C1QB encodes the B chain of the secreted complement recognition protein C1q. Six copies each of the A, B and C chains assemble into six collagen-like stems ending in heterotrimeric globular heads. The B-chain globular module recognizes immunoglobulins, while its collagen-like region helps recruit the C1r/C1s protease tetramer. These recognition and assembly functions initiate the classical complement pathway without conferring protease activity on C1QB. As part of intact C1q, the B chain also contributes to phosphatidylserine recognition and inhibitory immunoreceptor signaling. Complement-dependent synaptic remodeling has been demonstrated in rodents; these studies generally test the assembled C1q system rather than an autonomous B-chain activity.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0001786 phosphatidylserine binding | IDA PMID:18250442 C1q binds phosphatidylserine and likely acts as a multiligan... | ACCEPT | Summary: The B chain contributes to phosphatidylserine recognition by heterotrimeric C1q. Reason: Human serum C1q and its heterotrimeric globular region bind phosphatidylserine in cosedimentation and surface-plasmon-resonance assays. The inspected crystal Results locate the principal phosphoserine pocket on the C chain, with an additional A-chain crystal contact; they do not establish an autonomous B-chain phosphatidylserine site. Retain the experimentally curated complex-subunit assertion, preserve its source qualifier, and represent the activity as a contribution in the core synthesis. This is not evidence that every C1q chain independently binds this lipid. Supporting Evidence: PMID:18250442 phosphoserine is bound to subunit C |
| GO:0001791 IgM binding | IDA PMID:12847249 Modular organization of the carboxyl-terminal, globular head... | ACCEPT | Summary: The recombinant human B-chain globular module recognizes immunoglobulins, with a preference for IgG over IgM. Reason: The complete abstract reports purified human MBP-ghA, MBP-ghB and MBP-ghC modules expressed in E. coli and differential IgG/IgM binding by ELISA. MBP-ghB preferentially binds IgG rather than IgM and inhibits C1q-dependent hemolysis on both IgG- and IgM-sensitized erythrocytes. The preference does not mean absence of IgM binding. Full Methods and concentration-response data were not available in the canonical cache. Supporting Evidence: |
| GO:0001791 IgM binding | IDA PMID:19006321 Interaction of human C1q with IgG and IgM: revisited. | ACCEPT | Summary: The human B-chain globular surface participates in C1q recognition of IgM. Reason: The complete abstract describes A/C-chain point mutants and inhibitory scFv epitope mapping that implicates B-chain Arg108/Arg109 in immunoglobulin recognition. It is not an isolated B-chain mutagenesis experiment. Retain the curated IgM-binding activity, also independently supported by the recombinant human B-module study. |
| GO:0005515 protein binding | IPI PMID:12960167 The crystal structure of the globular head of complement pro... | KEEP AS NON CORE | Summary: C1QB associates with C1QA within the C1q globular heterotrimer. Reason: The exact GOA partner is C1QA (P02745). The complete structural abstract describes a compact heterotrimer held together mainly by non-polar interactions. This independently supports noncovalent subunit association; the full atomic contact table was not inspected. A generic interaction does not by itself establish a more specific binding MF. Retain the supported interaction as non-core under the project instruction. Supporting Evidence: |
| GO:0005515 protein binding | IPI PMID:21054788 CD91 interacts with mannan-binding lectin (MBL) through the ... | KEEP AS NON CORE | Summary: The annotated C1QB–C1QA association is independently established, although this paper-specific assay was not inspected. Reason: The exact partner is C1QA (P02745). The cached abstract emphasizes MBL/CD91 and does not expose the curated C1q partner assay; that is not evidence of a wrong-gene citation. Human C1q structural evidence independently establishes the same A/B assembly, so defer to the experimental curator for this biologically settled interaction while explicitly leaving this source-specific experiment unverified. No CD91-binding function is inferred from this row. |
| GO:0005515 protein binding | IPI PMID:28018340 Analysis of the Interaction between Globular Head Modules of... | KEEP AS NON CORE | Summary: The human B-chain globular module directly binds the mature gC1qR/C1QBP protein. Reason: The exact partner is Q07021-PRO_0000018590. Inspected Methods and Results describe purified human MBP-globular modules, ELISA and far-Western assays that directly support ghB–gC1qR binding. PBMC colocalization and proliferation effects provide cellular context but do not by themselves establish a specific receptor-signaling mechanism for this binary interaction. Retain the supported binding as non-core without inventing a more precise MF. Supporting Evidence: |
