Membrane Attack Complex

**Semantic type:** Amino Acid, Peptide, or Protein

**Definition:** A protein complex composed of five activated complement proteins that form a transmembrane pore in pathogen cell membranes. Formation of the complex is initiated by C5 convertase cleavage of complement C5 that yields C5b. C5b forms a complex with C6 and then C7; this initial complex has an exposed hydrophobic site that can insert into the pathogen's cell membrane. Then the trimeric C8 is recruited to the complex and the C5b-6-7-8 complex promotes the polymerization of 10-16 molecules of C9, which form the pore. If enough of these pores penetrate the cell membrane of the pathogen, the targeted cell will lyse and die.

**Synonyms:** - C5b-6-7-8-9 - C5b-9 - COMPLEMENT C5B-9 - Complement C5b-9 Complex - MAC - MAC - Membrane-Attack Complex - TCC - TCC - Terminal Complement Complex - Terminal Complement Complex