A novel extracellular calcium-dependent cysteine proteinase from Crithidia deanei

Proteolytic inhibitors as alternative medicines to treat trypanosomatid-caused diseases: experience with calpain inhibitors

The treatment for tropical neglected diseases, such as Chagas disease (CD) and leishmaniasis, is extremely limited to a handful of drugs that suffer from unacceptable toxicity, tough administration routes, like parenteral, and increasing treatment failures due to the parasite resistance. Consequently, there is urgency for the development of new therapeutic options to treat such diseases. Since peptidases from these parasites are responsible for crucial functions in their biology, these molecules have been explored as alternative targets. In this context, a myriad of proteolytic inhibitors has been developed against calcium-dependent cysteine-type peptidases, collectively called calpains, which are implicated in several human pathophysiological diseases. These molecules are highly expanded in the genome of trypanosomatids and they have been reported participating in several parasite biological processes. In the present perspective, we discuss our almost two decades of experience employing the calpain inhibitors as an interesting shortcut to a possible repurpose strategy to treat CD and leishmaniasis.

The Diverse Calpain Family in Trypanosomatidae: Functional Proteins Devoid of Proteolytic Activity?

Calpains are calcium-dependent cysteine peptidases that were originally described in mammals and, thereafter, their homologues were identified in almost all known living organisms. The deregulated activity of these peptidases is associated with several pathologies and, consequently, huge efforts have been made to identify selective inhibitors. Trypanosomatids, responsible for life-threatening human diseases, possess a large and diverse family of calpain sequences in their genomes. Considering that the current therapy to treat trypanosomatid diseases is limited to a handful of drugs that suffer from unacceptable toxicity, tough administration routes, like parenteral, and increasing treatment failures, a repurposed approach with calpain inhibitors could be a shortcut to successful chemotherapy. However, there is a general lack of knowledge about calpain functions in these parasites and, currently, the proteolytic activity of these proteins is still an open question. Here, we highlight the current research and perspectives on trypanosomatid calpains, overview calpain description in these organisms, and explore the potential of targeting the calpain system as a therapeutic strategy. This review gathers the current knowledge about this fascinating family of peptidases as well as insights into the puzzle: are we unable to measure calpain activity in trypanosomatids, or are the functions of these proteins devoid of proteolytic activity in these parasites?

Expression and cellular localisation of Trypanosoma cruzi calpains

BACKGROUND

Calpains are present in almost all organisms and comprise a family of calcium-dependent cysteine peptidases implicated in crucial cellular functions. Trypanosoma cruzi, the causative agent of Chagas disease, presents an expansion on this gene family with unexplored biological properties.

OBJECTIVES

Here, we searched for calpains in the T. cruzi genome, evaluated the mRNA levels, calpain activity and the protein expression and determined the cellular localisation in all three parasite life cycle forms.

METHODS/FINDINGS

Sixty-three calpain sequences were identified in T. cruzi CL Brener genome, with fourteen domain arrangements. The comparison of calpain mRNA abundance by quantitative polymerase chain reaction (qPCR) revealed seven up-regulated sequences in amastigotes and/or bloodstream trypomastigotes and five in epimastigotes. Western Blotting analysis revealed seven different molecules in the three parasite forms, and one amastigote-specific, while no proteolytic activity could be detected. Flow cytometry assays revealed a higher amount of intracellular calpains in amastigotes and/or trypomastigotes in comparison to epimastigotes. Finally, ultrastructural analysis revealed the presence of calpains in the cytoplasm, vesicular and plasma membranes of the three parasite forms, and in the paraflagellar rod in trypomastigotes.

CONCLUSION

Calpains are differentially expressed and localised in the T. cruzi life cycle forms. This study adds data on the calpain occurrence and expression pattern in T. cruzi.

