Characterization of ecto-phosphatase activities of Trypanosoma cruzi: a comparative study between Colombiana and Y strains

Identification and characterization of an ectophosphatase activity involved in Acanthamoeba castellanii adhesion to host cells

Acanthamoeba castellanii is a free-living amoeba and an opportunistic pathogen for humans that can cause encephalitis and, more commonly, Acanthamoeba keratitis. During its life cycle, A. castellanii may present as proliferative and infective trophozoites or resistant cysts. The adhesion of trophozoites to host cells is a key first step in the pathogenesis of infection. A major virulence protein of Acanthamoeba is a mannose-binding protein (MBP) that mediates the adhesion of amoebae to cell surfaces. Ectophosphatases are ecto-enzymes that can dephosphorylate extracellular substrates and have already been described in several microorganisms. Regarding their physiological roles, there is consistent evidence that ectophosphatase activities play an important role in parasite-host interactions. In the present work, we identified and biochemically characterized the ectophosphatase activity of A. castellanii. The ectophosphatase activity is acidic, stimulated by magnesium, cobalt and nickel, and presents the following apparent kinetic parameters: Km = 2.12 ± 0.54 mM p-NPP and Vmax = 26.12 ± 2.53 nmol p-NP × h-1 × 10-6 cells. We observed that sodium orthovanadate, ammonium molybdate, sodium fluoride, and inorganic phosphate are able to inhibit ectophosphatase activity. Comparing the two stages of the A. castellanii lifecycle, ectophosphatase activity is significantly higher in trophozoites than in cysts. The ectophosphatase activity is stimulated by mannose residues and is significantly increased when trophozoites interact with LLC-MK2 cells. The inhibition of ectophosphatase by pretreatment with sodium orthovanadate also inhibits the adhesion of trophozoites to epithelial cells. These results allow us to conclude that the ectophosphatase activity of A. castellanii is somehow important for the adhesion of trophozoites to their host cells. According to our data, we believe that the activation of MBP by mannose residues triggers the stimulation of ectophosphatase activity to facilitate the adhesion process.

Euglena gracilis: Biochemical properties of a membrane bound ecto-phosphatase activity modulated by fluoroaluminate complexes and different trophic conditions

The ecto-phosphatases belong to a group of enzymes closely associated with the cell surface that has its catalytic site facing the extracellular environment, where different phosphorylated substrates can be hydrolyzed. In the present work, we biochemically characterized the ecto-phosphatase activity of the freshwater microalgae Euglena gracilis, a model microorganism, ubiquitously distributed and resistant to several environmental stressors. The ecto-phosphatase activity is acidic, stimulated by copper and presents the following apparent kinetic parameters: Km = 2.52 ± 0.12 mM p-NPP and Vmax = 3.62 ± 0.06 nmol p-NP × h-1 × 106 cells. We observed that zinc, orthovanadate, molybdate, fluoride, and inorganic phosphate inhibit the ecto-phosphatase activity with different magnitudes. Fluoroaluminate complexes are also inhibitors of this ecto-phosphatase activity. They can be formed in the enzyme reaction conditions and are likely to occur in a natural environment where E. gracilis can be found. The ecto-phosphatase activity is constant through the culture growth phases and is negatively modulated after continuous subculturing in the dark when a shift from phototrophic to the heterotrophic metabolism is likely. The analysis of those biochemical parameters may contribute to understanding the role of E. gracilis ecto-phosphatase activity in natural environments.

