Identification of highly conserved Trypanosoma cruzi antigens for the development of a universal serological diagnostic assay

Chagas Disease is an important neglected tropical disease caused by Trypanosoma cruzi. There is no gold standard for diagnosis and commercial serological tests perform poorly in certain locations. By aligning T. cruzi genomes covering parasite genetic and geographic diversity, we identified highly conserved proteins that could serve as universal antigens for improved diagnosis. Their antigenicity was tested in high-density peptide microarrays using well-characterized plasma samples, including samples presenting true infections but discordant serology. Individual and combination of epitopes were also evaluated in peptide-ELISAs. We identified >1400 highly conserved T. cruzi proteins evaluated in microarrays. Remarkably, T. cruzi positive controls had a different epitope recognition profile compared to serologically discordant samples. In particular, multiple T. cruzi antigens used in current tests and their strain-variants, and novel epitopes thought to be broadly antigenic failed to be recognized by discordant samples. Nonetheless, >2000 epitopes specifically recognized by IgGs from both positive controls and discordant samples were identified. Evaluation of selected peptides in ELISA further illustrated the extensive variation in antibody profiles among subjects and a peptide combination could outperform a commercial ELISA, increasing assay sensitivity from 52.3% to 72.7%. Individual variation in antibody profiles rather than T. cruzi diversity appears to be the main factor driving differences in serological diagnostic performance according to geography, which will be important to further elucidate. ELISA with a combination of peptides recognized by a greater number of individuals could better capture infections, and further development may lead to an optimal antigen mixture for a universal diagnostic assay.

Antifungal and Antiparasitic Activities of Metallocene-Containing Fluconazole Derivatives

The search for new anti-infectives based on metal complexes is gaining momentum. Among the different options taken by researchers, the one involving the use of organometallic complexes is probably the most successful one with a compound, namely, ferroquine, already in clinical trials against malaria. In this study, we describe the preparation and in-depth characterization of 10 new (organometallic) derivatives of the approved antifungal drug fluconazole. Our rationale is that the sterol 14α-demethylase is an enzyme part of the ergosterol biosynthesis route in Trypanosoma and is similar to the one in pathogenic fungi. To demonstrate our postulate, docking experiments to assess the binding of our compounds with the enzyme were also performed. Our compounds were then tested on a range of fungal strains and parasitic organisms, including the protozoan parasite Trypanosoma cruzi (T. cruzi) responsible for Chagas disease, an endemic disease in Latin America that ranks among some of the most prevalent parasitic diseases worldwide. Of high interest, the two most potent compounds of the study on T. cruzi that contain a ferrocene or cobaltocenium were found to be harmless for an invertebrate animal model, namely, Caenorhabditis elegans (C. elegans), without affecting motility, viability, or development.

Non-histone protein methylation in Trypanosoma cruzi epimastigotes

Post-translational methylation of proteins, which occurs in arginines and lysines, modulates several biological processes at different levels of cell signaling. Recently, methylation has been demonstrated in the regulation beyond histones, for example, in the dynamics of protein-protein and protein-nucleic acid interactions. However, the presence and role of non-histone methylation in Trypanosoma cruzi, the etiologic agent of Chagas disease, has not yet been elucidated. Here, we applied mass spectrometry-based-proteomics (LC-MS/MS) to profile the methylproteome of T. cruzi epimastigotes, describing a total of 1252 methyl sites in 824 proteins. Functional enrichment and protein-protein interaction analysis show that protein methylation impacts important biological processes of the parasite, such as translation, RNA and DNA binding, amino acid, and carbohydrate metabolism. In addition, 171 of the methylated proteins were previously reported to bear phosphorylation sites in T. cruzi, including flagellar proteins and RNA binding proteins, indicating that there may be an interplay between these different modifications in non-histone proteins. Our results show that a broad spectrum of functions is affected by methylation in T. cruzi, indicating its potential to impact important processes in the biology of the parasite and other trypanosomes.

X-ray diffraction and in vivo studies reveal the quinary structure of Trypanosoma cruzi nucleoside diphosphate kinase 1: a novel helical oligomer structure

Trypanosoma cruzi is a flagellated protozoan parasite that causes Chagas disease, which represents a serious health problem in the Americas. Nucleoside diphosphate kinases (NDPKs) are key enzymes that are implicated in cellular energy management. TcNDPK1 is the canonical isoform in the T. cruzi parasite. TcNDPK1 has a cytosolic, perinuclear and nuclear distribution. It is also found in non-membrane-bound filaments adjacent to the nucleus. In the present work, X-ray diffraction and in vivo studies of TcNDPK1 are described. The structure reveals a novel, multi-hexameric, left-handed helical oligomer structure. The results of directed mutagenesis studies led to the conclusion that the microscopic TcNDPK1 granules observed in vivo in T. cruzi parasites are made up by the association of TcNDPK1 oligomers. In the absence of experimental data, analysis of the interactions in the X-ray structure of the TcNDPK1 oligomer suggests the probable assembly and disassembly steps: dimerization, assembly of the hexamer as a trimer of dimers, hexamer association to generate the left-handed helical oligomer structure and finally oligomer association in a parallel manner to form the microscopic TcNDPK1 filaments that are observed in vivo in T. cruzi parasites. Oligomer disassembly takes place on the binding of substrate in the active site of TcNDPK1, leading to dissociation of the hexamers. This study constitutes the first report of such a protein arrangement, which has never previously been seen for any protein or NDPK. Further studies are needed to determine its physiological role. However, it may suggest a paradigm for protein storage reflecting the complex mechanism of action of TcNDPK1.

The farther the better: Investigating how distance from human self affects the propensity of a peptide to be presented on cell surface by MHC class I molecules, the case of Trypanosoma cruzi

More than twenty years ago the reverse vaccinology paradigm came to light trying to design new vaccines based on the analysis of genomic information in order to select those pathogen peptides able to trigger an immune response. In this context, focusing on the proteome of Trypanosoma cruzi, we investigated the link between the probabilities for pathogen peptides to be presented on a cell surface and their distance from human self. We found a reasonable but, as far as we know, undiscovered property: the farther the distance between a peptide and the human-self the higher the probability for that peptide to be presented on a cell surface. We also found that the most distant peptides from human self bind, on average, a broader collection of HLAs than expected, implying a potential immunological role in a large portion of individuals. Finally, introducing a novel quantitative indicator for a peptide to measure its potential immunological role, we proposed a pool of peptides that could be potential epitopes and that can be suitable for experimental testing. The software to compute peptide classes according to the distance from human self is free available at http://www.iasi.cnr.it/~dsantoni/nullomers.

