Mitochondrial dehydrogenases in the aerobic respiratory chain of the rodent malaria parasite Plasmodium yoelii yoelii

Aurachins, Bacterial Antibiotics Interfering with Electron Transport Processes

Aurachins are farnesylated quinolone alkaloids of bacterial origin and excellent inhibitors of the respiratory chain in pro- and eukaryotes. Therefore, they have become important tool compounds for the investigation of electron transport processes and they also serve as lead structures for the development of antibacterial and antiprotozoal drugs. Especially aurachin D proved to be a valuable starting point for structure-activity relationship studies. Aurachin D is a selective inhibitor of the cytochrome bd oxidase, which has received increasing attention as a target for the treatment of infectious diseases caused by mycobacteria. Moreover, aurachin D possesses remarkable activities against Leishmania donovani, the causative agent of leishmaniasis. Aurachins are naturally produced by myxobacteria of the genus Stigmatella as well as by some Streptomyces and Rhodococcus strains. The recombinant production of these antibiotics turned out to be challenging due to their complex biosynthesis and their inherent toxicity. Recently, the biotechnological production of aurachin D was established in E. coli with a titer which is higher than previously reported from natural producer organisms.

The mystery of massive mitochondrial complexes: the apicomplexan respiratory chain

The mitochondrial respiratory chain is an essential pathway in most studied eukaryotes due to its roles in respiration and other pathways that depend on mitochondrial membrane potential. Apicomplexans are unicellular eukaryotes whose members have an impact on global health. The respiratory chain is a drug target for some members of this group, notably the malaria-causing Plasmodium spp. This has motivated studies of the respiratory chain in apicomplexan parasites, primarily Toxoplasma gondii and Plasmodium spp. for which experimental tools are most advanced. Studies of the respiratory complexes in these organisms revealed numerous novel features, including expansion of complex size. The divergence of apicomplexan mitochondria from commonly studied models highlights the diversity of mitochondrial form and function across eukaryotic life.

Siccanin Is a Dual-Target Inhibitor of Plasmodium falciparum Mitochondrial Complex II and Complex III

Plasmodium falciparum contains several mitochondrial electron transport chain (ETC) dehydrogenases shuttling electrons from the respective substrates to the ubiquinone pool, from which electrons are consecutively transferred to complex III, complex IV, and finally to the molecular oxygen. The antimalarial drug atovaquone inhibits complex III and validates this parasite’s ETC as an attractive target for chemotherapy. Among the ETC dehydrogenases from P. falciparum, dihydroorotate dehydrogenase, an essential enzyme used in de novo pyrimidine biosynthesis, and complex III are the two enzymes that have been characterized and validated as drug targets in the blood-stage parasite, while complex II has been shown to be essential for parasite survival in the mosquito stage; therefore, these enzymes and complex II are considered candidate drug targets for blocking parasite transmission. In this study, we identified siccanin as the first (to our knowledge) nanomolar inhibitor of the P. falciparum complex II. Moreover, we demonstrated that siccanin also inhibits complex III in the low-micromolar range. Siccanin did not inhibit the corresponding complexes from mammalian mitochondria even at high concentrations. Siccanin inhibited the growth of P. falciparum with IC₅₀ of 8.4 μM. However, the growth inhibition of the P. falciparum blood stage did not correlate with ETC inhibition, as demonstrated by lack of resistance to siccanin in the yDHODH-3D7 (EC₅₀ = 10.26 μM) and Dd2-ELQ300 strains (EC₅₀ = 18.70 μM), suggesting a third mechanism of action that is unrelated to mitochondrial ETC inhibition. Hence, siccanin has at least a dual mechanism of action, being the first potent and selective inhibitor of P. falciparum complexes II and III over mammalian enzymes and so is a potential candidate for the development of a new class of antimalarial drugs.

