MAC - Membrane Attack Complex - Complement System

Membrane Attack Complex formation through interaction of its complement system constitutive parts. The complex is typically formed on the surface of intruding pathogenic bacteria through activation of the complement system, when C5 convertase cleaves a C5 molecule into C5a and C5b. It is composed of four complement proteins (C5b, C6, C7 and C8), which bind to the outer membrane surface, and of a fifth protein, C9, polymerizing into a ring-like structure, put across the membrane and allowing free diffusion through it. This disrupts the osmotic environment of the cell and kills it promptly.