Trypanosoma cruzi Presenilin-Like Transmembrane Aspartyl Protease: Characterization and Cellular Localization

The increasing detection of infections of Trypanosoma cruzi, the etiological agent of Chagas disease, in non-endemic regions beyond Latin America has risen to be a major public health issue. With an impact in the millions of people, current treatments rely on antiquated drugs that produce severe side effects and are considered nearly ineffective for the chronic phase. The minimal progress in the development of new drugs highlights the need for advances in basic research on crucial biochemical pathways in T. cruzi to identify new targets. Here, we report on the T. cruzi presenilin-like transmembrane aspartyl enzyme, a protease of the aspartic class in a unique phylogenetic subgroup with T. vivax separate from protozoans. Computational analyses suggest it contains nine transmembrane domains and an active site with the characteristic PALP motif of the A22 family. Multiple linear B-cell epitopes were identified by SPOT-synthesis analysis with Chagasic patient sera. Two were chosen to generate rabbit antisera, whose signal was primarily localized to the flagellar pocket, intracellular vesicles, and endoplasmic reticulum in parasites by whole-cell immunofluorescence. The results suggest that the parasitic presenilin-like enzyme could have a role in the secretory pathway and serve as a target for the generation of new therapeutics specific to the T. cruzi.

Antiproliferative activity of the dibenzylideneacetone derivate (E)-3-ethyl-4-(4-nitrophenyl)but‑3-en-2-one in Trypanosoma cruzi

Chagas disease is one of the most prevalent neglected diseases in the world. The illness is caused by Trypanosoma cruzi, a protozoan parasite with a complex life cycle and three morphologically distinct developmental stages. Nowadays, the only treatment is based on two nitro-derivative drugs, benznidazole and nifurtimox, which cause serious side effects. Since the treatment is limited, the search for new treatment options for patients with Chagas disease is highly necessary. In this study we analyzed the substance A11K3, a dibenzylideneacetone (DBA). DBAs have an acyclic dienone attached to aryl groups in both β-positions and studies have shown that they have biological activity against tumors cells, bacteria, and protozoa such as T. cruzi and Leishmania spp. Here we show that A11K3 is active against all three T. cruzi evolutionary forms: the epimastigote (IC₅₀ = 3.3 ± 0.8), the trypomastigote (EC₅₀ = 24 ± 4.3) and the intracellular amastigote (IC₅₀ = 9.3 ± 0.5 µM). A cytotoxicity assay in LLCMK₂ cells showed a CC₅₀ of 239.2 ± 15.7 µM giving a selectivity index (CC₅₀/IC₅₀) of 72.7 for epimastigotes, 9.9 for trypomastigotes and 25.9 for intracellular amastigotes. Morphological and ultrastructural analysis of the parasites treated with A11K3 by TEM and SEM revealed alterations in the Golgi complex, mitochondria, plasma membrane and cell body, with an increase of autophagic vacuoles and lipid bodies. Biochemical assays of A11K3-treated T. cruzi showed an increase of ROS, plasma membrane ruptures, lipid peroxidation, mitochondrial membrane depolarization with a decrease in ATP and accumulation of autophagic vacuoles. The results lead to the hypothesis that A11K3 causes death of the protozoan through events such as plasma membrane and mitochondrial alterations and autophagy, characteristic of cell collapse.

Global changes in nitration levels and DNA binding profile of Trypanosoma cruzi histones induced by incubation with host extracellular matrix

Adhesion of T. cruzi trypomastigotes to components of the extracellular matrix (ECM) is an important step in mammalian host cell invasion. We have recently described a significant increase in the tyrosine nitration levels of histones H2A and H4 when trypomastigotes are incubated with components of the ECM. In this work, we used chromatin immunoprecipitation (ChIP) with an anti-nitrotyrosine antibody followed by mass spectrometry to identify nitrated DNA binding proteins in T. cruzi and to detect alterations in nitration levels induced upon parasite incubation with the ECM. Histone H1, H2B, H2A and H3 were detected among the 9 most abundant nitrated DNA binding proteins using this proteomic approach. One nitrated tyrosine residue (Y29) was identified in Histone H2B in the MS/MS spectrum. In addition, we observed a significant increase in the nitration levels of histones H1, H2B, H2A and H4 upon parasite incubation with ECM. Finally, we used ChIP-Seq to map global changes in the DNA binding profile of nitrated proteins. We observed a significant change in the binding pattern of nitrated proteins to DNA after parasite incubation with ECM. This work provides the first global profile of nitrated DNA binding proteins in T. cruzi and additional evidence for modification in the nitration profile of histones upon parasite incubation with ECM. Our data also indicate that the parasite interaction with the ECM induces alterations in chromatin structure, possibly affecting nuclear functions.

Identification of Novel Trypanosoma cruzi Proteasome Inhibitors Using a Luminescence-Based High-Throughput Screening Assay

Chagas' disease, caused by the protozoan parasite Trypanosoma cruzi, is a potentially life-threatening condition that has become a global issue. Current treatment is limited to two medicines that require prolonged dosing and are associated with multiple side effects, which often lead to treatment discontinuation and failure. One way to address these shortcomings is through target-based drug discovery on validated T. cruzi protein targets. One such target is the proteasome, which plays a crucial role in protein degradation and turnover through chymotrypsin-, trypsin-, and caspase-like catalytic activities. In order to initiate a proteasome drug discovery program, we isolated proteasomes from T. cruzi epimastigotes and characterized their activity using a commercially available glow-like luminescence-based assay. We developed a high-throughput biochemical assay for the chymotrypsin-like activity of the T. cruzi proteasome, which was found to be sensitive, specific, and robust but prone to luminescence technology interference. To mitigate this, we also developed a counterscreen assay that identifies potential interferers at the levels of both the luciferase enzyme reporter and the mechanism responsible for a glow-like response. Interestingly, we also found that the peptide substrate for chymotrypsin-like proteasome activity was not specific and was likely partially turned over by other catalytic sites of the protein. Finally, we utilized these biochemical tools to screen 18,098 compounds, exploring diverse drug-like chemical space, which allowed us to identify 39 hits that were active in the primary screening assay and inactive in the counterscreen assay.

Isolation and Characterization of Extracellular Vesicles Derived from Trypanosoma cruzi

Extracellular vesicles (EVs) are heterogeneous membrane-surrounded structures that participate in cellular communications, which comprise exosomes and microvesicles. These vesicles have different biogenesis, and their physiological and pathological roles in chronic and infectious diseases are under constant investigation. In Chagas disease, Trypanosoma cruzi EVs have been described using different approaches. The isolation of T. cruzi-derived EVs has been done mainly using the differential centrifugation technique, and different strategies have been employed for characterization of them. Here, we describe the method to isolate EVs by differential centrifugation and a detection protocol for EVs in T. cruzi-host cell interaction to allow further investigations about this parasite.

Purification of Glycosylphosphatidylinositol-Anchored Mucins from Trypanosoma cruzi Trypomastigotes and Synthesis of α-Gal-Containing Neoglycoproteins: Application as Biomarkers for Reliable Diagnosis and Early Assessment of Chemotherapeutic Outcomes of Chagas Disease

Chagas disease (ChD), caused by the protozoan parasite Trypanosoma cruzi, affects millions of people worldwide. Chemotherapy is restricted to two drugs, which are partially effective and may cause severe side effects, leading to cessation of treatment in a significant number of patients. Currently, there are no biomarkers to assess therapeutic efficacy of these drugs in the chronic stage. Moreover, no preventive or therapeutic vaccines are available. In this chapter, we describe the purification of Trypanosoma cruzi trypomastigote-derived glycosylphosphatidylinositol (GPI)-anchored mucins (tGPI-mucins) for their use as antigens for the reliable primary or confirmatory diagnosis and as prognostic biomarkers for early assessment of cure following ChD chemotherapy. We also describe, as an example, the synthesis of a potential tGPI-mucin-derived α-Gal-terminating glycan and its coupling to a carrier protein for use as diagnostic and prognostic biomarker in ChD.

