Purification of particulate malate dehydrogenase and phosphoenolpyruvate carboxykinase from Leishmania mexicana mexicana

Deciphering Host-Parasite Interplay in Leishmania Infection through a One Health View of Proteomics Studies on Drug Resistance

Recent efforts in the study of vector-borne parasitic diseases (VBPDs) have emphasized an increased consideration for preventing drug resistance and promoting the environmental safety of drugs, from the beginning of the drug discovery pipeline. The intensive use of the few available antileishmanial drugs has led to the spreading of hyper-resistant Leishmania infantum strains, resulting in a chronic burden of the disease. In the present work, we have investigated the biochemical mechanisms of resistance to antimonials, paromomycin, and miltefosine in three drug-resistant parasitic strains from human clinical isolates, using a whole-cell mass spectrometry proteomics approach. We identified 14 differentially expressed proteins that were validated with their transcripts. Next, we employed functional association networks to identify parasite-specific proteins as potential targets for novel drug discovery studies. We used SeqAPASS analysis to predict susceptibility based on the evolutionary conservation of protein drug targets across species. MATH-domain-containing protein, adenosine triphosphate (ATP)-binding cassette B2, histone H4, calpain-like cysteine peptidase, and trypanothione reductase emerged as top candidates. Overall, this work identifies new biological targets for designing drugs to prevent the development of Leishmania drug resistance, while aligning with One Health principles that emphasize the interconnected health of people, animals, and ecosystems.

Characterization of Differentially Abundant Proteins Among Leishmania (Viannia) braziliensis Strains Isolated From Atypical or Typical Lesions

Leishmania (Viannia) braziliensis is the main etiological agent of cutaneous and mucocutaneous leishmaniasis in Latin America. Non-ulcerated atypical tegumentary leishmaniasis cases caused by L. braziliensis have been reported in several regions of the American continent, including the Xacriabá indigenous reserve in São João das Missões/Minas Gerais, Brazil. Parasites isolated from these atypical clinical lesions are resistant to antimony-based therapeutics. In the present study, proteins displaying differential abundance in two strains of L. braziliensis isolated from patients with atypical lesions compared with four strains isolated from patients with typical lesions were identified using a quantitative proteomics approach based on tandem mass tag labeling (TMT) and mass spectrometry. A total of 532 (P<0.05) differentially abundant proteins were identified (298 upregulated and 234 downregulated) in strains from atypical lesions compared to strains from typical lesions. Prominent positively regulated proteins in atypical strains included those that may confer greater survival inside macrophages, proteins related to antimony resistance, and proteins associated with higher peroxidase activity. Additionally, we identified proteins showing potential as new drug and vaccine targets. Our findings contribute to the characterization of these intriguing L. braziliensis strains and provide a novel perspective on Atypical Cutaneous Leishmaniasis (ACL) cases that have been associated with therapeutic failures.

Interaction of frataxin, an iron binding protein, with IscU of Fe-S clusters biogenesis pathway and its upregulation in AmpB resistant Leishmania donovani

Leishmania donovani is a unicellular protozoon parasite that causes visceral leishmaniasis (VL), which is a fatal disease if left untreated. Certain Fe-S proteins of the TCA cycle and respiratory chain have been found in the Leishmania parasite but the precise mechanisms for their biogenesis and the maturation of Fe-S clusters remains unknown. Fe-S clusters are ubiquitous cofactors of proteins that perform critical cellular functions. The clusters are biosynthesized by the mitochondrial Iron-Sulphur Cluster (ISC) machinery with core protein components that include the catalytic cysteine desulphurase IscS, the scaffold proteins IscU and IscA, and frataxin as an iron carrier/donor. However, no information regarding frataxin, its regulation, or its role in drug resistance is available for the Leishmania parasite. In this study, we characterized Ld-frataxin to investigate its role in the ISC machinery of L. donovani. We expressed and purified the recombinant Ld-frataxin protein and observed its interaction with Ld-IscU by co-purification and pull-down assay. Furthermore, we observed that the cysteine desulphurase activity of the purified Ld-IscS protein was stimulated in the presence of Ld-frataxin and Ld-IscU, particularly in the presence of iron; neither Ld-frataxin nor Ld-IscU alone had significant effects on Ld-IscS activity. Interestingly, RT-PCR and western blotting showed that Ld-frataxin is upregulated in AmpB-resistant isolates compared to sensitive strains, which may support higher Fe-S protein activity in AmpB-resistant L. donovani. Additionally, Ld-frataxin was localized in the mitochondria, as revealed by digitonin fractionation and indirect immunofluorescence. Thus, our results suggest the role of Ld-frataxin as an iron binding/carrier protein for Fe-S cluster biogenesis that physically interacts with other core components of the ISC machinery within the mitochondria.

