C5 convertase

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C5 convertase
Enzyme classification
EC, category 3.4.21.43 ,  serine protease
MEROPS S01.194
Response type Hydrolysis of a spec. Arg-Xaa peptide bond
Substrate C3 (C5)
Products C3a + C3b (C5a + C5b)

C5 convertase is an enzyme complex that is involved in the complement system of the immune system . The active subunit (C2a) is a serine protease that catalyzes the hydrolysis of the C5 protein in C5a and C5b .

Layout and function

Two forms of C5 convertase are known. A form is built up via the so-called classical route from the complement components C4b, C2a and C3b, which form the C4b2a3b complex - the C5 convertase. The component C4b is created by the cleavage of the complement component C4 by the serine protease C1s. C4b exposes a highly reactive thioester that can easily form a covalent bond with nucleophiles. The complement component C2 binds to C4b. The component C2b is split off from C2 by C1s. A C4b2a complex - the C3 convertase - remains. This enzyme is in turn able to split the complement component C3 into C3a and C3b. C3b also has - in analogy to C4b - a highly reactive thioester group.

Via the alternative route , C5 convertase is formed from two complement components of type C3b and one Bb component as C3bBb3b. The Bb component is obtained by splitting factor B by factor D into components Ba and Bb. The component C3b is obtained by cleavage of C3 with the aid of C3 convertase (= C4b2a). This creates fragments C3a and C3b.

C5 convertase splits the complement component C5 into the two components C5a (11  kDa ) and C5b (190 kDa). While C5a is a multifunctional anaphylatoxin with chemotactic properties, which is mainly detectable in blood serum, C5b on the cell membrane of a target cell is the starting point for the formation of the membrane attack complex .

literature

  • MK Pangburn and N. Rawal: Structure and function of complement C5 convertase enzymes. In: Biochem Soc Trans 30, 2002, pp. 1006-1010. PMID 12440962 (Review)
  • G. Hegasy: Complement regulator factor H from Sus scrofa: cloning, functional characterization and molecular pathogenesis of the deficiency. Dissertation, University of Hamburg, 2002 (full text) (PDF; 3.1 MB)
  • G. Löffler among others: Biochemistry and Pathobiochemistry. Verlag Springer, 2007, ISBN 978-3-540-32680-9 , pp. 1130-1132.

Individual evidence

  1. ↑ AW Dodds et al: The reaction mechanism of the internal thioester in the human complement component C4. In: Nature 379, 1996, pp. 177-179. PMID 8538770
  2. ↑ HJ Müller-Eberhard et al .: Formation and functional significance of a molecular complex derived from the second and the fourth component of human complement. In: J Exp Med 125, 1967, pp. 359-380. PMID 6019133 ; PMC 2138355 (free full text)
  3. ^ W. Vogt et al .: A new function of the activated third component of complement: binding to C5, an essential step for C5 activation. In: Immunology 34, 1978, pp. 29-40. PMID 624565 ; PMC 1457321 (free full text)
  4. ↑ MA Niemann: Amino-terminal sequence of human factor B of the alternative complement pathway and its cleavage fragments, Ba and Bb. In: Biochemistry 19, 1980, pp. 1576-1583. PMID 6769474
  5. ^ MA Niemann et al: Amino acid sequence of human D of the alternative complement pathway. In: Biochemistry 23, 1984, pp. 2482-2486. PMID 6383466
  6. ↑ Z. Fishelson et al .: Characterization of the initial C3 convertase of the alternative pathway of human complement. In: J Immunol 132, 1984, pp. 1430-1434. PMID 6559201

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