Differential expression of proteins in genetically distinct Trypanosoma cruzi samples (TcI and TcII DTUs) isolated from chronic Chagas disease cardiac patients

BACKGROUND

Trypanosoma cruzi, a hemoflagellate protozoan parasite and the etiological agent of Chagas disease (CD), exhibits great genetic and biological diversity. Infected individuals may present clinical manifestations with different levels of severity. Several hypotheses have been proposed to attempt to correlate the diversity of clinical signs and symptoms to the genetic variability of T. cruzi. This work aimed to investigate the differential expression of proteins from two distinct genetic groups of T. cruzi (discrete typing units TcI and TcII), isolated from chronically infected individuals displaying the cardiac form of CD. For this purpose, epimastigote forms of the two isolates were cultured in vitro and the cells recovered for protein extraction. Comparative two-dimensional (2D) gel electrophoreses were performed and differentially expressed spots selected for identification by mass spectrometry, followed by database searching and protein categorization.

RESULTS

The 2D electrophoretic profiles revealed the complex composition of the T. cruzi extracted proteome. Protein spots were distributed along the entire pH and molecular mass ranges attesting for the integrity of the protein preparations. In total, 46 differentially expressed proteins were identified present in 40 distinct spots found in the comparative gel analyses. Of these, 16 displayed upregulation in the gel from TcI-typed parasites and 24 appeared overexpressed in the gel from TcII-typed parasites. Functional characterization of differentially expressed proteins revealed major alterations associated with stress response, lipid and amino acid metabolism in parasites of the TcII isolate, whilst those proteins upregulated in the TcI sample were primarily linked to central metabolic pathways.

CONCLUSIONS

The comparative 2D-gel electrophoresis allowed detection of major differences in protein expression between two T. cruzi isolates, belonging to the TcI and TcII genotypes. Our findings suggest that patients displaying the cardiac form of the disease harbor parasites capable of exhibiting distinct proteomic profiles. This should be of relevance to disease prognosis and treatment.

A strategy based on thermal flexibility to design triosephosphate isomerase proteins with increased or decreased kinetic stability

Kinetic stability of proteins determines their susceptibility to irreversibly unfold in a time-dependent process, and therefore its half-life. A residue displacement analysis of temperature-induced unfolding molecular dynamics simulations was recently employed to define the thermal flexibility of proteins. This property was found to be correlated with the activation energy barrier (E_act) separating the native from the transition state in the denaturation process. The E_act was determined from the application of a two-state irreversible model to temperature unfolding experiments using differential scanning calorimetry (DSC). The contribution of each residue to the thermal flexibility of proteins is used here to propose multiple mutations in triosephosphate isomerase (TIM) from Trypanosoma brucei (TbTIM) and Trypanosoma cruzi (TcTIM), two parasites closely related by evolution. These two enzymes, taken as model systems, have practically identical structure but large differences in their kinetic stability. We constructed two functional TIM variants with more than twice and less than half the activation energy of their respective wild-type reference structures. The results show that the proposed strategy is able to identify the crucial residues for the kinetic stability in these enzymes. As it occurs with other protein properties reflecting their complex behavior, kinetic stability appears to be the consequence of an extensive network of inter-residue interactions, acting in a concerted manner. The proposed strategy to design variants can be used with other proteins, to increase or decrease their functional half-life.

Trypanosoma cruzi: analysis of two different strains after piplartine treatment

The hemoflagellate protozoan, Trypanosoma cruzi, mainly transmitted by triatomine insects through blood transfusion or from mother-to-child, causes Chagas' disease. This is a serious parasitic disease that occurs in Latin America, with considerable social and economic impact. Nifurtimox and benznidazole, drugs indicated for treating infected persons, are effective in the acute phase, but poorly effective during the chronic phase. Therefore, it is extremely urgent to find innovative chemotherapeutic agents and/or effective vaccines. Since piplartine has several biological activities, including trypanocidal activity, the present study aimed to evaluate it on two T. cruzi strains proteome. Considerable changes in the expression of some important enzymes involved in parasite protection against oxidative stress, such as tryparedoxin peroxidase (TXNPx) and methionine sulfoxide reductase (MSR) was observed in both strains. These findings suggest that blocking the expression of the two enzymes could be potential targets for therapeutic studies.

Involvement of STI1 protein in the differentiation process of Trypanosoma cruzi

The protozoan Trypanosoma cruzi is a parasite exposed to several environmental stressors inside its invertebrate and vertebrate hosts. Although stress conditions are involved in its differentiation processes, little information is available about the stress response proteins engaged in these activities. This work reports the first known association of the stress-inducible protein 1 (STI1) with the cellular differentiation process in a unicellular eukaryote. Albeit STI1 expression is constitutive in epimastigotes and metacyclic trypomastigotes, higher protein levels were observed in late growth phase epimastigotes subjected to nutritional stress. Analysis by indirect immunofluorescence revealed that T. cruzi STI1 (TcSTI1) is located throughout the cell cytoplasm, with some cytoplasmic granules appearing in greater numbers in late growing epimastigotes and late growing epimastigotes subjected to nutritional stress. We observed that part of the fluorescence signal from both TcSTI1 and TcHSP70 colocalized around the nucleus. Gene silencing of sti1 in Trypanosoma brucei did not affect cell growth. Similarly, the growth of T. cruzi mutant parasites with a single allele sti1 gene knockout was not affected. However, the differentiation of epimastigotes in metacyclic trypomastigotes (metacyclogenesis) was compromised. Lower production rates and numbers of metacyclic trypomastigotes were obtained from the mutant parasites compared with the wild-type parasites. These data indicate that reduced levels of TcSTI1 decrease the rate of in vitro metacyclogenesis, suggesting that this protein may participate in the differentiation process of T. cruzi.

High-resolution profiling of linear B-cell epitopes from mucin-associated surface proteins (MASPs) of Trypanosoma cruzi during human infections

BACKGROUND

The Trypanosoma cruzi genome bears a huge family of genes and pseudogenes coding for Mucin-Associated Surface Proteins (MASPs). MASP molecules display a 'mosaic' structure, with highly conserved flanking regions and a strikingly variable central and mature domain made up of different combinations of a large repertoire of short sequence motifs. MASP molecules are highly expressed in mammal-dwelling stages of T. cruzi and may be involved in parasite-host interactions and/or in diverting the immune response.

METHODS/PRINCIPLE FINDINGS

High-density microarrays composed of fully overlapped 15mer peptides spanning the entire sequences of 232 non-redundant MASPs (~25% of the total MASP content) were screened with chronic Chagasic sera. This strategy led to the identification of 86 antigenic motifs, each one likely representing a single linear B-cell epitope, which were mapped to 69 different MASPs. These motifs could be further grouped into 31 clusters of structurally- and likely antigenically-related sequences, and fully characterized. In contrast to previous reports, we show that MASP antigenic motifs are restricted to the central and mature region of MASP polypeptides, consistent with their intracellular processing. The antigenicity of these motifs displayed significant positive correlation with their genome dosage and their relative position within the MASP polypeptide. In addition, we verified the biased genetic co-occurrence of certain antigenic motifs within MASP polypeptides, compatible with proposed intra-family recombination events underlying the evolution of their coding genes. Sequences spanning 7 MASP antigenic motifs were further evaluated using distinct synthesis/display approaches and a large panel of serum samples. Overall, the serological recognition of MASP antigenic motifs exhibited a remarkable non normal distribution among the T. cruzi seropositive population, thus reducing their applicability in conventional serodiagnosis. As previously observed in in vitro and animal infection models, immune signatures supported the concurrent expression of several MASPs during human infection.

