Complement membrane attack complex

The membrane attack complex ( engl. membrane attack complex, MAC ) is a component of the immune system and causes in the target cell cytolysis by their death.

Signaling cascade structure and function

Existing in humans of 1,676 amino acids complement component C5 by the enzyme C5 convertase into two components C5a (74 amino acids) and the significantly larger C5b cleaved. C5b attaches the cell membrane of the target cell and constituting the first component of the membrane attack complex. To this polypeptide around the complement components C6 and C7 are first attached to C5b67 complex. After that, still outsourced to the C8 component for C5b678 complex. C8 itself is a complex of the two subunits C8 and C8 β - α - γ. The C8 - α - γ - subunit is hydrophobic and permeates the bilayer of the cell membrane. It initiates the polymerization of complement component C9. In this case, 6 to 16 units of C9, which consists of 537 amino acids, the new annular C5b678poly9 complex - added - the finished membrane attack complex. The hydrophobic side of C9 is directed to the cell membrane and the hydrophilic side to the pore center. This structure of the Membanangriffskomplexes forms in the target cell a transmembrane channel ( pore) diameter of approximately 10 nm. This pore interferes with the selective permeability of the cell membrane and it can be an unobstructed water and electrolyte exchange to take place between the cell interior and cell environment, which ultimately leads to cell lysis and thus the death of the cell.