Characterization of L-amino Acid Oxidase Derived from Crotalus adamanteus Venom: Procoagulant and Anticoagulant Activities

Snake venom enzymes of the L-amino acid oxidase (LAAO) class are responsible for tissue hemorrhage, edema, and derangement of platelet function. However, what role, if any, these flavoenzymes play in altering plasmatic coagulation have not been well defined. Using coagulation kinetomic analyses (thrombelastograph-based), it was determined that the LAAO derived from Crotalus adamanteus venom displayed a procoagulant activity associated with weak clot strength (no factor XIII activation) similar to thrombin-like enzymes. The procoagulant activity was not modified in the presence of reduced glutathione, demonstrating that the procoagulant activity was likely due to deamination, and not hydrogen peroxide generation by the LAAO. Further, unlike the raw venom of the same species, the purified LAAO was not inhibited by carbon monoxide releasing molecule-2 (CORM-2). Lastly, exposure of the enzyme to phenylmethylsulfonyl fluoride (PMSF) resulted in the LAAO expressing anticoagulant activity, preventing contact activation generated thrombin from forming a clot. In sum, this investigation for the first time characterized the LAAO of a snake venom as both a fibrinogen polymerizing and an anticoagulant enzyme acting via oxidative deamination and not proteolysis as is the case with thrombin-like enzymes (e.g., serine proteases). Using this thrombelastographic approach, future investigation of purified enzymes can define their biochemical nature.

In Vitro Inhibition of Leishmania Attachment to Sandfly Midguts and LL-5 Cells by Divalent Metal Chelators, Anti-gp63 and Phosphoglycans

Leishmania braziliensis and Leishmania infantum are the causative agents of cutaneous and visceral leishmaniasis, respectively. Several aspects of the vector-parasite interaction involving gp63 and phosphoglycans have been individually assayed in different studies. However, their role under the same experimental conditions was not studied yet. Here, the roles of divalent metal chelators, anti-gp63 antibodies and purified type I phosphoglycans (PGs) were evaluated during in vitro parasite attachment to the midgut of the vector. Parasites were treated with divalent metal chelators or anti-gp63 antibodies prior to the interaction with Lutzomyia longipalpis/Lutzomyia intermedia midguts or sand fly LL-5 cells. In vitro binding system was used to examine the role of PG and gp63 in parallel. Treatment with divalent metal chelators reduced Le. infantum adhesion to the Lu. longipalpis midguts. The most effective compound (Phen) inhibited the binding in both vectors. Similar results were observed in the interaction between both Leishmania species and the cell line LL-5. Finally, parallel experiments using anti-gp63-treated parasites and PG-incubated midguts demonstrated that both approaches substantially inhibited attachment in the natural parasite-vector pairs Le. infantum/Lu. longipalpis and Le. braziliensis/Lu. intermedia. Our results suggest that gp63 and/or PG are involved in parasite attachment to the midgut of these important vectors.

Why calpain inhibitors are interesting leading compounds to search for new therapeutic options to treat leishmaniasis?

Leishmaniasis is a neglected disease, which needs improvements in drug development, mainly due to the toxicity, parasite resistance and low compliance of patients to treatment. Therefore, the development of new chemotherapeutic compounds is an urgent need. This opinion article will briefly highlight the feasible use of calpain inhibitors as leading compounds to search for new therapeutic options to treat leishmaniasis. The milestone of this approach is to take advantage on the myriad of inhibitors developed against calpains, some of which are in advanced clinical trials. The deregulated activity of these enzymes is associated with several pathologies, such as strokes, diabetes and Parkinson's disease, to name a few. In Leishmania, calpain upregulation has been associated to drug resistance and virulence. Whereas the difficulties in developing new drugs for neglected diseases are more economical than biotechnological, repurposing approach with compounds already approved for clinical use by the regulatory agencies can be an interesting shortcut to a successful chemotherapeutic treatment for leishmaniasis.