| GO:0005515 protein binding | IPI PMID:28325905 Evidence for C1q-mediated crosslinking of CD33/LAIR-1 inhibi... | KEEP AS NON CORE | Summary: C1QB–C1QA assembly is supported; this row must not be relabeled as a CD33 interaction. Reason: The exact GOA partner is C1QA (P02745), not CD33 or LAIR-1. The inspected paper uses intact human C1q and fragments in receptor-binding and signaling experiments but does not separately resolve an A/B binary assay in the accessed sections. Independent C1q structural evidence establishes the curated A/B association. Retain that non-core association with its original source and partner; evaluate whole-C1q receptor signaling separately. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | UNDECIDED | Summary: The source-specific C1QB–UBQLN2 screen record remains unverified. Reason: The exact GOA partner is UBQLN2 (Q9UHD9). The paper presents a human binary-interaction map using yeast two-hybrid assays; the complete abstract and selected general sections were available, but the exact C1QB–UBQLN2 supplementary record, construct and validation result were not inspected. This access limitation does not contradict the experimental annotation. Retain uncertainty rather than remove generic binding or infer physiological colocalization. Supporting Evidence: |
| GO:0005515 protein binding | IPI PMID:7240 Isolation, by partial pepsin digestion, of the three collage... | KEEP AS NON CORE | Summary: The C1q A/B subunit association is supported independently of its covalent linkage. Reason: The original human C1q pepsin-fragment abstract describes collagen-like regions and a covalently linked A/B peptide. A disulfide linkage alone is not proof of the selective noncovalent activity meant by GO binding. Independent globular-domain structural evidence shows a heterotrimer held together by non-polar contacts and supports the same C1QA partner. Retain the curated association as non-core, without treating the covalent peptide result as a binary noncovalent assay. |
| GO:0005576 extracellular region | EXP PMID:29449492 Structures of C1-IgG1 provide insights into how danger patte... | ACCEPT | Summary: The C1q B chain functions in the extracellular C1 recognition complex. Reason: The complete abstract describes C1–IgG1 structures and complement recognition by the assembled complex. This extracellular role is independently demonstrated using purified human serum and recombinant C1q. The original cryo-EM Methods and figure images were not inspected; no intracellular pool or B-chain catalytic activity is inferred. |
| GO:0005576 extracellular region | EXP PMID:708376 Amino acid sequence of the N-terminal 108 amino acid residue... | ACCEPT | Summary: Human C1q B chain is an extracellular secreted protein. Reason: The original abstract directly identifies the sequence of the human C1q B chain but is not itself a cellular secretion assay. The preserved UniProt signal peptide/secreted annotation and independently inspected human serum C1q experiments establish extracellular localization, supporting retention of the experimental curation. |
| GO:0005576 extracellular region | IBA GO_REF:0000033 | ACCEPT | Summary: C1QB is a secreted extracellular recognition-complex subunit. Reason: The exact non-negated PTN008355511 extracellular-region IBD includes human C1QB among experimentally grounded descendants. Target self-evidence is legitimate, not circular. Human serum C1q assays and the preserved secreted UniProt record independently support extracellular localization; full-tree/MSA reconstruction was not performed. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN008355511 SUPPORTS TRANSFER Exact IBD joined; original seed identifiers remain unchanged. No donor-count or target-self circularity argument. |
| GO:0005576 extracellular region | IDA PMID:18250442 C1q binds phosphatidylserine and likely acts as a multiligan... | ACCEPT | Summary: Human C1q binds exposed phosphatidylserine from the extracellular space. Reason: Purified human serum C1q and its globular region bind phosphatidylserine and the surface of apoptotic HeLa cells in the inspected biochemical and cellular experiments. The B chain is a constituent of this extracellular assembly, not a membrane-spanning receptor. Supporting Evidence: |
| GO:0005576 extracellular region | IEA GO_REF:0000044 | ACCEPT | Summary: The UniProt secretion mapping is consistent with the experimentally established extracellular protein. Reason: The machine source maps the preserved UniProt secreted-location vocabulary to extracellular region. The signal peptide and direct human serum C1q experiments support the mapping; it does not assert a particular extracellular matrix or vesicle compartment. |