Functional characterization and subcellular localization of the three malate dehydrogenase isozymes in Leishmania spp

As part of a study on the malate dehydrogenase isozymes (MDHs) from Trypanosomatids, three different fractions with MDH activity were obtained from crude extracts of Leishmania mexicana promastigotes combining two different chromatographic steps. Gel filtration chromatography in native conditions showed that most of the MDH activity present in the crude extracts eluted in a single peak, which corresponded to a lower apparent molecular mass ( congruent with 57kDa) than the value expected for typical MDHs. To further characterize the leishmanial isozymes, three putative MDH genes, presumably corresponding to the mitochondrial, glycosomal and cytosolic isoforms were amplified by PCR, cloned into bacterial expression vectors, and the recombinant enzymes purified. Digitonin extraction of intact L. mexicana promastigotes and immunofluorescence microscopy of L. major promastigotes confirmed the subcellular compartmentation of each of the three isozymes. Western blot analysis showed that the three MDHs are developmentally regulated. At the protein level, these isozymes are remarkably more abundant in amastigotes than in promastigotes of L. mexicana. Altogether our results demonstrate the presence of three MDH isoforms with slightly distinct biochemical properties and different subcellular localization in Leishmania spp. Presumably the functional and biochemical features of these isozymes reflect the metabolic adaptation to the different nutrient sources these parasites have to face along their life cycle. These results also emphasize the differences among Trypanosomatids in this area of metabolism, since in the case of Trypanosoma brucei the cMDH is the only isoform expressed in bloodstream trypomastigotes, whereas in Trypanosoma cruzi cMDH is absent.

The mitochondrial FAD-dependent glycerol-3-phosphate dehydrogenase of Trypanosomatidae and the glycosomal redox balance of insect stages of Trypanosoma brucei and Leishmania spp

The genes for the mitochondrial FAD-dependent glycerol-3-phosphate dehydrogenase were identified in Trypanosoma brucei and Leishmania major genomes. We have expressed the L. major gene in Saccharomyces cerevisiae and confirmed the subcellular localization and activity of the produced enzyme. Using cultured T. brucei procyclic and Leishmania mexicana promastigote cells with a permeabilized plasma membrane and containing intact glycosomes, it was shown that dihydroxyacetone phosphate is converted into pyruvate, and stimulates oxygen consumption, indicating that all components of the glycerol 3-phosphate/dihydoxyacetone phosphate shuttle between glycosomes and mitochondrion are present in these insect stages of both organisms. A computer model has been prepared for the energy and carbohydrate metabolism of these cells. It was used in an elementary mode analysis to get insight into the metabolic role of the shuttle in these insect-stage parasites. Our analysis suggests that the shuttle fulfils important roles for these organisms, albeit different from its well-known function in the T. brucei bloodstream form. It allows (1) a high yield of further metabolizable glycolytic products by decreasing the need to produce a secreted end product of glycosomal metabolism, succinate; (2) the consumption of glycerol and glycerol 3-phosphate derived from lipids; and (3) to keep the redox balance of the glycosome finely tuned due to a highly flexible and redundant system.