Expression of calpain-like proteins and effects of calpain inhibitors on the growth rate of Angomonas deanei wild type and aposymbiotic strains

Background

Angomonas deanei is a trypanosomatid parasite of insects that has a bacterial endosymbiont, which supplies amino acids and other nutrients to its host. Bacterium loss induced by antibiotic treatment of the protozoan leads to an aposymbiotic strain with increased need for amino acids and results in increased production of extracellular peptidases. In this work, a more detailed examination of A. deanei was conducted to determine the effects of endosymbiont loss on the host calpain-like proteins (CALPs), followed by testing of different calpain inhibitors on parasite proliferation.

Results

Western blotting showed the presence of different protein bands reactive to antibodies against calpain from Drosophila melanogaster (anti-Dm-calpain), lobster calpain (anti-CDPIIb) and cytoskeleton-associated calpain from Trypanosoma brucei (anti-CAP5.5), suggesting a possible modulation of CALPs influenced by the endosymbiont. In the cell-free culture supernatant of A. deanei wild type and aposymbiotic strains, a protein of 80 kDa cross-reacted with the anti-Dm-calpain antibody; however, no cross-reactivity was found with anti-CAP5.5 and anti-CDPIIb antibodies. A search in A. deanei genome for homologues of D. melanogaster calpain, T. brucei CAP5.5 and lobster CDPIIb calpain revealed the presence of hits with at least one calpain conserved domain and also with theoretical molecular mass consistent with the recognition by each antibody. No significant hit was observed in the endosymbiont genome, indicating that calpain molecules might be absent from the symbiont. Flow cytometry analysis of cells treated with the anti-calpain antibodies showed that a larger amount of reactive epitopes was located intracellularly. The reversible calpain inhibitor MDL28170 displayed a much higher efficacy in diminishing the growth of both strains compared to the non-competitive calpain inhibitor PD150606, while the irreversible calpain inhibitor V only marginally diminished the proliferation.

Conclusions

Altogether, these results indicate that distinct calpain-like molecules are expressed by A. deanei, with a possible modulation in the expression influenced by the endosymbiont. In addition, treatment with MDL28170 affects the growth rate of both strains, as previously determined in the human pathogenic species Leishmania amazonensis and Trypanosoma cruzi, with whom A. deanei shares immunological and biochemical relationships.

Proteolytic activity of gut bacteria isolated from the velvet bean caterpillar Anticarsia gemmatalis

The development of proteinase inhibitors as potential insect control agents has been constrained by insect adaptation to these compounds. The velvet bean caterpillar (Anticarsia gemmatalis) is a key soybean pest species that is well-adapted to proteinase inhibitors, particularly serine-proteinase inhibitors, which are abundant in the caterpillar host. The expression of diverse proteolytic enzymes by gut symbionts may allow the velvet bean caterpillar to circumvent proteinase inhibitors produced by the host plant. In this study, we characterized the proteolytic activity of the four nonpathogenic species of gut bacteria isolated from the velvet bean caterpillar-Bacillus cereus, Enterococcus gallinarum, Enterococcus mundtii and Staphylococcus xylosus. Two proteinase substrates, N-α-benzoyl-L-Arg-p-nitroanilide (L-BApNA) and N-α-p-tosyl-L-Arg methyl ester (L-TAME) and five proteinase inhibitors [aprotinin, E-64, ethylenediamine tetraacetic acid (EDTA), pepstatin and N-α-tosyl-L-lysine chloromethyl ketone (TLCK)] as well as CaCl2, pH and temperature profiles were used to characterize the expressed proteolytic activity of these bacterial strains in vitro. Kinetic parameters for proteolytic activity were also estimated. The results of these experiments indicated that serine- and cysteine-proteinase activities were expressed by all four gut bacteria symbionts of the velvet bean caterpillar. The cysteine- and serine-proteinase activities of these gut symbionts were distinct and different from that of gut proteinases of the caterpillar itself. This finding provides support for the potential involvement of gut symbionts in the mitigation of the negative effects of serine-proteinase inhibitors in the velvet bean caterpillar.

