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The membrane attack complex (MAC) or terminal complement complex (TCC) is a structure typically formed on the surface of pathogenic bacterial cells as a result of the activation of the host's alternative pathway, classical pathway, or lectin pathway of the complement system, and it is one of the effector proteins of the immune system. The membrane-attack complex (MAC) forms transmembrane channels. These channels disrupt the phospholipid bilayer of target cells, leading to cell lysis and death. A number of proteins participate in the assembly of the MAC. Freshly activated C5b binds to C6 to form a C5b-6 complex, then to C7 forming the C5b-6-7 complex. The C5b-6-7 complex binds to C8, which is composed of three chains (alpha, beta, and gamma), thus forming the C5b-6-7-8 complex. C5b-6-7-8 subsequently binds to C9 and acts as a catalyst in the polymerization of C9. Active MAC has a subunit composition of C5b-C6-C7-C8-C9. ==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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Complement membrane attack complex」の詳細全文を読む スポンサード リンク
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