Purification and characterization of hexokinase from Leishmania mexicana

Galactokinase-like protein from Leishmania donovani: Biochemical and structural characterization of a recombinant protein

Leishmaniasis is a spectrum of conditions caused by infection with the protozoan Leishmania spp. parasites. Leishmaniasis is endemic in 98 countries around the world, and resistance to current anti-leishmanial drugs is rising. Our work has identified and characterised a previously unstudied galactokinase-like protein (GalK) in Leishmania donovani, which catalyses the MgATP-dependent phosphorylation of the C-1 hydroxyl group of d-galactose to galactose-1-phosphate. Here, we report the production of the catalytically active recombinant protein in E. coli, determination of its substrate specificity and kinetic constants, as well as analysis of its molecular envelope using in solution X-ray scattering. Our results reveal kinetic parameters in range with other galactokinases with an average apparent Km value of 76 μM for galactose, Vmax and apparent Kcat values with 4.46376 × 10-9 M/s and 0.021 s-1, respectively. Substantial substrate promiscuity was observed, with galactose being the preferred substrate, followed by mannose, fructose and GalNAc. LdGalK has a highly flexible protein structure suggestive of multiple conformational states in solution, which may be the key to its substrate promiscuity. Our data presents novel insights into the galactose salvaging pathway in Leishmania and positions this protein as a potential target for the development of pharmaceuticals seeking to interfere with parasite substrate metabolism.

Discovery and biochemical characterization of two hexokinases from Crassostrea gigas

Hexokinases (HKs) play a vital role in glucose metabolism, which controls the first committed step catalyzing the production of glucose-6-phosphate from glucose. Two HKs (CGIHK1 and CGIHK2) from the Pacific oyster Crassostrea giga were cloned and characterized. CGIHK1 and CGIHK2 were recombinantly expressed in Escherichia coli and successfully purified by the Ni-NTA column. The optimum pH of the two enzymes was pH 8.0 and 8.5, respectively. The optimum temperature of the two enzymes was 42 °C and 50 °C, respectively. Both enzymes showed a clear requirement for divalent magnesium and were strongly inhibited by SDS. CGIHK1 exhibited highly strict substrate specificity to glucose, while CGIHK2 could also catalyze other 11 monosaccharide substrates. This is the first report on the in vitro biosynthesis of glucose-6-phosphate by the hexokinases from Crassostrea gigas. The facile expression and purification procedures combined with different substrate specificities make CGIHK1 and CGIHK2 candidates for the biosynthesis of glucose-6-phosphate and other sugar-phosphates.

Molecular characterization of hexokinase (HK) in Haemaphysalis longicornis and evaluation of HK protein- and DNA-based vaccines against adult ticks

BACKGROUND

Haemaphysalis longicornis is an obligate hematophagous ectoparasite, which transmits various pathogens to humans, livestock and wild animals. Hexokinase (HK) is a key regulatory enzyme of the glycolytic pathway in the organisms. However, little is known about hexokinase and its functions in ticks.

RESULTS

The open reading frame of the H. longicornis HK (HlHK) gene was 1425 bp and encoded a protein of 474 amino acids, containing conserved domains for glucose, glucose 6-phosphate, and adenosine triphosphate. The expression of HlHK gene was detected at different developmental stages and in different tissues of unfed female ticks. Enzyme-linked immunosorbent assay revealed that both HK protein- and DNA-based vaccines increased the antibody levels of the immunized animals. A vaccination trail on rabbits against H. longicornis infestation indicated that the rHlHK protein and HlHK DNA vaccines reduced the number of attached female ticks by 9% and 12%, egg mass weight by 36% and 34%, and egg hatching rate by 41% and 17%, respectively. Overall, protein vaccination conferred 65.6% protection against adult female ticks, whereas the DNA vaccine conferred 51.8% protection.