Deep Insight into the Phosphatomes of Parasitic Protozoa and a Web Resource ProtozPhosDB

Phosphorylation dynamically regulates the function of proteins by maintaining a balance between protein kinase and phosphatase activity. A comprehensive understanding of the role phosphatases in cellular signaling is lacking in case of protozoans of medical and veterinary importance worldwide. The drugs used to treat protozoal diseases have many undesired effects and the development of resistance, highlights the need for new effective and safer antiprotozoal agents. In the present study we have analyzed phosphatomes of 15 protozoans of medical significance. We identified ~2000 phosphatases, out of which 21% are uncharacterized proteins. A significant positive correlation between phosphatome and proteome size was observed except for E. histolytica, having highest density of phosphatases irrespective of its proteome size. A difference in the number of phosphatases among different genera shows the variation in the signaling pathways they are involved in. The phosphatome of parasites is dominated by ser/thr phosphatases contrary to the vertebrate host dominated by tyrosine phosphatases. Phosphatases were widely distributed throughout the cell suggesting physiological adaptation of the parasite to regulate its host. 20% to 45% phosphatome of different protozoa consists of ectophosphatases, i.e. crucial for the survival of parasites. A database and a webserver "ProtozPhosDB" can be used to explore the phosphatomes of protozoans of medical significance.

Kinetic characterization of a novel acid ectophosphatase from Enterobacter asburiae

Expression of acid ectophosphatase by Enterobacter asburiae, isolated from Cattleya walkeriana (Orchidaceae) roots and identified by the 16S rRNA gene sequencing analysis, was strictly regulated by phosphorus ions, with its optimal activity being observed at an inorganic phosphate concentration of 7 mM. At the optimum pH 3.5, intact cells released p-nitrophenol at a rate of 350.76 ± 13.53 nmol of p-nitrophenolate (pNP)/min/10(8) cells. The membrane-bound enzyme was obtained by centrifugation at 100,000 × g for 1 h at 4 °C. p-Nitrophenylphosphate (pNPP) hydrolysis by the enzyme follows "Michaelis-Menten" kinetics with V = 61.2 U/mg and K0.5 = 60 μM, while ATP hydrolysis showed V = 19.7 U/mg, K0.5 = 110 μM, and nH = 1.6 and pyrophosphate hydrolysis showed V = 29.7 U/mg, K0.5 = 84 μM, and nH = 2.3. Arsenate and phosphate were competitive inhibitors with K i = 0.6 mM and K i = 1.8 mM, respectively. p-Nitrophenyl phosphatase (pNPPase) activity was inhibited by vanadate, while p-hydroxymercuribenzoate, EDTA, calcium, copper, and cobalt had no inhibitory effects. Magnesium ions were stimulatory (K0.5 = 2.2 mM and nH = 0.5). Production of an acid ectophosphatase can be a mechanism for the solubilization of mineral phosphates by microorganisms such as Enterobacter asburiae that are versatile in the solubilization of insoluble minerals, which, in turn, increases the availability of nutrients for plants, particularly in soils that are poor in phosphorus.

CK2 Secreted by Leishmania braziliensis Mediates Macrophage Association Invasion: A Comparative Study between Virulent and Avirulent Promastigotes

CK2 is a protein kinase distributed in different compartments of Leishmania braziliensis: an externally oriented ecto-CK2, an intracellular CK2, and a secreted CK2. This latter form is constitutively secreted from the parasite (CsCK2), but such secretion may be highly enhanced by the association of specific molecules, including enzyme substrates, which lead to a higher enzymatic activity, called inductively secreted CK2 (IsCK2). Here, we examined the influence of secreted CK2 (sCK2) activity on the infectivity of a virulent L. braziliensis strain. The virulent strain presented 121-fold higher total CK2 activity than those found in an avirulent strain. The use of specific CK2 inhibitors (TBB, DRB, or heparin) inhibited virulent parasite growth, whereas no effect was observed in the avirulent parasites. When these inhibitors were added to the interaction assays between the virulent L. braziliensis strain and macrophages, association index was drastically inhibited. Polyamines enhanced sCK2 activity and increased the association index between parasites and macrophages. Finally, sCK2 and the supernatant of the virulent strain increased the association index between the avirulent strain and macrophages, which was inhibited by TBB. Thus, the kinase enzyme CK2 seems to be important to invasion mechanisms of L. braziliensis.

