CFI
Function
Trypsin-like serine protease that plays an essential role in regulating the immune response by controlling all complement pathways. Inhibits these pathways by cleaving three peptide bonds in the alpha-chain of C3b and two bonds in the alpha-chain of C4b thereby inactivating these proteins (PubMed:17320177, PubMed:7360115). Essential cofactors for these reactions include factor H and C4BP in the fluid phase and membrane cofactor protein/CD46 and CR1 on cell surfaces (PubMed:12055245, PubMed:2141838, PubMed:9605165). The presence of these cofactors on healthy cells allows degradation of deposited C3b by CFI in order to prevent undesired complement activation, while in apoptotic cells or microbes, the absence of such cofactors leads to C3b-mediated complement activation and subsequent opsonization (PubMed:28671664).
Involvement in disease
Hemolytic uremic syndrome, atypical, 3
AHUS3
An atypical form of hemolytic uremic syndrome. It is a complex genetic disease characterized by microangiopathic hemolytic anemia, thrombocytopenia, renal failure and absence of episodes of enterocolitis and diarrhea. In contrast to typical hemolytic uremic syndrome, atypical forms have a poorer prognosis, with higher death rates and frequent progression to end-stage renal disease.
None
Disease susceptibility is associated with variants affecting the gene represented in this entry. Other genes may play a role in modifying the phenotype.
Complement factor I deficiency
CFI deficiency
Autosomal recessive condition associated with a propensity to pyogenic infections.
None
The disease is caused by variants affecting the gene represented in this entry.
Macular degeneration, age-related, 13
ARMD13
A form of age-related macular degeneration, a multifactorial eye disease and the most common cause of irreversible vision loss in the developed world. In most patients, the disease is manifest as ophthalmoscopically visible yellowish accumulations of protein and lipid that lie beneath the retinal pigment epithelium and within an elastin-containing structure known as Bruch membrane.
None
Disease susceptibility is associated with variants affecting the gene represented in this entry.
Sequence Similarities
Belongs to the peptidase S1 family.
Tissue Specificity
Expressed in the liver by hepatocytes (PubMed:6327681). Also present in other cells such as monocytes, fibroblasts or keratinocytes (PubMed:17320177, PubMed:6444659).
Cellular localization
- Secreted
- Extracellular space
- Secreted
Alternative names
IF, CFI, Complement factor I, C3B/C4B inactivator