Biochemical Studies of Mitochondrial Malate: Quinone Oxidoreductase from Toxoplasma gondii

Toxoplasma gondii is a protozoan parasite that causes toxoplasmosis and infects almost one-third of the global human population. A lack of effective drugs and vaccines and the emergence of drug resistant parasites highlight the need for the development of new drugs. The mitochondrial electron transport chain (ETC) is an essential pathway for energy metabolism and the survival of T. gondii. In apicomplexan parasites, malate:quinone oxidoreductase (MQO) is a monotopic membrane protein belonging to the ETC and a key member of the tricarboxylic acid cycle, and has recently been suggested to play a role in the fumarate cycle, which is required for the cytosolic purine salvage pathway. In T. gondii, a putative MQO (TgMQO) is expressed in tachyzoite and bradyzoite stages and is considered to be a potential drug target since its orthologue is not conserved in mammalian hosts. As a first step towards the evaluation of TgMQO as a drug target candidate, in this study, we developed a new expression system for TgMQO in FN102(DE3)TAO, a strain deficient in respiratory cytochromes and dependent on an alternative oxidase. This system allowed, for the first time, the expression and purification of a mitochondrial MQO family enzyme, which was used for steady-state kinetics and substrate specificity analyses. Ferulenol, the only known MQO inhibitor, also inhibited TgMQO at IC₅₀ of 0.822 μM, and displayed different inhibition kinetics compared to Plasmodium falciparum MQO. Furthermore, our analysis indicated the presence of a third binding site for ferulenol that is distinct from the ubiquinone and malate sites.

Complexome profile of Toxoplasma gondii mitochondria identifies divergent subunits of respiratory chain complexes including new subunits of cytochrome bc1 complex

The mitochondrial electron transport chain (mETC) and F1Fo-ATP synthase are of central importance for energy and metabolism in eukaryotic cells. The Apicomplexa, important pathogens of humans causing diseases such as toxoplasmosis and malaria, depend on their mETC in every known stage of their complicated life cycles. Here, using a complexome profiling proteomic approach, we have characterised the Toxoplasma mETC complexes and F1Fo-ATP synthase. We identified and assigned 60 proteins to complexes II, IV and F1Fo-ATP synthase of Toxoplasma, of which 16 have not been identified previously. Notably, our complexome profile elucidates the composition of the Toxoplasma complex III, the target of clinically used drugs such as atovaquone. We identified two new homologous subunits and two new parasite-specific subunits, one of which is broadly conserved in myzozoans. We demonstrate all four proteins are essential for complex III stability and parasite growth, and show their depletion leads to decreased mitochondrial potential, supporting their assignment as complex III subunits. Our study highlights the divergent subunit composition of the apicomplexan mETC and F1Fo-ATP synthase complexes and sets the stage for future structural and drug discovery studies.

Novel Characteristics of Mitochondrial Electron Transport Chain from Eimeria tenella

Eimeria tenella is an intracellular apicomplexan parasite, which infects cecal epithelial cells from chickens and causes hemorrhagic diarrhea and eventual death. We have previously reported the comparative RNA sequence analysis of the E. tenella sporozoite stage between virulent and precocious strains and showed that the expression of several genes involved in mitochondrial electron transport chain (ETC), such as type II NADH dehydrogenase (NDH-2), complex II (succinate:quinone oxidoreductase), malate:quinone oxidoreductase (MQO), and glycerol-3-phosphate dehydrogenase (G3PDH), were upregulated in virulent strain. To study E. tenella mitochondrial ETC in detail, we developed a reproducible method for preparation of mitochondria-rich fraction from sporozoites, which maintained high specific activities of dehydrogenases, such as NDH-2 followed by G3PDH, MQO, complex II, and dihydroorotate dehydrogenase (DHODH). Of particular importance, we showed that E. tenella sporozoite mitochondria possess an intrinsic ability to perform fumarate respiration (via complex II) in addition to the classical oxygen respiration (via complexes III and IV). Further analysis by high-resolution clear native electrophoresis, activity staining, and nano-liquid chromatography tandem-mass spectrometry (nano-LC-MS/MS) provided evidence of a mitochondrial complex II-III-IV supercomplex. Our analysis suggests that complex II from E. tenella has biochemical features distinct to known orthologues and is a potential target for the development of new anticoccidian drugs.