CONCLUSIONS/SIGNIFICANCE

In spite of their conspicuous expression and potential roles in parasite biology, this study constitutes the first unbiased, high-resolution profiling of linear B-cell epitopes from T. cruzi MASPs during human infection.

Immunization with Tc52 or its amino terminal domain adjuvanted with c-di-AMP induces Th17+Th1 specific immune responses and confers protection against Trypanosoma cruzi

The development of new adjuvants enables fine modulation of the elicited immune responses. Ideally, the use of one or more adjuvants should result in the induction of a protective immune response against the specific pathogen. We have evaluated the immune response and protection against Trypanosoma cruzi infection in mice vaccinated with recombinant Tc52 or its N- and C-terminal domains (NTc52 and CTc52) adjuvanted either with the STING (Stimulator of Interferon Genes) agonist cyclic di-AMP (c-di-AMP), a pegylated derivative of α-galactosylceramide (αGC-PEG), or oligodeoxynucleotides containing unmethylated CpG motifs (ODN-CpG). All groups immunized with the recombinant proteins plus adjuvant: Tc52+c-di-AMP, NTc52+c-di-AMP, CTc52+c-di-AMP, NTc52+c-di-AMP+αGC-PEG, NTc52+CpG, developed significantly higher anti-Tc52 IgG titers than controls. Groups immunized with c-di-AMP and Tc52, NTc52 or CTc52 showed the highest Tc52-specific IgA titers in nasal lavages. All groups immunized with the recombinant proteins plus adjuvant developed a strong specific cellular immune response in splenocytes and lymph node cells with significant differences for groups immunized with c-di-AMP and Tc52, NTc52 or CTc52. These groups also showed high levels of Tc52-specific IL-17 and IFN-γ producing cells, while NTc52+CpG group only showed significant difference with control in IFN-γ producing cells. Groups immunized with c-di-AMP and Tc52, NTc52 or CTc52 developed predominantly a Th17 and Th1immune response, whereas for NTc52+CpG it was a dominant Th1 response. It was previously described that αGC-PEG inhibits Th17 differentiation by activating NKT cells. Thus, in this work we have also included a group immunized with both adjuvants (NTc52+c-di-AMP+αGC-PEG) with the aim to modulate the Th17 response induced by c-di-AMP. This group showed a significant reduction in the number of Tc52-specific IL-17 producing splenocytes, as compared to the group NTc52+c-di-AMP, which has in turn correlated with a reduction in protection against infection. These results suggest that the Th17 immune response developed after immunizing with NTc52+c-di-AMP could have a protective role against T. cruzi infection. Groups NTc52+c-di-AMP, Tc52+c-di-AMP and NTc52PB, were the ones that showed better protection against infection with lower parasitemia and weight loss, and higher survival.

Chagas disease is a parasitic disease caused by a protozoan parasite (Trypanosoma cruzi) which has a complex life cycle including insect vector and mammalians. In Latin America, 7–10 million people are infected, 100 million people are at risk of infection, and about 56,000 new infection cases and 12,000 deaths are registered annually. Migration spread the geographic distribution of the disease to North America and Europe. The infection in humans has an initial acute stage followed by a chronic stage where up to 30% of patients develop cardiac alterations and 10% develop digestive, neurological or mixed alterations. The acute infection is hardly detected and there is not drug to treat the chronic infection. Thus, there is an urgent need for prophylactic and therapeutic vaccines development. Several attempts to find a vaccine antigen has been made and the protein Tc52 is a good candidate. In a vaccine composition, as important as the antigen is the adjuvants, which are substances able to increase, improve or modified the immune response. This research provides information about the immune response and protection against Trypanosoma cruzi infection elicited by Tc52 or portions of this molecule using different adjuvants.

The N-myristoylome of Trypanosoma cruzi

Protein N-myristoylation is catalysed by N-myristoyltransferase (NMT), an essential and druggable target in Trypanosoma cruzi, the causative agent of Chagas' disease. Here we have employed whole cell labelling with azidomyristic acid and click chemistry to identify N-myristoylated proteins in different life cycle stages of the parasite. Only minor differences in fluorescent-labelling were observed between the dividing forms (the insect epimastigote and mammalian amastigote stages) and the non-dividing trypomastigote stage. Using a combination of label-free and stable isotope labelling of cells in culture (SILAC) based proteomic strategies in the presence and absence of the NMT inhibitor DDD85646, we identified 56 proteins enriched in at least two out of the three experimental approaches. Of these, 6 were likely to be false positives, with the remaining 50 commencing with amino acids MG at the N-terminus in one or more of the T. cruzi genomes. Most of these are proteins of unknown function (32), with the remainder (18) implicated in a diverse range of critical cellular and metabolic functions such as intracellular transport, cell signalling and protein turnover. In summary, we have established that 0.43-0.46% of the proteome is N-myristoylated in T. cruzi approaching that of other eukaryotic organisms (0.5-1.7%).

Expression and the Peculiar Enzymatic Behavior of the Trypanosoma cruzi NTH1 DNA Glycosylase

Trypanosoma cruzi, the etiological agent of Chagas’ disease, presents three cellular forms (trypomastigotes, epimastigotes and amastigotes), all of which are submitted to oxidative species in its hosts. However, T. cruzi is able to resist oxidative stress suggesting a high efficiency of its DNA repair machinery.The Base Excision Repair (BER) pathway is one of the main DNA repair mechanisms in other eukaryotes and in T. cruzi as well. DNA glycosylases are enzymes involved in the recognition of oxidative DNA damage and in the removal of oxidized bases, constituting the first step of the BER pathway. Here, we describe the presence and activity of TcNTH1, a nuclear T. cruzi DNA glycosylase. Surprisingly, purified recombinant TcNTH1 does not remove the thymine glycol base, but catalyzes the cleavage of a probe showing an AP site. The same activity was found in epimastigote and trypomastigote homogenates suggesting that the BER pathway is not involved in thymine glycol DNA repair. TcNTH1 DNA-binding properties assayed in silico are in agreement with the absence of a thymine glycol removing function of that parasite enzyme. Over expression of TcNTH1 decrease parasite viability when transfected epimastigotes are submitted to a sustained production of H₂O₂.Therefore, TcNTH1 is the only known NTH1 orthologous unable to eliminate thymine glycol derivatives but that recognizes and cuts an AP site, most probably by a beta-elimination mechanism. We cannot discard that TcNTH1 presents DNA glycosylase activity on other DNA base lesions. Accordingly, a different DNA repair mechanism should be expected leading to eliminate thymine glycol from oxidized parasite DNA. Furthermore, TcNTH1 may play a role in the AP site recognition and processing.

