Terminal Pathway

Lytic part of the complement system pathway

The formation of C5 convertase is the first step of the terminal pathway. This convertase is either formed by components of the classical/lectin pathway (C4b2a3b) or the alternative pathway (C3b2BbP) that cleaves C5 to C5a and C5b.

When the C5a is released it acts as a potent anaphylatoxin. C5b is the first component of the self-assembly of Membrane Attack Complex (MAC) or its soluble counterpart soluble Terminal Complement Complex (sTCC). 

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 for C8.

The whole complex can then bind several molecules of C9 (n=1-18) resulting in the trans-membrane MAC lesion.

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