CONCLUSION

This is the first report of the molecular characterization of the HK protein and sequencing of the HK gene from H. longicornis. Positive results from vaccination trials on rabbits of the recombinant HK protein and HK DNA suggest that these novel anti-tick vaccines potentially can be used as viable tick control tools for the management of the Asian longhorned tick. Additionally, inhibition of glucose metabolism may be a new strategy for tick control. © 2023 Society of Chemical Industry.

Carbohydrate metabolism in trypanosomatids: New insights revealing novel complexity, diversity and species-unique features

The human pathogenic trypanosomatid species collectively called the "TriTryp parasites" - Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. - have complex life cycles, with each of these parasitic protists residing in a different niche during their successive developmental stages where they encounter diverse nutrients. Consequently, they adapt their metabolic network accordingly. Yet, throughout the life cycles, carbohydrate metabolism - involving the glycolytic, gluconeogenic and pentose-phosphate pathways - always plays a central role in the biology of these parasites, whether the available carbon and free energy sources are saccharides, amino acids or lipids. In this paper, we provide an updated review of the carbohydrate metabolism of the TriTryps, highlighting new data about this metabolic network, the interconnection of its pathways and the compartmentalisation of its enzymes within glycosomes, cytosol and mitochondrion. Differences in the expression of the branches of the metabolic network between the successive life-cycle stages of each of these parasitic trypanosomatids are discussed, as well as differences between them. Recent structural and kinetic studies have revealed unique regulatory mechanisms for some of the network's key enzymes with important species-specific variations. Furthermore, reports of multiple post-translational modifications of trypanosomal glycolytic enzymes suggest that additional mechanisms for stage- and/or environmental cues that regulate activity are operational in the parasites. The detailed comparison of the carbohydrate metabolism of the TriTryps has thus revealed multiple differences and a greater complexity, including for the reduced metabolic network in bloodstream-form T. brucei, than previously appreciated. Although these parasites are related, share many cytological and metabolic features and are grouped within a single taxonomic family, the differences highlighted in this review reflect their separate evolutionary tracks from a common ancestor to the extant organisms. These differences are indicative of their adaptation to the different insect vectors and niches occupied in their mammalian hosts.

Glycosome heterogeneity in kinetoplastids

Kinetoplastid parasites have essential organelles called glycosomes that are analogous to peroxisomes present in other eukaryotes. While many of the processes that regulate glycosomes are conserved, there are several unique aspects of their biology that are divergent from other systems and may be leveraged as therapeutic targets for the treatment of kinetoplastid diseases. Glycosomes are heterogeneous organelles that likely exist as sub-populations with different protein composition and function in a given cell, between individual cells, and between species. However, the limitations posed by the small size of these organelles makes the study of this heterogeneity difficult. Recent advances in the analysis of small vesicles by flow-cytometry provide an opportunity to overcome these limitations. In this review, we describe studies that document the diverse nature of glycosomes and propose an approach to using flow cytometry and organelle sorting to study the diverse composition and function of these organelles. Because the cellular machinery that regulates glycosome protein import and biogenesis is likely to contribute, at least in part, to glycosome heterogeneity we highlight some ways in which the glycosome protein import machinery differs from that of peroxisomes in other eukaryotes.

Molecular characterization and serodiagnostic potential of Echinococcus granulosus hexokinase

Background

Cystic echinococcosis (CE), caused by the larval stage of Echinococcus granulosus (sensu stricto), is a life-threatening but neglected zoonosis. Glycolytic enzymes are crucial molecules for the survival and development of E. granulosus. The aim of this study was to investigate the molecular characterization, immunogenicity, tissue distribution and serodiagnostic potential of E. granulosus hexokinase (EgHK), the first key enzyme in the glycolytic pathway.

Methods

EgHK was cloned and expressed in Escherichia coli. Specific serum antibodies were evaluated in mice immunized with recombinant EgHK (rEgHK). The location of EgHK in the larval stage of E. granulosus was determined using fluorescence immunohistochemistry, and the potential of rEgHK as a diagnostic antigen was investigated in patients with CE using indirect enzyme-linked immunosorbent assay (ELISA).

