FunctionConstituent of the membrane attack complex (MAC) that plays a key role in the innate and adaptive immune response by forming pores in the plasma membrane of target cells. C9 is the pore-forming subunit of the MAC.
Involvement in diseaseDefects in C9 are a cause of complement component 9 deficiency (C9D) [MIM:613825]. A rare defect of the complement classical pathway associated with susceptibility to severe recurrent infections, predominantly by Neisseria gonorrhoeae or Neisseria meningitidis.
Sequence similaritiesBelongs to the complement C6/C7/C8/C9 family. Contains 1 EGF-like domain. Contains 1 LDL-receptor class A domain. Contains 1 MACPF domain. Contains 1 TSP type-1 domain.
Post-translational modificationsThrombin cleaves factor C9 to produce C9a and C9b. Phosphorylation sites are present in the extracelllular medium.
Cellular localizationSecreted. Cell membrane. Secreted as soluble monomer. Oligomerizes at target membranes, forming a pre-pore. A conformation change then leads to the formation of a 100 Angstrom diameter pore.