C1QB

Chr 1p36.12

complement C1q B chain

MANE:: ENST00000509305.6

OMIM: 120570 ↗NCBI: 713 ↗Ensembl ↗

Annotations refreshed 1 month ago.

Predicted protein structure

AlphaFold predicted structure

C1QB · P02746

v62025-08-01

Predicted Aligned Error matrix for C1QB — diagonal shows residue index, colour shows pairwise prediction confidence (lower is better) — Predicted Aligned Error

Mean pLDDT

78.6/ 100

Confident

253 residues

Confidence breakdown

Very high(≥ 90)47%
Confident(70–90)11%
Low(50–70)34%
Very low(< 50)8%

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

Disease associations (Open Targets)

immunodeficiency due to a classical component pathway complement deficiency
0.66
C1Q deficiency
0.60
C1Q deficiency 1
0.55
C1Q deficiency 2
0.47
systemic lupus erythematosus
0.47
complement deficiency
0.46
complication
0.34
medical procedure
0.34
trauma complication
0.34
hereditary disease
0.19

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

Protein function (UniProt)

Complement C1q subcomponent subunit B

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)