Results

Recombinant EgHK could be identified in the sera of patients with CE and in mouse anti-rEgHK sera. High titers of specific immunoglobulin G were induced in mice after immunization with rEgHK. EgHK was mainly located in the tegument, suckers and hooklets of protoscoleces and in the germinal layer and laminated layer of the cyst wall. The sensitivity and specificity of the rEgHK-ELISA reached 91.3% (42/46) and 87.8% (43/49), respectively.

Conclusions

We have characterized the sequence, structure and location of EgHK and investigated the immunoreactivity, immunogenicity and serodiagnostic potential of rEgHK. Our results suggest that EgHK may be a promising candidate for the development of vaccines against E. granulosus and an effective antigen for the diagnosis of human CE.

Kinetic and oligomeric study of Leishmania braziliensis nicotinate/nicotinamide mononucleotide adenylyltransferase

Nicotinamide adenine dinucleotide (NAD) is an essential coenzyme involved in REDOX reactions and oxidative stress defense systems. Furthermore, NAD is used as substrate by proteins that regulate essential cellular functions as DNA repair, genetic, and signal transduction, among many others. NAD biosynthesis can be completed through the de novo and salvage pathways, which converge at the common step catalyzed by the nicotinate/nicotinamide mononucleotide adenylyltransferase (NMNAT EC: 2.7.7.1/18). Here, we report the kinetic characterization of the NMNAT of Leishmania braziliensis (LbNMNAT), one of the etiological agents of leishmaniasis, a relevant parasitic disease. The expression and homogeneous purification of the recombinant 6xHis-LbNMNAT protein was carried out and its kinetic study, which included analysis of K m , V max , K cat and the equilibrium constant (K D ) for both the forward and reverse reactions, was completed. The oligomeric state of the recombinant 6xHis-LbNMNAT protein was studied through size exclusion chromatography. Our results indicated the highest and lowest K m values for ATP and NAD, respectively. According to the calculated K D , the pyrophosphorolytic cleavage of NAD is favored in vitro. Moreover, the recombinant 6xHis-LbNMNAT protein showed a monomeric state, although it exhibits a structural element involved in potential subunits interaction. Altogether, our results denote notable differences of the LbNMNAT protein in relation to the human orthologs HsNMNAT1-3. These differences constitute initial findings that have to be continued to finally propose the NMNAT as a promissory pharmacological target in L. braziliensis.

Structure, Properties, and Function of Glycosomes in Trypanosoma cruzi

Glycosomes are peroxisome-related organelles that have been identified in kinetoplastids and diplonemids. The hallmark of glycosomes is their harboring of the majority of the glycolytic enzymes. Our biochemical studies and proteome analysis of Trypanosoma cruzi glycosomes have located, in addition to enzymes of the glycolytic pathway, enzymes of several other metabolic processes in the organelles. These analyses revealed many aspects in common with glycosomes from other trypanosomatids as well as features that seem specific for T. cruzi. Their enzyme content indicates that T. cruzi glycosomes are multifunctional organelles, involved in both several catabolic processes such as glycolysis and anabolic ones. Specifically discussed in this minireview are the cross-talk between glycosomal metabolism and metabolic processes occurring in other cell compartments, and the importance of metabolite translocation systems in the glycosomal membrane to enable the coordination between the spatially separated processes. Possible mechanisms for metabolite translocation across the membrane are suggested by proteins identified in the organelle's membrane-homologs of the ABC and MCF transporter families-and the presence of channels as inferred previously from the detection of channel-forming proteins in glycosomal membrane preparations from the related parasite T. brucei. Together, these data provide insight in the way in which different parts of T. cruzi metabolism, although uniquely distributed over different compartments, are integrated and regulated. Moreover, this information reveals opportunities for the development of drugs against Chagas disease caused by these parasites and for which currently no adequate treatment is available.

