Plasmodium falciparum (Pf), the causative agent of malaria, has an iron-sulfur cluster-containing class I fumarate hydratase (FH) that catalyzes the interconversion of fumarate to malate, a wellknown reaction in the tricarboxylic acid cycle. In humans, the same reaction is catalyzed by class II FH that has no sequence or structural homology with the class I enzyme from Plasmodium. Fumarate is generated in large quantities in the parasite as a byproduct of AMP synthesis and is converted to malate by FH and then used in the generation of the key metabolites oxaloacetate, aspartate, and pyruvate. Previous studies have identified the FH reaction as being essential to P. falciparum, but biochemical characterizations of PfFH that may provide leads for the development of specific inhibitors are lacking. Here, we report on the kinetic characterization of purified recombinant PfFH, functional complementation of fh deficiency in Escherichia coli, and mitochondrial localization in the parasite. We found that the substrate analog mercaptosuccinic acid is a potent PfFH inhibitor, with a K i value in the nanomolar range. The fh gene could not be knocked out in Plasmodium berghei when transfectants were introduced into BALB/c mice; however, fh knockout was successful when C57BL/6 mice were used as host, suggesting that the essentiality of the fh gene to the parasite was mouse strain dependent.Plasmodium falciparum (Pf), the causative agent of the most lethal form of malaria, during its intra-erythrocytic asexual stages, derives ATP primarily from glycolysis with low contribution from mitochondrial pathways (1, 2). The bulk of pyruvate formed is converted to lactic acid with a minor amount entering the tricarboxylic acid (TCA) cycle, the flux through which is upregulated in sexual stages (2). Key intermediates that anaplerotically feed into the TCA cycle are α-ketoglutarate derived from glutamate, oxaloacetate (OAA) from phosphoenolpyruvate, and fumarate from adenosine 5΄-monophosphate (AMP) synthesis. Synthesis of AMP in the parasite is solely from inosine-5΄-monophosphate (IMP) through a pathway involving the enzymes adenylosuccinate synthetase (ADSS) and adenylosuccinate lyase (ASL). The net reaction of ADSS and ASL involves consumption of GTP and aspartate and, generation of GDP, P i and fumarate. In the rapidly dividing parasite with an AT-rich genome and high energy requirements, leading to a high demand for adenine pools, one would expect a high flux of fumarate generation. The parasite does not secrete fumarate but instead, the carbon derived from this metabolite can be traced in malate, OAA, aspartate, pyruvate (through PEP) and lactate (3). The metabolic significance of this fumarate anaplerosis is still obscure. In this context, fumarate hydratase (FH, fumarase) the key enzyme to metabolize fumarate becomes an Fumarate hydratase (fumarase, E.C. 4.2.1.2) catalyzes the reversible conversion of fumarate to malate. The stereospecific reaction involves the anti-addition of a water molecule across the carbon-carbon...

Plasmodium falciparum (Pf), the causative agent of malaria has an iron-sulfur cluster-containing class I fumarate hydratase (FH) that catalyzes the interconversion of fumarate to malate, a wellknown reaction in the tricarboxylic acid cycle. In humans, the same reaction is catalyzed by class II FH that has no sequence or structural homology with the class I enzyme. Fumarate, generated in large quantities in the parasite as a byproduct of AMP synthesis is converted to malate by the action of FH, and subsequently used in the generation of the key metabolites oxaloacetate, aspartate and pyruvate. Here we report on the kinetic characterization of purified recombinant PfFH, functional complementation of fh deficiency in Escherichia coli and mitochondrial localization in the parasite. The substrate analog, mercaptosuccinic acid was found to be a potent inhibitor of PfFH with a K i value in the nanomolar range. Knockout of the fh gene was not possible in P. berghei when drug-selection of the transfectants was performed in BALB/c mice while the gene was amenable to knockout when C57BL/6 mice were used as host, thereby indicating mouse-strain dependent essentiality of the fh gene to the parasite.Plasmodium falciparum (Pf), the causative agent of the most lethal form of malaria, during its intraerythrocytic asexual stages, derives ATP primarily from glycolysis with low contribution from mitochondrial pathways (1, 2). The bulk of pyruvate formed is converted to lactic acid with a minor amount entering the tricarboxylic acid (TCA) cycle, the flux through which is upregulated in sexual stages (2). Key intermediates that anaplerotically feed into the TCA cycle are α-ketoglutarate derived from glutamate, oxaloacetate (OAA) from phosphoenolpyruvate, and fumarate from adenosine 5΄-monophosphate (AMP) synthesis. Synthesis of AMP in the parasite is solely from inosine-5΄-monophosphate (IMP) through a pathway involving the enzymes adenylosuccinate synthetase (ADSS) and adenylosuccinate lyase (ASL). The net reaction of ADSS and ASL involves consumption of GTP and aspartate and, generation of GDP, P i and fumarate. In the rapidly dividing parasite with an AT-rich genome and high energy requirements, leading to a high demand for adenine pools, one would expect a high flux of fumarate generation. The parasite does not secrete fumarate but instead, the carbon derived from this metabolite can be traced in malate, OAA, aspartate, pyruvate (through PEP) and lactate (3). The metabolic significance of this fumarate anaplerosis is still obscure. In this context, fumarate hydratase (FH, fumarase) the key enzyme to metabolize fumarate becomes an important candidate for further investigation.Fumarate hydratase (fumarase, E.C. 4.2.1.2) catalyzes the reversible conversion of fumarate to malate. The stereospecific reaction peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/158956 doi: bioRxiv preprint first posted onli...