Staphylococcus aureus metalloprotease aureolysin cleaves complement C3 to mediate immune evasion

J Immunol. 2011 Jun 1;186(11):6445-53. doi: 10.4049/jimmunol.1002948. Epub 2011 Apr 18.


Complement is one of the first host defense barriers against bacteria. Activated complement attracts neutrophils to the site of infection and opsonizes bacteria to facilitate phagocytosis. The human pathogen Staphylococcus aureus has successfully developed ways to evade the complement system, for example by secretion of specific complement inhibitors. However, the influence of S. aureus proteases on the host complement system is still poorly understood. In this study, we identify the metalloprotease aureolysin as a potent complement inhibitor. Aureolysin effectively inhibits phagocytosis and killing of bacteria by neutrophils. Furthermore, we show that aureolysin inhibits the deposition of C3b on bacterial surfaces and the release of the chemoattractant C5a. Cleavage analyses show that aureolysin cleaves the central complement protein C3. Strikingly, there was a clear difference between the cleavages of C3 in serum versus purified conditions. Aureolysin cleaves purified C3 specifically in the α-chain, close to the C3 convertase cleavage site, yielding active C3a and C3b. However, in serum we observe that the aureolysin-generated C3b is further degraded by host factors. We pinpointed these factors to be factor H and factor I. Using an aureolysin mutant in S. aureus USA300, we show that aureolysin is essential and sufficient for C3 cleavage by bacterial supernatant. In short, aureolysin acts in synergy with host regulators to inactivate C3 thereby effectively dampening the host immune response.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / immunology*
  • Bacterial Proteins / metabolism
  • Blotting, Western
  • Complement Activation / immunology
  • Complement C3 / immunology*
  • Complement C3 / metabolism
  • Complement C3-C5 Convertases / immunology
  • Complement C3-C5 Convertases / metabolism
  • Complement C3a / immunology
  • Complement C3a / metabolism
  • Complement C3b / immunology
  • Complement C3b / metabolism
  • Cytotoxicity, Immunologic / immunology
  • Host-Pathogen Interactions / immunology
  • Humans
  • Immune Evasion / immunology*
  • Metalloendopeptidases / genetics
  • Metalloendopeptidases / immunology*
  • Metalloendopeptidases / metabolism
  • Mutation
  • Neutrophils / immunology
  • Phagocytosis / immunology
  • Staphylococcal Infections / immunology*
  • Staphylococcal Infections / microbiology
  • Staphylococcus aureus / enzymology
  • Staphylococcus aureus / immunology*
  • Staphylococcus aureus / physiology
  • U937 Cells


  • Bacterial Proteins
  • Complement C3
  • Complement C3a
  • Complement C3b
  • Complement C3-C5 Convertases
  • Metalloendopeptidases
  • aureolysin