Effect of secondary anchor amino acid substitutions on the immunogenic properties of an HLA-A*0201-restricted T cell epitope derived from the Trypanosoma cruzi KMP-11 protein

The TcTLE peptide (TLEEFSAKL) is a CD8(+) T cell HLA-A*0201-restricted epitope derived from the Trypanosoma cruzi KMP-11 protein that is efficiently processed, presented and recognized by CD8(+) T cells from chagasic patients. Since the immunogenic properties of wild-type epitopes may be enhanced by suitable substitutions in secondary anchor residues, we have studied the effect of introducing specific mutations at position 3, 6 and 7 of the TcTLE peptide. Mutations (E3L, S6V and A7F) were chosen on the basis of in silico predictions and in vitro assays were performed to determine the TcTLE-modified peptide binding capacity to the HLA-A*0201 molecule. In addition, the functional activity of peptide-specific CD8(+) T cells in HLA-A2(+) chagasic patients was also interrogated. In contrast to bioinformatics predictions, the TcTLE-modified peptide was found to have lower binding affinity and stability than the original peptide. Nevertheless, CD8(+) T cells from chronic chagasic patients recognized the TcTLE-modified peptide producing TNF-α and INF-γ and expressing CD107a/b, though in less extension than the response triggered by the original peptide. Overall, although the amino acids at positions 3, 6 and 7 of TcTLE are critical for the peptide affinity, they have a limited effect on the immunogenic properties of the TcTLE epitope.

Structural and functional analysis of a platelet-activating lysophosphatidylcholine of Trypanosoma cruzi

Background

Trypanosoma cruzi is the causative agent of the life-threatening Chagas disease, in which increased platelet aggregation related to myocarditis is observed. Platelet-activating factor (PAF) is a potent intercellular lipid mediator and second messenger that exerts its activity through a PAF-specific receptor (PAFR). Previous data from our group suggested that T. cruzi synthesizes a phospholipid with PAF-like activity. The structure of T. cruzi PAF-like molecule, however, remains elusive.

Methodology/Principal findings

Here, we have purified and structurally characterized the putative T. cruzi PAF-like molecule by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). Our ESI-MS/MS data demonstrated that the T. cruzi PAF-like molecule is actually a lysophosphatidylcholine (LPC), namely sn-1 C18:1(delta 9)-LPC. Similar to PAF, the platelet-aggregating activity of C18:1-LPC was abrogated by the PAFR antagonist, WEB 2086. Other major LPC species, i.e., C16:0-, C18:0-, and C18:2-LPC, were also characterized in all T. cruzi stages. These LPC species, however, failed to induce platelet aggregation. Quantification of T. cruzi LPC species by ESI-MS revealed that intracellular amastigote and trypomastigote forms have much higher levels of C18:1-LPC than epimastigote and metacyclic trypomastigote forms. C18:1-LPC was also found to be secreted by the parasite in extracellular vesicles (EV) and an EV-free fraction. A three-dimensional model of PAFR was constructed and a molecular docking study was performed to predict the interactions between the PAFR model and PAF, and each LPC species. Molecular docking data suggested that, contrary to other LPC species analyzed, C18:1-LPC is predicted to interact with the PAFR model in a fashion similar to PAF.

Conclusions/Significance

Taken together, our data indicate that T. cruzi synthesizes a bioactive C18:1-LPC, which aggregates platelets via PAFR. We propose that C18:1-LPC might be an important lipid mediator in the progression of Chagas disease and its biosynthesis could eventually be exploited as a potential target for new therapeutic interventions.

Chagas disease, caused by the parasite Trypanosoma cruzi, was exclusively confined to Latin America but it has recently spread to other regions of the world. Chagas disease affects 8–10 million people and kills thousands of them every year. Lysophosphatidylcholine (LPC) is a major bioactive phospholipid of human plasma low-density lipoproteins (LDL). Platelet-activating factor (PAF) is a phospholipid similar to LPC and a potent intercellular mediator. Both PAF and LPC have been reported to act on mammalian cells through PAF receptor (PAFR). Previous data from our group suggested that T. cruzi produces a phospholipid with PAF activity. Here, we describe the structural and functional analysis of different species of LPC from T. cruzi, including a LPC with a fatty acid chain of 18 carbon atoms and one double bond (C18:1-LPC). We also show that C18:1-LPC is able to induce rabbit platelet aggregation, which is abrogated by a PAFR antagonist. In addition, a three-dimensional model of human PAFR was constructed. Contrary to other T. cruzi LPC molecules, C18:1-LPC is predicted to interact with the PAFR model in a fashion similar to PAF. Further studies are needed to validate the biosynthesis of T. cruzi C18:1-LPC as a potential drug target in Chagas disease.

Antibodies against mucin-based glycopeptides affect Trypanosoma cruzi cell invasion and tumor cell viability

This study describes the synthesis of glycopeptides NHAc[βGal]-(Thr)2 -[αGalNAc]-(Thr)2 -[αGlcNAc]-(Thr)2 Gly-OVA (1-OVA) and NHAc[βGal-αGalNAc]-(Thr)3 -[αLacNAc]-(Thr)3 -Gly-OVA (2-OVA) as mimetics of both T. cruzi and tumor mucin glycoproteins. These glycopeptides were obtained by solid-phase synthesis, which involved the prior preparation of the protected glycosyl amino acids αGlcNAc-ThrOH (3), αGalNAc-ThrOH (4), βGal-ThrOH (5), αLacNAc-ThrOH (6), and βGal-αGalNAc-ThrOH (7) through glycosylation reactions. Immunizations of mice with glycopeptides 1-OVA and 2-OVA induced high antibody titers (1:16 000), as verified by ELISA tests, whereas flow cytometry assays showed the capacity of the obtained anti-glycopeptides 1-OVA and 2-OVA antibodies to recognize both T. cruzi and MCF-7 tumor cells. In addition, antisera induced by glycopeptides 1-OVA and 2-OVA were also able to inhibit T. cruzi fibroblast cell invasion (70 %) and to induce antibody-mediated cellular cytotoxicity (ADCC) against MCF-7 cells, with 50 % reduction of cell viability.

Unraveling the differences of the hydrolytic activity of Trypanosoma cruzi trans-sialidase and Trypanosoma rangeli sialidase: a quantum mechanics-molecular mechanics modeling study

Chagas' disease, also known as American trypanosomiasis, is a lethal, chronic disease that currently affects more than 10 million people in Central and South America. The trans-sialidase from Trypanosoma cruzi (T. cruzi, TcTS) is a crucial enzyme for the survival of this parasite: sialic acids from the host are transferred to the cell surface glycoproteins of the trypanosome, thereby evading the host's immune system. On the other hand, the sialidase of T. rangeli (TrSA), which shares 70% sequence identity with TcTS, is a strict hydrolase and shows no trans-sialidase activity. Therefore, TcTS and TrSA represent an excellent framework to understand how different catalytic activities can be achieved with extremely similar structures. By means of combined quantum mechanics-molecular mechanics (QM/MM, SCC-DFTB/Amberff99SB) calculations and umbrella sampling simulations, we investigated the hydrolysis mechanisms of TcTS and TrSA and computed the free energy profiles of these reactions. The results, together with our previous computational investigations, are able to explain the catalytic mechanism of sialidases and describe how subtle differences in the active site make TrSA a strict hydrolase and TcTS a more efficient trans-sialidase.