Alternative Type II NAD(P)H Dehydrogenases in the Mitochondria of Protists and Fungi

Plants, fungi, and some protists possess a more branched electron transport chain in their mitochondria compared to canonical one. In these organisms, the electron transport chain contains several rotenone-insensitive NAD(P)H dehydrogenases. Some are located on the outer surface, and others are located on the inner surface of the inner mitochondrial membrane. The putative role of these enzymes still remains elusive, but they may prevent the overreduction of the electron transport chain components and decrease the production of reaction oxygen species as a consequence. The last two decades resulted in the discovery of alternative rotenone-insensitive NAD(P)H dehydrogenases present in representatives of fungi and protozoa. The aim of this review is to gather and focus on current information concerning molecular and functional properties, regulation, and the physiological role of fungal and protozoan alternative NAD(P)H dehydrogenases.

Biochemical studies of membrane bound Plasmodium falciparum mitochondrial L-malate:quinone oxidoreductase, a potential drug target

Plasmodium falciparum is an apicomplexan parasite that causes the most severe malaria in humans. Due to a lack of effective vaccines and emerging of drug resistance parasites, development of drugs with novel mechanisms of action and few side effects are imperative. To this end, ideal drug targets are those essential to parasite viability as well as absent in their mammalian hosts. The mitochondrial electron transport chain (ETC) of P. falciparum is one source of such potential targets because enzymes, such as L-malate:quinone oxidoreductase (PfMQO), in this pathway are absent humans. PfMQO catalyzes the oxidation of L-malate to oxaloacetate and the simultaneous reduction of ubiquinone to ubiquinol. It is a membrane protein, involved in three pathways (ETC, the tricarboxylic acid cycle and the fumarate cycle) and has been shown to be essential for parasite survival, at least, in the intra-erythrocytic asexual stage. These findings indicate that PfMQO would be a valuable drug target for development of antimalarial with novel mechanism of action. Up to this point in time, difficulty in producing active recombinant mitochondrial MQO has hampered biochemical characterization and targeted drug discovery with MQO. Here we report for the first time recombinant PfMQO overexpressed in bacterial membrane and the first biochemical study. Furthermore, about 113 compounds, consisting of ubiquinone binding site inhibitors and antiparasitic agents, were screened resulting in the discovery of ferulenol as a potent PfMQO inhibitor. Finally, ferulenol was shown to inhibit parasite growth and showed strong synergism in combination with atovaquone, a well-described anti-malarial and bc₁ complex inhibitor.

Suppression of experimental cerebral malaria by disruption of malate:quinone oxidoreductase

Background

Aspartate, which is converted from oxaloacetate (OAA) by aspartate aminotransferase, is considered an important precursor for purine salvage and pyrimidine de novo biosynthesis, and is thus indispensable for the growth of Plasmodium parasites at the asexual blood stages. OAA can be produced in malaria parasites via two routes: (i) from phosphoenolpyruvate (PEP) by phosphoenolpyruvate carboxylase (PEPC) in the cytosol, or (ii) from fumarate by consecutive reactions catalyzed by fumarate hydratase (FH) and malate:quinone oxidoreductase (MQO) in the mitochondria of malaria parasites. Although PEPC-deficient Plasmodium falciparum and Plasmodium berghei (rodent malaria) parasites show a growth defect, the mutant P. berghei can still cause experimental cerebral malaria (ECM) with similar dynamics to wild-type parasites. In contrast, the importance of FH and MQO for parasite viability, growth and virulence is not fully understood because no FH- and MQO-deficient P. falciparum has been established. In this study, the role of FH and MQO in the pathogenicity of asexual-blood-stage Plasmodium parasites causing cerebral malaria was examined.

Results

First, FH- and MQO-deficient parasites were generated by inserting a luciferase-expressing cassette into the fh and mqo loci in the genome of P. berghei ANKA strain. Second, the viability of FH-deficient and MQO-deficient parasites that express luciferase was determined by measuring luciferase activity, and the effect of FH or MQO deficiency on the development of ECM was examined. While the viability of FH-deficient P. berghei was comparable to that of control parasites, MQO-deficient parasites exhibited considerably reduced viability. FH activity derived from erythrocytes was also detected. This result and the absence of phenotype in FH-deficient P. berghei parasites suggest that fumarate can be metabolized to malate by host or parasite FH in P. berghei-infected erythrocytes. Furthermore, although the growth of FH- and MQO-deficient parasites was impaired, the development of ECM was suppressed only in mice infected with MQO-deficient parasites.

