Structural and active site analysis of plasmepsins of Plasmodium falciparum: Potential anti-malarial targets

The binding landscape of plasmepsin V and the implications for flap dynamics

Plasmepsin V belongs to the plasmepsin family of aspartic proteases.

Flap flexibility amongst plasmepsins I, II, III, IV, and V: Sequence, structural, and molecular dynamics analyses

Herein, for the first time, we comparatively report the opening and closing of apo plasmepsin I - V. Plasmepsins belong the aspartic protease family of enzymes, and are expressed during the various stages of the P. falciparum lifecycle, the species responsible for the most lethal and virulent malaria to infect humans. Plasmepsin I, II, IV and HAP degrade hemoglobin from infected red blood cells, whereas plasmepsin V transport proteins crucial to the survival of the malaria parasite across the endoplasmic reticulum. Flap-structures covering the active site of aspartic proteases (such as HIV protease) are crucial to the conformational flexibility and dynamics of the protein, and ultimately control the binding landscape. The flap-structure in plasmepsins is made up of a flip tip in the N-terminal lying perpendicular to the active site, adjacent to the flexible loop region in the C-terminal. Using molecular dynamics, we propose three parameters to better describe the opening and closing of the flap-structure in apo plasmepsins. Namely, the distance, d1, between the flap tip and the flexible region; the dihedral angle, ϕ, to account for the twisting motion; and the TriCα angle, θ1. Simulations have shown that as the flap-structure twists, the flap and flexible region move apart opening the active site, or move toward each other closing the active site. The data from our study indicate that of all the plasmepsins investigated in the present study, Plm IV and V display the highest conformational flexibility and are more dynamic structures versus Plm I, II, and HAP.

Structural studies of vacuolar plasmepsins

Plasmepsins (PMs) are pepsin-like aspartic proteases present in different species of parasite Plasmodium. Four Plasmodium spp. (P. vivax, P. ovale, P. malariae, and the most lethal P. falciparum) are mainly responsible for causing human malaria that affects millions worldwide. Due to the complexity and rate of parasite mutation coupled with regional variations, and the emergence of P. falciparum strains which are resistant to antimalarial agents such as chloroquine and sulfadoxine/pyrimethamine, there is constant pressure to find new and lasting chemotherapeutic drug therapies. Since many proteases represent therapeutic targets and PMs have been shown to play an important role in the survival of parasite, these enzymes have recently been identified as promising targets for the development of novel antimalarial drugs. The genome of P. falciparum encodes 10 PMs (PMI, PMII, PMIV-X and histo-aspartic protease (HAP)), 4 of which (PMI, PMII, PMIV and HAP) reside within the food vacuole, are directly involved in degradation of human hemoglobin, and share 50-79% amino acid sequence identity. This review focuses on structural studies of only these four enzymes, including their orthologs in other Plasmodium spp.. Almost all original crystallographic studies were performed with PMII, but more recent work on PMIV, PMI, and HAP resulted in a more complete picture of the structure-function relationship of vacuolar PMs. Many structures of inhibitor complexes of vacuolar plasmepsins, as well as their zymogens, have been reported in the last 15 years. Information gained by such studies will be helpful for the development of better inhibitors that could become a new class of potent antimalarial drugs. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Computational perspectives into plasmepsins structure-function relationship: implications to inhibitors design

The development of efficient and selective antimalariais remains a challenge for the pharmaceutical industry. The aspartic proteases plasmepsins, whose inhibition leads to parasite death, are classified as targets for the design of potent drugs. Combinatorial synthesis is currently being used to generate inhibitor libraries for these enzymes, and together with computational methodologies have been demonstrated capable for the selection of lead compounds. The high structural flexibility of plasmepsins, revealed by their X-ray structures and molecular dynamics simulations, made even more complicated the prediction of putative binding modes, and therefore, the use of common computational tools, like docking and free-energy calculations. In this review, we revised the computational strategies utilized so far, for the structure-function relationship studies concerning the plasmepsin family, with special focus on the recent advances in the improvement of the linear interaction estimation (LIE) method, which is one of the most successful methodologies in the evaluation of plasmepsin-inhibitor binding affinity.