| GO:0005576 extracellular region | NAS PMID:28104818 Structure and activation of C1, the complex initiating the c... | ACCEPT | Summary: C1QB is part of the extracellular C1 recognition machinery. Reason: The complete abstract and selected structural Results describe C1q assembled with the C1r2C1s2 protease tetramer. Independently inspected human C1q purification and ligand assays support extracellular localization. The proposed intercomplex protease-activation model does not assign catalysis to the B chain. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-166753 | ACCEPT | Summary: The Reactome reaction places C1q B chain in an extracellular C1 assembly. Reason: The complete cached Reactome entry describes C4 cleavage by C1s in the extracellular complement system and includes the C1q-containing assembly. Retain the location assertion. Reaction membership here does not make C1QB the protease or inhibitor performing the catalytic step. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-166792 | ACCEPT | Summary: The Reactome reaction places C1q B chain in an extracellular C1 assembly. Reason: The complete cached Reactome entry describes C2 cleavage by C1s in the extracellular complement system and includes the C1q-containing assembly. Retain the location assertion. Reaction membership here does not make C1QB the protease or inhibitor performing the catalytic step. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-173626 | ACCEPT | Summary: The Reactome reaction places C1q B chain in an extracellular C1 assembly. Reason: The complete cached Reactome entry describes C1r activation in the extracellular complement system and includes the C1q-containing assembly. Retain the location assertion. Reaction membership here does not make C1QB the protease or inhibitor performing the catalytic step. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-173631 | ACCEPT | Summary: The Reactome reaction places C1q B chain in an extracellular C1 assembly. Reason: The complete cached Reactome entry describes C1s activation in the extracellular complement system and includes the C1q-containing assembly. Retain the location assertion. Reaction membership here does not make C1QB the protease or inhibitor performing the catalytic step. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-8852266 | ACCEPT | Summary: The Reactome reaction places C1q B chain in an extracellular C1 assembly. Reason: The complete cached Reactome entry describes C1 inhibitor binding to activated C1 in the extracellular complement system and includes the C1q-containing assembly. Retain the location assertion. Reaction membership here does not make C1QB the protease or inhibitor performing the catalytic step. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-8852481 | ACCEPT | Summary: The Reactome reaction places C1q B chain in an extracellular C1 assembly. Reason: The complete cached Reactome entry describes dissociation of the inhibited C1 assembly in the extracellular complement system and includes the C1q-containing assembly. Retain the location assertion. Reaction membership here does not make C1QB the protease or inhibitor performing the catalytic step. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-9021306 | ACCEPT | Summary: The Reactome reaction places C1q B chain in an extracellular C1 assembly. Reason: The complete cached Reactome entry describes inactivation of C1r/C1s by C1 inhibitor in the extracellular complement system and includes the C1q-containing assembly. Retain the location assertion. Reaction membership here does not make C1QB the protease or inhibitor performing the catalytic step. |
| GO:0005602 complement component C1 complex | IBA GO_REF:0000033 | ACCEPT | Summary: C1QB is an integral constituent of the C1q-containing C1 complex. Reason: The exact PTN002693048 C1-complex IBD contains human C1QB, human C1QC and rat donor RGD:2229. Independent recombinant human C1q and C1 structural work establish this assembly. B-chain Lys61 is explicitly implicated in C1r/C1s recruitment by the PMID:23650384 abstract; neither B-chain membership nor recruitment confers serine-protease catalysis. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002693048 SUPPORTS TRANSFER Exact IBD joined; original seed identifiers remain unchanged. No donor-count or target-self circularity argument. |
| GO:0005602 complement component C1 complex | IDA PMID:23650384 Expression of recombinant human complement C1q allows identi... | ACCEPT | Summary: Human C1QB supplies a protease-recruitment surface in the C1 complex. Reason: The canonical complete abstract and an authenticated fuller normal-fetch variant were read. Full-length human A/B/C chains expressed in HEK293-F cells reconstitute C1q; mutating mature B-chain Lys61 disrupts recruitment of C1r2C1s2 and C1 activation while retaining tested ligand recognition. The inspected Methods and Results establish direct structural participation in C1 assembly, not intrinsic proteolysis. The fuller variant was not substituted for the preserved abstract-only canonical cache. Supporting Evidence: |
