Biochemistry of the Coccidia

Coombs, Graham H.; Denton, Helen; Brown, Samantha M.A.; Thong, Kam-Wah

doi:10.1016/s0065-308x(08)60046-9

Cited by 30 publications

(15 citation statements)

References 361 publications

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“…The protist E. gracilis has a unique mitochondrion because it functions as a facultatively anaerobic organelle that produces ATP in the presence or absence of oxygen (Buetow, 1989). Euglena could represent a good model for a relic respiratory activity intermediate between aerobic and anaerobic metabolism (Nakazawa et al 2000) which would fit with preliminary evidence for a similar system in C. parvum (Coombs et al 1997 ;Entrala & Mascaro, 1997 pyruvate metabolism to that in the mitochondrion, remains to be functionally characterized and localized in C. parvum. Pyridine nucleotide transhydrogenase (PNT) is a key enzyme for the proton pump of the inner membrane and is associated with the generation of an electron gradient, and in E. histolytica, is thought to be associated with the mitosome (Weston et al 2001) while in E. tenella it has been localized to the refractile body of the sporozoite (Vermeulen et al 1993).…”

Section: Discussionmentioning

confidence: 94%

Characterization of a mitochondrion-like organelle inCryptosporidium parvum

et al. 2004

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Cryptosporidium parvum is a protozoan parasite that causes widespread diarrhoeal disease in humans and other animals and is responsible for large waterborne outbreaks of cryptosporidiosis. Unlike many organisms belonging to the phylum Apicomplexa, such as Plasmodium spp. and Toxoplasma gondii, there is no clinically proven drug treatment against this parasite. Aspects of the basic biology of C. parvum remain poorly understood, including a detailed knowledge of key metabolic pathways, its genome organization and organellar complement. Previous studies have proposed that C. parvum lacks a relic plastid organelle, or 'apicoplast', but that it may possess a mitochondrion. Here we characterize a mitochondrion-like organelle in C. parvum by (i) ultrastructural and morphological description (ii) localization of heterologous mitochondrial chaperonin antibody probes (iii) phylogenetic analysis of genes encoding mitochondrial transport proteins (iv) identification and analysis of mitochondrion-associated gene sequences. Our descriptive morphological analysis was performed by energy-filtering transmission electron microscopy (EFTEM) of C. hominis and C. parvum. The 'mitochondrion-like' organelle was characterized by labelling the structure with a heterologous mitochondrial chaperonin probe (hsp60) both in immunoelectron microscopy (IMEM) and immunofluorescence (IMF). Phylogenetic analysis of the mitochondrial import system and housekeeping components (hsp60 and hsp70-dnaK) suggested that the C. parvum mitochondrion-like organelle is likely to have descended from a common ancestral apicomplexan mitochondrion. We also identified a partial cDNA sequence coding for an alternative oxidase (AOX) gene, a component of the electron transport chain which can act as an alternative to the terminal mitochondrial respiratory complexes III and IV, which has not yet been reported in any other member of this phylum. Degenerate primers developed to identify selected mitochondrial genes failed to identify either cytochrome oxidase subunit I, or cytochrome b. Taken together, our data aim to provide new insights into the characterization of this Cryptosporidium organelle and a logical framework for future functional investigation.

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Section: Discussionmentioning

confidence: 94%

Characterization of a mitochondrion-like organelle inCryptosporidium parvum

et al. 2004

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“…As the substrate PEP can be provided from gluconeogenesis pathway through mitochondrial PEP carboxykinase (NCBI ID BAC02911), this unusual "short cut" might contribute to the rapid switching from gluconeogenesis to the oxidative phosphorylation. However, the fate of the product pyruvate is currently unknown, as pyruvate dehydrogenase complex does not localize in the mitochondrion (59,64), whereas T. gondii tricarboxylic acid cycle is functional in the tachyzoite stage (71)(72)(73). The metabolic pathway connecting pyruvate with tricarboxylic acid cycle in the mitochondria in the apicomplexan parasites has been the unsolved question (34,59,63,64).…”

Section: Discussionmentioning

confidence: 99%

A Novel GDP-dependent Pyruvate Kinase Isozyme from Toxoplasma gondii Localizes to Both the Apicoplast and the Mitochondrion

