C1QA

Chr 1p36.12

complement C1q A chain

MANE:: ENST00000374642.8

OMIM: 120550 ↗NCBI: 712 ↗Ensembl ↗

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Predicted protein structure

AlphaFold predicted structure

C1QA · P02745

v62025-08-01

Predicted Aligned Error matrix for C1QA — diagonal shows residue index, colour shows pairwise prediction confidence (lower is better) — Predicted Aligned Error

Mean pLDDT

82.6/ 100

Confident

245 residues

Confidence breakdown

Very high(≥ 90)52%
Confident(70–90)17%
Low(50–70)31%
Very low(< 50)0%

Open interactive 3D viewer

AlphaFold (Jumper et al., 2021) · CC BY 4.0

Clinical relevance (Genomics England PanelApp)

Diagnostic Grade (Green)

COVID-19 research
BIALLELIC, autosomal or pseudoautosomal
Primary immunodeficiency or monogenic inflammatory bowel disease
BIALLELIC, autosomal or pseudoautosomal
Intellectual disability
BIALLELIC, autosomal or pseudoautosomal

Disease associations (Open Targets)

immunodeficiency due to a classical component pathway complement deficiency
0.62
C1Q deficiency
0.60
C1Q deficiency 1
0.59
complement deficiency
0.46
dengue disease
0.37
systemic lupus erythematosus related to C1QA
0.37
smoking initiation
0.28
benign urinary system neoplasm
0.28
hereditary disease
0.19
infection
0.09

Score is the Open Targets composite evidence score (0-1). Higher = stronger gene-disease association.

Protein function (UniProt)

Complement C1q subcomponent subunit A

Core component of the complement C1 complex, a multiprotein complex that initiates the classical pathway of the complement system, a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system (PubMed:12847249, PubMed:19006321, PubMed:24626930, PubMed:29449492, PubMed:3258649, PubMed:34155115, PubMed:6249812, PubMed:6776418). The classical complement pathway is initiated by the C1Q subcomplex of the C1 complex, which specifically binds IgG or IgM immunoglobulins complexed with antigens, forming antigen-antibody complexes on the surface of pathogens: C1QA, together with C1QB and C1QC, specifically recognizes and binds the Fc regions of IgG or IgM via its C1q domain (PubMed:12847249, PubMed:19006321, PubMed:24626930, PubMed:29449492, PubMed:3258649, PubMed:6776418). Immunoglobulin-binding activates the proenzyme C1R, which cleaves C1S, initiating the proteolytic cascade of the complement system (PubMed:29449492). The C1Q subcomplex is activated by a hexamer of IgG complexed with antigens, while it is activated by a pentameric IgM (PubMed:19706439, PubMed:24626930, PubMed:29449492). The C1Q subcomplex also recognizes and binds phosphatidylserine exposed on the surface of cells undergoing programmed cell death, possibly promoting activation of the complement system (PubMed:18250442)