preprint":false},{"pmid":"7590866","id":"PMC_7590866","title":"Human complement proteins C3b, C4b, factor H and properdin react with specific sites in gp120 and gp41, the envelope proteins of HIV-1.","date":"1995","source":"Immunobiology","url":"https://pubmed.ncbi.nlm.nih.gov/7590866","citation_count":61,"is_preprint":false},{"pmid":"7592941","id":"PMC_7592941","title":"Serum amyloid P component binding to C4b-binding protein.","date":"1995","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/7592941","citation_count":60,"is_preprint":false},{"pmid":"21915248","id":"PMC_21915248","title":"Human pentraxin 3 binds to the complement regulator c4b-binding protein.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21915248","citation_count":58,"is_preprint":false},{"pmid":"6480575","id":"PMC_6480575","title":"Ultrastructure of C4b-binding protein fragments formed by limited proteolysis using chymotrypsin.","date":"1984","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/6480575","citation_count":58,"is_preprint":false},{"pmid":"10528211","id":"PMC_10528211","title":"C1q and C4b bind simultaneously to CR1 and additively support erythrocyte adhesion.","date":"1999","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/10528211","citation_count":57,"is_preprint":false},{"pmid":"20022381","id":"PMC_20022381","title":"Binding of the complement inhibitor C4b-binding protein to Lyme disease Borreliae.","date":"2009","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/20022381","citation_count":56,"is_preprint":false},{"pmid":"2480119","id":"PMC_2480119","title":"Evidence that C4b-binding protein is an acute phase protein.","date":"1989","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/2480119","citation_count":56,"is_preprint":false},{"pmid":"15294999","id":"PMC_15294999","title":"Complete complement components C4A and C4B deficiencies in human kidney diseases and systemic lupus erythematosus.","date":"2004","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/15294999","citation_count":56,"is_preprint":false},{"pmid":"16403222","id":"PMC_16403222","title":"Real-time PCR quantification of human complement C4A and C4B genes.","date":"2006","source":"BMC genetics","url":"https://pubmed.ncbi.nlm.nih.gov/16403222","citation_count":55,"is_preprint":false},{"pmid":"3512717","id":"PMC_3512717","title":"Covalent binding properties of the C4A and C4B isotypes of the fourth component of human complement on several C1-bearing cell surfaces.","date":"1986","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/3512717","citation_count":55,"is_preprint":false},{"pmid":"35648811","id":"PMC_35648811","title":"Targeting C3b/C4b and VEGF with a bispecific fusion protein optimized for neovascular age-related macular degeneration therapy.","date":"2022","source":"Science translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/35648811","citation_count":54,"is_preprint":false},{"pmid":"21212281","id":"PMC_21212281","title":"The pH-regulated antigen 1 of Candida albicans binds the human complement inhibitor C4b-binding protein and mediates fungal complement evasion.","date":"2011","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21212281","citation_count":54,"is_preprint":false},{"pmid":"8118537","id":"PMC_8118537","title":"Decreased plasma concentrations of the C4B complement protein in autism.","date":"1994","source":"Archives of pediatrics & adolescent medicine","url":"https://pubmed.ncbi.nlm.nih.gov/8118537","citation_count":52,"is_preprint":false},{"pmid":"15179322","id":"PMC_15179322","title":"Functions of human complement inhibitor C4b-binding protein in relation to its structure.","date":"2004","source":"Archivum immunologiae et therapiae experimentalis","url":"https://pubmed.ncbi.nlm.nih.gov/15179322","citation_count":51,"is_preprint":false},{"pmid":"18556068","id":"PMC_18556068","title":"C4b-binding protein in Alzheimer's disease: binding to Abeta1-42 and to dead cells.","date":"2008","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/18556068","citation_count":49,"is_preprint":false},{"pmid":"17475865","id":"PMC_17475865","title":"Interaction with C4b-binding protein contributes to nontypeable Haemophilus influenzae serum resistance.","date":"2007","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/17475865","citation_count":49,"is_preprint":false},{"pmid":"2148521","id":"PMC_2148521","title":"A mechanism of activation of the alternative complement pathway by the classical pathway: protection of C3b from inactivation by covalent attachment to C4b.","date":"1990","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/2148521","citation_count":48,"is_preprint":false},{"pmid":"9626699","id":"PMC_9626699","title":"Structural investigation of C4b-binding protein by molecular modeling: localization of putative binding sites.","date":"1998","source":"Proteins","url":"https://pubmed.ncbi.nlm.nih.gov/9626699","citation_count":48,"is_preprint":false},{"pmid":"2138067","id":"PMC_2138067","title":"Differences between C4A and C4B in the handling of immune complexes: the enhancement of CR1 binding is more important than the inhibition of immunoprecipitation.","date":"1990","source":"Clinical and experimental immunology","url":"https://pubmed.ncbi.nlm.nih.gov/2138067","citation_count":47,"is_preprint":false},{"pmid":"7688369","id":"PMC_7688369","title":"Identification of residues 413-433 of plasma protein S as essential for binding to C4b-binding protein.","date":"1993","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/7688369","citation_count":47,"is_preprint":false},{"pmid":"12440957","id":"PMC_12440957","title":"Structural and functional studies of complement inhibitor C4b-binding protein.","date":"2002","source":"Biochemical Society transactions","url":"https://pubmed.ncbi.nlm.nih.gov/12440957","citation_count":45,"is_preprint":false},{"pmid":"2418113","id":"PMC_2418113","title":"Characterization of the human glomerular C3 receptor as the C3b/C4b complement type one (CR1) receptor.","date":"1986","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/2418113","citation_count":45,"is_preprint":false},{"pmid":"2958190","id":"PMC_2958190","title":"The polymorphism of the C3b/C4b receptor in the normal population and in patients with systemic lupus erythematosus.","date":"1987","source":"Clinical and experimental immunology","url":"https://pubmed.ncbi.nlm.nih.gov/2958190","citation_count":45,"is_preprint":false},{"pmid":"14522582","id":"PMC_14522582","title":"Effects of zinc on factor I cofactor activity of C4b-binding protein and factor H.","date":"2003","source":"Archives of biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/14522582","citation_count":43,"is_preprint":false},{"pmid":"19155499","id":"PMC_19155499","title":"Complement inhibitor C4b-binding protein interacts directly with small glycoproteins of the extracellular matrix.","date":"2009","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/19155499","citation_count":43,"is_preprint":false},{"pmid":"11359834","id":"PMC_11359834","title":"A novel interaction between type IV pili of Neisseria gonorrhoeae and the human complement regulator C4B-binding protein.","date":"2001","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/11359834","citation_count":42,"is_preprint":false},{"pmid":"27595425","id":"PMC_27595425","title":"Conserved patterns hidden within group A Streptococcus M protein hypervariability recognize human C4b-binding protein.","date":"2016","source":"Nature microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/27595425","citation_count":41,"is_preprint":false},{"pmid":"8702842","id":"PMC_8702842","title":"The amino-terminal module of the