Conclusions

These findings suggest that MQO-mediated mitochondrial functions are required for development of ECM of asexual-blood-stage Plasmodium parasites.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1898-5) contains supplementary material, which is available to authorized users.

Glutathione-deficient Plasmodium berghei parasites exhibit growth delay and nuclear DNA damage

Plasmodium parasites are exposed to endogenous and exogenous oxidative stress during their complex life cycle. To minimize oxidative damage, the parasites use glutathione (GSH) and thioredoxin (Trx) as primary antioxidants. We previously showed that disruption of the Plasmodium berghei gamma-glutamylcysteine synthetase (pbggcs-ko) or the glutathione reductase (pbgr-ko) genes resulted in a significant reduction of GSH in intraerythrocytic stages, and a defect in growth in the pbggcs-ko parasites. In this report, time course experiments of parasite intraerythrocytic development and morphological studies showed a growth delay during the ring to schizont progression. Morphological analysis shows a significant reduction in size (diameter) of trophozoites and schizonts with increased number of cytoplasmic vacuoles in the pbggcs-ko parasites in comparison to the wild type (WT). Furthermore, the pbggcs-ko mutants exhibited an impaired response to oxidative stress and increased levels of nuclear DNA (nDNA) damage. Reduced GSH levels did not result in mitochondrial DNA (mtDNA) damage or protein carbonylations in neither pbggcs-ko nor pbgr-ko parasites. In addition, the pbggcs-ko mutant parasites showed an increase in mRNA expression of genes involved in oxidative stress detoxification and DNA synthesis, suggesting a potential compensatory mechanism to allow for parasite proliferation. These results reveal that low GSH levels affect parasite development through the impairment of oxidative stress reduction systems and damage to the nDNA. Our studies provide new insights into the role of the GSH antioxidant system in the intraerythrocytic development of Plasmodium parasites, with potential translation into novel pharmacological interventions.

Colponemids represent multiple ancient alveolate lineages

The alveolates comprise three well-studied protist lineages of significant environmental, medical, and economical importance: apicomplexans (e.g., Plasmodium), dinoflagellates (e.g., Symbiodinium), and ciliates (e.g., Tetrahymena). These major lineages have evolved distinct and unusual characteristics, the origins of which have proved to be difficult evolutionary puzzles. Mitochondrial genomes are a prime example: all three groups depart from canonical form and content, but in different ways. Reconstructing such ancient transitions is difficult without deep-branching lineages that retain ancestral characteristics. Here we describe two such lineages and how they illuminate the ancestral state of alveolate mitochondrial genomes. We established five clonal cultures of colponemids, predatory alveolates without cultured representatives and molecular data. Colponemids represent at least two independent lineages at the phylum level in multilocus phylogenetic analysis; one sister to apicomplexans and dinoflagellates, and the other at a deeper position. A genome survey from one strain showed that ancestral state of the mitochondrial genomes in the three major alveolate lineages consisted of an unusual linear chromosome with telomeres and a substantially larger gene set than known alveolates. Colponemid sequences also identified several environmental lineages as colponemids, altogether suggesting an untapped potential for understanding the origin and evolution of apicomplexans, dinoflagellates, and ciliates.

Critical roles of the mitochondrial complex II in oocyst formation of rodent malaria parasite Plasmodium berghei

It is generally accepted that the mitochondria play central roles in energy production of most eukaryotes. In contrast, it has been thought that Plasmodium spp., the causative agent of malaria, rely mainly on cytosolic glycolysis but not mitochondrial oxidative phosphorylation for energy production during blood stages. However, Plasmodium spp. possesses all genes necessary for the tricarboxylic acid (TCA) cycle and most of the genes for electron transport chain (ETC) enzymes. Therefore, it remains elusive whether oxidative phosphorylation is essential for the parasite survival. To elucidate the role of TCA metabolism and ETC in malaria parasites, we deleted the gene for flavoprotein (Fp) subunit, Pbsdha, one of four components of complex II, a catalytic subunit for succinate dehydrogenase activity. The Pbsdha(-) parasite grew normally at blood stages in mouse. In contrast, ookinete formation of Pbsdha(-) parasites in the mosquito stage was severely impaired. Finally, Pbsdha(-) ookinetes failed in oocyst formation, leading to complete malaria transmission blockade. These results suggest that malaria parasite may switch the energy metabolism from glycolysis to oxidative phosphorylation to adapt to the insect vector where glucose is not readily available for ATP production.