Metabolic changes in glucose transporter-deficient Leishmania mexicana and parasite virulence

Leishmania mexicana are parasitic protozoa that express a variety of glycoconjugates that play important roles in their biology as well as the storage carbohydrate beta-mannan, which is an essential virulence factor for survival of intracellular amastigote forms in the mammalian host. Glucose transporter null mutants, which are viable as insect form promastigotes but not as amastigotes, do not take up glucose and other hexoses but are still able to synthesize these glycoconjugates and beta-mannan, although at reduced levels. Synthesis of these carbohydrate-containing macromolecules could be accounted for by incorporation of non-carbohydrate precursors into carbohydrates by gluconeogenesis. However, the significantly reduced level of the virulence factor beta-mannan in the glucose transporter null mutants compared with wild-type parasites may contribute to the non-viability of these null mutants in the disease-causing amastigote stage of the life cycle.

Protein kinases as targets for anti-parasitic chemotherapy

Parasitic protozoa infecting humans have a staggering impact on public health, especially in the developing world. Furthermore, several protozoan species are major pathogens of domestic animals and have a considerable impact on food production. In many instances, the parasites have developed resistance against available chemotherapeutic agents, making the search for alternative drugs a priority. In line with the current interest in protein kinases inhibitors as potential drugs against a variety of diseases, the possibility that protein kinases may represent targets for novel anti-parasitic agents is being explored. Research into parasite protein kinases has benefited greatly from genome and EST sequencing projects, with the genomes of a few species fully sequenced (notably that of the human malaria parasite Plasmodium falciparum) and several more under way. The overall picture that emerged from research in this area shows that the phylogenetic isolation of parasitic protozoa is reflected by atypical structural and functional properties of many of their protein kinase homologues. Likewise, evidence is emerging, which suggests that the organisation of some otherwise well-conserved signal transduction pathways is divergent in some parasitic species. The differences between protein kinases of a parasite and their homologues in its host cell suggest that specific inhibition of the former can be achieved. The development of anti-parasitic drugs based on protein kinase inhibition is being pursued following two avenues: one consists of screening chemical libraries on recombinant enzymes; several protein kinases from parasitic protozoa are now available for this approach. The second approach relies on the identification of the molecular targets of kinase inhibitors which display anti-parasitic properties. This has led to promising developments in a few instances, in particular regarding PKG as a drug target against Eimeria and Toxoplasma, and purvalanol B, a purine-based CDK inhibitor which appears to affect unexpected targets in several protozoan parasites. The recent resolution of the structure of a Plasmodium protein kinase complexed with small inhibitory molecules opens the way to a rational approach towards the design of anti-parasitic drugs based on kinase inhibition.

Intracellular Targets of Paullones. Identification following affinity purification on immobilized inhibitor

Numerous inhibitors of cyclin-dependent kinases and glycogen synthase kinase-3 (GSK-3) are being developed in view of their potential applications against cancers and neurodegenerative disorders. Among these, paullones constitute a family of potent and apparently selective cyclin-dependent kinase and GSK-3 inhibitors. However, their actual intracellular targets remain to be identified. To address this issue we have immobilized a paullone, gwennpaullone, on an agarose matrix. Extracts from various cell types and tissues were screened for proteins interacting with this matrix. This approach validated GSK-3alpha and GSK-3beta as major intracellular paullone targets and also mitochondrial, but not cytoplasmic, malate dehydrogenase (MDH). Mitochondrial MDH was indeed inhibited by micromolar concentrations of paullones. Mitochondrial MDH was the major paullone-binding protein in the parasitic protozoon Leishmania mexicana, and paullones inhibited growth of the parasite. This simple batchwise affinity chromatography approach constitutes a straightforward method for the identification of intracellular targets of this particular class of novel anti-mitotic compounds. It has revealed an unexpected target, mitochondrial MDH, the inhibition of which may participate in the pharmacological effects of paullones.

