Cross-Talk between Malarial Cysteine Proteases and Falstatin: The BC Loop as a Hot-Spot Target

Abstract

Cysteine proteases play a crucial role in the development of the human malaria parasites Plasmodium falciparum and Plasmodium vivax. Our earlier studies demonstrated that these enzymes are equipped with specific domains for defined functions and further suggested the mechanism of activation of cysteine proteases. The activities of these proteases are regulated by a new class of endogenous inhibitors of cysteine proteases (ICPs). Structural studies of the ICPs of Trypanosoma cruzi (chagasin) and Plasmodium berghei (PbICP) indicated that three loops (termed BC, DE, and FG) are crucial for binding to target proteases. Falstatin, an ICP of P. falciparum, appears to play a crucial role in invasion of erythrocytes and hepatocytes. However, the mechanism of inhibition of cysteine proteases by falstatin has not been established. Our study suggests that falstatin is the first known ICP to function as a multimeric protein. Using site-directed mutagenesis, hemoglobin hydrolysis assays and peptide inhibition studies, we demonstrate that the BC loop, but not the DE or FG loops, inhibits cysteine proteases of P. falciparum and P. vivax via hydrogen bonds. These results suggest that the BC loop of falstatin acts as a hot-spot target for inhibiting malarial cysteine proteases. This finding suggests new strategies for the development of anti-malarial agents based on protease-inhibitor interactions.

Synthesis of novel benzimidazole acrylonitriles for inhibition of Plasmodium falciparum growth by dual target inhibition

“…A, B, C, and D, and hence desired drug interaction could be obtained by any chain/monomer. However, for performing docking studies chain B was selected because only its sequence was complete and was devoid of any mutations …”

Protein-Protein Interactions in Malaria: Emerging Arena for Future Chemotherapeutics

“…Substantial effort has been made to develop rational strategies in designing PPI inhibitors for target proteins that have no well-defined binding site (so-called "hot-spot") and, thus, have previously been considered undruggable (Figure 4). [44,45].…”

“…More importantly, three loop regions termed BC-, DE-, and FG loops Protein-Protein Interactions in Malaria: Emerging Arena for Future Chemotherapeutics DOI: http://dx.doi.org /10.5772/intechopen.89217 were shown to be involved in active site inhibition (Figure 5A,B) [44]. However, further studies with the P. falciparum ICP, falstatin, indicated that unlike other ICPs, just the BC loop was sufficient for falcipain inhibition and that Asn289 of falstatin formed stabilizing hydrogen bonds and hydrophobic interactions ( Figure 5C,D) [45].…”

Expression of cysteine proteinases and cystatins in parasites and use of cysteine proteinase inhibitors in parasitic diseases. Part III: Protozoa (2): Plasmodium spp.

“…Later, utilizing site-directed mutagenesis, hemoglobin hydrolysis assays and peptide inhibition studies, Indian investigators demonstrated that only the first loop (BC) specifically inhibits FPs and VPs via hydrogen bonds. This loop was suggested as a drug target for development of an effective potent antimalarial novel CPI [158] .…”