Membrane attack complex

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

Signal cascade, structure and function

The membrane attack complex
Schematic sequence of the formation of the membrane attack complex

In humans from 1676 amino acids existing complement component 5 is determined by the enzyme C5 convertase (74 amino acids) and the significantly larger C5b cleaved into the two components C5a. C5b attaches to the cell membrane of the target cell and forms the first component of the membrane attack complex. First, the complement components C6 and C7 are attached to this polypeptide to form the C5b67 complex. Then component C8 is still added to form the C5b678 complex. C8 itself is a complex of the two subunits C8-β and C8-α-γ. The C8-α-γ subunit is hydrophobic and penetrates the double layer of the cell membrane. It initiates the polymerization of the complement component C9 . This involves adding 6 to 16 units of C9, which consists of 537 amino acids, to the new ring-shaped C5b678poly9 complex - the finished membrane attack complex. The hydrophobic side of C9 is directed towards the cell membrane and the hydrophilic side towards the pore center. This structure of the membrane attack complex forms a transmembrane channel (pore) approximately 10 nm in diameter in the target cell  . This pore disrupts the selective permeability of the cell membrane and an unhindered exchange of water and electrolytes between the cell interior and the cell environment can take place, which ultimately leads to cytolysis and thus to death of the cell.

Individual evidence

  1. ^ NCBI: complement component 5 [Homo sapiens ]. Accessed December 27, 2009
  2. ^ Membrane attack complex.  In: Online Mendelian Inheritance in Man . (English)
  3. ↑ O. Bohana-Kashtan et al: Cell signals transduced by complement. In: Molecular Immunology 41, 2004, pp. 583-597. PMID 15219997 doi : 10.1016 / j.molimm.2004.04.007 (Review)

further reading

Reference books
  • D. Bitter-Suermann and U. Hadding: Complement system. In: Immunologie D. Gemsa et al. (Editors), Verlag Georg Thieme, 1991, pp. 63-78.
  • CA Janeway et al: Immunobiology - The Immune System in Health and Disease. Garland Publishing, 2001, ISBN 0-815-33217-3
Review article
  • PJ Sims and T. Wiedmer: Induction of cellular procoagulant activity by the membrane attack complex of complement. In: Semin Cell Biol 6, 1995, pp. 275-282. PMID 8562920
  • AF Esser: The membrane attack complex of complement. Assembly, structure and cytotoxic activity. In: Toxicology 87, 1994, pp. 229-247. PMID 8160186
  • BP Morgan: Mechanisms of tissue damage by the membrane attack complex of complement. In: Complement Inflamm 6, 1989, pp. 104-111. PMID 2656078
  • HJ Müller-Eberhard: The membrane attack complex of complement. In: Annu Rev Immunol 4, 1986, pp. 503-528. PMID 3518749
  • HJ Müller-Eberhard: The membrane attack complex. In: Semin Immunopathol 7, 1984, pp. 93-141. PMID 6387983
Original research
  • RG Leslie, CH Nielsen: The classical and alternative pathways of complement activation play distinct roles in spontaneous C3 fragment deposition and membrane attack complex (MAC) formation on human B lymphocytes. In: Immunology. Volume 111, Number 1, January 2004, pp. 86-90, PMID 14678202 , PMC 1782389 (free full text).

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