Red algal parasites: models for a life history evolution that leaves photosynthesis behind again and again

Many of the most virulent and problematic eukaryotic pathogens have evolved from photosynthetic ancestors, such as apicomplexans, which are responsible for a wide range of diseases including malaria and toxoplasmosis. The primary barrier to understanding the early stages of evolution of these parasites has been the difficulty in finding parasites with closely related free-living lineages with which to make comparisons. Parasites found throughout the florideophyte red algal lineage, however, provide a unique and powerful model to investigate the genetic origins of a parasitic lifestyle. This is because they share a recent common ancestor with an extant free-living red algal species and parasitism has independently arisen over 100 times within this group. Here, we synthesize the relevant hypotheses with respect to how these parasites have proliferated. We also place red algal research in the context of recent developments in understanding the genome evolution of other eukaryotic photosynthesizers turned parasites.

Arrested oocyst maturation in Plasmodium parasites lacking type II NADH:ubiquinone dehydrogenase

The Plasmodium mitochondrial electron transport chain has received considerable attention as a potential target for new antimalarial drugs. Atovaquone, a potent inhibitor of Plasmodium cytochrome bc(1), in combination with proguanil is recommended for chemoprophylaxis and treatment of malaria. The type II NADH:ubiquinone oxidoreductase (NDH2) is considered an attractive drug target, as its inhibition is thought to lead to the arrest of the mitochondrial electron transport chain and, as a consequence, pyrimidine biosynthesis, an essential pathway for the parasite. Using the rodent malaria parasite Plasmodium berghei as an in vivo infection model, we studied the role of NDH2 during Plasmodium life cycle progression. NDH2 can be deleted by targeted gene disruption and, thus, is dispensable for the pathogenic asexual blood stages, disproving the candidacy for an anti-malarial drug target. After transmission to the insect vector, NDH2-deficient ookinetes display an intact mitochondrial membrane potential. However, ndh2(-) parasites fail to develop into mature oocysts in the mosquito midgut. We propose that Plasmodium blood stage parasites rely on glycolysis as the main ATP generating process, whereas in the invertebrate vector, a glucose-deprived environment, the malaria parasite is dependent on an intact mitochondrial respiratory chain.

Extracellular Toxoplasma gondii tachyzoites do not require carbon source uptake for ATP maintenance, gliding motility and invasion in the first hour of their extracellular life

Apicomplexan parasites undergo metabolic shifts in adaptation to environmental changes. Here, we investigate the metabolic requirements which are responsible for ATP homeostasis in the extracellular stage of Toxoplasma gondii. Surprisingly, we found that freshly released tachyzoites are able to maintain a constant ATP level during the first hour of extracellular incubation without the acquisition of external carbon sources. We further demonstrated that the extent of gliding motility and that of host cell invasion is independent from the availability of external carbon sources during this one hour extracellular period. The ATP level and the invasion efficiency of extracellular parasites were severely decreased by treatment with the glycolysis inhibitor, 2-deoxy-d-glucose, but not by the F(0)F(1)-ATPase inhibitor, oligomycin. This suggests that although the uptake of glucose itself is not required during the 1h incubation period, extracellular parasites depend on the activity of the glycolytic pathway for ATP homeostasis. Furthermore, active glycolysis was evident by the secretion of lactate into the culture medium, even in the absence of external carbon sources. Together, our studies suggest that tachyzoites are independent from external carbon sources within the first hour of their extracellular life, which is the most relevant time span for finding a new host cell, but rely on the glycolytic metabolisation of internal carbon sources for ATP maintenance, gliding motility and host cell invasion.

