Dipeptidyl aminopeptidases (DPAPs) have recently been identified as essential cysteine proteases playing important roles during the erythrocytic cycle of Plasmodium falciparum (Fig 1). DPAP1 is involved in parasite growth and its inhibition is sufficient to prevent parasite replication both in vitro and in vivo. DPAP3 is an important regulator of parasite egress that seems to be at the top of the proteolytic pathway that controls this process.
Moreover, DPAP3 is very active at merozoite stage, thus suggesting an additional role in RBC invasion. We are currently combining chemical, genetic, and proteomic approaches to investigate the molecular functions of DPAP3 in schizogony, parasite egress, and RBC invasion.
Overall, we believe that DPAPs are promising antimalarial targets because a pan-DPAP inhibitor will target the parasite at different asexual stages, thus decreasing the chance of drug resistance. Moreover, DPAPs might play important roles during malaria transmission since they are also expressed at liver and insect stages.
A. Egress. In order to escape the RBC, the parasite has to break down the PV (parasitophorous vacuole) and RBC membranes, thus requiring the action of multiple proteases (SUB1, human calpain-1, SERAs). DPAP3 is at the top of the proteolytic pathway that controls parasite egress and is a critical regulator of this process.
B. Invasion. As the parasite enters the RBC it sheds its protein coat thus requiring the action of proteases such as SUB2 or rhomboids. DPAP3 is very active in purified merozoites, suggesting that it might play an additional role during RBC invasion. Whether DPAP3 is essential for invasion or ring formation, and what its molecular functions are at this stage are some of the questions we are pursuing in the lab.
C. Growth. After RBC invasion, the parasite imports hemoglobin into its digestive vacuole where it is degraded by a variety of proteases. This pathway provides amino acids for protein synthesis and liberates space within the RBC for the parasite to growth. DPAP1 inhibition prevents parasite growth and is sufficient to block parasite replication both in vitro and in vivo.
D. Schizogony. DPAP3 might also play an important role during schizogony since inhibition of DPAP3 at trophozoite stage delays schizont maturation.