C9

This gene encodes the final component of the complement system. It participates in the formation of the Membrane Attack Complex (MAC). The MAC assembles on bacterial membranes to form a pore, permitting disruption of bacterial membrane organization. Mutations in this gene cause component C9 deficiency.

complement C9

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 (PubMed:9634479, PubMed:9212048, PubMed:26841934).
C9 is the pore-forming subunit of the MAC (PubMed:4055801, PubMed:26841934, PubMed:30111885).

Cell killing Source: UniProtKB
Complement activation Source: Reactome
Complement activation, alternative pathway Source: UniProtKB-KW
Complement activation, classical pathway Source: UniProtKB-KW
Cytolysis Source: UniProtKB-KW
Protein homooligomerization Source: UniProtKB
Regulation of complement activation Source: Reactome

Secreted; Target 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.

Complement component 9 deficiency (C9D): A rare defect of the complement classical pathway associated with susceptibility to severe recurrent infections predominantly by Neisseria gonorrhoeae or Neisseria meningitidis. Some patients may develop dermatomyositis.
Macular degeneration, age-related, 15 (ARMD15): 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.

Thrombin cleaves factor C9 to produce C9a and C9b.
Phosphorylation sites are present in the extracellular medium.
Initially, positions and connectivity of disulfide bonds were based on peptide sequencing done for the human protein (PubMed:8603752). The crystal structures for the human and mouse proteins corrected the positions and connectivities of the disulfide bonds (PubMed:30111885). The distance between Cys-57 and Cys-94 in the monomeric mouse protein precludes formation of a disulfide bond, contrary to what is seen in the structure of the human polymeric form of the protein (Probable).