C4b-binding protein beta-chain contains the protein S-binding site.","date":"1996","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8702842","citation_count":41,"is_preprint":false},{"pmid":"23508668","id":"PMC_23508668","title":"Analysis of genes coding for CD46, CD55, and C4b-binding protein in patients with idiopathic, recurrent, spontaneous pregnancy loss.","date":"2013","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/23508668","citation_count":40,"is_preprint":false},{"pmid":"27758680","id":"PMC_27758680","title":"Complement C4A and C4B Gene Copy Number Study in Alzheimer's Disease Patients.","date":"2017","source":"Current Alzheimer research","url":"https://pubmed.ncbi.nlm.nih.gov/27758680","citation_count":39,"is_preprint":false},{"pmid":"31069934","id":"PMC_31069934","title":"Improving Polysulfides Adsorption and Redox Kinetics by the Co4 N Nanoparticle/N-Doped Carbon Composites for Lithium-Sulfur Batteries.","date":"2019","source":"Small (Weinheim an der Bergstrasse, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/31069934","citation_count":39,"is_preprint":false},{"pmid":"7959726","id":"PMC_7959726","title":"The gene coding for the beta-chain of C4b-binding protein (C4BPB) has become a pseudogene in the mouse.","date":"1994","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/7959726","citation_count":39,"is_preprint":false},{"pmid":"17853297","id":"PMC_17853297","title":"Complement C4B protein in schizophrenia.","date":"2008","source":"The world journal of biological psychiatry : the official journal of the World Federation of Societies of Biological Psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/17853297","citation_count":39,"is_preprint":false},{"pmid":"23946775","id":"PMC_23946775","title":"Expression and clinical significance of complement C3, complement C4b1 and apolipoprotein E in pancreatic cancer.","date":"2013","source":"Oncology letters","url":"https://pubmed.ncbi.nlm.nih.gov/23946775","citation_count":37,"is_preprint":false},{"pmid":"10583388","id":"PMC_10583388","title":"Both G-type domains of protein S are required for the high-affinity interaction with C4b-binding protein.","date":"1999","source":"European journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10583388","citation_count":37,"is_preprint":false},{"pmid":"10608879","id":"PMC_10608879","title":"Transcriptional regulatory elements of the human gene for cytochrome P450c21 (steroid 21-hydroxylase) lie within intron 35 of the linked C4B gene.","date":"1999","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10608879","citation_count":37,"is_preprint":false},{"pmid":"37419978","id":"PMC_37419978","title":"Complement is activated by elevated IgG3 hexameric platforms and deposits C4b onto distinct antibody domains.","date":"2023","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/37419978","citation_count":36,"is_preprint":false},{"pmid":"17984207","id":"PMC_17984207","title":"Defining targets for complement components C4b and C3b on the pathogenic neisseriae.","date":"2007","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/17984207","citation_count":36,"is_preprint":false},{"pmid":"21262398","id":"PMC_21262398","title":"A high-quality secretome of A549 cells aided the discovery of C4b-binding protein as a novel serum biomarker for non-small cell lung cancer.","date":"2011","source":"Journal of proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/21262398","citation_count":36,"is_preprint":false},{"pmid":"30323030","id":"PMC_30323030","title":"The Pneumococcal Surface Proteins PspA and PspC Sequester Host C4-Binding Protein To Inactivate Complement C4b on the Bacterial Surface.","date":"2018","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/30323030","citation_count":34,"is_preprint":false},{"pmid":"2956264","id":"PMC_2956264","title":"The protein S-binding site localized to the central core of C4b-binding protein.","date":"1987","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/2956264","citation_count":34,"is_preprint":false},{"pmid":"2022920","id":"PMC_2022920","title":"Structure of the gene coding for the alpha polypeptide chain of the human complement component C4b-binding protein.","date":"1991","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/2022920","citation_count":32,"is_preprint":false},{"pmid":"22076784","id":"PMC_22076784","title":"Increased frequency of complement C4B deficiency in rheumatoid arthritis.","date":"2012","source":"Arthritis and rheumatism","url":"https://pubmed.ncbi.nlm.nih.gov/22076784","citation_count":31,"is_preprint":false},{"pmid":"2460456","id":"PMC_2460456","title":"Binding site for vitamin K-dependent protein S on complement C4b-binding protein.","date":"1988","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/2460456","citation_count":31,"is_preprint":false},{"pmid":"10382758","id":"PMC_10382758","title":"Structure-activity relationships within the N-terminal short consensus repeats (SCR) of human CR1 (C3b/C4b receptor, CD35): SCR 3 plays a critical role in inhibition of the classical and alternative pathways of complement activation.","date":"1999","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/10382758","citation_count":31,"is_preprint":false},{"pmid":"22102907","id":"PMC_22102907","title":"Functional recruitment of human complement inhibitor C4B-binding protein to outer membrane protein Rck of Salmonella.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22102907","citation_count":30,"is_preprint":false},{"pmid":"7561114","id":"PMC_7561114","title":"Isoforms of human C4b-binding protein. II. Differential modulation of the C4BPA and C4BPB genes by acute phase cytokines.","date":"1995","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/7561114","citation_count":30,"is_preprint":false},{"pmid":"3264881","id":"PMC_3264881","title":"The fluid-phase binding of human C4 and its genetic variants, C4A3 and C4B1, to immunoglobulins.","date":"1988","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/3264881","citation_count":29,"is_preprint":false},{"pmid":"2937839","id":"PMC_2937839","title":"Alternative complement pathway activation by C4b deposited during classical pathway activation.","date":"1986","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/2937839","citation_count":29,"is_preprint":false},{"pmid":"8125996","id":"PMC_8125996","title":"Quantitative analysis of C4b dimer binding to distinct sites on the C3b/C4b receptor (CR1).","date":"1994","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8125996","citation_count":29,"is_preprint":false},{"pmid":"3295051","id":"PMC_3295051","title":"Phylogeny of C4b-C3b cleaving activity: similar fragmentation patterns of human C4b and C3b produced by lower animals.","date":"1987","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/3295051","citation_count":29,"is_preprint":false},{"pmid":"21805441","id":"PMC_21805441","title":"C4b-binding protein: a forgotten factor in thrombosis and hemostasis.","date":"2011","source":"Seminars in thrombosis and hemostasis","url":"https://pubmed.ncbi.nlm.nih.gov/21805441","citation_count":28,"is_preprint":false},{"pmid":"8300581","id":"PMC_8300581","title":"A protein S binding site on C4b-binding protein involves beta chain residues 31-45.","date":"1994","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8300581","citation_count":28,"is_preprint":false},{"pmid":"28205620","id":"PMC_28205620","title":"Association between C4, C4A, and C4B copy number variations and susceptibility to autoimmune diseases: a meta-analysis.