Global response of Plasmodium falciparum to hyperoxia: a combined transcriptomic and proteomic approach

Background

Over its life cycle, the Plasmodium falciparum parasite is exposed to different environmental conditions, particularly to variations in O₂ pressure. For example, the parasite circulates in human venous blood at 5% O₂ pressure and in arterial blood, particularly in the lungs, at 13% O₂ pressure. Moreover, the parasite is exposed to 21% O₂ levels in the salivary glands of mosquitoes.

Methods

To study the metabolic adaptation of P. falciparum to different oxygen pressures during the intraerythrocytic cycle, a combined approach using transcriptomic and proteomic techniques was undertaken.

Results

Even though hyperoxia lengthens the parasitic cycle, significant transcriptional changes were detected in hyperoxic conditions in the late-ring stage. Using PS 6.0™ software (Ariadne Genomics) for microarray analysis, this study demonstrate up-expression of genes involved in antioxidant systems and down-expression of genes involved in the digestive vacuole metabolism and the glycolysis in favour of mitochondrial respiration. Proteomic analysis revealed increased levels of heat shock proteins, and decreased levels of glycolytic enzymes. Some of this regulation reflected post-transcriptional modifications during the hyperoxia response.

Conclusions

These results seem to indicate that hyperoxia activates antioxidant defence systems in parasites to preserve the integrity of its cellular structures. Moreover, environmental constraints seem to induce an energetic metabolism adaptation of P. falciparum. This study provides a better understanding of the adaptive capabilities of P. falciparum to environmental changes and may lead to the development of novel therapeutic targets.

Biochemical and biophysical characterization of succinate: quinone reductase from Thermus thermophilus

Enzymes serving as respiratory complex II belong to the succinate:quinone oxidoreductases superfamily that comprises succinate:quinone reductases (SQRs) and quinol:fumarate reductases. The SQR from the extreme thermophile Thermus thermophilus has been isolated, identified and purified to homogeneity. It consists of four polypeptides with apparent molecular masses of 64, 27, 14 and 15kDa, corresponding to SdhA (flavoprotein), SdhB (iron-sulfur protein), SdhC and SdhD (membrane anchor proteins), respectively. The existence of [2Fe-2S], [4Fe-4S] and [3Fe-4S] iron-sulfur clusters within the purified protein was confirmed by electron paramagnetic resonance spectroscopy which also revealed a previously unnoticed influence of the substrate on the signal corresponding to the [2Fe-2S] cluster. The enzyme contains two heme b cofactors of reduction midpoint potentials of -20mV and -160mV for b(H) and b(L), respectively. Circular dichroism and blue-native polyacrylamide gel electrophoresis revealed that the enzyme forms a trimer with a predominantly helical fold. The optimum temperature for succinate dehydrogenase activity is 70°C, which is in agreement with the optimum growth temperature of T. thermophilus. Inhibition studies confirmed sensitivity of the enzyme to the classical inhibitors of the active site, as there are sodium malonate, sodium diethyl oxaloacetate and 3-nitropropionic acid. Activity measurements in the presence of the semiquinone analog, nonyl-4-hydroxyquinoline-N-oxide (NQNO) showed that the membrane part of the enzyme is functionally connected to the active site. Steady-state kinetic measurements showed that the enzyme displays standard Michaelis-Menten kinetics at a low temperature (30°C) with a K(M) for succinate of 0.21mM but exhibits deviation from it at a higher temperature (70°C). This is the first example of complex II with such a kinetic behavior suggesting positive cooperativity with k' of 0.39mM and Hill coefficient of 2.105. While the crystal structures of several SQORs are already available, no crystal structure of type A SQOR has been elucidated to date. Here we present for the first time a detailed biophysical and biochemical study of type A SQOR-a significant step towards understanding its structure-function relationship.

