Blocking effect of a biotinylated protease inhibitor on the egress of Plasmodium falciparum merozoites from infected red blood cells.

The malaria parasite Plasmodium falciparum invades human red blood cells. Before infecting new erythrocytes, the merozoites have to exit their host cell to get into the blood plasma. Knowledge about the mechanism of egress is scarce, but it is thought that proteases are basically involved in this step. We have introduced a biotinylated dibenzyl aziridine-2,3-dicarboxylate (bADA) as an irreversible cysteine protease inhibitor to study the mechanism of merozoite release and to identify the proteases involved. The compound acts on parasite proteins in the digestive vacuole and in the host cell cytosol, as judged by fluorescence microscopy. The inhibitor blocks rupture of the host cell membrane, leading to clustered merozoite structures, as evidenced by immunoelectron microscopy. Interestingly, bADA did not prevent rupture of the parasitophorous vacuole membrane (PVM) that surrounds the parasite during the period of intraerythrocytic maturation. The compound appears to be a valuable template for the development of inhibitors specific for individual plasmodial proteases, which would be useful tools to dissect the molecular mechanisms underlying the process of merozoite release and consequently to develop potent antimalarial drugs.