Identification of a functional prostanoid-like receptor in the protozoan parasite, Trypanosoma cruzi

Trypanosoma cruzi infection in humans and experimental animals causes Chagas disease which is often accompanied by myocarditis, cardiomyopathy, and vasculopathy. T. cruzi-derived thromboxane A2 (TXA2) modulates vasculopathy and other pathophysiological features of Chagasic cardiomyopathy. Here, we provide evidence that epimastigotes, trypomastigotes, and amastigotes of T. cruzi (Brazil and Tulahuen strains) express a biologically active prostanoid receptor (PR) that is responsive to TXA2 mimetics, e.g. IBOP. This putative receptor, TcPR, is mainly localized in the flagellar membrane of the parasites and shows a similar glycosylation pattern to that of bona fide thromboxane prostanoid (TP) receptors obtained from human platelets. Furthermore, TXA2-PR signal transduction activates T. cruzi-specific MAPK pathways. While mammalian TP is a G-protein coupled receptor (GPCR); T. cruzi genome sequencing has not demonstrated any confirmed GPCRs in these parasites. Based on this genome sequencing it is likely that TcPR is unique in these protists with no counterpart in mammals. TXA2 is a potent vasoconstrictor which contributes to the pathogenesis of Chagasic cardiovascular disease. It may, however, also control parasite differentiation and proliferation in the infected host allowing the infection to progress to a chronic state.

Crystal structure of the complex mAb 17.2 and the C-terminal region of Trypanosoma cruzi P2β protein: implications in cross-reactivity

Patients with Chronic Chagas' Heart Disease possess high levels of antibodies against the carboxyl-terminal end of the ribosomal P2ß protein of Trypanosoma cruzi (TcP2ß). These antibodies, as well as the murine monoclonal antibody (mAb) 17.2, recognize the last 13 amino acids of TcP2ß (called the R13 epitope: EEEDDDMGFGLFD) and are able to cross-react with, and stimulate, the ß1 adrenergic receptor (ß1-AR). Indeed, the mAb 17.2 was able to specifically detect human β1-AR, stably transfected into HEK cells, by flow cytometry and to induce repolarisation abnormalities and first degree atrioventricular conduction block after passive transfer to naïve mice. To study the structural basis of this cross-reactivity, we determined the crystal structure of the Fab region of the mAb 17.2 alone at 2.31 Å resolution and in complex with the R13 peptide at 1.89 Å resolution. We identified as key contact residues on R13 peptide Glu3, Asp6 and Phe9 as was previously shown by alanine scanning. Additionally, we generated a model of human β1-AR to elucidate the interaction with anti-R13 antibodies. These data provide an understanding of the molecular basis of cross-reactive antibodies induced by chronic infection with Trypanosoma cruzi.

Characterization of TcHMGB, a high mobility group B family member protein from Trypanosoma cruzi

High mobility group B (HMGB) proteins are highly abundant non-histone chromatin proteins that play important roles in the execution and control of many nuclear functions. Based on homology searches, we identified the coding sequence for the TcHMGB protein, an HMGB family member from Trypanosoma cruzi. TcHMGB has two HMG box domains, similar to mammalian HMGBs, but lacks the typical C-terminal acidic tail. Instead, it contains a 110 amino acid long N-terminal domain. The TcHMGB N-terminal domain is conserved between the TriTryp sequences (70-80% similarity) and seems to be characteristic of kinetoplastid HMGBs. Despite these differences, TcHMGB maintains HMG box architectural functions: we demonstrated that the trypanosomatid HMGB binds distorted DNA structures such as cruciform DNA in gel shift assays. TcHMGB is also able to bend linear DNA as determined by T4 ligase circularization assays, similar to other HMGB family members. Immunofluorescence and western blot assays showed that TcHMGB is a nuclear protein expressed in all life cycle stages. Protein levels, however, seem to vary throughout the life cycle, which may be related to previously described changes in heterochromatin distribution and transcription rates.

Proton transfer facilitated by ligand binding. An energetic analysis of the catalytic mechanism of Trypanosoma cruzi trans-sialidase

Trans-sialidase is a crucial enzyme for the infection of Trypanosoma cruzi, the protozoa responsible for Chagas' disease in humans. This enzyme catalyzes the transfer of sialic acids from mammalian host cells to parasitic cell surfaces in order to mask the infection from the host's immune system. It represents a promising target for the development of therapeutics to treat the disease and has been subject of extensive structural studies. Elaborate experiments suggested formation of a long-lived covalent intermediate in the catalytic mechanism and identified a Tyr/Glu pair as an unusual catalytic couple. This requires that the tyrosine hydroxyl proton is transferred to the carboxylate group of glutamate before the nucleophilic attack. Since the solution pK(a)s of tyrosine and glutamate are very different, this transfer can only be accomplished if the reaction environment selectively stabilizes the product state. We compute the free energy profile for the proton transfer in different environments, and our results indicate that it can take place in the active site of trans-sialidase, but only after substrate binding. By means of the energy decomposition method, we explain the influence that the active site residues exert on the reaction and how the pattern is changed when the substrate is present. This study represents an initial step that can shed light on our understanding of the catalytic mechanism of this reaction.

Functional characterization of NADP-dependent isocitrate dehydrogenase isozymes from Trypanosoma cruzi

Trypanosoma cruzi exhibits two putative isocitrate dehydrogenases (IDHs). Both idh genes were cloned and the recombinant enzymes expressed in Escherichia coli. Our results showed that T. cruzi IDHs are strictly dependent on NADP(+) and display apparent affinities towards isocitrate and the coenzyme in the low micromolar range. In T. cruzi, IDHs are cytosolic and mitochondrial enzymes, and there is no evidence for the typical Krebs cycle-related NAD-dependent IDH. Hence, like in Trypanosoma brucei, the Krebs cycle is not a canonical route in T. cruzi. However, the citrate produced in the mitochondrion could be isomerized into isocitrate in the cytosol and the mitochondrion by means of the putative aconitase, which would provide the substrate for both IDHs. The cytosolic IDH is significantly more abundant in amastigotes, cell-derived and metacyclic trypomastigotes than in epimastigotes. This observation fits in well with the expected oxidative burst this pathogen has to face when infecting the mammalian host.