| GO:0005602 complement component C1 complex | IDA PMID:2988513 Molecular modelling of human complement subcomponent C1q and... | ACCEPT | Summary: C1QB is a subunit of human C1q assembled with C1r2C1s2. Reason: The complete original abstract describes neutron scattering and hydrodynamic modeling of human C1q and its C1r2C1s2 complex. Independent recombinant human assembly experiments corroborate complex membership. The scattering model is not treated as an atomic B-chain contact map. |
| GO:0005602 complement component C1 complex | IDA PMID:34155115 C1q binding to surface-bound IgG is stabilized by C1r(2)s(2)... | ACCEPT | Summary: The B chain belongs to the C1q recognition unit of C1. Reason: Inspected human C1q/C1 binding experiments, protease depletion/reconstitution and C1-inhibitor treatment distinguish isolated C1q from C1. C1r2s2 stabilizes IgG-bound C1q, supporting the assembled complex. The B chain is a structural recognition component rather than one of the serine proteases. Supporting Evidence: |
| GO:0005602 complement component C1 complex | IDA PMID:6249812 Activation of a complex of C1r and C1s subcomponents of huma... | ACCEPT | Summary: Membership of C1QB in the C1 complex is independently established. Reason: The original cache has bibliographic metadata but no usable abstract or experimental body, so this source-specific experiment was not verified. Independent human recombinant C1q and structural C1 studies firmly establish the same complex membership; retain the curator assertion on that corroboration without claiming the original paper was read. |
| GO:0005602 complement component C1 complex | IDA PMID:6952210 Ultrastructure of the first component of human complement: e... | ACCEPT | Summary: Human C1q, including its B chains, is part of the C1 complex. Reason: The complete abstract describes electron microscopy of crosslinked human C1 and the relationship of C1q to C1r/C1s. It supports assembly-level membership, not isolated B-chain activity or an independently inspected high-resolution contact map. |
| GO:0005602 complement component C1 complex | NAS PMID:28104818 Structure and activation of C1, the complex initiating the c... | ACCEPT | Summary: C1QB contributes to the C1q recognition subcomplex of C1. Reason: The structural paper describes the C1q–C1r2C1s2 assembly and a model of activation. Retain complex membership, corroborated by recombinant human C1q reconstitution; the proposed protease activation geometry is not required to infer B-chain membership. |
| GO:0005602 complement component C1 complex | TAS PMID:1706597 Characterization and organization of the genes encoding the ... | ACCEPT | Summary: Human C1QB encodes one of the three chain types assembling C1q in C1. Reason: The complete gene-organization abstract identifies the human A-, B- and C-chain sequences and their C1q assembly. Independent human C1q/C1 reconstitution directly corroborates the TAS complex annotation. Gene identification alone is not treated as a protease assay. |
| GO:0006956 complement activation | TAS PMID:1706597 Characterization and organization of the genes encoding the ... | MODIFY | Summary: Refine general complement activation to the directly supported classical pathway. Reason: C1QB directly contributes recognition and C1r/C1s recruitment to classical complement initiation, as established by human recombinant B-module binding and full-length C1q reconstitution. The original broad complement-activation assertion is biologically correct, but GO:0006958 captures the specific pathway already supported elsewhere in this review. Refine this existing assertion to the classical pathway rather than retaining its redundant parent as a separate core assertion. C1r/C1s perform proteolysis; C1QB supplies recognition and assembly contacts. The original source object is unchanged, and no NEW assertion is added. Proposed replacements: complement activation, classical pathway |
| GO:0006958 complement activation, classical pathway | IBA GO_REF:0000033 | ACCEPT | Summary: The C1q B chain contributes recognition and assembly work to classical complement initiation. Reason: The exact PTN002693048 classical-pathway IBD is experimentally grounded by human C1QB/C1QC and zebrafish descendants. Its inspected PAINT snapshot lists one additional zebrafish seed absent from this GOA WITH/FROM snapshot; preserve both authentic source records rather than invent a failure or edit the machine assertion. Human recombinant recognition and C1 activation evidence supports the target role. C1r/C1s perform cleavage; C1QB supplies ligand/protease recruitment surfaces. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002693048 SUPPORTS TRANSFER Exact IBD joined; original seed identifiers remain unchanged. No donor-count or target-self circularity argument. |
