C9
Function
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:26841934, PubMed:9212048, PubMed:9634479). C9 is the pore-forming subunit of the MAC (PubMed:26841934, PubMed:30111885, PubMed:4055801).
Involvement in disease
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.
None
Disease susceptibility is associated with variants affecting the gene represented in this entry.
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.
None
Disease susceptibility is associated with variants affecting the gene represented in this entry.
Post-translational modifications
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).
Sequence Similarities
Belongs to the complement C6/C7/C8/C9 family.
Tissue Specificity
Plasma (at protein level).
Cellular localization
- Secreted
- Target cell membrane
- Multi-pass membrane protein
- 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.
Alternative names
Complement component C9, C9