Ecto-nucleotidases and Ecto-phosphatases from Leishmania and Trypanosoma parasites

Ecto-enzymes can be defined as membrane-bound proteins that have their active site facing the extracellular millieu. In trypanosomatids, the physiological roles of these enzymes remain to be completed elucidated; however, many important events have already been related to them, such as the survival of parasites during their complex life cycle and the successful establishment of host infection. This chapter focuses on two remarkable classes of ecto-enzymes: ecto-nucleotidases and ecto-phosphatases, summarizing their occurrence and possible physiological roles in Leishmania and Trypanosoma genera. Ecto-nucleotidases are characterized by their ability to hydrolyze extracellular nucleotides, playing an important role in purinergic signaling. By the action of these ecto-enzymes, parasites are capable of modulating the host immune system, which leads to a successful parasite infection. Furthermore, ecto-nucleotidases are also involved in the purine salvage pathway, acting in the generation of nucleosides that are able to cross plasma membrane via specialized transporters. Another important ecto-enzyme present in a vast number of pathogenic organisms is the ecto-phosphatase. These enzymes are able to hydrolyze extracellular phosphorylated substrates, releasing free inorganic phosphate that can be internalized by the cell, crossing the plasma membrane through a Pi-transporter. Ecto-phosphatases are also involved in the invasion and survival of parasite in the host cells. Several alternative functions have been suggested for these enzymes in parasites, such as participation in their proliferation, differentiation, nutrition and protection. In this context, the present chapter provides an overview of recent discoveries related to the occurrence of ecto-nucleotidase and ecto-phosphatase activities in Leishmania and Trypanosoma parasites.

Trypanosoma cruzi: effects of heat shock on ecto-ATPase activity

In this work, we demonstrate that Trypanosoma cruzi Y strain epimastigotes exhibit Mg2+-dependent ecto-ATPase activity that is stimulated by heat shock. When the epimastigotes were incubated at 37°C for 2h, the ecto-ATPase activity of the cells was 43.95±0.97 nmol Pi/h×10(7) cells, whereas the ecto-ATPase activity of cells that were not exposed to heat shock stress was 16.97±0.30 nmol Pi/h×10(7) cells. The ecto-ATPase activities of cells, that were exposed or not exposed to heat shock stress had approximately the same Km values (2.25±0.26 mM ATP and 1.55±0.23 mM ATP, respectively) and different Vmax values. The heat-shocked cells had higher Vmax values (54.38±3.07 nmol Pi/h×10(7) cells) than the cells that were not exposed to heat shock (19.38±1.76 nmol Pi/h×10(7) cells). We also observed that the ecto-phosphatase and ecto-5'nucleotidase activities of cells that had been incubated at 28°C or 37°C were the same. Interestingly, cycloheximide, an inhibitor of protein synthesis, suppressed the heat shock effect of ecto-ATPase activity on T. cruzi. The Mg2+-dependent ecto-ATPase activity from the Y strain (high virulence) was approximately 2-fold higher than that of Dm28c (a clone with low virulence). In addition, these two strains presented different responses to heat shock with regard to their ecto-ATPase activities; Y strain epimastigotes had a stimulation of 2.52-fold while the Dm28c strain had a 1.71-fold stimulation. In this context, the virulent trypomastigote form of T. cruzi, Dm28c, had an ecto-ATPase activity that was more than 7-fold higher (66.67±5.98 nmol Pi/h×10(7) cells) than that of the insect epimastigote forms (8.91±0.76 nmol Pi/h×10(7) cells). This difference increased to approximately 10-fold when both forms were subjected to heat shock stress (181.14±16.48 nmol Pi/h×10(7) cells for trypomastigotes and 16.71±1.17 nmol Pi/h×10(7) cells for epimastigotes at 37°C). The ecto-ATPase activity of a plasma membrane-enriched fraction obtained from T. cruzi epimastigotes was not increased by heat treatment, which suggested that cytoplasmic components had an influence on enzyme activation by heat shock stress.