| GO:0006958 complement activation, classical pathway | IDA PMID:12847249 Modular organization of the carboxyl-terminal, globular head... | ACCEPT | Summary: The human globular B-chain module contributes directly to antibody-triggered classical complement activation. Reason: The complete abstract reports immunoglobulin binding by recombinant MBP-ghB and inhibition of C1q-dependent hemolysis on antibody-sensitized erythrocytes. These recognition experiments support C1QB participation at initiation rather than intrinsic downstream protease activity. Detailed assay concentrations and full Methods were not accessed. |
| GO:0006958 complement activation, classical pathway | IDA PMID:19006321 Interaction of human C1q with IgG and IgM: revisited. | ACCEPT | Summary: The B-chain immunoglobulin-recognition surface contributes to classical complement initiation. Reason: The original abstract combines human C1q immunoglobulin-binding assays with inhibitory scFv epitope mapping involving B-chain Arg108/Arg109. It does not report a purified B-chain protease. Independent human recombinant recognition/reconstitution work supports the process annotation. |
| GO:0006958 complement activation, classical pathway | IDA PMID:23650384 Expression of recombinant human complement C1q allows identi... | ACCEPT | Summary: Human B-chain protease-recruitment contacts are required for reconstituted C1 activation. Reason: The inspected fuller Results and Methods demonstrate that mature B-chain Lys61 substitution impairs C1r2C1s2 recruitment and activation by recombinant human C1q. This identifies structural work done by the gene product itself; C1r/C1s perform the cleavage reactions. The canonical abstract independently reports the B-chain contact and activation assays. Supporting Evidence: |
| GO:0006958 complement activation, classical pathway | IDA PMID:24626930 Complement is activated by IgG hexamers assembled at the cel... | ACCEPT | Summary: C1q recognizes surface-assembled IgG to initiate the classical pathway. Reason: The inspected main text combines IgG Fc-interface mutants, cell-surface complement assays, soluble IgG hexamers and structural visualization of C1 recruitment. It establishes work performed by the C1q recognition assembly, of which C1QB is a structural and ligand-binding constituent. It is not a B-chain-only mutant experiment; B-specific participation is independently established. |
| GO:0006958 complement activation, classical pathway | IDA PMID:29449492 Structures of C1-IgG1 provide insights into how danger patte... | ACCEPT | Summary: C1q-containing C1 links IgG recognition to classical complement activation. Reason: The complete original abstract reports C1–IgG1 cryo-EM structures and IgG1 mutagenesis linking recognition to complement activation. Retain the complex-subunit process annotation, corroborated by human recombinant C1q. Full original Methods, structural images and individual B-chain contacts were not inspected. |
| GO:0006958 complement activation, classical pathway | IDA PMID:3258649 The binding site for C1q on IgG. | ACCEPT | Summary: C1q immunoglobulin recognition contributes to the classical pathway. Reason: The complete source abstract describes a C1q-binding site in mouse IgG2b, not human C1QB mutagenesis. It interrogates the immunoglobulin side of the recognition reaction. Independently established human B-module binding and C1q reconstitution support retention of the curated human process assertion without recasting the original construct as a human B chain. |
| GO:0006958 complement activation, classical pathway | IDA PMID:34155115 C1q binding to surface-bound IgG is stabilized by C1r(2)s(2)... | ACCEPT | Summary: C1q recognition of antibody-coated targets supports classical complement activation. Reason: Inspected experiments use human C1q/C1 and immunoglobulin-depleted human serum, antibody-coated S. aureus and model surfaces, with C1q binding and C3b deposition readouts. C1r2s2 stabilizes the recognition complex. The B chain participates as a C1q constituent; downstream C3b deposition or neutrophil uptake is not a B-chain protease or phagocyte activity. Supporting Evidence: |
| GO:0006958 complement activation, classical pathway | IDA PMID:6249812 Activation of a complex of C1r and C1s subcomponents of huma... | ACCEPT | Summary: C1QB participates in classical pathway initiation, although the original source body is unavailable. Reason: PMID:6249812 is metadata-only in the canonical cache, so its original experiments were not inspected. Independent human C1q reconstitution, B-chain recruitment-site mutagenesis and antibody-triggered complement assays directly establish this same process. Retain the biologically established experimental annotation on independent support and explicitly leave the original assay unverified. |
| GO:0006958 complement activation, classical pathway | IDA PMID:6776418 The Clq receptor site on immunoglobulin G. | ACCEPT | Summary: C1q engagement of immunoglobulin contributes to classical complement initiation. Reason: The complete original abstract addresses the IgG site recognized by C1q. It supports the recognition interaction but is not interpreted as a B-chain-only perturbation. Independent human B-module and whole-C1q activation experiments establish direct participation by C1QB and support retention. |