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28205620","citation_count":28,"is_preprint":false},{"pmid":"1815762","id":"PMC_1815762","title":"Determination of serum levels of complement component C4b-binding protein: influence of age and inflammation.","date":"1991","source":"International journal of clinical & laboratory research","url":"https://pubmed.ncbi.nlm.nih.gov/1815762","citation_count":28,"is_preprint":false},{"pmid":"18432942","id":"PMC_18432942","title":"Human complement components C4A and C4B genetic diversities: complex genotypes and phenotypes.","date":"2005","source":"Current protocols in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/18432942","citation_count":27,"is_preprint":false},{"pmid":"11847209","id":"PMC_11847209","title":"Structural requirements of anticoagulant protein S for its binding to the complement regulator C4b-binding protein.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11847209","citation_count":27,"is_preprint":false},{"pmid":"17202363","id":"PMC_17202363","title":"lgtC expression modulates resistance to C4b deposition on an invasive nontypeable Haemophilus influenzae.","date":"2007","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/17202363","citation_count":27,"is_preprint":false},{"pmid":"2967718","id":"PMC_2967718","title":"Plasma concentrations of C4b-binding protein and vitamin K-dependent protein S in term and preterm infants: low levels of protein S-C4b-binding protein complexes.","date":"1988","source":"British journal of haematology","url":"https://pubmed.ncbi.nlm.nih.gov/2967718","citation_count":26,"is_preprint":false},{"pmid":"19660812","id":"PMC_19660812","title":"Stringent regulation of complement lectin pathway C3/C5 convertase by C4b-binding protein (C4BP).","date":"2009","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/19660812","citation_count":26,"is_preprint":false},{"pmid":"2650988","id":"PMC_2650988","title":"Two isotypes of human C4, C4A and C4B have different structure and function.","date":"1989","source":"Complement and inflammation","url":"https://pubmed.ncbi.nlm.nih.gov/2650988","citation_count":25,"is_preprint":false},{"pmid":"17526744","id":"PMC_17526744","title":"Heptose I glycan substitutions on Neisseria gonorrhoeae lipooligosaccharide influence C4b-binding protein binding and serum resistance.","date":"2007","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/17526744","citation_count":25,"is_preprint":false},{"pmid":"1825786","id":"PMC_1825786","title":"Solution-phase equilibrium binding interaction of human protein S with C4b-binding protein.","date":"1991","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/1825786","citation_count":25,"is_preprint":false},{"pmid":"19284503","id":"PMC_19284503","title":"Complement inhibitor C4b-binding protein in primary Sjögren's syndrome and its association with other disease markers.","date":"2009","source":"Scandinavian journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/19284503","citation_count":24,"is_preprint":false},{"pmid":"22737222","id":"PMC_22737222","title":"Copy number analysis of complement C4A, C4B and C4A silencing mutation by real-time quantitative polymerase chain reaction.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22737222","citation_count":24,"is_preprint":false},{"pmid":"3180739","id":"PMC_3180739","title":"C4-mediated inhibition of immune precipitation and differences in inhibitory action of genetic variants, C4A3 and C4B1.","date":"1988","source":"Complement (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/3180739","citation_count":23,"is_preprint":false},{"pmid":"8144890","id":"PMC_8144890","title":"Binding of C3b and C4b by the CR1-like site in murine CR1.","date":"1994","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/8144890","citation_count":23,"is_preprint":false},{"pmid":"15998580","id":"PMC_15998580","title":"Complete deficiencies of complement C4A and C4B including 2-bp insertion in codon 1213 are genetic risk factors of systemic lupus erythematosus in Thai populations.","date":"2005","source":"Journal of autoimmunity","url":"https://pubmed.ncbi.nlm.nih.gov/15998580","citation_count":23,"is_preprint":false},{"pmid":"8325877","id":"PMC_8325877","title":"The human C4b-binding protein beta-chain gene.","date":"1993","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8325877","citation_count":22,"is_preprint":false},{"pmid":"9774728","id":"PMC_9774728","title":"The C4b-binding protein-protein S interaction is hydrophobic in nature.","date":"1998","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/9774728","citation_count":22,"is_preprint":false},{"pmid":"2247091","id":"PMC_2247091","title":"The mechanism of activation of the alternative pathway of complement by cell-bound C4b.","date":"1990","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/2247091","citation_count":22,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":48705,"output_tokens":10332,"usd":0.150548},"stage2":{"model":"claude-opus-4-6","input_tokens":14499,"output_tokens":2883,"usd":0.216855},"total_usd":0.367403,"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\": 1984,\n      \"finding\": \"C4b-binding protein (C4BP) has a spider-like ultrastructure composed of seven identical disulfide-linked tentacle subunits (~70 kDa each) arranged around a central ringlike core (~160 kDa), as revealed by electron microscopy of chymotrypsin-generated fragments.\",\n      \"method\": \"Limited proteolysis + electron microscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural characterization by EM with biochemical fractionation, foundational paper\",\n      \"pmids\": [\"6480575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"C4BP belongs to a multi-gene family of C3b/C4b-binding regulatory proteins that share a common ~60-amino-acid short consensus repeat (SCR/CCP) structural element, including factor H, CR1, DAF, and C2/factor B.\",\n      \"method\": \"Amino acid and nucleotide sequencing, structural comparison\",\n      \"journal\": \"Immunology today\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — primary sequence analysis establishing domain architecture, replicated across multiple proteins\",\n      \"pmids\": [\"25289982\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"C4B isotype binds predominantly via ester linkages to cell surfaces, while C4A preferentially forms amide bonds; C4B deposited during classical pathway activation can activate the alternative complement pathway.\",\n      \"method\": \"Chemical modification of erythrocyte amino groups, SDS-PAGE of radiolabeled C4 isotypes on multiple cell lines; hemolytic assays with C2-deficient serum and Mg-EGTA conditions\",\n      \"journal\": \"Journal of immunology / Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical assays with multiple cell types and chemical modification controls, replicated across multiple papers\",\n      \"pmids\": [\"3512717\", \"2937839\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"The protein S-binding site on C4BP is located in the central core (~160 kDa chymotrypsin fragment), not the tentacles, and requires intact disulfide bonds; protein S protects this site from proteolysis.\",\n      \"method\": \"Chymotrypsin proteolysis, immunoblotting with polyclonal antisera, direct binding assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution and proteolysis with functional binding readout\",\n      \"pmids\": [\"2956264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"A novel ~45 kDa beta-chain subunit in C4BP is directly involved in protein S binding; chymotrypsin cleavage of this subunit abolishes protein S binding, and protein S protects the beta-chain from proteolysis.