Ecto-phosphatases in protozoan parasites: possible roles in nutrition, growth and ROS sensing

The cellular plasma membrane contains enzymes whose active sites face the external medium rather than the cytoplasm. The activities of these enzymes, referred to as ecto-enzymes, can be measured using living cells. Ecto-phosphatases are ecto-enzymes that presumably hydrolyze extracellular phosphorylated substrates, releasing free inorganic phosphate. Although, several alternative functions have been suggested for these enzymes, such as participation in proliferation, differentiation, adhesion, virulence, and infection, little is known about the physiological roles of these enzymes in protozoa parasites. In this review, we discuss the principal features of ecto-phosphatases in protozoan parasites that are causative agents of important diseases such as Chagas' disease, leishmaniasis, amoebiasis, giardiasis, trichomoniasis and, sleeping sickness.

Possible roles of ectophosphatases in host-parasite interactions

The interaction and survival of pathogens in hostile environments and in confrontation with host immune responses are important mechanisms for the establishment of infection. Ectophosphatases are enzymes localized at the plasma membrane of cells, and their active sites face the external medium rather than the cytoplasm. Once activated, these enzymes are able to hydrolyze phosphorylated substrates in the extracellular milieu. Several studies demonstrated the presence of surface-located ecto-phosphatases in a vast number of pathogenic organisms, including bacteria, protozoa, and fungi. Little is known about the role of ecto-phosphatases in host-pathogen interactions. The present paper provides an overview of recent findings related to the virulence induced by these surface molecules in protozoa and fungi.

Trypanosoma brucei brucei: effects of ferrous iron and heme on ecto-nucleoside triphosphate diphosphohydrolase activity

Trypanosoma brucei brucei is the causative agent of animal African trypanosomiasis, also called nagana. Procyclic vector form resides in the midgut of the tsetse fly, which feeds exclusively on blood. Hemoglobin digestion occurs in the midgut resulting in an intense release of free heme. In the present study we show that the magnesium-dependent ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase) activity of procyclic T. brucei brucei is inhibited by ferrous iron and heme. The inhibition of E-NTPDase activity by ferrous iron, but not by heme, was prevented by pre-incubation of cells with catalase. However, antioxidants that permeate cells, such as PEG-catalase and N-acetyl-cysteine prevented the inhibition of E-NTPDase by heme. Ferrous iron was able to induce an increase in lipid peroxidation, while heme did not. Therefore, both ferrous iron and heme can inhibit E-NTPDase activity of T. brucei brucei by means of formation of reactive oxygen species, but apparently acting through distinct mechanisms.

Protease expression analysis in recently field-isolated strains ofTrypanosoma cruzi: a heterogeneous profile of cysteine protease activities between TC I and TC II major phylogenetic groups

Protease expression among TCI and TCII field isolates was analysed. Gelatin-containing gels revealed hydrolysis bands with molecular masses ranging from 45 to 66 kDa. The general protease expression profile showed that TCII isolates presented higher heterogeneity compared to TCI. By utilizing protease inhibitors, we showed that all active proteases at acid pH are cysteine-proteases and all proteases active at alkaline pH are metalloproteases. However, the expression of cruzipain, theT. cruzimajor cysteine-protease, did not reproduce a heterogeneous TCII cysteine zymogram profile. Dendogram analyses based on presence/absence matrices of proteases and cruzipain bands showed a TCI separation from the TCII group with 50–60% similarity. We suggest that the observed cysteine protease diversification contributes to differential host infection between TCI and II genotypes.

