The many paths to artemisinin resistance in Plasmodium falciparum.

Emerging resistance against artemisinin (ART) poses a major challenge in controlling malaria. Parasites with mutations in PfKelch13, the major marker for ART resistance, are known to reduce hemoglobin endocytosis, induce unfolded protein response (UPR), elevate phosphatidylinositol-3-phosphate (PI3P) levels, and stimulate autophagy. Nonetheless, PfKelch13-independent resistance is also reported, indicating extensive complementation by reconfiguration in the parasite metabolome and transcriptome.

Autophagy Underlies the Proteostasis Mechanisms of Artemisinin Resistance in P. falciparum Malaria.

Emerging resistance to artemisinin (ART) has become a challenge for reducing worldwide malaria mortality and morbidity. The C580Y mutation in Plasmodium falciparum Kelch13 has been identified as the major determinant for ART resistance in the background of other mutations, which include the T38I mutation in autophagy-related protein ATG18. Increased endoplasmic reticulum phosphatidylinositol-3-phosphate (ER-PI3P) vesiculation, unfolded protein response (UPR), and oxidative stress are the proteostasis mechanisms proposed to cause ART resistance.

Autophagy-related protein PfATG18 participates in food vacuole dynamics and autophagy-like pathway in Plasmodium falciparum.

Plasmodium falciparum has a limited repertoire of autophagy-related genes (ATGs), and the functions of various proteins of the autophagy-like pathway are not fully established in this protozoan parasite. Studies suggest that some of the autophagy proteins are crucial for parasite growth. PfATG18, for example, is essential for parasite replication and has a noncanonical role in apicoplast biogenesis.

Structural Analysis of Sec62-Autophagy Interacting Motifs (AIM) and Atg8 Interactions for Its Implications in RecovER-phagy in .

Autophagy is a degradative pathway associated with many pathological and physiological processes crucial for cell survival. During ER stress, while selective autophagy occurs via ER-phagy, the re-establishment of physiologic ER homeostasis upon resolution of a transient ER stress is mediated by recovER-phagy. Recent studies demonstrated that recovER-phagy is governed via association of Sec62 as an ER-resident autophagy receptor through its autophagy interacting motifs (AIM)/LC3-interacting region (LIR) toAtg8/LC3.

Basal and starvation-induced autophagy mediates parasite survival during intraerythrocytic stages of .

The precise role of autophagy in remains largely unknown. Although a limited number of autophagy genes have been identified in this apicomplexan, only Atg8 has been characterized to a certain extent. On the basis of the expression levels of Atg8 and the putative Atg5, we report that the basal autophagy in this parasite is quite robust and mediates not only the intraerythrocytic development but also fresh invasion of red blood cells (RBCs) in the subsequent cycles.

Centromere and its associated proteins-what we know about them in Plasmodium falciparum.

The complex life cycle of intracellular parasitic protozoans entails multiple rounds of DNA replication and mitosis followed by cytokinesis to release daughter parasites. To gain insights into mitotic events it is imperative to identify the biomarkers that constitute the chromosome segregation machinery in the parasite. Chromosomal loci called centromeres and their associated proteins play an essential role in accurate chromosome segregation.

Presence of novel triple mutations in the pvdhfr from Plasmodium vivax in Mangaluru city area in the southwestern coastal region of India.

Background: Genes encoding dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) are the targets of sulfadoxine-pyrimethamine (SP) present in artemisinin based combination therapy (ACT; artesunate + sulfadoxine pyrimethamine) for Plasmodium falciparum. Although SP is generally not used to treat vivax infection, mutations in dhfr and dhps that confer antifolate resistance in Plasmodium vivax are common; which may be attributed to its sympatric existence with P. falciparum.

Drug resistance genes: pvcrt-o and pvmdr-1 polymorphism in patients from malaria endemic South Western Coastal Region of India.

Background: Malaria is highly prevalent in many parts of India and is mostly caused by the parasite species Plasmodium vivax followed by Plasmodium falciparum. Chloroquine (CQ) is the first-line treatment for blood stage P. vivax parasites, but cases of drug resistance to CQ have been reported from India.

Apicoplast fatty acid synthesis is essential for pellicle formation at the end of cytokinesis in Toxoplasma gondii.

