CFI - Complement factor I - human protein (Function)
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CFI »  Complement factor I   [ EC ]
Protein also known as:  C3B/C4B inactivator. Cleaved into:  Complement factor I heavy chain; Complement factor I light chain.
Gene name:  CFI
Family name: Peptidase S1
Entry whose protein(s) existence is based on evidence at protein level
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Responsible for cleaving the alpha-chains of C4b and C3b in the presence of the cofactors C4-binding protein and factor H respectively.  
  • CuratedUniProtKB
GO molecular function 
Metal ion bindingdefinition[GO:0046872]  
  • IEAUniProtKB KW
Scavenger receptor activitydefinition[GO:0005044] silver  
  • IEAInterPro 2 GO
Serine-type endopeptidase activitydefinition[GO:0004252] silver  
  • IEAInterPro 2 GO
GO biological process 
Complement activation, classical pathwaydefinition[GO:0006958]  
  • IEAUniProtKB KW
  • IEAUniProtKB KW
Receptor-mediated endocytosisdefinition[GO:0006898]  
  • IEAInterPro 2 GO
Enzymatic activity 
This protein acts as an enzyme. It is known to catalyze the following reaction
EC Inactivates complement subcomponents C3b, iC3b and C4b by proteolytic cleavage.  
  • CuratedUniProtKB
More information is available from:
According to KEGG, this protein belongs to the following pathways:
Complement and coagulation cascades  hsa04610+3426  
Staphylococcus aureus infection  hsa05150+3426  
According to Reactome, this protein belongs to the following pathway:
Regulation of Complement cascade  REACT_118707  


Biological process 
Complement pathway  definition   [KW-0180]
Immunity  definition   [KW-0391]
Innate immunity  definition   [KW-0399]
Molecular function 
Hydrolase  definition   [KW-0378]
Protease  definition   [KW-0645]
Serine protease  definition   [KW-0720]
Technical term 
Reference proteome  definition   [KW-1185]

Further external links

GeneWiki: Complement_factor_I
GenomeRNAi: 3426
PRO: PR:P05156