Isolation of Glycosomes from Trypanosoma cruzi

Glycosomes are peroxisome-related organelles of trypanosomatids in which the glycolytic and some other metabolic pathways are compartmentalized. We describe here two methods for the purification of glycosomes from Trypanosoma cruzi for preparative purposes, differential and isopycnic centrifugation. These are two techniques that allow the separation of different cellular compartments based on their different physicochemical characteristics. The first type of centrifugation is a rapid method that does not require large inputs and allows for fractions enriched in specific cell compartments to be obtained. The second type of centrifugation is a more elaborate method, but enables highly purified cellular compartments to be isolated. The success in obtaining these purified, intact organelles critically depends on using an appropriate method for controlled rupture of the cells.

Redox Regulation of Hexokinases

SIGNIFICANCE

Hexokinases are key enzymes that are responsible for the first reaction of glycolysis, but they also moonlight other cellular processes, including mitochondrial redox signaling regulation. Modulation of hexokinase activity and spatiotemporal location by reactive oxygen and nitrogen species as well as other gasotransmitters serves as the basis for a unique, underexplored method of tight and flexible regulation of these fundamental enzymes. Recent Advances: Redox modifications of thiols serve as a molecular code that enables the precise and complex regulation of hexokinases. Redox regulation of hexokinases is also used by multiple parasites to cause widespread and severe diseases, including malaria, Chagas disease, and sleeping sickness. Redox-active molecules affect each other, and the moonlighting activity of hexokinases provides another feedback loop that affects the cellular redox status and is hijacked in malignantly transformed cells.

CRITICAL ISSUES

Several compounds affect the redox status of hexokinases in vivo. These include the dehydroascorbic acid (oxidized form of vitamin C), pyrrolidinium porrolidine-1-carbodithioate (contraceptive), peroxynitrite (product of ethanol metabolism), alloxan (a glucose analog), and isobenzothiazolinone ebselen. However, very limited information is available regarding which amino acid residues in hexokinases are affected by redox signaling. Except in cases of monogenic diabetes, direct evidence is absent for disease phenotypes that are associated with variations within motifs that are susceptible to redox signaling.

FUTURE DIRECTIONS

Further studies should address the propensity of hexokinases and their disease-associated variants to participate in redox regulation. Robust and straightforward proteomic methods are needed to understand the context and consequences of hexokinase-mediated redox regulation in health and disease.

The crystal structure of glucokinase from Leishmania braziliensis

Glucokinase from pathogenic protozoa of the genus Leishmania is a potential drug target for the chemotherapeutic treatment against leishmaniasis because this enzyme is located at a nodal point between two critically important metabolic pathways, glycolysis and the pentose phosphate pathway (PPP). L. braziliensis glucokinase (LbGlcK) was evaluated for its structural characterization and enzymatic performance. The enzyme catalyzes the phosphorylation of d-glucose with co-substrate ATP to yield the products G6P and ADP. LbGlcK had K_M values determined as 6.61 ± 2.63 mM and 0.338 ± 0.080 mM for d-glucose and ATP, respectively. The 1.85 Å resolution X-ray crystal structure of the apo form of LbGlcK was determined and a homodimer was revealed where each subunit (both in open conformations) included the typical small and large domains. Structural comparisons were assessed in relationship to Homo sapiens hexokinase IV and Trypanosoma cruzi glucokinase. Comparisons revealed that all residues important for making hydrogen bonding interactions with d-glucose in the active site and catalysis were strictly conserved. LbGlcK was screened against four glucosamine analogue inhibitors and the stronger inhibitor of the series, HPOP-GlcN, had a K_i value of 56.9 ± 16.6 μM that exhibited competitive inhibition. For the purpose of future structure-based drug design experimentation, L. braziliensis glucokinase was observed to be very similar to T. cruzi glucokinase even though there was a 44% protein sequence identity between the two enzymes.

