Complement Membrane Attack Complex - Structure and Function

Structure and Function

It is composed of a complex of four complement proteins (C5b, C6, C7, and C8) that bind to the outer surface of the plasma membrane, and many copies of a fifth protein (C9) that hook up to one another, forming a ring in the membrane. C6-C9 all contain a common MACPF domain. This region is homologous to cholesterol-dependent cytolysins from Gram-positive bacteria.

The ring structure formed by C9 is a pore in the membrane that allows free diffusion of molecules in and out of the cell. If enough pores form, the cell is no longer able to survive.

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