Identification and characterization of a secreted M28 aminopeptidase protein in Acanthamoeba

Acanthamoeba is a free-living pathogenic protozoan that is distributed in different environmental reservoirs, including lakes and soil. Pathogenic Acanthamoeba can cause severe human diseases, such as blinding keratitis and granulomatous encephalitis. Therefore, it is important to understand the pathogenic relationship between humans and Acanthamoeba. By comparison of systemic analysis results for Acanthamoeba isolates, we identified a novel secreted protein of Acanthamoeba, an M28 aminopeptidase (M28AP), which targets of the human innate immune defense. We investigated the molecular functions and characteristics of the M28AP protein by anti-M28 antibodies and a M28AP mutant strain generated by the CRISPR/Cas9 system. Human complement proteins such as C3b and iC3b were degraded by Acanthamoeba M28AP. We believe that M28AP is an important factor in human innate immunity. This study provides new insight for the development of more efficient medicines to treat Acanthamoeba infection.