| GO:0006958 complement activation, classical pathway | NAS PMID:11527969 Substrate specificities of recombinant mannan-binding lectin... | ACCEPT | Summary: Classical complement participation is correct for C1QB, independently of lectin-pathway protease assays. Reason: The complete source abstract compares recombinant MASP-1/MASP-2 substrate specificity with classical-pathway C1r/C1s. It does not establish protease catalysis by C1QB, and no such activity is inferred. Independent human C1q recognition/reconstitution evidence supports the broad NAS classical-pathway assertion. The full original contextual discussion was not inspected, so the citation is not declared wrong-gene from its abstract alone. |
| GO:0007165 signal transduction | IEA GO_REF:0000108 | ACCEPT | Summary: C1QB contributes to receptor signaling as part of a C1q ligand assembly. Reason: The electronic assertion follows the existing receptor-ligand MF through inter-ontology inference. Human C1q binding to CD33, CD33 ITIM phosphorylation in monocytes and whole-C1q-dependent CD33/LAIR-1 crosslinking provide independent direct signaling evidence. This is complex-contributed ligand function, not autonomous B-chain receptor signaling, kinase activity or evidence that gC1qR binding alone defines the pathway. Supporting Evidence: |
| GO:0009986 cell surface | EXP PMID:34155115 C1q binding to surface-bound IgG is stabilized by C1r(2)s(2)... | ACCEPT | Summary: C1q can bind extracellular cell surfaces through antibody recognition. Reason: The inspected paper measures C1q on antibody-coated S. aureus and on defined model surfaces. This supports extracellular surface association of the assembled protein. It does not establish a transmembrane or constitutively cell-anchored B chain; broader mammalian cell-surface binding is independently demonstrated on apoptotic HeLa cells and human PBMCs. |
| GO:0009986 cell surface | IEA GO_REF:0000044 | ACCEPT | Summary: The UniProt cell-surface mapping describes extracellular ligand-bound C1q. Reason: The preserved location mapping is consistent with C1q binding to apoptotic-cell membranes and immune-cell surfaces in human experiments. This is peripheral association of a secreted recognition complex, not membrane insertion of C1QB or proof of a presynaptic membrane compartment. |
| GO:0019864 IgG binding | IDA PMID:24626930 Complement is activated by IgG hexamers assembled at the cel... | ACCEPT | Summary: C1QB contributes to IgG recognition by C1q. Reason: The inspected human antibody/serum experiments identify IgG hexamers as a platform for C1q recruitment and complement activation. Although that paper tests the assembled C1q complex and IgG variants, independent recombinant human ghB experiments establish B-module IgG recognition. Retain the curated binding assertion without implying every chain makes the same contact. |
| GO:0019864 IgG binding | IDA PMID:29449492 Structures of C1-IgG1 provide insights into how danger patte... | ACCEPT | Summary: The B chain contributes to IgG binding in the C1–IgG1 complex. Reason: The source already explicitly uses contributes_to. The complete abstract reports structures of C1 bound to IgG1 and IgG1 mutagenesis; full original Methods and chain-specific contact tables were not inspected. Preserve the contribution qualifier and distinguish complex geometry from the independently demonstrated isolated B-module recognition. |
| GO:0019864 IgG binding | IDA PMID:3258649 The binding site for C1q on IgG. | ACCEPT | Summary: C1QB is a constituent of the C1q immunoglobulin-binding assembly. Reason: The original abstract tests mouse IgG2b mutations to identify its C1q-binding surface; it does not test a mouse or human B-chain mutation. Independent human ghB binding data directly establish the human target activity and justify curator deference for this reciprocal ligand-side assay. |
| GO:0019864 IgG binding | IDA PMID:6776418 The Clq receptor site on immunoglobulin G. | ACCEPT | Summary: Human C1QB participates in C1q binding to IgG. Reason: The original complete abstract examines the C1q receptor site on immunoglobulin G. Retain the curated binding activity on this ligand-side context plus direct recombinant human B-module experiments. Neither an isolated B-chain assay nor a specific species of IgG absent from the abstract is invented. |
| GO:0031012 extracellular matrix | HDA PMID:25037231 Extracellular matrix signatures of human primary metastatic ... | UNDECIDED | Summary: The source-specific C1QB extracellular-matrix proteomics detection remains unverified. Reason: The inspected Methods/Results describe ECM-enriched fractions from human colon tumors and liver metastases and LC-MS/MS protein inventories. The exact C1QB peptide/protein entry in the relevant additional tables was not inspected. Known extracellular secretion alone does not settle ECM localization in this experiment; retain uncertainty without declaring a false positive. Supporting Evidence: |