Inorganic polyphosphate interacts with nucleolar and glycosomal proteins in trypanosomatids

Inorganic polyphosphate (polyP) is a polymer of three to hundreds of phosphate units bound by high-energy phosphoanhydride bonds and present from bacteria to humans. Most polyP in trypanosomatids is concentrated in acidocalcisomes, acidic calcium stores that possess a number of pumps, exchangers, and channels, and are important for their survival. In this work, using polyP as bait we identified > 25 putative protein targets in cell lysates of both Trypanosoma cruzi and Trypanosoma brucei. Gene ontology analysis of the binding partners found a significant over-representation of nucleolar and glycosomal proteins. Using the polyphosphate-binding domain (PPBD) of Escherichia coli exopolyphosphatase (PPX), we localized long-chain polyP to the nucleoli and glycosomes of trypanosomes. A competitive assay based on the pre-incubation of PPBD with exogenous polyP and subsequent immunofluorescence assay of procyclic forms (PCF) of T. brucei showed polyP concentration-dependent and chain length-dependent decrease in the fluorescence signal. Subcellular fractionation experiments confirmed the presence of polyP in glycosomes of T. brucei PCF. Targeting of yeast PPX to the glycosomes of PCF resulted in polyP hydrolysis, alteration in their glycolytic flux and increase in their susceptibility to oxidative stress.

Characterization of phosphate transporter(s) and understanding their role in Leishmania donovani parasite

Inorganic phosphate (Pi) is shown to be involved in excretion of methylglyoxal (MG) in the promastigote form of Leishmania donovani parasite. Absence of Pi leads to its accumulation inside the parasite. Accumulation of MG is toxic to the parasite and utilizes glyoxylase as well as excretory pathways for its detoxification. In addition, Pi is also reported to regulate activities of ectoenzymes and energy metabolism (glucose to pyruvate) etc. Thus, it is known to cumulatively affect the growth of Leishmania parasite. Hence the transporters, which allow the movement of Pi across the membrane, can prove to be a crucial drug target. Therefore, we characterized two phosphate transporters in Leishmania (i) H+ dependent myo-inositol transporter (LdPHO84), and (ii) Na+ dependent transporter (LdPHO89), based on similar studies done previously on other lower organisms and trypanosomatids. We tried to understand the secondary structure of these two proteins and confirm modulation in their expression with the change in Pi concentration outside. Moreover, their modes of action were also measured in the presence of specific inhibitors (LiF, CCCP). Further analysis on the physiological role of these transporters in various stages of the parasite life cycle needs to be entrenched.

Kinetic and molecular characterization of the pyruvate phosphate dikinase from Trypanosoma cruzi

Trypanosoma cruzi, like other trypanosomatids analyzed so far, can use both glucose and amino acids as carbon and energy source. In these parasites, glycolysis is compartmentalized in glycosomes, authentic but specialized peroxisomes. The major part of this pathway, as well as a two-branched glycolytic auxiliary system, are present in these organelles. The first enzyme of one branch of this auxiliary system is the PPi-dependent pyruvate phosphate dikinase (PPDK) that converts phosphoenolpyruvate (PEP), inorganic pyrophosphate (PPi) and AMP into pyruvate, inorganic phosphate (Pi) and ATP, thus contributing to the ATP/ADP balance within the glycosomes. In this work we cloned, expressed and purified the T. cruzi PPDK. It kinetic parameters were determined, finding KM values for PEP, PPi and AMP of 320, 70 and 17 μM, respectively. Using molecular exclusion chromatography, two native forms of the enzyme were found with estimated molecular weights of 200 and 100 kDa, corresponding to a homodimer and monomer, respectively. It was established that T. cruzi PPDK's specific activity can be enhanced up to 2.6 times by the presence of ammonium in the assay mixture. During growth of epimastigotes in batch culture an apparent decrease in the specific activity of PPDK was observed. However, when its activity is normalized for the presence of ammonium in the medium, no significant modification of the enzyme activity per cell in time was found.