Identification and characterization of T cell-stimulating antigens from Leishmania by CD4 T cell expression cloning

Persistent immunity against Leishmania: infections in humans is mediated predominantly by CD4(+) T cells of the Th1 phenotype. Herein we report the expression cloning of eight Leishmania: Ags using parasite-specific T cell lines derived from an immune donor. The Ags identified by this technique include the flagellar proteins alpha- and beta-tubulin, histone H2b, ribosomal protein S4, malate dehydrogenase, and elongation factor 2, as well as two novel parasite proteins. None of these proteins have been previously reported as T cell-stimulating Ags from Leishmania: beta-tubulin-specific T cell clones generated against Leishmania: major amastigotes responded to Leishmania:-infected macrophages and dendritic cells. IFN-gamma enzyme-linked immunospot analysis demonstrated the presence of T cells specific for several of these Ags in PBMC from self-healing cutaneous leishmaniasis patients infected with either Leishmania: tropica or L. major. The responses elicited by Leishmania: histone H2b were particularly striking in terms of frequency of histone-specific T cells in PBMC (1 T cell of 6000 PBMC) as well as the percentage of responding donors (86%, 6 of 7). Ags identified by T cells from immune donors might constitute potential vaccine candidates for leishmaniasis.

Phosphoenolpyruvate carboxykinase from Trypanosoma cruzi. Purification and physicochemical and kinetic properties

Phospho enolpyruvate carboxykinase (PEPCK) has been purified to homogeneity from epimastigotes of the Tul 0 strain of Trypanosoma cruzi. The physicochemical parameters determined allowed the calculation of an average molecular mass of 120 kDa; the subunit molecular mass, about 61 kDa, is in good agreement with the value of 58.6 kDa recently determined from the sequence by Sommer et al. (FEBS Lett. 359 (1994) 125-129). The PEPCK from T. cruzi presented, in addition to its molecular mass, typical properties of other ATP-linked PEPCKs, namely strict specificity for ADP in the carboxylation reaction and lower specificity in the decarboxylation and exchange reactions, and synergistic activation by CdCl2 or MgCl2 when added in addition to MnCl2. The enzyme presented hysteretic behaviour, shown by a lag period in the carboxylation reaction, which was affected by dilution and preincubation. The decarboxylation reaction catalyzed by the T. cruzi PEPCK was not inhibited by excess of ATP-Mn. The apparent Km values for the carboxylation reaction, including the low value for PEP (0.035 mM) are compatible with an important role of PEPCK, as suggested by previous NMR experiments, on the CO2 fixation in vivo which leads to succinate excretion during aerobic fermentation of glucose.

Purification and characterization of phospho enol pyruvate carboxykinase from Trypanosoma brucei

ATP-dependent phospho enol pyruvate carboxykinase (EC 4.1.1.49; PEPCK, ATP) was purified from glycosomes of cultured procyclic Trypanosoma brucei to electrophoretic homogeneity. The purified enzyme exhibited a mean specific activity of 83 units mg-1, as measured in the carboxylation direction at 30 degrees C. A similar activity was obtained for the decarboxylation reaction. The enzyme was shown to be a homodimer in solution with a subunit molecular mass of 59 kDa. Amino acid sequence analysis suggested that the PEPCK (ATP) is identical to the trypanosomal protein p60, the sequence of which was previously predicted from the corresponding nucleotide sequence by other investigators. The basic nature of the enzyme was indicated by a high isoelectric point (pH 8.9). The enzyme was found to be strictly dependent on adenosine nucleotides for activity, as well as on the presence of Mn2+. Mg2+ was found to be ineffective as activator of the trypanosomal enzyme, but a combination of subsaturating (< or = 300 microM) concentrations of Mn2+ and high concentrations of Mg2+ caused a synergistic effect on the carboxylation activity, indicating a dual cation requirement. Mn2+ is necessary to activate the enzyme and Mn2+ or Mg2+ most likely forms the cation-nucleotide complex as the active form of the substrate. Relatively high (5 mM) levels of ATP were required to produce a significant inhibition of the carboxylation reaction. Quinolinic acid, a structural analogue of oxaloacetate, completely inhibited the decarboxylation reaction at a 1 mM concentration. The apparent Michaelis constants of the enzyme were 490 microM for PEP, 37 microM for oxaloacetate, 40 microM for ADP, 10.3 microM for ATP, 970 microM for Mn2+ and 26 mM for HCO3-. Endogenous substrate concentrations were found to be 327 nmol PEP, 1486 nmol ADP, 4200 nmol ATP and 11.5 nmol Mn2+ (ml cell volume)-1. Our kinetic data suggest that under physiological conditions PEPCK (ATP) in T. brucei is bidirectional and that its activity is regulated primarily by mass action. The physiological relevance of the enzyme in procyclic T. brucei is discussed.