| GO:0031012 extracellular matrix | HDA PMID:28675934 Characterization of the Extracellular Matrix of Normal and D... | UNDECIDED | Summary: The C1QB entry in the ECM proteomics dataset was not inspected. Reason: The available canonical text includes the abstract and selected actual Results/Discussion on ECM preparation, solubilization and fractionation. The target-level C1QB data in the supplementary protein tables were not accessed. The full_text_available flag does not supply that missing record. Extracellular secretion is compatible with, but does not independently prove, the specific matrix annotation. Supporting Evidence: |
| GO:0045202 synapse | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: Synaptic C1q localization is supported in a mouse context. Reason: The exact donor P14106 is mouse C1qb (official Reactome cross-reference MGI:88224). The newly cached PMID:18083105 abstract describes postnatal synaptic C1q and deficient synapse elimination in C1q/C3-deficient mice; PMID:27033548 main Results show C1q with PSD95 puncta. These concern assembled C1q, and the knockout named in the latter is C1qa rather than a B-chain-specific intervention. Retain contextual C1QB orthology with that complex-level and species boundary; no human imaging claim. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: UniProtKB:P14106 SUPPORTS TRANSFER Exact source accession preserved; species and assay limitations described in reason. No donor-count or target-self circularity argument. |
| GO:0045202 synapse | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: The rat ortholog supports contextual synaptic localization of the C1q assembly. Reason: Official reviewed UniProt identifies P31721 as rat C1qb. The exact rat-specific source experiment behind this ISS is not independently recovered here. The curated transfer is biologically consistent with assembled C1q localization and direct mouse synaptic C1q evidence, so retain it with explicit curator deference rather than alleging a wrong donor or pretending the mouse experiment directly assayed rat/human C1QB. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: UniProtKB:P31721 SUPPORTS TRANSFER Exact source accession preserved; species and assay limitations described in reason. No donor-count or target-self circularity argument. |
| GO:0048018 receptor ligand activity | IBA GO_REF:0000033 | ACCEPT | Summary: Assembled C1q has signaling-receptor ligand activity to which C1QB contributes. Reason: The exact PTN008355511 receptor-ligand IBD is grounded in adiponectin-family experimental descendants; this is a curator node assertion, not pairwise transfer from an adiponectin name. Independent human whole-C1q/globular-region binding to CD33 and CD33 ITIM phosphorylation in PMID:28325905 support the target complex activity. This supports activity in the A/B/C assembly without establishing isolated B-chain signaling sufficiency. Direct ghB-gC1qR binding in PMID:28018340 is supportive interaction evidence but alone does not prove every receptor-signaling mechanism. The core records a contributed receptor-ligand activity grounded in the human-monocyte CD33 experiments; no unrelated adiponectin metabolic mechanism is inferred. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN008355511 SUPPORTS TRANSFER Exact IBD joined; original seed identifiers remain unchanged. No donor-count or target-self circularity argument. |
| GO:0062167 complement component C1q complex | IDA PMID:24626930 Complement is activated by IgG hexamers assembled at the cel... | ACCEPT | Summary: C1QB is a structural subunit of the C1q recognition complex. Reason: The inspected IgG-hexamer work recruits intact C1q, whose A/B/C heterotrimeric architecture is independently established by human structural and recombinant studies. Retain the precise C1q-complex membership; it is distinct from the larger C1 complex containing C1r/C1s. |
| GO:0062167 complement component C1q complex | IPI PMID:29449492 Structures of C1-IgG1 provide insights into how danger patte... | ACCEPT | Summary: The B chain belongs to the C1q component within the C1–IgG1 assembly. Reason: The complete structural abstract describes C1–IgG1 complexes. Established human C1q heterotrimer structure independently confirms B-chain membership. Retain the curated IPI cellular-component annotation without converting structural coassembly into an unsupported isolated-chain catalytic function. |
| GO:0072562 blood microparticle | HDA PMID:22516433 Proteomic analysis of microvesicles from plasma of healthy d... | KEEP AS NON CORE | Summary: Detected in an extracellular-vesicle proteome. The protein is plausible EV content, but this is not where it functions. Reason: Secreted complement C1q subunit with experimental phosphatidylserine binding (IDA). MISEV2018 (PMID:30637094) category 5 allows secreted proteins onto EVs through promiscuous (proteoglycan, lipid) receptors on the EV surface, so the detection is plausible. True, but not its core location. (Manual re-review for OMICS_EVIDENCE, 2026-10-10; previous action: UNDECIDED.) Supporting Evidence: |