Hysteresis and positive cooperativity as possible regulatory mechanisms of Trypanosoma cruzi hexokinase activity

In Trypanosoma cruzi, the causal agent of Chagas disease, the first six or seven steps of glycolysis are compartmentalized in glycosomes, which are authentic but specialized peroxisomes. Hexokinase (HK), the first enzyme in the glycolytic pathway, has been an important research object, particularly as a potential drug target. Here we present the results of a specific kinetics study of the native HK from T. cruzi epimastigotes; a sigmoidal behavior was apparent when the velocity of the reaction was determined as a function of the concentration of its substrates, glucose and ATP. This behavior was only observed at low enzyme concentration, while at high concentration classical Michaelis-Menten kinetics was displayed. The progress curve of the enzyme's activity displays a lag phase of which the length is dependent on the protein concentration, suggesting that HK is a hysteretic enzyme. The hysteretic behavior may be attributed to slow changes in the conformation of T. cruzi HK as a response to variations of glucose and ATP concentrations in the glycosomal matrix. Variations in HK's substrate concentrations within the glycosomes may be due to variations in the trypanosome's environment. The hysteretic and cooperative behavior of the enzyme may be a form of regulation by which the parasite can more readily adapt to these environmental changes, occurring within each of its hosts, or during the early phase of transition to a new host.

Sequence analysis and molecular characterization of Clonorchis sinensis hexokinase, an unusual trimeric 50-kDa glucose-6-phosphate-sensitive allosteric enzyme

Clonorchiasis, which is induced by the infection of Clonorchis sinensis (C. sinensis), is highly associated with cholangiocarcinoma. Because the available examination, treatment and interrupting transmission provide limited opportunities to prevent infection, it is urgent to develop integrated strategies to prevent and control clonorchiasis. Glycolytic enzymes are crucial molecules for trematode survival and have been targeted for drug development. Hexokinase of C. sinensis (CsHK), the first key regulatory enzyme of the glycolytic pathway, was characterized in this study. The calculated molecular mass (Mr) of CsHK was 50.0 kDa. The obtained recombinant CsHK (rCsHK) was a homotrimer with an Mr of approximately 164 kDa, as determined using native PAGE and gel filtration. The highest activity was obtained with 50 mM glycine-NaOH at pH 10 and 100 mM Tris-HCl at pH 8.5 and 10. The kinetics of rCsHK has a moderate thermal stability. Compared to that of the corresponding negative control, the enzymatic activity was significantly inhibited by praziquantel (PZQ) and anti-rCsHK serum. rCsHK was homotropically and allosterically activated by its substrates, including glucose, mannose, fructose, and ATP. ADP exhibited mixed allosteric effect on rCsHK with respect to ATP, while inorganic pyrophosphate (PPi) displayed net allosteric activation with various allosteric systems. Fructose behaved as a dose-dependent V activator with the substrate glucose. Glucose-6-phosphate (G6P) displayed net allosteric inhibition on rCsHK with respect to ATP or glucose with various allosteric systems in a dose-independent manner. There were differences in both mRNA and protein levels of CsHK among the life stages of adult worm, metacercaria, excysted metacercaria and egg of C. sinensis, suggesting different energy requirements during different development stages. Our study furthers the understanding of the biological functions of CsHK and supports the need to screen for small molecule inhibitors of CsHK to interfere with glycolysis in C. sinensis.

Channel-forming activities in the glycosomal fraction from the bloodstream form of Trypanosoma brucei

BACKGROUND

Glycosomes are a specialized form of peroxisomes (microbodies) present in unicellular eukaryotes that belong to the Kinetoplastea order, such as Trypanosoma and Leishmania species, parasitic protists causing severe diseases of livestock and humans in subtropical and tropical countries. The organelles harbour most enzymes of the glycolytic pathway that is responsible for substrate-level ATP production in the cell. Glycolysis is essential for bloodstream-form Trypanosoma brucei and enzymes comprising this pathway have been validated as drug targets. Glycosomes are surrounded by a single membrane. How glycolytic metabolites are transported across the glycosomal membrane is unclear.