\",\n      \"method\": \"SDS-PAGE, gel filtration in 6M guanidine HCl, chymotrypsin protection assay, N-terminal sequencing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with proteolysis protection assay identifying specific subunit\",\n      \"pmids\": [\"2970465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"The protein S-binding site on C4BP maps to a peptide near the C-terminus of the alpha-chain core (residues Ser447–Tyr467), identified by monoclonal antibody MFbp16 affinity chromatography and competition binding with protein S.\",\n      \"method\": \"Chymotrypsin digestion, affinity chromatography on MFbp16-Sepharose, competition binding assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical mapping with monoclonal antibody and competition, single lab\",\n      \"pmids\": [\"2460456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"C4A3 binds immunoglobulins (IgG, IgM, IgA) in the fluid phase approximately 3–4 times more efficiently than C4B1, with C4A forming predominantly amide linkages and C4B1 forming both amide and ester bonds.\",\n      \"method\": \"Fluid-phase binding assay with purified C4, C1s and antibody; covalent bond characterization\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified components and bond-type characterization\",\n      \"pmids\": [\"3264881\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"C4BP circulates in plasma as two subpopulations: a major form (seven alpha-chains + one beta-chain) that binds protein S, and a minor form lacking the beta-chain that cannot bind protein S, establishing the beta-chain as the sole protein S binding subunit.\",\n      \"method\": \"Subpopulation isolation, SDS-PAGE, direct protein S binding assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical fractionation with direct functional binding confirmation\",\n      \"pmids\": [\"2532155\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"C4BP synthesis and secretion is induced by IL-6 and TNF-α in the HepG2 hepatoma cell line, and plasma C4BP levels are elevated in acute pneumonia patients, establishing C4BP as an acute phase protein.\",\n      \"method\": \"Cell culture with cytokine stimulation, plasma measurements in pneumonia patients\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-based assay plus clinical correlation, single lab\",\n      \"pmids\": [\"2480119\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Nascent C3b covalently attaches to C4b, and C3b in C4b–C3b complexes is protected from inactivation by factors H and I, providing a mechanism by which classical pathway activation recruits and amplifies the alternative pathway.\",\n      \"method\": \"In vitro reconstitution with purified complement components, kinetic protection assays, surface plasmon resonance-type binding\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with purified components, quantitative protection assays\",\n      \"pmids\": [\"2148521\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"C4b deposited on cell surfaces activates the alternative pathway by binding the C3 convertase C3bBbP through a C3b interaction, amplifying C3b deposition; this requires C3b, properdin, factor B, and factor D but does not involve direct C4bBb formation.\",\n      \"method\": \"Hemolytic assays, radiolabeled component binding studies, C5-deficient serum experiments\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with defined purified components and genetic-deficiency controls\",\n      \"pmids\": [\"2247091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"C4A is more effective than C4B in enhancing CR1-mediated binding of immune complexes to erythrocytes, whereas C4B is only modestly less efficient at inhibiting immunoprecipitation; the major functional difference between the isotypes is at the level of CR1 binding.\",\n      \"method\": \"CR1 binding assay with purified C4A and C4B, immune precipitation inhibition assay\",\n      \"journal\": \"Clinical and experimental immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — comparative in vitro functional assay with purified isotypes\",\n      \"pmids\": [\"2138067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"The C4BP alpha-chain gene spans >40 kb, is organized into 12 exons with each of the eight SCR repeats encoded by individual exons (except SCR2 which is split), and contains acute phase and liver-specific regulatory elements in its promoter region.\",\n      \"method\": \"Genomic cloning, exon mapping, sequence analysis, comparison with mouse C4BP alpha transcript\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — complete gene structure determination\",\n      \"pmids\": [\"2022920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"C4BP beta-chain gene spans >10 kb, encodes three SCR domains plus a C-terminal non-repeat region, and produces two distinct mRNA classes from different transcription start sites; the alpha- and beta-chain genes are closely linked at chromosome 1q32.\",\n      \"method\": \"Genomic cloning, Northern blot, primer extension, S1 nuclease protection, cDNA isolation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — complete gene structure determination with multiple methods\",\n      \"pmids\": [\"8325877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Protein S residues 413–434 (particularly the PSP-420 peptide, residues 420–434) are essential for binding to C4BP; a monoclonal antibody (LJ-56) against this region blocks complex formation and specifically recognizes free protein S but not the protein S:C4BP complex.\",\n      \"method\": \"Synthetic peptide inhibition assay, ELISA, polyclonal and monoclonal antibody inhibition studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — peptide mapping and antibody epitope confirmation, multiple orthogonal approaches\",\n      \"pmids\": [\"7688369\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Beta-chain residues 31–45 of C4BP (with the sequence YxLVG being critical) provide a protein S-binding site; peptide beta(31-45) inhibits the protein S:C4BP interaction and blocks protein S APC-cofactor activity.\",\n      \"method\": \"Synthetic peptide inhibition assays, surface plasmon resonance binding, coagulation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — peptide mapping with functional coagulation readout, multiple methods\",\n      \"pmids\": [\"8300581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Complement receptor CR1 (CD35) has two functional sites: site 1 (SCR1–2) binds C4b and serves as cofactor for C4b cleavage; site 2 (SCR8–9) binds primarily C3b but also C4b with greater cofactor activity for C4b cleavage than site 1.\",\n      \"method\": \"Substitution mutagenesis of CR1 constructs, binding assays, cofactor activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with functional binding and cofactor assays\",\n      \"pmids\": [\"8175757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Murine C4BPB gene has become a pseudogene due to two in-frame stop codons, while the human gene is functional; this explains the absence of protein S binding by murine C4BP and reveals an evolutionary difference in the coagulation–complement interface.\",\n      \"method\": \"Genomic cloning, sequence analysis of multiple mouse strains, Southern blotting\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct sequence determination across multiple strains demonstrating stop codons\",\n      \"pmids\": [\"7959726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Serum amyloid P component (SAP) binds to the central core of C4BP (not the tentacles) with high affinity (Kd ~30 nM) in a calcium-dependent, carbohydrate-dependent manner; the C4BP beta-chain is not required for SAP binding.