Initiation: C5-C7
The membrane attack complex is initiated when the complement protein C5 convertase cleaves C5 into C5a and C5b.
Another complement protein, C6, binds to C5b.
The C5bC6 complex is bound by C7.
This junction alters the configuration of the protein molecules exposing a hydrophobic site on C7 that allows the C7 to insert into the phospholipid bilayer of the pathogen.
Read more about this topic: Complement Membrane Attack Complex