[Role of three ELISA tests using promastigote homogenates of Leishmania braziliensis, L. amazonensis and L. guyanensis in the diagnosis of tegumentary leishmaniasis]

It is important to know whether the variability of species of Leishmania parasites circulating in a region affects the performance of the ELISA test for the diagnosis of leishmaniasis. Therefore, the aim of this study was to analyze the reactivity of the ELISA using homogenates of promastigotes of Leishmania (V.) braziliensis (ELISAb), Leishmania (L) amazonensis (ELISAa) and Leishmania (V.) guyanensis (ELISAg) against different sera groups. Samples from individuals with cutaneous leishmaniasis (n = 37), mucocutaneous leishmaniasis (n = 8), healthy controls (n = 52), persons infected with Trypanosoma cruzi (n = 11) and mixed infections (n = 14) were included in the study. We calculated sensitivities, specificities, cut offs, and predictive values for the three tests and compared them using ANOVA, kappa index, ROC curves comparison, and confidence intervals calculated by the bootstrap method. Significant differences were found when comparing the OD levels of sera from patients with cutaneous leishmaniasis against healthy controls, but there were no differences when comparing the different ELISAs. The sensitivities calculated for ELISAb and ELISAa were 84.6 and of 88.5% for ELISAg, while the value of specificity for the three tests was 96.2. The kappa index (0.87) and comparison of ROC curves showed similar performance for the three ELISAs (p = 0.225). The high reactivity obtained for these ELISAs in sera of patients with mucocutaneous leishmaniasis indicates this test as an important complement in the diagnosis of the disease.

Comparative in vivo antiangiogenic effects of calreticulin from Trypanosoma cruzi and Homo sapiens sapiens

Angiogenesis is a complex multi-step process of neovascularization arising from preexisting blood vessels whose generation is regulated by pro- and anti-angiogenic factors. Both Trypanosoma cruzi calreticulin (TcCRT) and its human counterpart (HuCRT) are antiangiogenic. This is the first report where the TcCRT and HuCRT anti-angiogenic properties are compared in vivo. In the chick embryonic chorioallantoid membrane assay (CAM) and at equimolar concentrations, TcCRT displayed significantly higher antiangiogenic activities than its human counterpart. LPS had marginal effects at the concentrations present in the recombinant protein preparations and the TcCRT antiangiogenic effects were largely inhibited by specific polyclonal antibodies, thus, reinforcing the fact that the observed TcCRT effects can be attributed to the parasite-derived molecule and not to the endotoxin. The antiangiogenic TcCRT effects correlate with its anti-tumor in vivo effects, as recently shown in our laboratory.

Role of the gp85/trans-sialidases in Trypanosoma cruzi tissue tropism: preferential binding of a conserved peptide motif to the vasculature in vivo

Background

Transmitted by blood-sucking insects, the unicellular parasite Trypanosoma cruzi is the causative agent of Chagas' disease, a malady manifested in a variety of symptoms from heart disease to digestive and urinary tract dysfunctions. The reasons for such organ preference have been a matter of great interest in the field, particularly because the parasite can invade nearly every cell line and it can be found in most tissues following an infection. Among the molecular factors that contribute to virulence is a large multigene family of proteins known as gp85/trans-sialidase, which participates in cell attachment and invasion. But whether these proteins also contribute to tissue homing had not yet been investigated. Here, a combination of endothelial cell immortalization and phage display techniques has been used to investigate the role of gp85/trans-sialidase in binding to the vasculature.

Methods

Bacteriophage expressing an important peptide motif (denominated FLY) common to all gp85/trans-sialidase proteins was used as a surrogate to investigate the interaction of this motif with the endothelium compartment. For that purpose phage particles were incubated with endothelial cells obtained from different organs or injected into mice intravenously and the number of phage particles bound to cells or tissues was determined. Binding of phages to intermediate filament proteins has also been studied.

Findings and Conclusions

Our data indicate that FLY interacts with the endothelium in an organ-dependent manner with significantly higher avidity for the heart vasculature. Phage display results also show that FLY interaction with intermediate filament proteins is not limited to cytokeratin 18 (CK18), which may explain the wide variety of cells infected by the parasite. This is the first time that members of the intermediate filaments in general, constituted by a large group of ubiquitously expressed proteins, have been implicated in T. cruzi cell invasion and tissue homing.

Chagas' disease, caused by the protozoon Trypanosoma cruzi, is an ailment affecting approximately 12–14 million people in Iberoamerica and is becoming increasingly important in North America and Europe as a result of migratory currents. The parasite invades mainly cells of the heart or the walls of the digestive tract. The patients with symptoms develop heart disease or gastrointestinal motor disorders. We and others have implicated the T. cruzi gp85/trans-sialidase surface protein family in the attachment of the parasite to the host cells. These proteins share a peptide motif called FLY. The involvement of FLY in parasite interaction with endothelial cells from different organs has been studied using bacteriophages expressing the FLY peptide as surrogates. We found that phages expressing FLY bind to endothelial cells in an organ dependent manner, particularly in the heart. Also, this peptide binds strongly to intermediate cell filaments, like cytokeratins and vimentin. These results indicate that FLY might be an important contributor to tissue tropism. It also supports the notion that the vasculature and the endothelial cells are important players in Chagas' disease. These data may have important implications in the pathology of Chagas' disease and novel therapeutic approaches for patients afflicted with this disease.

Structural characterization of CYP51 from Trypanosoma cruzi and Trypanosoma brucei bound to the antifungal drugs posaconazole and fluconazole

BACKGROUND

Chagas Disease is the leading cause of heart failure in Latin America. Current drug therapy is limited by issues of both efficacy and severe side effects. Trypansoma cruzi, the protozoan agent of Chagas Disease, is closely related to two other major global pathogens, Leishmania spp., responsible for leishmaniasis, and Trypansoma brucei, the causative agent of African Sleeping Sickness. Both T. cruzi and Leishmania parasites have an essential requirement for ergosterol, and are thus vulnerable to inhibitors of sterol 14alpha-demethylase (CYP51), which catalyzes the conversion of lanosterol to ergosterol. Clinically employed anti-fungal azoles inhibit ergosterol biosynthesis in fungi, and specific azoles are also effective against both Trypanosoma and Leishmania parasites. However, modification of azoles to enhance efficacy and circumvent potential drug resistance has been problematic for both parasitic and fungal infections due to the lack of structural insights into drug binding.

METHODOLOGY/PRINCIPAL FINDINGS

We have determined the crystal structures for CYP51 from T. cruzi (resolutions of 2.35 A and 2.27 A), and from the related pathogen T. brucei (resolutions of 2.7 A and 2.6 A), co-crystallized with the antifungal drugs fluconazole and posaconazole. Remarkably, both drugs adopt multiple conformations when binding the target. The fluconazole 2,4-difluorophenyl ring flips 180 degrees depending on the H-bonding interactions with the BC-loop. The terminus of the long functional tail group of posaconazole is bound loosely in the mouth of the hydrophobic substrate binding tunnel, suggesting that the major contribution of the tail to drug efficacy is for pharmacokinetics rather than in interactions with the target.

CONCLUSIONS/SIGNIFICANCE

The structures provide new insights into binding of azoles to CYP51 and mechanisms of potential drug resistance. Our studies define in structural detail the CYP51 therapeutic target in T. cruzi, and offer a starting point for rationally designed anti-Chagasic drugs with improved efficacy and reduced toxicity.

Synthesis of trisaccharides containing internal galactofuranose O-linked in Trypanosoma cruzi mucins

The trisaccharides beta-D-Galf-(1-->2)-beta-D-Galf-(1-->4)-D-GlcNAc (5) and beta-D-Galp-(1-->2)-beta-D-Galf-(1-->4)-D-GlcNAc (6) constitute novel structures isolated as alditols when released by reductive beta-elimination from mucins of Trypanosoma cruzi (Tulahuen strain). Trisaccharides 5 and 6 were synthesized employing the aldonolactone approach. Thus, a convenient D-galactono-1,4-lactone derivative was used for the introduction of the internal galactofuranose and the trichloroacetimidate method was employed for glycosylation reactions. Due to the lack of anchimeric assistance on O-2 of the galactofuranosyl precursor, glycosylation studies were performed under different conditions. The nature of the solvent strongly determined the stereochemical course of the glycosylation reactions when the galactofuranosyl donor was substituted either by 2-O-Galp or 2-O-Galf.