\",\n      \"method\": \"SAP-Sepharose affinity chromatography, quantitative affinity chromatography, recombinant C4BP constructs\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — affinity chromatography with recombinant deletion constructs and quantitative binding constants\",\n      \"pmids\": [\"7592941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"IL-6, IL-1β, and IFN-γ differentially upregulate C4BPA and C4BPB gene expression in Hep3B cells; TNF-α downregulates both; IFN-γ combined with TNF-α produces a synergistic 10-fold induction of C4BP alpha-mRNA with minimal C4BP beta-mRNA increase, providing a mechanism to maintain C4BP beta homeostasis during acute phase response.\",\n      \"method\": \"Cytokine stimulation of Hep3B cells, Northern blot analysis of C4BPA and C4BPB mRNAs, analysis of C4BP isoforms in acute phase patient samples\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-based gene expression with clinical correlation, multiple cytokines tested\",\n      \"pmids\": [\"7561114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The entire protein S-binding site on C4BP resides within SCR-1 of the beta-chain; alpha/beta-chain chimeras replacing only SCR-1 of the alpha-chain with beta-chain SCR-1 confer full protein S binding affinity (Ka ~2.3×10⁸ M⁻¹).\",\n      \"method\": \"Recombinant alpha/beta chain chimera expression in eukaryotic cells, protein S binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — domain-swap chimeras with quantitative binding measurements\",\n      \"pmids\": [\"8702842\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The C4BP beta-chain SCR-1 interaction with protein S is primarily hydrophobic in nature, mediated by a solvent-exposed hydrophobic cluster; ionic interactions contribute minimally.\",\n      \"method\": \"Homology modeling, inter-species sequence comparison, binding studies with salt and detergent\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — experimental binding with computational modeling, single lab\",\n      \"pmids\": [\"9774728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Modeling of C4BP alpha-chain 8 CCP modules identified a cluster of positively charged residues at the CCP1–CCP2 interface as the principal binding site for C4b, heparin, and bacterial Arp/Sir proteins.\",\n      \"method\": \"Computer modeling combined with monoclonal antibody mapping and heparin binding experiments\",\n      \"journal\": \"Proteins\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — computational modeling with experimental antibody and heparin binding support, single lab\",\n      \"pmids\": [\"9626699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Both G domains (G1 and G2) of the sex-hormone-binding globulin-like region of protein S contribute to C4BP binding; full-affinity binding requires both domains, with G1 contributing more than G2.\",\n      \"method\": \"Recombinant protein S/Gas6 chimeras, surface plasmon resonance, microtiter plate binding assays\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — domain-swap chimeras with quantitative SPR measurements\",\n      \"pmids\": [\"10583388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"CR1 has a single C1q binding site on LHR-D; C1q and C4b bind CR1 independently and additively support erythrocyte adhesion, confirming CR1 as the receptor for all major complement opsonic ligands.\",\n      \"method\": \"BIAcore binding analysis, erythrocyte adhesion assay, anti-CR1 Fab inhibition\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — SPR with independent binding confirmation and cellular adhesion assay\",\n      \"pmids\": [\"10528211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Type IV pili of N. gonorrhoeae bind C4BP via the N-terminal part of PilC at CCP1 and CCP2 of the C4BP alpha-chain through ionic interactions; this binding overlaps only partially with the MCP (CD46) binding site on pili.\",\n      \"method\": \"Direct binding assay with isolated pili, C4BP mutants lacking individual CCPs, competition assays with C4b and NaCl titration\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — binding with deletion mutants and competition assays defining molecular interface\",\n      \"pmids\": [\"11359834\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Membrane cofactor protein (MCP/CD46) is the primary cofactor mediating C4b cleavage on MCP-expressing cells; fluid-phase C4BP does not significantly cleave cell-surface C4b in this model. For C3b deposited via the classical pathway, factor H is the primary cofactor.\",\n      \"method\": \"FACS and Western blotting on MCP-transfected cells, function-blocking monoclonal antibody, Mg-EGTA pathway-specific conditions\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-based experiments with transfection, specific mAb blockade, and pathway-selective conditions\",\n      \"pmids\": [\"12055245\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"OmpA of E. coli K1 binds the alpha-chain CCP3 of C4BP through hydrophobic interactions (not inhibited by C4b, heparin, or salt), recruiting C4BP to the bacterial surface and conferring serum resistance.\",\n      \"method\": \"Flow cytometry, CCP deletion mutants of recombinant C4BP, competition with synthetic CCP3 peptides, serum bactericidal assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — recombinant deletion mutant mapping with functional bactericidal assay\",\n      \"pmids\": [\"12444142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Protein S mediates binding of C4BP to apoptotic cells by binding phosphatidylserine exposed on the apoptotic cell surface; this binding is calcium-dependent and blockable by annexin V, localizing complement regulatory activity to apoptotic cells.\",\n      \"method\": \"Binding assays with Jurkat apoptosis model, blocking with anti-PS Gla domain antibodies and annexin V, C4b interaction confirmation\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-based assay with specific blocking antibodies and functional complement readout\",\n      \"pmids\": [\"12193728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The C4b-binding site on C4BP requires CCP1–3 of the alpha-chain and is mediated by a cluster of positively charged amino acids at the CCP1–CCP2 interface; loss of C4b binding abolishes all classical pathway inhibitory activity of C4BP.\",\n      \"method\": \"Homology-based modeling, recombinant mutagenesis, complement functional assays\",\n      \"journal\": \"Biochemical Society transactions\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with functional complement assay readout\",\n      \"pmids\": [\"12440957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Protein S binding to C4BP is mediated by a cluster of surface-exposed hydrophobic amino acids on CCP1 of the beta-chain; heparin binding requires CCP1–3 of the alpha-chain with CCP2 being most important.\",\n      \"method\": \"Homology-based computer modeling, recombinant mutagenesis, binding assays\",\n      \"journal\": \"Biochemical Society transactions\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with binding assays identifying specific residues\",\n      \"pmids\": [\"12440957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The alpha-chain of C4BP binds directly to CD40 on human B cells at a site distinct from CD40L, inducing B-cell proliferation, upregulation of CD54 and CD86, and IL-4-dependent IgE isotype switching; this effect requires CD40 and IKKγ/NEMO signaling.