Plays an essential role in immune evasion by helping bacteria to resist complement-mediated killing by neutrophils. Inhibits the deposition of host C3b on bacterial surfaces and the release of the chemoattractant C5a by cleaving the central complement protein C3. The cleavage site renders the C3b molecule vulnerable to proteolytic degradation by host regulators (PubMed:21502375). Cleaves and inactivates host SERPINA1, which is an endogenous protease inhibitor essential for controlling neutrophil serine protease elastase (PubMed:3533918). Also plays an essential role in the cleavage and subsequent activation of the serine protease SspA (glutamyl endopeptidase) which is involved in colonization and infection of human tissues (PubMed:17878159). Cleavage of insulin B chain with specificity similar to that of thermolysin, preferring hydrophobic P1' residues. Activates the glutamyl endopeptidase (EC 3.4.21.19) of Staphylococcus aureus. Binds 3 Ca(2+) ions per subunit. Binds 1 zinc ion per subunit. Monomer. Belongs to the peptidase M4 family.