Lytic part of the complement pathway
The formation of C5 convertase is the first step of the terminal pathway. This convertase ether formed by components of the classical/lectin pathway (C4b2a3b) or the alternative pathway (C3b2BbP) cleaves C5 to C5a and C5b. The C5a is released and act as a potent anaphylatoxin. The C5b is the first component of the self-assembly of Membrane Attack Complex (MAC) or its suable counterpart soluble Terminal Complement Complex (TCC). Although self-assembly, the process is highly regulated and performed in a highly regular order. MAC is a supramolecular construction composed of C5b, C6, C7, C8 and several molecules of C9. In the first step C5b in complex with C6 bind C7 which change the structure of C7 allowing for the whole complex to be inserted in the target membrane and serve as a receptor fo C8. The whole complex can then bind several molecules of C9 (n=1-18) resulting in the trans-membrane MAC lesion.
The Illustration shows the Terminal pathway. Additional information can be found if you place the cursor on the different parts of the illustration.