Plasmodium falciparum: Biochemical characterization of the cysteine protease falcipain-2′

The Plasmodium falciparum cysteine proteases falcipain-2 and falcipain-3 are hemoglobinases and potential antimalarial drug targets. The falcipain-2′ gene was identified recently and is nearly identical in sequence to falcipain-2. The product of this gene has not been studied previously. The mature protease domain of falcipain-2′ was expressed in Escherichia coli, purified, and refolded to active enzyme. Functional analysis revealed similar biochemical properties to those of falcipain-2, including pH optima (pH 5.5-7.0), reducing requirements, and substrate preference. Studies with cysteine protease inhibitors showed similar inhibition of falcipain-2 and falcipain-2′, although specificities were not identical. Considering activity against the presumed biological substrate, both enzymes readily hydrolyzed hemoglobin. Our results confirm that falcipain-2′ is an active hemoglobinase and suggest that falcipain-2 and falcipain-2′ play similar roles in erythrocytic parasites but that, for promising cysteine protease inhibitors, it will be important to confirm activity against this additional target.