Prodomain processing of recombinant plasmepsin II and IV, the aspartic proteases of Plasmodium falciparum, is auto- and trans-catalytic

Prodomain processing of the four food vacuole plasmepsins (PMs), the malarial aspartic proteases, is prerequisite for their activity on hemoglobin degradation of the parasite Plasmodium falciparum. Although previous studies have suggested the involvement of a calpain-like PM convertase in the processing of PMs, the underlying mechanism of their processing remains to be clarified. Here, to investigate the mechanism by which food vacuole PM II and IV are processed, we used their wild-type and mutant proteins in which the catalytic Asp residue in two active-site motifs was mutated, as well as protease inhibitors. Autocatalytic processing of wild-type PM II and IV was inhibited only by an aspartic protease inhibitor pepstatin A. Unexpectedly, their proteolytic activities were inhibited not only by pepstatin A but also by calpain inhibitor ALLN. The active-site mutants of both PM II and IV showed neither autocatalytic processing nor proteolytic activities. However, the mutants of both PMs were efficiently processed upon incubation with their respective wild type proteins. Furthermore, the mutants of both PMs were processed upon incubation with each other's wild-type PM in both pepstatin A- and ALLN-sensitive manners. These results suggest that the processing of PM II and IV occurs via an intra- and inter-molecular autocatalytic event as well as via a transcatalytic event between them.