Inhibition of Plasmodium falciparum cysteine proteases by the sugarcane cystatin CaneCPI-4

• DOI: 10.1016/j.parint.2017.12.005
• Publication Date: 2017-12-26T20:43:10Z
• Authors: Pollyana M.S. Melo; Sarah El Chamy Maluf; Mauro F. Azevedo; Thaysa Paschoalin; Alexandre Budu; Piero Bagnaresi; Flávio Henrique-S...; Andrea Soares-Costa; Marcos L. Gazarini; Adriana K. Carmona
• Keywords: Hemeproteins; 0301 basic medicine; Plasmodium; Erythrocytes; 572; Plasmodium falciparum; Cysteine Proteinase Inhibitors; Falcipain; Cystatins; 3. Good health; Antimalarials; Cysteine Endopeptidases; Inhibitory Concentration 50; 03 medical and health sciences; Cysteine Proteases; Canecystatin; Humans; Cysteine protease; Inhibition; Plant Proteins

Malaria is a disease caused by Plasmodium parasites that affects hundreds of millions of people. Plasmodium proteases are involved in invasion, erythrocyte egress and degradation of host proteins. Falcipains are well-studied cysteine peptidases located in P. falciparum food vacuoles that participate in hemoglobin degradation. Cystatins are natural cysteine protease inhibitors that are implicated in a wide range of regulatory processes. Here, we report that a cystatin from sugarcane, CaneCPI-4, is selectively internalized into P. falciparum infected erythrocytes and is not processed by the parasite proteolytic machinery. Furthermore, we demonstrated the inhibition of P. falciparum cysteine proteases by CaneCPI-4, suggesting that it can exert inhibitory functions inside the parasites. The inhibition of the proteolytic activity of parasite cells is specific to this cystatin, as the addition of an anti-CaneCPI-4 antibody completely abolished the inhibition. We extended the studies to recombinant falcipain-2 and falcipain-3 and demonstrated that CaneCPI-4 strongly inhibits these enzymes, with IC50 values of 12nM and 42nM, respectively. We also demonstrated that CaneCPI-4 decreased the hemozoin formation in the parasites, affecting the parasitemia. Taken together, this study identified a natural molecule as a potential antimalarial that specifically targets falcipains and also contributes to a better understanding of macromolecule acquisition by Plasmodium falciparum infected RBCs.