Biochemical characterization of aminopeptidase N2 from Toxoplasma gondii

Aminopeptidase N (APN) is a member of the highly conserved M1 family of metalloproteases, and is considered to be a valuable target for the treatment of a variety of diseases, e.g., cancer, malaria, and coccidiosis. In this study, we identified an APN gene (TgAPN2) in the Toxoplasma gondii genome, and performed a biochemical characterization of the recombinant TgAPN2 (rTgAPN2) protein. Active rTgAPN2 was first produced and purified in Escherichia coli. The catalytic activity of the enzyme was verified using a specific fluorescent substrate, H-Ala-MCA; the rTgAPN2 was relatively active in the absence of added metal ions. The addition of some metal ions, especially Zn²⁺, inhibited the activity of the recombinant enzyme. The activity of rTgAPN2 was reduced in the presence of the EDTA chelator in the absence of added metal ions. The optimum pH for enzyme activity was 8.0; the enzyme was active in the 3-10 pH range. The substrate preference of rTgAPN2 was evaluated. The enzyme showed a preference for substrates containing N-terminal Ala and Arg residues. Finally, bestatin and amastatin were shown to inhibit the activity of the enzyme. In conclusion, rTgAPN2 shared general characteristics with the M1 family of aminopeptidases but also had some unique characteristics. This provides a basis for the function of aminopeptidases and the study of drug targets.