C3-convertase

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There are two forms of C3-convertase (EC 3.4.21.43).

• The first is an enzyme composed of the C4b-C2a complex, which forms during the Classical pathway of the complement system. It is formed when C1s cleaves off C2b from a membrane-bound C4b-C2a complex.

• The second consists of the C3bBb complex, which forms during the alternative complement pathway. It is formed when membrane bound C3b binds to factor B which is in turn cleaved by factor D into Ba and Bb. Bb remains bound to C3b while Ba is released into the surrounding medium.

Once formed, both C3-convertases will catalyze the proteolytic cleavage of C3 into C3a and C3b (hence the name "C3-convertase"). C3b can then act as an opsonizer or itself become a C3-convertase.

A convertase (of either type) with an additional 3b (C4b2a3b or C3bBb3b) is known as "C5-convertase".

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• MeSH C3+convertase

v • d • e Proteins: complement system (C, L, A) Activators CLA: C3-convertase - C5-convertase - MAC (C6, C7, C8, C9) - L: Mannan-binding lectin - A: Factor P/Properdin Enzymes C: C1Q/C1R/C1S - C4 (C4a) - C2 - CLA: C3 (C3a, C3b/iC3b) - C5 (C5a) - L: MASP1 - MASP2 - A: Complement factor B - Factor D Inhibitors CLA: C1-inhibitor - Decay accelerating factor - Factor I - CL: C4BP - A: Factor H Complement receptors CR1 - CR2 - CR3 - CR4 - CD11b/CD11c/CD18 - Anaphylatoxin (C3a, C5a)

v • d • e Endopeptidases: serine proteases/serine endopeptidases (EC 3.4.21) Digestive enzymes Enteropeptidase - Trypsin - Chymotrypsin - Elastase (Neutrophil, Pancreatic) Coagulation factors: Thrombin - Factor VIIa - Factor IXa - Factor Xa - Factor XIa - Factor XIIa - Kallikrein (PSA) fibrinolysis: Plasmin - Tissue plasminogen activator - Urinary plasminogen activator Complement system Factor B - Factor D - Factor I - MASP (MASP1, MASP2) - C3-convertase Other immune system Chymase - Granzyme - Tryptase - Proteinase 3/Myeloblastin Venombin Ancrod - Batroxobin Other Acrosin - Prolyl endopeptidase - Pronase - Proprotein convertases (1, 2) - Subtilisin/Furin - Streptokinase - S1P