METHODS/PRINCIPAL FINDINGS

We hypothesized that glycosomal membrane, similarly to membranes of yeast and mammalian peroxisomes, contains channel-forming proteins involved in the selective transfer of metabolites. To verify this prediction, we isolated a glycosomal fraction from bloodstream-form T. brucei and reconstituted solubilized membrane proteins into planar lipid bilayers. The electrophysiological characteristics of the channels were studied using multiple channel recording and single channel analysis. Three main channel-forming activities were detected with current amplitudes 70-80 pA, 20-25 pA, and 8-11 pA, respectively (holding potential +10 mV and 3.0 M KCl as an electrolyte). All channels were in fully open state in a range of voltages ±150 mV and showed no sub-conductance transitions. The channel with current amplitude 20-25 pA is anion-selective (P(K+)/P(Cl-)∼0.31), while the other two types of channels are slightly selective for cations (P(K+)/P(Cl-) ratios ∼1.15 and ∼1.27 for the high- and low-conductance channels, respectively). The anion-selective channel showed an intrinsic current rectification that may suggest a functional asymmetry of the channel's pore.

CONCLUSIONS/SIGNIFICANCE

These results indicate that the membrane of glycosomes apparently contains several types of pore-forming channels connecting the glycosomal lumen and the cytosol.

Temperature-induced protein secretion by Leishmania mexicana modulates macrophage signalling and function

Protozoan parasites of genus Leishmania are the causative agents of leishmaniasis. These digenetic microorganisms undergo a marked environmental temperature shift (TS) during transmission from the sandfly vector (ambient temperature, 25-26°C) to the mammalian host (37°C). We have observed that this TS induces a rapid and dramatic increase in protein release from Leishmania mexicana (cutaneous leishmaniasis) within 4 h. Proteomic identification of the TS-induced secreted proteins revealed 72 proteins, the majority of which lack a signal peptide and are thus thought to be secreted via nonconventional mechanisms. Interestingly, this protein release is accompanied by alterations in parasite morphology including an augmentation in the budding of exovesicles from its surface. Here we show that the exoproteome of L. mexicana upon TS induces cleavage and activation of the host protein tyrosine phosphatases, specifically SHP-1 and PTP1-B, in a murine bone-marrow-derived macrophage cell line. Furthermore, translocation of prominent inflammatory transcription factors, namely NF-κB and AP-1 is altered. The exoproteome also caused inhibition of nitric oxide production, a crucial leishmanicidal function of the macrophage. Overall, our results provide strong evidence that within early moments of interaction with the mammalian host, L. mexicana rapidly releases proteins and exovesicles that modulate signalling and function of the macrophage. These modulations can result in attenuation of the inflammatory response and deactivation of the macrophage aiding the parasite in the establishment of infection.

Enolase: a key player in the metabolism and a probable virulence factor of trypanosomatid parasites-perspectives for its use as a therapeutic target

Glycolysis and glyconeogenesis play crucial roles in the ATP supply and synthesis of glycoconjugates, important for the viability and virulence, respectively, of the human-pathogenic stages of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania spp. These pathways are, therefore, candidate targets for antiparasite drugs. The glycolytic/gluconeogenic enzyme enolase is generally highly conserved, with similar overall fold and identical catalytic residues in all organisms. Nonetheless, potentially important differences exist between the trypanosomatid and host enzymes, with three unique, reactive residues close to the active site of the former that might be exploited for the development of new drugs. In addition, enolase is found both in the secretome and in association with the surface of Leishmania spp. where it probably functions as plasminogen receptor, playing a role in the parasite's invasiveness and virulence, a function possibly also present in the other trypanosomatids. This location and possible function of enolase offer additional perspectives for both drug discovery and vaccination.