\",\n      \"method\": \"Direct binding assays, B-cell proliferation and differentiation assays, experiments with B cells from CD40- and IKKγ/NEMO-deficient patients, colocalization in germinal centers\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding plus functional cellular readout validated with genetic-deficiency patient cells and tissue colocalization\",\n      \"pmids\": [\"12818164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Zinc at micromolar concentrations enhances C4BP cofactor activity toward C4b/C3b by increasing affinity between C4b/C3b and cofactor proteins; millimolar zinc concentrations inhibit cofactor activity by aggregating C4b/C3b.\",\n      \"method\": \"Cofactor activity assays, 65Zn binding studies, fluorescent chelator Kd measurements, surface plasmon resonance\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative binding and activity measurements with multiple methods\",\n      \"pmids\": [\"14522582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"M. catarrhalis UspA2 and UspA1 bind C4BP alpha-chain at CCP2, CCP5, and CCP7; surface-bound C4BP retains cofactor activity for C4b degradation, conferring serum resistance.\",\n      \"method\": \"Flow cytometry, RIA, recombinant UspA binding assays with C4BP deletion mutants, cofactor activity assay for C4b degradation\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping with deletion mutants and functional complement assay\",\n      \"pmids\": [\"15383594\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"C. albicans hyphal and yeast forms bind C4BP at CCP1–2 of the alpha-chain; surface-bound C4BP retains cofactor activity for C4b inactivation and mediates adhesion of C. albicans to host endothelial cells.\",\n      \"method\": \"Confocal microscopy, flow cytometry, ELISA, absorption from human serum, recombinant deletion constructs, monoclonal antibodies\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple binding methods with domain mapping and functional complement and adhesion assays\",\n      \"pmids\": [\"15501796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The C4BP–protein S complex inhibits phagocytosis of apoptotic cells by macrophages; free protein S enhances phagocytosis, but when complexed to C4BP, the protein S proengulfment activity is blocked while C4BP localizes to apoptotic cell surfaces via protein S.\",\n      \"method\": \"Phagocytosis assay with primary human macrophages and THP-1 cells, complement-depleted serum reconstitution, anti-Gla domain antibody blocking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional cellular assay with serum reconstitution and specific blocking antibody\",\n      \"pmids\": [\"15096498\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"N. gonorrhoeae porin (Por) binds human C4BP in a species-specific manner to evade complement; Por1B-bearing strains bind chimpanzee C4BP but not rodent/lagomorph C4BP, explaining the host restriction of gonorrhea.\",\n      \"method\": \"Serum bactericidal assays with species-specific sera, C4BP binding studies, C4BP reconstitution in heterologous sera\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional bactericidal assay with species comparison and reconstitution experiment\",\n      \"pmids\": [\"16275906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CRP binds C4BP, with the binding site localized to the central core of C4BP; C4BP lacking beta-chain and protein S (an acute-phase form) binds CRP with higher affinity; C4BP–CRP complexes exist in patient serum and C4BP retains full complement regulatory activity in the presence of CRP.\",\n      \"method\": \"ELISA with recombinant CRP and phosphorylcholine-CRP, proteolytic C4BP fragment binding, ionic strength titration, patient serum analysis, complement activation assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple binding methods with domain localization and functional complement readout, patient serum confirmation\",\n      \"pmids\": [\"16751408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Y. enterocolitica uses both YadA and Ail outer membrane proteins as C4BP receptors; Ail-mediated C4BP binding is blocked by O-antigen and outer core LPS. Surface-bound C4BP retains factor I-mediated C4b degradation activity.\",\n      \"method\": \"C4BP binding assays with LPS/protein mutant panel, flow cytometry, cofactor activity assay\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic mutant analysis with functional complement assay\",\n      \"pmids\": [\"18769718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"N. gonorrhoeae Por1B selectively binds C4b via amide linkages (at loops 4–5) and C3b via ester linkages; all Opa proteins (A,B,C,D,E,F,I) bind both C4b and C3b; C4Ab preferentially forms monomers/heterodimers while C4Bb participates in C5 convertase heterodimer formation.\",\n      \"method\": \"Hybrid Por1A/1B molecule analysis, serum with only C4A isoform, Opa-specific variant strains, bond-type characterization\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic mutant and isoform-specific analysis with bond-type characterization\",\n      \"pmids\": [\"17984207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"C4BP binds Aβ1-42 peptide directly via the C4BP alpha-chain and localizes to amyloid plaques and apoptotic cells in Alzheimer's disease brain, limiting complement activation on these targets in vitro.\",\n      \"method\": \"Immunohistochemistry, in vitro binding assay with dead brain cells and Aβ1-42, complement activation assay\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding assay with functional complement readout, single lab\",\n      \"pmids\": [\"18556068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"C4BP binds directly to small leucine-rich repeat proteins (SLRPs: osteoadherin, chondroadherin, fibromodulin, PRELP) predominantly via its central core; C4BP binding does not impair complement inhibitory activity but limits C9 deposition activated by SLRPs in serum.\",\n      \"method\": \"Direct binding assays with C4BP fragments/mutants, electron microscopy, C9 deposition assay with C4BP-depleted serum\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping with multiple deletion mutants, EM, and functional complement assay\",\n      \"pmids\": [\"19155499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"C4BP regulates the lectin pathway C3/C5 convertase with ~7–13-fold greater affinity for C4b deposited via the lectin pathway than the classical pathway; at high C4b density, all seven alpha-chains of C4BP can simultaneously engage C4b.\",\n      \"method\": \"Reconstituted complement assays on zymosan and E(Man), stoichiometric analysis of C4b per C4BP\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative in vitro reconstitution establishing pathway-specific affinities\",\n      \"pmids\": [\"19660812\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Dengue, West Nile, and yellow fever virus NS1 directly binds C4BP with binding sites on NS1 that partially overlap the C4b-binding sites; soluble NS1 recruits C4BP to inactivate C4b in solution and on plasma membranes, representing a second complement-evasion mechanism.\",\n      \"method\": \"Direct binding assays, mapping studies with C4BP mutants, C4b inactivation assays on plasma membrane\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — binding domain mapping with functional C4b inactivation assay, tested for three flaviviruses\",\n      \"pmids\": [\"21642539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PTX3 binds C4BP at SCR1–3 of the C4BP alpha-chain; PTX3 does not compete with factor H for C4BP binding but is inhibited by C1q and L-ficolin; C4BP recruited by PTX3 on extracellular matrix or late apoptotic cells retains complement regulatory activity and reduces C5b-9 deposition.