Calpains: potential targets for alternative chemotherapeutic intervention against human pathogenic trypanosomatids

The treatment for both leishmaniasis and trypanosomiasis, which are severe human infections caused by trypanosomatids belonging to Leishmania and Trypanosoma genera, respectively, is extremely limited because of concerns of toxicity and efficacy with the available anti-protozoan drugs, as well as the emergence of drug resistance. Consequently, the urgency for the discovery of new trypanosomatid targets and novel bioactive compounds is particularly necessary. In this context, the investigation of changes in parasite gene expression between drug resistant/sensitive strains and in the up-regulation of virulence-related genes in infective forms has brought to the fore the involvement of calpain-like proteins in several crucial pathophysiological processes performed by trypanosomatids. These studies were encouraged by the publication of the complete genome sequences of three human pathogenic trypanosomatids, Trypanosoma brucei, Trypanosoma cruzi and Leishmania major, which allowed in silico analyses that in turn directed the identification of numerous genes with interesting chemotherapeutic characteristics, including a large family of calpain-related proteins, in which to date 23 genes were assigned as calpains in T. brucei, 40 in T. cruzi and 33 in L. braziliensis. In the present review, we intend to add to these biochemical/biological reports the investigations performed upon the inhibitory capability of calpain inhibitors against human pathogenic trypanosomatids.

Purification, kinetic characterization and properties of a novel thermo-tolerant extracellular protease from Kluyveromyces marxianus IFO 0288 with potential biotechnological interest

A novel extracellular hydrolase of ∼45kDa molecular mass was purified from Kluyveromyces marxianus IFO 0288 cultures and characterized as serine protease. The K(m)-value of protease (designated protease-KM-IFO-0288-A), which was found active in media containing elevated [NaCl] but lacking EDTAK(2), decreased with increasing [Ca(2+)]. The protease maintained considerable activity at the range of 10-60°C and pH 6.00-10.25, with optimum k(cat)/K(m)-value at 35.5°C and pH 7.75. It was strongly affected by specific irreversible inhibitors of serine proteases while was unaffected by inhibitors of cysteine proteases. Significant rate constants, activation energies, and proton inventories were estimated from the profiles of Michaelis-Menten parameters, versus pH, temperature and deuterium atom fraction, in the hydrolysis of Suc-AAPF-pNA showing that protease-KM-IFO-0288-A performs catalysis via a charge-relay system. The properties of protease-KM-IFO-0288-A suggest that K. marxianus represents a valuable source of extracellular protease of biotechnological interest which, given its GRAS status, could find several important applications.

MDL28170, a calpain inhibitor, affects Trypanosoma cruzi metacyclogenesis, ultrastructure and attachment to Rhodnius prolixus midgut

Background

Trypanosoma cruzi is the etiological agent of Chagas' disease. During the parasite life cycle, many molecules are involved in the differentiation process and infectivity. Peptidases are relevant for crucial steps of T. cruzi life cycle; as such, it is conceivable that they may participate in the metacyclogenesis and interaction with the invertebrate host.

Methodology/Principal Findings

In this paper, we have investigated the effect of the calpain inhibitor MDL28170 on the attachment of T. cruzi epimastigotes to the luminal midgut surface of Rhodnius prolixus, as well as on the metacyclogenesis process and ultrastructure. MDL28170 treatment was capable of significantly reducing the number of bound epimastigotes to the luminal surface midgut of the insect. Once the cross-reactivity of the anti-Dm-calpain was assessed, it was possible to block calpain molecules by the antibody, leading to a significant reduction in the capacity of adhesion to the insect guts by T. cruzi. However, the antibodies were unable to interfere in metacyclogenesis, which was impaired by the calpain inhibitor presenting a significant reduction in the number of metacyclic trypomastigotes. The calpain inhibitor also promoted a direct effect against bloodstream trypomastigotes. Ultrastructural analysis of epimastigotes treated with the calpain inhibitor revealed disorganization in the reservosomes, Golgi and plasma membrane disruption.