Saito

Nishi

Lim

et al. 2008

Journal of Biological Chemistry

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We previously reported a cytosolic pyruvate kinase (EC 2.7.1.40) from Toxoplasma gondii (TgPyKI) that differs from most eukaryotic pyruvate kinases in being regulated by glucose 6-phosphate rather than fructose 1,6-diphosphate. Another putative pyruvate kinase (TgPyKII) was identified from parasite genome, which exhibits 32% amino acid sequence identity to TgPyKI and retains pyruvate kinase signature motifs and amino acids essential for substrate binding and catalysis. Whereas TgPyKI is most closely related to plant/algal enzymes, phylogenetic analysis suggests a proteobacterial origin for TgPyKII. Enzymatic characterization of recombinant TgPyKII shows a high pH optimum at 8.5, and a preference for GDP as a phosphate recipient. Catalytic activity is independent of K ؉ , and no allosteric or regulatory effects were observed in the presence of fructose 1,6-diphosphate, fructose 2,6-diphosphate, glucose 6-phosphate, ribose 5-phosphate, AMP, or ATP. Unlike TgPyKI, native TgPyKII activity was exclusively associated with the membranous fraction of a T. gondii tachyzoite lysate. TgPyKII possesses a long N-terminal extension containing five putative start codons before the conserved region and localizes to both apicoplast and mitochondrion by immunofluorescence assay using native antibody and fluorescent protein fusion to the N-terminal extension. Further deletional and site-directed mutagenesis suggests that a translation product from 1st Met is responsible for the localization to the apicoplast, whereas one from 3rd Met is for the mitochondrion. This is the first study of a potential mitochondrial pyruvate kinase in any system. Toxoplasma gondii is an obligate intracellular protozoan parasite of warm-blooded animals, including humans (1). Although normally asymptomatic, toxoplasmosis is a significant problem in pregnant women infected early during gestation, immunocompromised individuals, and livestock. This parasite is a member of the phylum Apicomplexa, which includes many other parasites such as Plasmodium species responsible for malaria. Glucose is thought to be the main source of energy for the rapidly multiplying forms of both Toxoplasma and Plasmodium, which use the Embden-Meyerhof pathway for glycolytic phosphorylation (2).Pyruvate kinase catalyzes the essentially irreversible transphosphorylation from phosphoenolpyruvate (PEP) 4 to ADP-producing pyruvate (3). In most mammals and bacteria, pyruvate kinase is allosterically regulated by fructose 1,6-diphosphate (4) and thus plays a regulatory role in glycolysis. The product pyruvate feeds into many metabolic pathways, placing pyruvate kinase at a crucial metabolic intersection. Many organisms express multiple pyruvate kinase isozymes with different kinetic properties. For example, Escherichia coli bears two isozymes, type I and II, both of which are homotropically activated by the substrate PEP. The type I isozyme is also activated heterotropically by fructose 1,6-diphosphate and is inhibited by ATP (5), whereas the type II isozyme is activated by AMP and mo...

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“…On the basis of data from the use of 4-hydroxyquinolones (10 -12), clopidol (10), and hydroxamic acids (11,12), it has been proposed that Toxoplasma (12), as well as the related apicomplexan parasites Eimeria tenella (10) and Plasmodium falciparum (11), contains a plant-like alternative oxidase (11,12). It has also been suggested that the plastid-like organelles that occur in apicomplexan parasites (13)(14)(15), which have received considerable attention recently (16,17), may contain components of a respiratory chain (18), which could contribute to the respiration of the cell (12). Although the importance of the respiratory chain in T. gondii is unknown, it is thought that it is the target of the anti-Toxoplasma activity of the naphthoquinone atovaquone (19,20), which is currently used against toxoplasmosis in AIDS patients (19).…”

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confidence: 99%

Respiration and Oxidative Phosphorylation in the Apicomplexan Parasite Toxoplasma gondii

Vercesi¹,

Rodrigues²,

Uyemura³

et al. 1998

Journal of Biological Chemistry

106

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Respiration, oxidative phosphorylation, and the mitochondrial membrane potential (⌬⌿) of tachyzoites of the apicomplexan parasite Toxoplasma gondii were assayed in situ using very low concentrations of digitonin to render their plasma membrane permeable to succinate, ADP, safranin O, and other small molecules. The rate of basal respiration was slightly increased by digitonin when the cells were incubated in medium containing succinate. ADP promoted an oligomycin-sensitive transition from resting to phosphorylating respiration. Respiration was sensitive to antimycin A and cyanide, and N,N,N,N-tetramethyl-p-phenylenediamine (TMPD) was oxidized by antimycin A-poisoned mitochondria. The addition of ADP after TMPD/ascorbate also resulted in phosphorylating respiration. The antitoxoplasmosis drug atovaquone, at a very low concentration (0.03 M), totally inhibited respiration and disrupted the mitochondrial membrane potential. Atovaquone was shown to inhibit the respiratory chain of T. gondii and mammalian mitochondria between cytochrome b and c 1 as occurs with antimycin A 1 . Phosphorylation of ADP could not be obtained in permeabilized tachyzoites in the presence of either pyruvate, 3-oxo-glutarate, glutamate, isocitrate, dihydroorotate, ␣-glycerophosphate, or endogenous substrates. Although ADP phosphorylation was detected in the presence of malate, this activity was rotenone-insensitive and was probably due to the conversion of malate into succinate through a fumarate reductase activity that was detected in mitochondrial extracts. Together these results provide the first direct biochemical evidence that the respiratory chain and oxidative phosphorylation are functional in apicomplexan parasites, although the terminal respiratory pathway is different from that in the mammalian host.

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Biochemistry of the Coccidia

Cited by 30 publications

References 361 publications

Characterization of a mitochondrion-like organelle inCryptosporidium parvum

Characterization of a mitochondrion-like organelle inCryptosporidium parvum

A Novel GDP-dependent Pyruvate Kinase Isozyme from Toxoplasma gondii Localizes to Both the Apicoplast and the Mitochondrion

Respiration and Oxidative Phosphorylation in the Apicomplexan Parasite Toxoplasma gondii

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