C2 Gene (Complement C2)

Complement Component 2: Role in the Classical and Lectin Pathways of Complement Activation

Gene Information Card

Symbol C2
Full Name Complement C2
Gene Type Protein coding
Chromosomal Location 6p21.33
NCBI Gene ID 717 ncbi.nlm.nih.gov/gene/717
Ensembl ID ENSG00000166278
UniProt ID P06681
OMIM ID 217000
HGNC ID 1248
Aliases CO2, C3/C5 convertase

Description

The C2 gene encodes complement component 2, a serum glycoprotein that functions as a serine protease in the classical and lectin pathways of the complement system. C2 is cleaved by C1s or MASP-2 to form C2a and C2b; C2a combines with C4b to form the C3 convertase (C4b2a), essential for opsonization and immune clearance. Deficiency of C2 is the most common complement deficiency in individuals of European ancestry and is associated with increased susceptibility to infections and autoimmune diseases.

Disease Associations

Disease category Pathophysiological mechanism Genomic evidence
Complement C2 Deficiency Loss-of-function mutations impair C2 protein production or function, preventing formation of C3 convertase and downstream complement activation. ClinVar, OMIM
Systemic Lupus Erythematosus (SLE) C2 deficiency leads to impaired clearance of immune complexes and apoptotic cells, increasing risk of autoimmunity. OMIM, NCBI
Recurrent Bacterial Infections Defective opsonization due to C2 deficiency results in increased susceptibility to encapsulated bacteria (e.g., Streptococcus pneumoniae). ClinVar, OMIM

Expression Profile

Tissue Expression
Tissue nTPM level
Liver 24.8 High
Adipose Tissue 6.2 Medium
Lung 4.1 Medium
Spleen 3.5 Medium
Kidney 2.9 Low
Cell Line Expression
Cell Line nTPM Notes
HepG2 28.5 Hepatocyte cell line, high expression
THP-1 5.3 Monocyte cell line, moderate expression
A549 3.8 Lung epithelial cell line, low expression
Data source：Human Protein Atlas（proteinatlas.org）

Mutations & Variants

Hotspot Mutations
Variant Type Frequency Functional Description
c.841_849del (p.Gly281_Arg283del) Deletion Common in C2 deficiency Loss of function, prevents secretion
c.1930G>A (p.Gly644Arg) Missense Rare Impaired protein stability
c.534C>T (p.Arg178*) Nonsense Rare Premature stop, loss of function
Mutation functional classification

Loss of Function (LOF)

Most C2 mutations are loss-of-function, leading to reduced or absent C2 protein and impaired complement activation.

Gain of Function (GOF)

No gain-of-function mutations reported in C2.

Dominant Negative (DN)

No dominant-negative mutations reported; C2 deficiency is autosomal recessive.
View complete mutation data：
ClinVar：https://www.clinvar.com/gene/717
COSMIC：https://cancer.sanger.ac.uk/cosmic/gene/analysis?ln=C2

Gene Ontology (GO)

• complement activation (GO:0006956) • serine-type endopeptidase activity (GO:0004252)
• extracellular region (GO:0005576) • extracellular space (GO:0005615)
• complement activation (GO:0006958) • complement activation (GO:0001867)

Pathways

• Complement cascade (classical pathway)
• Complement cascade (lectin pathway)
• Immune system (Reactome R-HSA-168256)

Protein Summary

Complement component C2 is a 732-amino-acid glycoprotein (UniProt P06681) synthesized primarily in the liver. It contains a serine protease domain and is cleaved by C1s or MASP-2 into C2a (catalytic) and C2b. C2a binds C4b to form the C3 convertase (C4b2a), which cleaves C3 into C3a and C3b, propagating the complement cascade. C2 deficiency (OMIM 217000) is the most common complement deficiency in Caucasians, predisposing to recurrent infections and autoimmune diseases like SLE.

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Reference Databases

NCBI Gene https://www.ncbi.nlm.nih.gov/gene/717
OMIM https://www.omim.org/entry/217000
HGNC https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:1248
Ensembl https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000166278
UniProt https://www.uniprot.org/uniprot/P06681
ClinVar https://www.ncbi.nlm.nih.gov/clinvar/?term=C2%5Bgene%5D
COSMIC https://cancer.sanger.ac.uk/cosmic/gene/analysis?ln=C2
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