Conclusions/Significance

The presence of calpain and calpain-like molecules in a wide range of organisms suggests that these proteins could be necessary for basic cellular functions. Herein, we demonstrated the effects of MDL28170 in crucial steps of the T. cruzi life cycle, such as attachment to the insect midgut and metacyclogenesis, as well as in parasite viability and morphology. Together with our previous findings, these results help to shed some light on the functions of T. cruzi calpains. Considering the potential roles of these molecules on the interaction with both invertebrate and vertebrate hosts, it is interesting to improve knowledge on these molecules in T. cruzi.

Immunization of mice with a Trypanosoma cruzi-like strain isolated from a bat: predictive factors for involvement of eosinophiles in tissue damage

The granules of eosinophiles are cytotoxic to Trypanosoma cruzi trypomastigote and amastigote forms and to several cell types of the host, revealing their role in either parasite elimination or the production of tissue lesions. In this study, we evaluated the biological characteristics of T. cruzi infection that are responsible for the increase in tissue eosinophile levels in mice previously immunized with a bat isolated T. cruzi-like strain that does not infect mice. Nonisogeneic mice were divided into 24 groups that received from zero to three inoculations of T. cruzi-like RM1 strain, with or without adjuvant, followed by challenge with T. cruzi VIC or JG strains. Uni- and multivariate comparisons were performed comparing the tissue eosinophile levels with the parasitemia peak, severity of myositis in skeletal muscle, phase of infection, and the immunization strategies induced by the T. cruzi-like strain (adjuvant, number of reinoculations, and parasites). Although the severity of inflammation was higher in the acute phase, the score of tissue eosinophiles was similar in the acute and chronic phases of infection. In addition, there was a positive correlation among eosinophile levels and parasitemia peak. In the chronic phase, a greater eosinophile count was accompanied by an augmentation of myositis. Regardless of the phase of infection, we observed a positive correlation between the intensity of eosinophile infiltration and the number of sensitizations with T. cruzi-like strain. The multivariate analysis showed that the peak of parasitemia, number of inoculations with the T. cruzi-like strain, and severity of myositis were associated with greater tissue eosinophilia, in comparison with adjuvant, T. cruzi strains used in the challenge or tissue parasitism. Therefore, tissue eosinophile levels proved to be an important parameter in the pathogenesis of experimental Chagas disease in the acute and chronic phases of infection and might be related to reinfections, parasite multiplication ability, and severity of inflammatory process.

Detection of matrix metallopeptidase-9-like proteins in Trypanosoma cruzi

In this study, the cell-associated and extracellular peptidases of Trypanosoma cruzi grown in modified Roitman's complex (MRC) medium were analyzed by measuring peptidase activity in gelatin-containing zymograms. Our results showed that the cell-associated peptidases as well as peptidases extracellularly released by T. cruzi displayed two distinct proteolytic classes: cysteine and metallopeptidase activities. The major cysteine peptidase, cruzipain, synthesized by T. cruzi cells was detected in cellular parasite content, as a 50kDa reactive polypeptide, after probing with anti-cruzipain antibody. In addition, metallo-type peptidases belonging to the matrix metallopeptidase-9 (MMP-9) family were revealed, after Western blotting, as a 97kDa protein band in cellular extract and an 85kDa polypeptide in both cellular and secreted parasite extracts. The MMP-9-like activity present in cells and spent culture medium was immunoprecipitated by an anti-MMP-9 polyclonal antibody. The surface location of MMP-9-like proteins in T. cruzi was also evidenced by means of flow cytometry analysis. Furthermore, doxycycline that has direct MMP-9 inhibiting properties in vitro, inhibited MMP-9-like activities in gel zymography, immunoprecipitation and flow cytometry analyses. This is the first report of the presence of MMP-9-like molecules in T. cruzi. The presence of a matrix extracellular-degrading enzyme may play a role in the T. cruzi-host cell interaction, making this enzyme a potential target for future drug development against this pathogenic trypanosomatid.