\",\n      \"method\": \"ELISA, competition binding assays, complement deposition assays on ECM and apoptotic cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping with multiple competition assays and functional complement readout\",\n      \"pmids\": [\"21915248\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Candida Pra1 is the first fungal C4BP-binding protein; Pra1 binds C4BP at CCP4, CCP7, and CCP8 of the alpha-chain through ionic interactions; C4BP and factor H bind simultaneously to Pra1; surface-bound C4BP inhibits C4b and C3b deposition.\",\n      \"method\": \"ELISA, isothermal titration calorimetry, recombinant C4BP CCP deletion mutants, C4BP/factor H co-binding assays, C4b/C3b surface deposition assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — ITC for affinity measurement plus domain mapping and functional complement assay\",\n      \"pmids\": [\"21212281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Pneumococcal enolase binds C4BP at CCP1/CCP2 and CCP8 of the C4BP alpha-chain; C4BP and plasminogen bind distinct sites on enolase without competition; enolase-bound C4BP retains cofactor activity for C4b degradation.\",\n      \"method\": \"Dose-dependent binding assays, ionic strength titration, recombinant C4BP mutants lacking individual CCPs, C3b deposition assay, cofactor activity assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic CCP domain mapping with functional complement assay, two independent binding sites identified\",\n      \"pmids\": [\"22925928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Mutations in C4BPA (R120H, I126T, G423T) found in women with recurrent miscarriage affect the expression level and/or factor I cofactor activity of C4BP, while a CD46 variant (N213I) causes deficient protein processing and impaired cofactor activity for both C4b and C3b.\",\n      \"method\": \"Sequencing, recombinant protein expression, cofactor activity assay for factor I\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — recombinant mutagenesis with functional assay, clinical association context\",\n      \"pmids\": [\"23508668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"C4BP uses a conserved 'reading head' in CCP1–3 to detect hidden conserved sequence patterns within the hypervariable M protein regions of Group A Streptococcus, enabling broad (~90% M type) recognition; crystal structures of four M proteins in complex with C4BP revealed a uniform binding mechanism.\",\n      \"method\": \"Crystal structure determination of four M protein–C4BP complexes, functional binding validation\",\n      \"journal\": \"Nature microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple crystal structures with functional validation, mechanism established at atomic resolution\",\n      \"pmids\": [\"27595425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"B. burgdorferi OspC directly binds complement component C4b and competes with complement protein C2 for C4b binding, thereby inhibiting classical and lectin pathway activation; this confers bloodstream survival in vivo.\",\n      \"method\": \"Direct binding assays, C2 competition assay, in vivo mouse bloodstream survival experiments\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding with competition assay and in vivo validation\",\n      \"pmids\": [\"28873507\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Pneumococcal PspA and PspC both bind serum C4BP; deletion of PspA or PspC reduces C4BP deposition on bacteria, increases C4b and iC4b deposition, and reduces C4dg, establishing that PspA and PspC sequester C4BP to inactivate C4b and evade complement.\",\n      \"method\": \"Targeted gene deletion, serum opsonization assays, recombinant PspA/PspC binding assays, mouse infection experiments\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with functional complement deposition assay and in vivo virulence confirmation\",\n      \"pmids\": [\"30323030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CryoEM structures show that IgG3 forms elevated hexameric Fc platforms; mass spectrometry reveals that C1 (activated by IgG3) deposits C4b directly onto specific IgG3 residues proximal to the Fab domains, a consequence of the elevated height of the C1-IgG3 complex.\",\n      \"method\": \"CryoEM structure determination of IgG3-antigen-C1 complexes, mass spectrometry identification of C4b deposition sites\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structural determination combined with MS identification of C4b attachment sites\",\n      \"pmids\": [\"37419978\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"C4B (complement component 4B) is cleaved by activated C1 to generate C4b, which covalently attaches to targets preferentially via ester linkages (unlike C4A which forms amide bonds), initiates classical/lectin pathway C3 convertase assembly, can recruit the alternative pathway by protecting nascent C3b from inactivation, and is regulated by the soluble inhibitor C4BP—a spider-like multimer of seven alpha-chains (each bearing a C4b-binding site in CCP1-3) plus one beta-chain (bearing the protein S-binding site in CCP1-SCR1)—which acts as cofactor for factor I-mediated cleavage of C4b, with the C4BP–protein S complex additionally localizing complement regulation to apoptotic cell surfaces; numerous pathogens (N. gonorrhoeae, S. pyogenes, S. pneumoniae, C. albicans, E. coli, Borrelia, etc.) exploit C4BP by binding its alpha-chain CCPs to evade complement-mediated killing.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"C4B encodes the C4B isotype of complement component 4, a central effector of the classical and lectin complement pathways that, upon cleavage by activated C1, generates the opsonin C4b which covalently attaches to target surfaces preferentially via ester linkages—in contrast to C4A, which forms amide bonds and binds immune complexes more efficiently [PMID:3512717, PMID:3264881]. Surface-deposited C4b nucleates C3 convertase assembly and recruits the alternative pathway by protecting nascent C3b from factor H/I–mediated inactivation, thereby amplifying complement activation [PMID:2148521, PMID:2247091]. C4b activity is regulated by soluble C4b-binding protein (C4BP), a spider-shaped heptameric complex of alpha-chains (each bearing C4b-binding sites in CCP1–3) and one beta-chain (whose CCP1 binds protein S), which serves as cofactor for factor I–mediated cleavage of C4b; the C4BP–protein S complex additionally localizes complement regulation to apoptotic cell surfaces through protein S binding to phosphatidylserine [PMID:6480575, PMID:12440957, PMID:8702842, PMID:12193728]. Numerous bacterial and viral pathogens—including N. gonorrhoeae, S. pyogenes, E. coli K1, C. albicans, S. pneumoniae, and flavivirus NS1—exploit C4BP by engaging distinct alpha-chain CCP modules to recruit its cofactor activity and evade complement-mediated killing [PMID:27595425, PMID:12444142, PMID:21642539, PMID:30323030].\",\n  \"teleology\": [\n    {\n      \"year\": 1984,\n      \"claim\": \"Determining the ultrastructure of C4BP revealed how a multivalent regulator could simultaneously engage multiple C4b molecules, establishing the physical basis for its potent complement-inhibitory activity.\",\n      \"evidence\": \"Limited proteolysis and electron microscopy of purified C4BP showing seven tentacle subunits around a central core\",\n      \"pmids\": [\"6480575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of simultaneous C4b engagement was not measured\", \"No atomic-resolution structure of the full complex\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"Distinguishing the bond chemistry of C4A versus C4B isotypes explained their divergent biological roles: C4B's preference for ester linkages promotes efficient surface opsonization, while C4A's amide bonds favor immune complex handling.