C1QA

Protein identityUniProt · HPA

UniProt accession

P02745

Gene

C1QA

Ensembl

ENSG00000173372

Chromosome

1

Canonical length

245 aa

Protein class

Disease related genes, Human disease related genes, Plasma proteins, Predicted intracellular proteins, Predicted secreted proteins

Secretome location

Secreted to blood

OverviewNCBI Gene

This gene encodes the A-chain polypeptide of serum complement subcomponent C1q, which associates with C1r and C1s to yield the first component of the serum complement system. C1q deficiency is associated with lupus erythematosus and glomerulonephritis. C1q is composed of 18 polypeptide chains which include 6 A-chains, 6 B-chains, and 6 C-chains. Each chain contains an N-terminal collagen-like region and a C-terminal C1q globular domain. Alternate splicing results in multiple transcript variants. [provided by RefSeq, Nov 2016]

Canonical amino-acid sequenceUniProt

245 residues, UniProt reviewed canonical sequence.

>P02745|C1QA
     1  MEGPRGWLVL CVLAISLASM VTEDLCRAPD GKKGEAGRPG RRGRPGLKGE QGEPGAPGIR
    61  TGIQGLKGDQ GEPGPSGNPG KVGYPGPSGP LGARGIPGIK GTKGSPGNIK DQPRPAFSAI
   121  RRNPPMGGNV VIFDTVITNQ EEPYQNHSGR FVCTVPGYYY FTFQVLSQWE ICLSIVSSSR
   181  GQVRRSLGFC DTTNKGLFQV VSGGMVLQLQ QGDQVWVEKD PKKGHIYQGS EADSVFSGFL
   241  IFPSA

LocalizationUniProt · AlphaFold · HPA

Whether an antibody against C1QA can act on the native protein depends on physical access: surface and secreted proteins are reachable by circulating antibodies, intracellular proteins usually are not.

Antibody reachability

Cell surface

Secreted

No

Transmembrane segments

0

Mean surface accessibility (rSASA)

0.48

Highest tissue expression

1,056 nTPM

Expression across tissuesHPA

DiseaseUniProt · ClinVar · IEDB · PubMed

Four sources answering four different questions about C1QA.

Disease | AllUniProt

Conditions C1QA is implicated in, by any mechanism.

• C1q deficiency 1 (C1QD1) MIM:613652

Disease | GeneticClinVar

12 pathogenic / likely-pathogenic of 161 ClinVar records.

Conditions with pathogenic or likely-pathogenic variants.

• C1Q deficiency
• C1Q deficiency 1

Disease | ImmuneIEDB

Conditions an epitope on C1QA was assayed in.

• rheumatoid arthritis B cell
• systemic lupus erythematosus B cell
• lupus erythematosus B cell
• autoimmune glomerulonephritis B cell

Disease | AutoantibodyPubMed

Conditions in which antibodies against C1QA are reported. Each links to that disease's full target list.

• Lupus Erythematosus, Systemic 157
• Lupus Nephritis 128
• Vasculitis 18
• Urticaria 15
• Arthritis, Rheumatoid 14
• Proteinuria 9
• Glomerulonephritis 8
• Kidney Diseases 6
• Thrombosis 6
• Nephritis 4
• Scleroderma, Systemic 4
• Antiphospholipid Syndrome 3
• Neuromyelitis Optica 3
• Sjogren's Syndrome 3

Showing 14 of 16 — disease pages carrying at least 10 antigens.

ReferencesPubMed · IEDB

Publications for C1QA from three distinct lines of evidence, kept separate because they answer different questions: whether antibodies are directed at the protein, whether a B-cell epitope has been mapped on it, and whether a T-cell epitope has. Each is labelled with its source.

Sources: PubMed — antigen-level antibody evidence from a custom retrieval. Records matching a controlled set of autoantibody terms (the MeSH descriptors Autoantibodies and Autoantigens, with title and abstract term variants) were obtained through NCBI E-utilities, and their titles and abstracts parsed for constructions that direct an antibody at a named protein rather than for co-occurrence. Captured names were resolved against UniProt nomenclature and each antigen adjudicated individually against the source text. IEDB — curated epitope assays from the Immune Epitope Database (Vita et al., Nucleic Acids Research 2019). Bibliographic records from PubMed and MeSH, U.S. National Library of Medicine; citation metrics from NIH iCite (Hutchins et al., PLoS Biology 2016). Titles link to PubMed; abstracts are not reproduced here. The NLM does not endorse this analysis.

Genetic constraint and essentialitygnomAD · DepMap

Does the body need this protein intact? Low LOEUF or a strong DepMap dependency means loss or blockade of the protein is likely to be felt.

gnomAD LOEUF (loss-of-function intolerance)

1.15

gnomAD pLI

0

gnomAD missense Z

1.29

DepMap mean gene effect

0.09

DepMap dependency class

none

Cancer expressionTCGA

Across TCGA tumor cohorts, this protein is over-expressed in roughly 4% of surveyed tumor types (aggregate summary; per-cohort expression, alteration, and survival load in the interactive view).

OntologyGO

Biological processes

• astrocyte activation
• cell-cell signaling
• complement activation
• complement activation, classical pathway
• complement-mediated synapse pruning
• innate immune response
• microglial cell activation
• neuron remodeling
• synapse organization
• synapse pruning
• vertebrate eye-specific patterning

Molecular functions

• amyloid-beta binding
• IgG binding
• IgM binding
• phosphatidylserine binding

Cellular components

• cell surface
• collagen trimer
• complement component C1 complex
• complement component C1q complex
• extracellular matrix
• extracellular region
• extrinsic component of postsynaptic membrane
• extrinsic component of presynaptic membrane
• glutamatergic synapse
• postsynapse
• symbiont cell surface
• synapse

Protein domainsUniProt · Pfam · InterPro

• C1q domain
• Collagen triple helix repeat
• Tumour necrosis factor-like domain superfamily
• Collagen/C1q domain-containing
• C1q domain
• Collagen triple helix repeat (20 copies)

KeywordsUniProt

• Collagen
• Complement pathway
• Disulfide bond
• Glycoprotein
• Host-virus interaction
• Hydroxylation
• Immunity
• Innate immunity
• Repeat
• Secreted
• Signal

InteractionsUniProt · HPA

Protein binding partners of C1QA in the human serome: UniProt-annotated complex subunits plus reported interactors. Each links to its own Seroatlas record.

• CR1
• CD33
• UBQLN2