Developmental life cycle of Leishmania--cultivation and characterization of cultured extracellular amastigotes

The biochemistry and immunology of Leishmania promastigotes has been extensively studied; this is due primarily to the facility with which this stage, in contrast to the amastigotes stage, can be maintained in axenic culture. Several attempts to axenically culture lines of Leishmania amastigotes have been reported in the literature. This paper summarizes methods of adaptation (low pH, elevated temperature and culture medium) and characterization of several axenic lines of Leishmania amastigotes. Based on morphological, biological, immunological and biochemical evidence, these organisms appear to resemble amastigotes from infected macrophages or tissue. The axenically cultured amastigotes appear to be distinct from shocked (heat, serum deprivation, stressed) Leishmania promastigotes in the plethora of proteins synthesized, growth (multiplication) in culture, and developmental regulation observed. These data suggest that Leishmania organisms have a significant developmental response to certain signals (pH, temperature) mimicking their in vivo macrophage milieu. The response to other environmental parameters characteristic of the host-macrophage remain to be determined. These axenically cultured amastigotes should be of interest for further immunological, biochemical and developmental investigations of the disease-maintaining stage of this parasite.

A carbon-13 nuclear magnetic resonance analysis of the products of glucose metabolism in Leishmania pifanoi amastigotes and promastigotes

The major products of glucose metabolism were determined for amastigotes and promastigotes of Leishmania (mexicana) pifanoi under aerobic and anaerobic conditions using carbon-13 nuclear magnetic resonance. Under aerobic conditions, the major products for both forms were carbon dioxide, succinate, malate, acetate and alanine. Succinate was the dominant metabolite of promastigotes, whereas acetate and alanine were most abundant with amastigotes. Under anaerobic conditions, promastigotes produced glycerol as the dominant metabolite, along with lesser amounts of succinate, acetate and alanine; acetate and alanine remained major metabolites in amastigotes, with an increase in the relative amount of succinate and the production of some glycerol. Promastigotes generated carbon dioxide at a 5-fold greater rate than amastigotes under aerobic conditions, but this rate was reduced by more than 95% in the absence of oxygen. Amastigotes were relatively less affected by lack of oxygen and produced carbon dioxide at a rate comparable to promastigotes under anaerobic conditions. The presence of carbohydrates with a possible role in storage was detected in both promastigotes and amastigotes.

Trypanosoma brucei: two-dimensional gel analysis of the major glycosomal proteins during the life cycle

Kinetoplastid organisms possess a unique organelle, the glycosome, which compartmentalizes the Embden-Meyerhof segment of glycolysis and several other metabolic pathways. In Trypanosoma brucei many of the enzyme activities localized to the glycosome are stage regulated. Two-dimensional gel analysis was used to examine the characteristics, expression, and biosynthesis of the major glycosomal proteins. Two-dimensional gel maps of glycosomes from slender bloodforms and late intermediate-stumpy bloodforms (the precursors of procyclic forms) were indistinguishable, while those of procyclic form glycosomes showed extensive differences. Glycosomal phosphoenolpyruvate carboxykinase and malate dehydrogenase were identified to have subunit molecular weights of 60 and 34 kDa, respectively. We detected two hitherto undescribed glycosomal proteins, one of which is found only in bloodforms. All of the major proteins, except glucose phosphate isomerase, were highly basic. Stage regulation of glycosomal enzyme activities correlated with stage regulation of specific protein biosynthesis.