| GO:0098794 postsynapse | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: C1q associates with postsynaptic puncta in the mouse donor context. Reason: The exact donor is mouse C1qb/P14106. The actual PMID:27033548 main narrative reports C1q colocalization with PSD95-positive puncta by structured illumination microscopy. This supports a contextual complex-level postsynaptic location, without resolving a membrane leaflet or demonstrating isolated B-chain or human localization. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: UniProtKB:P14106 SUPPORTS TRANSFER Exact source accession preserved; species and assay limitations described in reason. No donor-count or target-self circularity argument. Supporting Evidence: |
| GO:0098883 synapse pruning | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: The C1q recognition assembly participates in contextual synapse pruning. Reason: The source is mouse C1qb/P14106. The actual PMID:27033548 main narrative combines synaptic C1q localization, C1qa knockout/anti-C1q intervention, downstream C3 deposition and CR3-dependent microglial engulfment. Retain the existing complex-level orthology assertion: C1q contributes recognition/complement initiation while microglia perform engulfment. Neither isolated B-chain loss-of-function nor a human experiment is claimed. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: UniProtKB:P14106 SUPPORTS TRANSFER Exact source accession preserved; species and assay limitations described in reason. No donor-count or target-self circularity argument. |
| GO:0098888 extrinsic component of presynaptic membrane | IBA GO_REF:0000033 | UNDECIDED | Summary: The exact inherited presynaptic-membrane location remains source-specific unresolved. Reason: The non-negated PTN002693048 IBD for GO:0098888 is present, with MGI:88224 C1qb and MGI:88225 C1qc experimental donors. Their identities are verified, but the precise direct experiment behind this fine presynaptic-membrane placement was not recovered in this bounded read. General synaptic C1q localization and postsynaptic PSD95 colocalization do not settle it. UNDECIDED records access/provenance limits, not donor-count weakness, an invalid node, or target-specific divergence. Propagation Review Root cause: UNRESOLVED Sources checked: PANTHER:PTN002693048 UNRESOLVED Exact IBD joined; original seed identifiers remain unchanged. No claim of target-specific loss or a bad donor. |
| GO:0098978 glutamatergic synapse | IBA GO_REF:0000033 | UNDECIDED | Summary: The exact inherited glutamatergic-synapse location remains source-specific unresolved. Reason: The non-negated PTN002693048 IBD for GO:0098978 and its mouse C1qb/C1qc donors are authentic. The precise donor assay for this subtype was not traced successfully; the direct MGI C1qb homology request failed. Accessible mouse hippocampal C1q/PSD95 and synapse-loss evidence supports general synaptic location, but does not independently close this exact source assertion. Retain UNDECIDED without claiming the term or propagation is wrong. Propagation Review Root cause: UNRESOLVED Sources checked: PANTHER:PTN002693048 UNRESOLVED Exact IBD joined; original seed identifiers remain unchanged. No claim of target-specific loss or a bad donor. |
| GO:0106139 symbiont cell surface | IDA PMID:34155115 C1q binding to surface-bound IgG is stabilized by C1r(2)s(2)... | ACCEPT | Summary: C1q can decorate the surface of antibody-coated S. aureus. Reason: The inspected Results and Methods directly measure human C1q binding to antibody-coated S. aureus strains, with controls for staphylococcal IgG-binding proteins and comparison of C1q with C1. This is extracellular deposition on a microbial surface, not secretion by the microbe or an intrinsic bacterial membrane protein. Preserve the host-protein symbiont-surface annotation. Supporting Evidence: |
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Download this section (compressed HTML)Q: Which human B-chain residues, if any, directly contact phosphatidylserine independently of the C-chain pocket in the intact heterotrimer?
Q: Which C1q chain surfaces mediate CD33/LAIR-1 signaling, and can B-chain substitutions separate that ligand function from complement initiation?
Q: Do the original rodent donor experiments directly establish the fine presynaptic-membrane and glutamatergic-synapse locations of C1QB?
Experiment: Reconstitute human C1q with targeted B-chain substitutions, confirm intact A/B/C assembly, and compare immunoglobulin binding, C1r/C1s recruitment, phosphatidylserine binding and CD33 signaling. Include C-chain pocket mutants and matched assembly controls to distinguish direct contacts from structural disruption.
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