Biomolecular interactions between Plasmodium and human host: A basis of targeted antimalarial therapy.

Malaria is one of the serious health concerns worldwide as it remains a clinical challenge due to the complex life cycle of the malaria parasite and the morphological changes it undergoes during infection. The malaria parasite multiplies rapidly and spreads in the population by changing its alternative hosts. These various morphological stages of the parasite in the human host cause clinical symptoms (anemia, fever, and coma). These symptoms arise due to the preprogrammed biology of the parasite in response to the human pathophysiological response. Thus, complete elimination becomes one of the major health challenges. Although malaria vaccine(s) are available in the market, they still contain to cause high morbidity and mortality. Therefore, an approach for eradication is needed through the exploration of novel molecular targets by tracking the epidemiological changes the parasite adopts. This review focuses on the various novel molecular targets.

Guanidinium Chloride-Induced Haemolysis Assay to Measure New Permeation Pathway Functionality in Rodent Malaria Plasmodium berghei.

Parasite-derived new permeation pathways (NPPs) expressed at the red blood cell (RBC) membrane enable Plasmodium parasites to take up nutrients from the plasma to facilitate their survival. Thus, NPPs represent a potential novel therapeutic target for malaria. The putative channel component of the NPP in the human malaria parasite P. falciparum is encoded by mutually exclusively expressed clag3.1/3.2 genes. Complicating the study of the essentiality of these genes to the NPP is the addition of three clag paralogs whose contribution to the P. falciparum channel is uncertain. Rodent malaria P. berghei contains only two clag genes, and thus studies of P. berghei clag genes could significantly aid in dissecting their overall contribution to NPP activity. Previous methods for determining NPP activity in a rodent model have utilised flux-based assays of radioisotope-labelled substrates or patch clamping. This study aimed to ratify a streamlined haemolysis assay capable of assessing the functionality of P. berghei NPPs. Several isotonic lysis solutions were tested for their ability to preferentially lyse infected RBCs (iRBCs), leaving uninfected RBCs (uRBCs) intact. The osmotic lysis assay was optimised and validated in the presence of NPP inhibitors to demonstrate the uptake of the lysis solution via the NPPs. Guanidinium chloride proved to be the most efficient reagent to use in an osmotic lysis assay to establish NPP functionality. Furthermore, following treatment with guanidinium chloride, ring-stage parasites could develop into trophozoites and schizonts, potentially enabling use of guanidinium chloride for parasite synchronisation. This haemolysis assay will be useful for further investigation of NPPs in P. berghei and could assist in validating its protein constituents.

How Malaria Parasites Acquire Nutrients From Their Host.

Plasmodium parasites responsible for the disease malaria reside within erythrocytes. Inside this niche host cell, parasites internalize and digest host hemoglobin to source amino acids required for protein production. However, hemoglobin does not contain isoleucine, an amino acid essential for Plasmodium growth, and the parasite cannot synthesize it de novo. The parasite is also more metabolically active than its host cell, and the rate at which some nutrients are consumed exceeds the rate at which they can be taken up by erythrocyte transporters. To overcome these constraints, Plasmodium parasites increase the permeability of the erythrocyte membrane to isoleucine and other low-molecular-weight solutes it requires for growth by forming new permeation pathways (NPPs). In addition to the erythrocyte membrane, host nutrients also need to cross the encasing parasitophorous vacuole membrane (PVM) and the parasite plasma membrane to access the parasite. This review outlines recent advances that have been made in identifying the molecular constituents of the NPPs, the PVM nutrient channel, and the endocytic apparatus that transports host hemoglobin and identifies key knowledge gaps that remain. Importantly, blocking the ability of Plasmodium to source essential nutrients is lethal to the parasite, and thus, components of these key pathways represent potential antimalaria drug targets.

An exclusive computational insight toward molecular mechanism of MMV007571, a multitarget inhibitor of Plasmodium falciparum.

Recently, two Malaria Box molecules namely MMV007571 and MMV020439 well known inhibitors of New Permeability Pathway (NPP) function also showed a secondary phenotype of inhibition of enzyme Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) and cytochrome bc1 complex in metabolic profile assays. Intricacies of their binding at the newly identified targets was need of the hour which motivated us to study their binding using molecular docking and dynamics simulations approach. Interestingly, molecular docking results of both MMV007571 and MMV020439 showed good binding affinity toward the Qo site of cytochrome bc1 complex while only MMV007571 illustrated notable binding characterstics for PfDHODH. Molecular Dynamics (MD) simulations when carried out for native-PfDHODH, PfDHODH-MMV007571 and PfDHODH-Genz667348 models (100 ns each) demonstrated the role of inhibitors over the N-terminus domain which experienced conformational transition from an open state (22 Å) to closed state (16 Å) in the protein-inhibitor models. Dynamics also indicated that the loop domain near cofactor flavin mononucleotide (FMN) attained more felxibility which further lead to its poor binding and may contribute to inhibition of the oxidation (catalytic) process. Moreover, the pharmacophoric features of MMV007571 was justified and may serve as a template for the design of novel series of more potent multitarget inhibitors against Plasmodium falciparum.AbbreviationsÅAngstromACTsArtemisinin combination therapiescyt bc1cytochrome bc1 complexhhour(s)KKelvinµMmicromolarMMVMedicine for malaria ventureNLucNanoluciferasenMnanomolarNPPNew permeation pathwayPDBProtein data bankPfDHODHPlasmodium falciparum dihydroorotate dehydrogenasePOPC1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholineRBCRed blood corpusclesRMSDRoot-mean-square deviationSPStandard precisionvdWvan der WaalsXPExtra precisionyDHODHYeast dihydroorotate dehydrogenaseCommunicated by Ramaswamy H. Sarma.