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. Component of the membrane attack complex (MAC). MAC assembly is initiated by proteolytic cleavage of C5 into C5a and C5b. C5b binds sequentially C6, C7, C8 and 12-14 copies of the pore-forming subunit C9 (By similarity). All cysteine residues are assumed to be cross-linked to one another. Individual modules containing an even number of conserved cysteine residues are supposed to have disulfide linkages only within the same module (By similarity). Belongs to the complement C6/C7/C8/C9 family.