Molecular and biochemical characterization of novel glucokinases from Trypanosoma cruzi and Leishmania spp

Glucokinase genes, found in the genome databases of Trypanosoma cruzi and Leishmania major, were cloned and sequenced. Their expression in Escherichia coli resulted in the synthesis of soluble and active enzymes, TcGlcK and LmjGlcK, with a molecular mass of 43 kDa and 46 kDa, respectively. The enzymes were purified, and values of their kinetic parameters determined. The K(m) values for glucose were 1.0 mM for TcGlcK and 3.3 mM for LmjGlcK. For ATP, the K(m) values were 0.36 mM (TcGlcK) and 0.35 mM (LmjGlcK). A lower K(m) value for glucose (2.55 mM) was found when the (His)(6)-tag was removed from the recombinant LmjGlcK, whereas the TcGlcK retained the same value. The V(max)'s of the T. cruzi and L. major GlcKs were 36.3 and 30.9 U/mg of protein, respectively. No inhibition was exerted by glucose-6-phosphate. Similarly, no inhibition by inorganic pyrophosphate was found in contrast to previous observations made for the T. cruzi and L. mexicana hexokinases. Both trypanosomatid enzymes were only able to phosphorylate glucose indicating that they are true glucokinases. Gel-filtration chromatography showed that the GlcK of both trypanosomatids may occur as a monomer or dimer, dependent on the protein concentration. Both GlcK sequences have a type-1 peroxisome-targeting signal. Indeed, they were shown to be present inside glycosomes using three different methods. These glucokinases present highest, albeit still a moderate 24% sequence identity with their counterpart from Trichomonas vaginalis, which has been classified into group A of the hexokinase family. This group comprises mainly eubacterial and cyanobacterial glucokinases. Indeed, multiple sequence comparisons, as well as kinetic properties, strongly support the notion that these trypanosomatid enzymes belong to group A of the hexokinases, in which they, according to a phylogenetic analysis, form a separate cluster.

The crystal structure of Trypanosoma cruzi glucokinase reveals features determining oligomerization and anomer specificity of hexose-phosphorylating enzymes

Glucose is an essential substrate for Trypanosoma cruzi, the protozoan organism responsible for Chagas' disease. The glucose is intracellularly phosphorylated to glucose 6-phosphate. Previously, a hexokinase responsible for this phosphorylation has been characterized. Recently, we identified an ATP-dependent glucokinase in T. cruzi exhibiting a tenfold lower substrate affinity compared to the hexokinase. Both enzymes, which belong to very different groups of the same family, are located inside glycosomes, the peroxisome-like organelles of Kinetoplastida that are known to contain the first seven glycolytic steps as well as enzymes of the oxidative branch of the pentose phosphate pathway. Here, we present the crystallographic structure of T. cruzi glucokinase, in complex with glucose and ADP. The structure suggests a loose tetrameric assembly formed by the association of two tight dimers. TcGlcK was previously reported to exist in a concentration-dependent equilibrium of monomeric and dimeric states. Here, we used mass spectrometry analysis to confirm the existence of TcGlcK monomeric and dimeric states. The analysis of subunit interactions and comparison with the bacterial glucokinases give insights into the forces promoting the stability of the different oligomeric states. Each T. cruzi glucokinase monomer contains one glucose and one ADP molecule. In contrast to hexokinases, which show a moderate preference for the alpha anomer of glucose, the electron density clearly shows the d-glucose bound in the beta configuration in the T.cruzi glucokinase. Kinetic assays with alpha and beta-d-glucose further confirm a moderate preference of the T. cruzi glucokinase for the beta anomer. Structural comparison of the glucokinase and hexokinases permits the identification of a possible mechanism for anomer selectivity in these hexose-phosphorylating enzymes. The preference for distinct anomers suggests that in T. cruzi hexokinase and glucokinase are not directly competing for the same substrate and are probably both present because they exert distinct physiological functions.