The phosphoenolpyruvate carboxykinase of Trypanosoma (Schizotrypanum) cruzi epimastigotes: molecular, kinetic, and regulatory properties

The phosphoenolpyruvate carboxykinase (ATP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.49) of the epimastigote form of Trypanosoma (Schizotrypanum) cruzi has been purified to homogeneity. The enzyme is composed of two apparently identical 42,000 +/- 500 subunits, is highly specific for adenine nucleotides, and has a strict requirement of Mn2+ ions for activity; the activation of the enzyme by ionic Mn2+ reveals that one Mn2+ ion required for each 42,000 subunit. Hyperbolic kinetics are observed for all substrates in the carboxylation reaction with Km (phosphoenolpyruvate) of 0.36 +/- 0.08 mM, Km (HCO-3) of 3.7 +/- 0.2 mM, and Km (Mg-ADP) of 39 +/- 1 microM. In the decarboxylation reaction the kinetics with respect to oxalacetic acid are also hyperbolic with a Km of 27 +/- 3 microM, but towards Mg-ATP there is a biphasic response: hyperbolic at low (less than 250 microM) concentrations with a Km of 39 +/- 1 microM, but at higher concentrations the nucleotide produces a strong inhibition of the enzyme activity. This inhibition is also observed with Mg-GTP and Mg-ITP which are not substrates of the reaction. The results are consistent with an important regulatory function of the enzyme in the amino-acid catabolism of T. cruzi.

The phosphofructokinase of Trypanosoma (Schizotrypanum) cruzi: purification and kinetic mechanism

The phosphofructokinase (ATP:D-fructose-6-phosphate 1-phosphotransferase, E.C.2.7.1.11) of Trypanosoma (Schizotrypanum) cruzi epimastigotes has been purified 180-fold, to apparent electrophoretic homogeneity, by differential centrifugation, gel filtration chromatography and anionic exchange chromatography. The minimum catalytic unit of the purified enzyme is a polypeptide of 17,000 +/- 1300 molecular weight, as shown by gel filtration chromatography and SDS-gel electrophoresis. Hanes-Woolf plots of initial rates and Mg-ATP or D-fructose-6-phosphate concentrations for varying values of the co-substrate concentration gave intersecting lines which indicate a sequential mechanism. No inhibition is observed at high Mg-ATP concentrations, confirming the result of a previous study using a partially purified enzyme. The pure enzyme displays both negative and positive cooperative kinetics at low (less than 0.8 mM) concentrations of D-fructose-6-phosphate, suggesting aggregation and/or activation phenomena induced by this substrate. Product inhibition studies at saturating and non-saturating concentrations of D-fructose-6-phosphate gave as the only compatible mechanism an iso-ordered bi-bi process with a probable order of entry to and exit from the active site being: D-fructose-6-phosphate followed by Mg-ATP and D-fructose-1,6-bisphosphate followed by Mg-ADP, respectively. The very important differences in both the structural and mechanistic aspects between this enzyme and its vertebrate and bacterial counterparts supports the notion of a highly unusual carbohydrate catabolism in this parasite.

Electrophoretic analysis of the polypeptides of Leishmania amastigotes and promastigotes

The polypeptides of Leishmania mexicana mexicana (M379), L. m. amazonensis (LV78), L. major (LV39) and L. d. donovani (LV39) amastigotes and cultured promastigotes have been analysed by SDS-polyacrylamide gel electrophoresis. The polypeptide banding patterns of the promastigotes of the four species were quite similar, but distinct differences were detected between those of amastigotes. The results suggest that the various species of Leishmania are adapted differently for survival and growth in the mammalian host. The polypeptides of L. m. mexicana amastigotes were very rapidly hydrolysed unless protected by the cysteine proteinase inhibitor leupeptin.