complement C2a; C3/C5 convertase

Function

• formed via cleavage of C2 by C1s4b complex
• combines with C4b to generate the C3 convertase selective cleavage of Arg-|-Ser bond in C3 alpha-chain to form C3a & C3b, & C5 convertase selective Arg-|-Xaa bond in C5 alpha-chain to form C5a & C5b

Pathology

• C2a interacts with Schistosoma haematobium TOR (via N-terminal extracellular domain)
  • this results in inhibition of the classical & lectin pathway of complement activation, probably due to interference with binding of C2a to C4b such that C3 convertase cannot be formed
• this confers resistance to complement-mediated cell lysis, allowing parasite survival & infection

More general terms

• complement C2
• serine protease trypsin family
• complement-activating enzyme