The apicomplexan protozoan Toxoplasma gondii, the causative agent of toxoplasmosis, harbors an apicoplast, a plastid-like organelle with essential metabolic functions. Although the FASII fatty acid biosynthesis pathway located in the apicoplast is essential for parasite survival, the cellular effects of FASII disruption in T. gondii had not been examined in detail.

The dimerization domain of PfCENP-C is required for its functions as a centromere protein in human malaria parasite Plasmodium falciparum.

Background: The conserved centromere-associated proteins, CENH3 (or CENP-A) and CENP-C are indispensable for the functional centromere-kinetochore assembly, chromosome segregation, cell cycle progression, and viability. The presence and functions of centromere proteins in Plasmodium falciparum are not well studied. Identification of PfCENP-C, an inner kinetochore protein (the homologue of human CENP-C) and its co-localization with PfCENH3 was recently reported.

Plasmodium falciparum CENH3 is able to functionally complement Cse4p and its, C-terminus is essential for centromere function.

The Plasmodium falciparum centromeric histone variant PfCENH3 has been shown to occupy a 4-4.5 kb region on each chromosome, but the experimental demonstration of its structure-function relationship remains unexplored. By functional complementation assays, we report that the C-terminus, specifically the CATD region within the HFD of PfCENH3 is essential in centromere function.

Apicoplast triose phosphate transporter (TPT) gene knockout is lethal for Plasmodium.

The C3, C5, C6 type sugar phosphate transporters bring sugars inside apicoplast, thus providing energy, reducing power and elements like carbon to apicoplast. Plasmodium berghei has two C3 type sugar phosphate transporters in the membrane of apicoplast: triose phosphate transporter (TPT) and phosphoenolpyruvate transporter (PPT). Here we report that P.

Insights into the substrate specificity of a thioesterase Rv0098 of mycobacterium tuberculosis through X-ray crystallographic and molecular dynamics studies.

The crystal structure of Rv0098, a long-chain fatty acyl-CoA thioesterase from Mycobacterium tuberculosis with bound dodecanoic acid at the active site provided insights into the mode of substrate binding but did not reveal the structural basis of substrate specificities of varying chain length. Molecular dynamics studies demonstrated that certain residues of the substrate binding tunnel are flexible and thus modulate the length of the tunnel. The flexibility of the loop at the base of the tunnel was also found to be important for determining the length of the tunnel for accommodating appropriate substrates.

15-Deoxyspergualin hinders physical interaction between basic residues of transit peptide in PfENR and Hsp70-1.

The apicoplast of Plasmodium harbors several metabolic pathways. The enzymes required to perform these reactions are all nuclearly encoded and apicoplast targeted (NEAT) proteins. Plasmodium falciparum Enoyl-ACP Reductase (PfENR) is one such NEAT protein.

Benzothiophene carboxamide derivatives as novel antimalarials.

Bromo-benzothiophene carboxamide derivatives have been shown in the preceding article to inhibit Plasmodium falciparum Enoyl-ACP reductase. Here, we report bromo-benzothiophene carboxamide derivatives as potent inhibitors of Plasmodium asexual blood-stages in vitro as well as in vivo in the mouse model. These compounds specifically impair the development of metabolically active trophozoite stage of intraerythrocytic cycle and the intravenous administration of 3-bromo-N-(4-fluorobenzyl)-benzo[b]thiophene-2-carboxamide (compound 6) enhances the longevity of P.

Benzothiophene carboxamide derivatives as inhibitors of Plasmodium falciparum enoyl-ACP reductase.

Benzothiophene derivatives like benzothiophene sulphonamides, biphenyls, or carboxyls have been synthesized and have found wide pharmacological usage. Here we report, bromo-benzothiophene carboxamide derivatives as potent, slow tight binding inhibitors of Plasmodium enoyl-acyl carrier protein (ACP) reductase (PfENR). 3-Bromo-N-(4-fluorobenzyl)-benzo[b]thiophene-2-carboxamide (compound 6) is the most potent inhibitor with an IC50 of 115 nM for purified PfENR.

Structural basis for the functional and inhibitory mechanisms of β-hydroxyacyl-acyl carrier protein dehydratase (FabZ) of Plasmodium falciparum.

