Secreted protease which is important for P.entomophila to counteract the local immune response of Drosophila (PubMed:16789834). Can degrade antimicrobial peptides (AMPs), e.g. Diptericin and Cecropin A. Thus, protects P.entomophila from the Drosophila antimicrobial peptides produced by the gut innate immune response, and promotes bacterial persistence in the Drosophila gut and killing of the host (PubMed:16789834). Is responsible for maturation of pro-Monalysin to the active toxin Monalysin, by cleaving its N-terminus (PubMed:21980286). Binds 8 Ca(2+) ions per subunit. Binds 1 zinc ion per subunit. Is probably secreted via the associated Type 1 transporter encoded by aprDEF. Is regulated by the GacS/GacA two-component system that controls P.entomophila pathogenicity. Seems also regulated by PrtR. Inactivation of aprA attenuates both the capacity to persist in the host and pathogenicity. The deletion mutants are able to survive to wild-type levels in immune-deficient Relish flies, indicating that the protease plays an important role in protection against the Drosophila Imd-dependent immune response. Moreover, they persist less well than wild-type bacteria in imd flies over-expressing Diptericin (PubMed:16789834). Pro-Monalysin is found in supernatant derived from the aprA-deletion mutant while the mature form predominates in supernatant from wild-type P.entomophila (PubMed:21980286). Belongs to the peptidase M10B family.