\",\n      \"evidence\": \"Chemical modification of erythrocyte amino groups, SDS-PAGE of radiolabeled C4 isotypes, and hemolytic assays with C2-deficient serum\",\n      \"pmids\": [\"3512717\", \"2937839\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for the thioester reactivity difference between isotypes was not resolved\", \"In vivo relevance of differential bond formation not directly tested\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"Identification of the C4BP beta-chain as the sole protein S–binding subunit resolved how C4BP bridges complement regulation and coagulation, and explained why beta-chain-lacking C4BP isoforms cannot sequester protein S.\",\n      \"evidence\": \"SDS-PAGE, gel filtration, chymotrypsin protection assays, and direct binding with subpopulation fractionation\",\n      \"pmids\": [\"2970465\", \"2532155\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic contacts between beta-chain and protein S were unknown\", \"Physiological regulation of beta-chain expression not yet addressed\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Demonstrating that surface-deposited C4b protects nascent C3b from inactivation and recruits the alternative pathway convertase C3bBbP established the mechanism by which classical pathway activation amplifies through the alternative loop.\",\n      \"evidence\": \"In vitro reconstitution with purified complement components and hemolytic assays with defined component additions\",\n      \"pmids\": [\"2148521\", \"2247091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of C4b–C3b protective interaction not resolved\", \"Relative contribution in vivo versus lectin pathway-deposited C4b unknown\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Domain-swap chimeras localized the protein S–binding site to SCR-1 (CCP1) of the C4BP beta-chain, while mutagenesis mapped the C4b-binding site to positively charged residues at the CCP1–2 interface of the alpha-chain, defining the two principal functional surfaces of C4BP.\",\n      \"evidence\": \"Recombinant alpha/beta-chain chimeras with quantitative binding assays, and site-directed mutagenesis with complement functional assays\",\n      \"pmids\": [\"8702842\", \"12440957\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution co-crystal of C4BP–C4b complex not available\", \"Role of CCP3 in C4b binding mechanism unclear\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Discovery that protein S targets the C4BP–protein S complex to phosphatidylserine on apoptotic cells revealed a mechanism for localizing complement regulation to dying cells, preventing inflammatory complement activation during apoptotic clearance.\",\n      \"evidence\": \"Binding assays on apoptotic Jurkat cells blocked by annexin V and anti-Gla domain antibodies\",\n      \"pmids\": [\"12193728\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this mechanism is sufficient to prevent autoimmunity in vivo was not tested\", \"Contribution relative to other apoptotic complement regulators (e.g., MCP) unresolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The unexpected finding that C4BP alpha-chain binds CD40 on B cells and induces proliferation, costimulatory molecule upregulation, and IgE class switching revealed a non-complement immune-modulatory function of C4BP.\",\n      \"evidence\": \"Direct binding assays, B-cell proliferation/differentiation assays with CD40-deficient and NEMO-deficient patient cells, germinal center colocalization\",\n      \"pmids\": [\"12818164\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of C4BP–CD40 interaction unknown\", \"In vivo contribution to B-cell responses not tested\", \"Whether this function is altered during acute phase response when alpha-chain-only C4BP rises\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Systematic mapping of pathogen exploitation of C4BP established that diverse bacteria and fungi bind distinct CCP modules of the alpha-chain (CCP1–2 for N. gonorrhoeae pili and C. albicans; CCP3 for E. coli OmpA; CCP2/5/7 for M. catarrhalis) to recruit functional C4BP and evade complement killing.\",\n      \"evidence\": \"Flow cytometry, recombinant C4BP CCP deletion mutants, competition assays, and serum bactericidal assays across multiple pathogen systems\",\n      \"pmids\": [\"11359834\", \"12444142\", \"15383594\", \"15501796\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether therapeutic blockade of specific CCPs could prevent immune evasion without disabling complement regulation\", \"Evolutionary arms race dynamics between pathogen ligands and C4BP polymorphisms not characterized\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Crystal structures of Group A Streptococcus M proteins bound to C4BP CCP1–3 revealed a conserved 'reading head' mechanism by which C4BP recognizes hidden sequence patterns in hypervariable M protein regions, explaining how ~90% of M types exploit C4BP.\",\n      \"evidence\": \"Crystal structures of four M protein–C4BP complexes with functional binding validation\",\n      \"pmids\": [\"27595425\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this reading head is also exploited by non-streptococcal pathogens\", \"No structure of full-length heptameric C4BP bound to M protein\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"CryoEM visualization of C1-activated IgG3 hexameric platforms combined with mass spectrometry identification of C4b deposition sites on IgG3 Fab-proximal residues established the spatial geometry of nascent C4b covalent attachment during classical pathway initiation.\",\n      \"evidence\": \"CryoEM structure of IgG3-antigen-C1 complexes and MS identification of C4b attachment sites\",\n      \"pmids\": [\"37419978\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the same attachment geometry applies to IgG1/IgG2-initiated activation\", \"Structural basis for C4b transition to C3 convertase on the antibody platform not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A complete atomic-resolution structure of the full heptameric C4BP in complex with C4b, and the structural basis for how C4BP serves simultaneously as factor I cofactor and alternative pathway regulator, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No full-length cryo-EM or crystal structure of heptameric C4BP–C4b complex\", \"Mechanism by which C4BP discriminates lectin vs. classical pathway-deposited C4b at the structural level is unknown\", \"In vivo validation of C4BPA mutations (R120H, I126T, G423T) as causative for recurrent miscarriage awaits larger cohorts and animal models\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [29, 32, 42, 44]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [28]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [28, 35]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 7, 37, 42]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [28, 43]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2, 9, 10, 29, 42, 48]},\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [15, 28]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [36, 50, 43]}\n    ],\n    \"complexes\": [\n      \"C4b-binding protein (C4BP) complex\",\n      \"C4BP–protein S complex\",\n      \"Classical pathway C3 convertase (C4b2a)\"\n    ],\n    \"partners\": [\n      \"C4BPA\",\n      \"C4BPB\",\n      \"PROS1\",\n      \"C2\",\n      \"C3\",\n      \"CR1\",\n      \"CFI\",\n      \"CD40\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}