Co-localization of putative calcium channels (phenylalkylamine-binding sites) on oil bodies in protoplasts from dark-grown sunflower seedling cotyledons

Oil bodies are spherical entities containing a triacylglycerol (TAG) matrix encased by a phospholipid monolayer, which is stabilized by oil body-specific proteins, principally oleosins. Biochemical investigations in the recent past have also demonstrated the expression of calcium-binding proteins, called caleosins, as a component of oil body membranes during seed germination. Using DM-Bodipy-phenylalkylamine (PAA; a fluorescent derivative of phenylalkylamine)-a fluorescent probe known to bind L-type calcium channel proteins, present investigations provide the first report on the localization and preferential accumulation of putative calcium channel proteins on/around oil bodies during peak lipolytic phase in protoplasts derived from dark-grown sunflower (Helianthus annuus L. cv Morden) seedling cotyledons. Specificity of DM-Bodipy-PAA labeling was confirmed by using bepridil, a non-fluorescent competitor of PAA while non-specific dye accumulation has been ruled out by using Bodipy-FL as control. Co-localization of fluorescence from DM-Bodipy-PAA binding sites (ex: 504 nm; em: 511 nm) and nile red fluorescing oil bodies (ex: 552 nm; em: 636 nm) has been undertaken by epifluorescence and confocal laser scanning microscopy (CLSM). It revealed the affinity of PAA-sensitive ion channels for the oil body surface. Findings from the current investigations highlight the significance of calcium and calcium channel proteins during oil body mobilization in sunflower.

Arrested growth of Trypanosoma cruzi by the calpain inhibitor MDL28170 and detection of calpain homologues in epimastigote forms

In this paper, we aimed to explore the effects of the calpain inhibitor III (MDL28170) and to detect calpain-like molecules (CALPs) in epimastigote forms of Trypanosoma cruzi isolate Dm28c. MDL28170 at 70 μM promoted a powerful reduction in the growth rate after 48 h. The IC50 value was calculated to be 31·7 μM. This inhibitor promoted an increase in the cellular volume, but not cell lysis, resulting in a trypanostatic effect. T. cruzi CALPs presented a strong cross-reactivity with anti-Drosophila melanogaster calpain and anti-cytoskeleton-associated protein from Trypanosoma brucei antibodies, and labelling was found mainly intracellularly. Furthermore, an 80 kDa reactive protein was detected by Western blotting assays. No significant cross-reactivity was found with anti-human brain calpain antibody. The expression of CALPs was decreased in cells kept for long periods in axenic cultures in comparison to a strain recently isolated from mice, as well as in MDL28170-treated cells, the latter being paralleled by an increased expression of cruzipain. Different levels of CALPs expression were also detected in distinct phylogenetic lineages, like Y strain (lineage TCI), Dm28c (TCII) and INPA6147 strain (Z3 zymodeme). These results may contribute for the investigation of the functions of CALPs in trypanosomatids.

Cysteine peptidases in Herpetomonas samuelpessoai are modulated by temperature and dimethylsulfoxide-triggered differentiation