Ecto-phosphatase activity on the external surface of Rhodnius prolixus salivary glands: modulation by carbohydrates and Trypanosoma rangeli

The salivary glands of insect's vectors are target organs to study the vectors-pathogens interactions. Rhodnius prolixus an important vector of Trypanosoma cruzi can also transmit Trypanosoma rangeli by bite. In the present study we have investigated ecto-phosphatase activity on the surface of R. prolixus salivary glands. Ecto-phosphatases are able to hydrolyze phosphorylated substrates in the extracellular medium. We characterized these ecto-enzyme activities on the salivary glands external surface and employed it to investigate R. prolixus-T. rangeli interaction. Salivary glands present a low level of hydrolytic activity (4.30+/-0.35 nmol p-nitrophenol (p-NP)xh(-1)xgland pair(-1)). The salivary glands ecto-phosphatase activity was not affected by pH variation; and it was insensitive to alkaline inhibitor levamisole and inhibited approximately 50% by inorganic phosphate (Pi). MgCl2, CaCl2 and SrCl2 enhanced significantly the ecto-phosphatase activity detected on the surface of salivary glands. The ecto-phosphatase from salivary glands surface efficiently releases phosphate groups from different phosphorylated amino acids, giving a higher rate of phosphate release when phospho-tyrosine is used as a substrate. This ecto-phosphatase activity was inhibited by carbohydrates as d-galactose and d-mannose. Living short epimastigotes of T. rangeli inhibited salivary glands ecto-phosphatase activity at 75%, while boiled parasites did not. Living long epimastigote forms induced a lower, but significant inhibitory effect on the salivary glands phosphatase activity. Interestingly, boiled long epimastigote forms did not loose the ability to modulate salivary glands phosphatase activity. Taken together, these data suggest a possible role for ecto-phosphatase on the R. prolixus salivary glands-T. rangeli interaction.

OppA, the ecto-ATPase of Mycoplasma hominis induces ATP release and cell death in HeLa cells

Background

In the facultative human pathogen Mycoplasma hominis, which belongs to the cell wall-less Mollicutes, the surface-localised substrate-binding domain OppA of the oligopeptide permease was characterised as the main ecto-ATPase.

Results

With the idea that extra-cellular ATP could only be provided by the infected host cells we analysed the ATP release of HeLa cells after incubation with different preparations of Mycoplasma hominis: intact bacterial cells, the membrane fraction with or without OppA, recombinant OppA as well as an ATPase-deficient OppA mutant. Release of ATP into the supernatant of the HeLa cells was primarily determined in all samples lacking ecto-ATPase activity of OppA. In the presence of the ATPase inhibitor DIDS the amount of ATP in the OppA-containing samples increased. This increase was maximal after incubation with fractions containing OppA protein indicating that OppA is involved in ATP release and subsequent hydrolysis. Real-time PCR analyses revealed that the proliferation of HeLa cells is reduced after infection with M. hominis and flow cytometry experiments established that OppA induces greater apoptosis than necrosis of HeLa cells whereas the preservation of ecto-ATPase activity of OppA induces apoptosis.

Conclusion

The OppA induced ATP-release and -hydrolysis induced cell death of M. hominis infected HeLa cells was predominantly due to apoptosis rather than necrosis. Future work will elucidate whether the induction of apoptosis is indispensable for survival of these non-invasive pathogen.

Leishmania amazonensis: characterization of an ouabain-insensitive Na+-ATPase activity

We characterized ouabain-insensitive Na+-ATPase activity present in the plasma membrane of Leishmania amazonensis and investigated its possible role in the growth of the parasite. An increase in Na+ concentration in the presence of 1mM ouabain, increased the ATPase activity with a V(max) of 154.1+/-13.5nmol Pi x h(-1) x mg(-1) and a K0.5 of 28.9+/-7.7mM. Furosemide and sodium orthovanadate inhibited the Na+-stimulated ATPase activity with an IC(50) of 270microM and 0.10microM, respectively. Furosemide inhibited the growth of L. amazonensis after 48h incubation, with maximal effect after 96h. The IC50 for furosemide was 840. On the other hand, ouabain (1mM) did not change the growth of the parasite. Taken together, these results show that L. amazonensis expresses a P-type, ouabain-insensitive Na+-ATPase that could be involved with the growth of the parasite.