Constituent 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.
Defects 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.
Belongs 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.
Thrombin cleaves factor C9 to produce C9a and C9b. Phosphorylation sites are present in the extracelllular medium.
Secreted. 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.