Cysteine peptidases of protozoa have been implicated in a variety of biological events, and the expression of these enzymes is modulated in response to distinct stimuli, including environmental changes and differentiation. In the present work, we have examined the expression of cysteine peptidases from Herpetomonas samuelpessoai grown at distinct temperatures and during dimethylsulfoxide (DMSO)-elicited differentiation. We demonstrated that a 45 kDa cysteine peptidase had its activity reduced during the parasite growth at 37 degrees C in comparison to 26 degrees C, and when cultured up to 72 h in the presence of DMSO. The modulation in the 45 kDa cysteine peptidase expression is connected to the differentiation process, since both temperature and DMSO are able to trigger the promastigote to paramastigote transformation in H. samuelpessoai. The possible immunological similarity of H. samuelpessoai proteins with well-known cysteine peptidases produced by trypanosomatid pathogens, including cruzipain (Trypanosoma cruzi) and cysteine peptidase b (cpb) from Leishmania mexicana, was also investigated, as well as with calpain molecules. The protein cellular lysate of H. samuelpessoai reacted with antibodies raised against cpb of L. mexicana and calpain of Drosophila melanogaster; however, no reaction was observed against cruzipain. The 35 kDa cpb-like protein had its expression diminished in DMSO-treated parasites, while the 80 kDa calpain-like molecule was enhanced and an additional 30 kDa calpain-related polypeptide was exclusively observed in these cells. Fluorescence microscopy and flow cytometry analyses corroborated these data. The results described above add H. samuelpessoai to the list of parasites whose differentiation seems to be correlated with cysteine peptidase expression.

Purification and kinetics of two novel thermophilic extracellular proteases from Lactobacillus helveticus, from kefir with possible biotechnological interest

Two thermophilic extracellular proteases, designated Lmm-protease-Lh ( approximately 29 kDa) and Hmm-protease-Lh ( approximately 62 kDa), were purified from the Lactobacillus helveticus from kefir, and found active in media containing dithiothreitol; the activity of Lmm-protease-Lh was increased significantly in media containing also EDTAK(2). Both novel proteases maintained full activity at 60 degrees C after 1-h incubation at 10 degrees C as well as at 80 degrees C, showing optimum k(cat)/K(m) values at pH 7.00 and 60 degrees C. Only irreversible inhibitors specific for cysteine proteinases strongly inhibited the activity of both novel enzymes, while they remained unaffected by irreversible inhibitors specific for serine proteinases. Both enzymes hydrolyzed the substrate Suc-FR-pNA via Michaelis-Menten kinetics; conversely, the substrate Cbz-FR-pNA was hydrolyzed by Lmm-protease-Lh via Michaelis-Menten kinetics and by Hmm-protease-Lh via substrate inhibition kinetics. Valuable rate constants and activation energies were estimated from the temperature-(k(cat)/K(m)) profiles of both enzymes, and useful results were obtained from the effect of different metallic ions on their Michaelis-Menten parameters.

Crithidia deanei: influence of parasite gp63 homologue on the interaction of endosymbiont-harboring and aposymbiotic strains with Aedes aegypti midgut

The present study demonstrates that the endosymbiont of Crithidia deanei influences the expression of surface gp63 molecules. Ultrastructural immunocytochemical analysis shows the presence of the gp63-like protein in the protozoan flagellum and flagellar pocket, either attached to shed membranes or in a free form. This molecule is glycosylphosphatidylinositol (GPI) anchored to the plasma membrane as demonstrated by phospholipase C (PLC) treatment and cross-reacting determinant detection by immunoblotting. The gp63 molecule mediates the adhesive process of the protozoan to Aedes aegypti explanted guts, since the binding was reduced by pre-incubating the C. deanei parasites (wild and aposymbiotic strains) with anti-gp63 antibodies, PLC or PLC followed by anti-gp63 antibodies incubation. In addition, the number of wild C. deanei bound to A. aegypti explanted guts was twice as that of aposymbiotic parasites. Flow cytometry assays revealed that the reactivity of the wild strain with anti-gp63 antibodies was approximately twice as that of the aposymbiotic strain. We may conclude that higher expression of surface gp63 by the wild strain of C. deanei may positively influence this interaction, posing a prominent advantage for the endosymbiont-containing trypanosomatids.