Diversity in mitochondrial metabolic pathways in parasitic protists Plasmodium and Cryptosporidium

Apicomplexans are obligate intracellular parasites and occupy diverse niches. They have remodeled mitochondrial carbon and energy metabolism through reductive evolution. Plasmodium lacks mitochondrial pyruvate dehydrogenase and H(+)-translocating NADH dehydrogenase (Complex I, NDH1). The mitochondorion contains a minimal mtDNA ( approximately 6kb) and carries out oxidative phosphorylation in the insect vector stages, by using 2-oxoglutarate as an alternative means of entry into the TCA cycle and a single-subunit flavoprotein as an alternative NADH dehydrogenase (NDH2). In the blood stages of mammalian hosts, mitochondrial enzymes are down-regulated and parasite energy metabolism relies mainly on glycolysis. Mitosomes of Cryptosporidium parvum and Cryptosporidium hominis (human intestine parasites) lack mtDNA, pyruvate dehydrogenase, TCA cycle enzymes except malate-quinone oxidoreductase (MQO), and ATP synthase subunits except alpha and beta. In contrast, mitosomes of Cryptosporidium muris (a rodent gastric parasite) retain all TCA cycle enzymes and functional ATP synthase and carry out oxidative phosphorylation with pyruvate-NADP(+) oxidoreductase (PNO) and a simple and unique respiratory chain consisting of NDH2 and alternative oxidase (AOX). Cryptosporidium and Perkinsus are early branching groups of chromoalveolates (apicomplexa and dinoflagellates, respectively), and both Cryptosporidium mitosome and Perkinsus mitochondrion use PNO, MQO, and AOX. All apicomplexan parasites and dinoflagellates share MQO, which has been acquired from epsilon-proteobacteria via lateral gene transfer. By genome data mining on Plasmodium, Cryptosporidium and Perkinsus, here we summarized their mitochondrial metabolic pathways, which are varied largely from those of mammalian hosts. We hope that our findings will help in understanding the apicomplexan metabolism and development of new chemotherapeutics with novel targets.

Versatility in the acquisition of energy and carbon sources by the Apicomplexa

Members of the phylum Apicomplexa are motile and rapidly dividing intracellular parasites, able to occupy a large spectrum of niches by infecting diverse hosts and invading various cell types. As obligate intracellular parasites, most apicomplexans only survive for a short period extracellularly, and, during this time, have a high energy demand to power gliding motility and invasion into new host cells. Similarly, these fast-replicating intracellular parasites are critically dependent on host-cell nutrients as energy and carbon sources, noticeably for the extensive membrane biogenesis imposed during growth and division. To access host-cell metabolites, the apicomplexans Toxoplasma gondii and Plasmodium falciparum have evolved strategies that exquisitely reflect adaptation to their respective niches. In the present review, we summarize and compare some recent findings regarding the energetic metabolism and carbon sources used by these two genetically tractable apicomplexans during host-cell invasion and intracellular growth and replication.

Gramicidin S and polymyxins: the revival of cationic cyclic peptide antibiotics

Gramicidin S and polymyxins are small cationic cyclic peptides and act as potent antibiotics against Gram-negative and Gram-positive bacteria by perturbing integrity of the bacterial membranes. Screening of a natural antibiotics library with bacterial membrane vesicles identified gramicidin S as an inhibitor of cytochrome bd quinol oxidase and an alternative NADH dehydrogenase (NDH-2) and polymyxin B as an inhibitor of NDH-2 and malate: quinone oxidoreductase. Our studies showed that cationic cyclic peptide antibiotics have novel molecular targets in the membrane and interfere ligand binding on the hydrophobic surface of enzymes. Improvement of the toxicity and optimization of the structures and clinical uses are urgently needed for their effective application in combating drug-resistant bacteria.

Identification of mitochondrial Complex II subunits SDH3 and SDH4 and ATP synthase subunits a and b in Plasmodium spp

While most protist mitochondrial enzymes could be identified in database, the membrane anchor subunits of Complex II and F(o)F(1)-ATP synthase of malaria parasites are not annotated. Based on the presence of structural fingerprints or proteomics data from other protists, here we present their candidates. In contrast to canonical subunits, Plasmodium Complex II anchors have two transmembrane helices and may coordinate heme b via Tyr in place of His. Transmembrane helix IV of ATP synthase subunit a lacks an essential Arg residue. Membrane anchors of Plasmodium Complex II and ATP synthase are divergent from orthologs and promising targets for new chemotherapeutics.