Factor I / membrane attack complex (IPR003884)

Short name: FacI_MAC

Overlapping homologous superfamilies


Domain relationships



This domain is found in complement component proteins, complement component factor 1 and agrin. Complement components C5b, C6, C7 C8 and C9 are the constituents 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. Its assembly is initiated by protelytic cleavage of C5 into C5a and C5b. C5b binds sequentially C6, C7, C8 and multiple copies of the pore-forming subunit C9. Factor I is responsible for cleaving alpha chains of C4B and C3B in the presence of the cofactors C4-binding protein and factor H respectively. Agrin is a component of the basal lamina that causes the aggregation of acetylcholine receptors and acetylcholine-esterase on the surface of muscle fibres of the neuromuscular junction.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.