Antileishmanial activity of MDL 28170, a potent calpain inhibitor

Several calpain inhibitors are under development and some are useful agents against important human pathogens. We therefore investigated the effect of MDL 28170, a potent calpain inhibitor, on the growth of Leishmania amazonensis. After 48 h of treatment, the inhibitor exhibited a dose-dependent antileishmanial activity, with a 50% lethal dose (LD(50)) of 23.3 microM. The inhibitor promoted cellular alterations, such as the parasites becoming short and round. A calpain-like protein migrating at 80 kDa was identified by Western blotting. In addition, the calpain-like molecules were identified on the cell surface of the flagellate. These results add new in vitro insights into the exploitation of calpain inhibitors in treating parasitic infections and add this family of peptidases to the list of potential targets for development of more potent and specific inhibitors against trypanosomatids.

Peptidases and gp63-like proteins in Herpetomonas megaseliae: possible involvement in the adhesion to the invertebrate host

The cell-associated and extracellular peptidases of Herpetomonas megaseliae grown in brain-heart infusion and in modified Roitman's complex media were analyzed by measuring peptidase activity on gelatin, casein and hemoglobin in zymograms. Casein was the best proteinaceous substrate for the peptidase detection on both growth conditions. However, no proteolytic activity was detected when hemoglobin was used. Our results showed that cellular cysteine peptidase (115-100, 40 and 35 kDa) and metallopeptidase (70 and 60 kDa) activities were detected on both media in casein and gelatin zymograms. Additionally, the use of casein in the gel revealed a distinct acidic metallopeptidase of 50 kDa when the parasite was cultured in the modified Roitman's complex medium. Irrespective of the culture medium composition, H. megaseliae released metallopeptidases exclusively in the extracellular environment. The presence of gp63-like molecules on the H. megaseliae surface was shown by flow cytometry using anti-gp63 antibody raised against recombinant gp63 from Leishmania mexicana. The pre-treatment of parasites with phospholipase C reduced the number of gp63-positive cells, suggesting that these molecules were glycosylphosphatidylinositol-anchored to the surface. Additionally, the supernatant obtained from phospholipase C-treated cells and probed with anti-cross-reacting determinant confirmed that at least a 52 kDa gp63-like molecule is glycosylphosphatidylinositol-anchored. Furthermore, we assessed a possible function for the gp63-like molecules in H. megaseliae on the interaction with explanted guts of its original host, Megaselia scalaris, and with an experimental model employing Aedes aegypti. Parasites pre-treated with either anti-gp63 antibody or phospholipase C showed a significant reduction in the adhesion to M. scalaris and A. aegypti guts. Similarly, the pre-treatment of the explanted guts with purified gp63 diminished the interaction process. Collectively, these results corroborate the ubiquitous existence of gp63 homologues in insect trypanosomatids and the potential adhesion of these molecules to invertebrate host tissues.

Proteolytic expression in Blastocrithidia culicis: influence of the endosymbiont and similarities with virulence factors of pathogenic trypanosomatids

Blastocrithidia culicis is an insect trypanosomatid that presents bacterial endosymbionts. The cell-associated and secreted proteinases of the endosymbiont-bearing and aposymbiotic strains were compared through the incorporation of proteinaceous substrates into sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Few qualitative changes could be detected in the proteolytic zymograms in the 2 strains studied when gelatin, casein, haemoglobin or bovine serum albumin (BSA) were tested. However, the level of proteolytic activities was significantly higher in the aposymbiotic strain. Some of the B. culicis proteins reacted in Western blots with antibodies raised against gp63, a zinc-metalloproteinase, and cruzipain, a cysteinyl-proteinase, which are virulence factors of the human pathogenic trypanosomatids, Leishmania spp. and Trypanosoma cruzi, respectively. The anti-cross-reacting determinant (CRD) antibody recognized 2 polypeptides (50 and 58 kDa) in the spent culture media and in the supernatant from glycosylphosphatidylinositol-phospholipase C (GPI-PLC)-treated cells, suggesting that these proteins are GPI-anchored to the plasma membrane. In addition, the anti-gp63 reacted with the 50 kDa protein. The identification of protein homologues in trypanosomatids with distinct life-cycles may help to determine the importance of proteinases in trypanosomatids.