The β-hydroxyacyl-acyl carrier protein dehydratase of Plasmodium falciparum (PfFabZ) catalyzes the third and important reaction of the fatty acid elongation cycle. The crystal structure of PfFabZ is available in hexameric (active) and dimeric (inactive) forms. However, PfFabZ has not been crystallized with any bound inhibitors until now.

Effect of substrate binding loop mutations on the structure, kinetics, and inhibition of enoyl acyl carrier protein reductase from Plasmodium falciparum.

Enoyl acyl carrier protein reductase (ENR), which catalyzes the final and rate limiting step of fatty acid elongation, has been validated as a potential drug target. Triclosan is known to be an effective inhibitor for this enzyme. We mutated the substrate binding site residue Ala372 of the ENR of Plasmodium falciparum (PfENR) to Methionine and Valine which increased the affinity of the enzyme towards triclosan to almost double, close to that of Escherichia coli ENR (EcENR) which has a Methionine at the structurally similar position of Ala372 of PfENR.

X-ray crystallographic analysis of the complexes of enoyl acyl carrier protein reductase of Plasmodium falciparum with triclosan variants to elucidate the importance of different functional groups in enzyme inhibition.

Triclosan, a well-known inhibitor of Enoyl Acyl Carrier Protein Reductase (ENR) from several pathogenic organisms, is a promising lead compound to design effective drugs. We have solved the X-ray crystal structures of Plasmodium falciparum ENR in complex with triclosan variants having different substituted and unsubstituted groups at different key functional locations. The structures revealed that 4 and 2' substituted compounds have more interactions with the protein, cofactor, and solvents when compared with triclosan.

Backbone chemical shift assignments of the acyl-acyl carrier protein intermediates of the fatty acid biosynthesis pathway of Plasmodium falciparum.

We report the backbone chemical shift assignments of the acyl-acyl carrier protein (ACP) intermediates of the fatty acid biosynthesis pathway of Plasmodium falciparum. The acyl-ACP intermediates butyryl (C(4)), -octanoyl (C(8)), -decanoyl (C(10)), -dodecanoyl (C(12)) and -tetradecanoyl (C(14))-ACPs display marked changes in backbone HN, C(alpha) and C(beta) chemical shifts as a result of acyl chain insertion into the hydrophobic core. Chemical shift changes cast light on the mechanism of expansion of the acyl carrier protein core.

SAR and pharmacophore models for the rhodanine inhibitors of Plasmodium falciparum enoyl-acyl carrier protein reductase.

Significance of type II fatty acid synthase pathway in the life cycle of malarial parasite has long been established. Enoyl acyl carrier protein (ACP) reductase of Plasmodium falciparum (PfENR) is the rate determining enzyme of its elongation module. Hence, PfENR has been a target for the development of antimalarials as well as vaccines.

Design, development, synthesis, and docking analysis of 2'-substituted triclosan analogs as inhibitors for Plasmodium falciparum enoyl-ACP reductase.

A structure-based approach has been adopted to develop 2'-substituted analogs of triclosan. The Cl at position 2' in ring B of triclosan was chemically substituted with other functional groups like NH(2), NO(2) and their inhibitory potencies against PfENR were determined. The binding energies of the 2' substituted analogs of triclosan for enoyl-acyl carrier protein reductase (ENR) of Plasmodium falciparum were determined using Autodock.

Triclosan inhibit the growth of the late liver-stage of Plasmodium.

Annually, approximately two million human deaths are caused worldwide by malaria, most of them being children. Plasmodium falciparum is the leading cause of cerebral malaria, the most severe and fatal form of disease. Moreover, the emergence of resistant strains to the existing drugs has worsened the situation.

Evolutionary significance of self-acylation property in acyl carrier proteins.

Acyl carrier protein is an integral component of many cellular metabolic processes. A number of studies have reported self-acylation behavior in acyl carrier proteins. Although ACPs exhibit high levels of similarity in their primary and tertiary structures, self-acylation behavior is restricted to only some ACPs that can be classified into two major families based on their function.

Structural insights into the acyl intermediates of the Plasmodium falciparum fatty acid synthesis pathway: the mechanism of expansion of the acyl carrier protein core.

Acyl carrier protein (ACP) plays a central role in fatty acid biosynthesis. However, the molecular machinery that mediates its function is not yet fully understood. Therefore, structural studies were carried out on the acyl-ACP intermediates of Plasmodium falciparum using NMR as a spectroscopic probe.