Trypanosoma cruzi SHSP16: Characterization of an alpha-crystallin small heat shock protein

This report describes the characterization of a member of the alpha-crystallin small heat shock protein family in a trypanosomatid, which was isolated from the human pathogen Trypanosoma cruzi. One alpha-crystallin small heat shock protein gene was identified in a database search. The coding region is located in an open reading frame of 429bp encoding a protein of 142 amino acids. The amino acid sequence was deduced from the isolated gene. The protein has an alpha-crystallin domain characteristic of the alpha-crystallin small heat shock proteins and a molecular weight of 15.9kDa, so the protein was designated SHSP16. Analysis of the nucleotide sequences of four different T. cruzi strains showed two different sequences, which correspond to the two main T. cruzi genetic groups. Gene expression analysis by RT-PCR showed increased transcription of the gene after the parasite was exposed to heat stress. Recombinant SHSP16 showed molecular chaperone activity in vitro, because it inhibited the thermal aggregation of the mitochondrial malate dehydrogenase enzyme.

Crystallization and preliminary X-ray diffraction analysis of Q4DV70 from Trypanosoma cruzi, a hypothetical protein with a putative thioredoxin domain

Q4DV70 is annotated in the Trypanosoma cruzi CL Brener genome as a hypothetical protein with a predicted thioredoxin-like fold, although the catalytic cysteine residues that are conserved in typical oxidoreductases are replaced by serine residues. Gene-expression analysis indicates that this protein is differentially expressed during the T. cruzi life cycle, suggesting that it plays an important role during T. cruzi development. The gene coding for Q4DV70 was cloned and the protein was overexpressed in Escherichia coli with an N-terminal His tag. Purification of Q4DV70 was carried out by affinity and size-exclusion chromatography and the His tag was removed by TEV protease digestion. Crystals of Q4DV70 were grown using the sitting-drop vapour-diffusion method. A diffraction data set was collected to 1.50 A resolution from a single crystal grown in 25% PEG 1500, 200 mM sodium thiocyanate pH 6.9, 10 mM phenol and 10% ethylene glycol. The crystal belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 35.04, b = 50.32, c = 61.18 A. The Q4DV70 structure was solved by molecular replacement using protein disulfide isomerase from yeast (PDB code 2b5e) as a search model. Initial refinement of the model indicated that the solution was correct. These data are being used for refinement of the model of Q4DV70.

Antiprotozoal activity of (8-hydroxymethylen)-trieicosanyl acetate isolated from Senna villosa

A white solid compound was isolated from the chloroform extract of the leaves of Senna villosa. The material was identified by (1)H-NMR, (13)C-NMR, IR and EM methods as (8-hydroxymethylen)-trieicosanyl acetate, a new compound with biological activity, which was tested in vitro at concentrations of 1.65, 3.3 and 6.6 microg/ml for inhibition of the growth of Trypanosoma cruzi epimastigotes and tripomastigotes. We observed inhibition of growth at all concentrations tested, and the effect at concentrations of 3.3 and 6.6 microg/ml was greater than that of gentian violet (positive control). At the concentration of 6.6 microg/ml, the compound showed the greatest inhibitory effect against the growth of both forms of the parasite.

Steroidogenic capacity of Trypanosoma cruzi trypomastigotes

American Trypanosomiasis is caused by the hemoflagellate Trypanosoma cruzi (T. cruzi) and affects millions of persons causing variable degrees of digestive and heart disturbances. As far as we concerned, T. cruzi capacity to synthesize steroid hormones has not been investigated. Therefore, the aim of this work was to investigate the capacity of T. cruzi trypomastigotes to transform tritiated steroid precursors into androgens and estrogens. The T. cruzi Tulahuén strain was obtained from mice blood. The trypomastigotes were cultured for 6 and 24h in Dulbbeco's modified Eagle's medium plus FCS and antibiotics. Tritiated dehydroepiandrosterone or androstendione were added to the culture media and parasites were incubated for 6 or 24h. The cultures were centrifuged and ether extracted. The steroids were analyzed by thin layer chromatography (TLC) in two solvent systems. After incubation with 3H-androstenedione, T. cruzi trypomastigotes synthesized 3H-testosterone (T), 3H-17beta-estradiol (E2) and 3H-estrone (E1). Metabolism of 3H-DHEA by the parasites yielded 3H-androstendione and 3H-androstendiol at 6h of incubation. The recrystallization procedure further demonstrated the 3H-androstendiol and 3H-17beta-estradiol syntheses. Results indicate for the first time that T. cruzi trypomastigotes produce androgens and estrogens when incubated in the presence of steroid precursors and suggest the presence of active parasite steroidogenic enzymes.

UV-MALDI mass spectrometry analysis of NBD-glycosphingolipids without an external matrix

Each day, advances in the instrumentation and operating protocols bring new applications and insights into the molecular processes of ultra violet-matrix assisted laser desorption/ionization-mass spectrometry (UV-MALDI MS), increasing its potential use. We report here an approach in which mass spectrometry analysis of sphingolipids has been performed using a fluorescent tag (nitrobenz-2-oxa-1, 3-diazole, NBD) covalently linked to the sphingoid base as matrix. Thus, different labeled-sphingolipids were analyzed: ceramide, dihydroceramide, acetylceramide, glucosylceramide, galactosylceramide, galactosyldihydroceramide. In addition an extract of glycosphingolipids obtained from epimastigote forms of Trypanosoma cruzi metabolically labeled with NBD-ceramide was analyzed. The goal of this work is to show that no matrix needs to be added for the mass spectrometry analysis as the same tag used to label the lipids may generate efficiently analyte ions to obtain high quality signals.

Proteomic analysis of metacyclic trypomastigotes undergoing Trypanosoma cruzi metacyclogenesis

Trypanosoma cruzi, the causative agent of the Chagas disease, has a complex life cycle alternating between replicative and noninfective forms with nonreplicative and infective forms of the parasite. Metacyclogenesis is a process that takes place in the invertebrate host, comprising morphogenetic transformation from a noninfective form to an infective form, such that parasites acquire the ability to invade human cells. We analyze here the metacyclogenesis process by 2D electrophoresis coupled to MALDI-TOF MS. A large proportion of unique proteins expressed during metacyclogenesis were observed. Interestingly, 50% of the spots were found to differ between epimastigotes and trypomastigotes. We provide a 2D map of the infective metacyclic trypomastigotes. Sixty six protein spots were successfully identified corresponding to 43 different proteins. We analyzed the expression profiles for the identified proteins along metacyclogenesis and classified them into three groups according to their maximal level of expression. We detected several isoforms for a number of proteins, some displaying differential expression during metacyclogenesis. These results suggest that posttranslational modifications may be a fundamental part of the parasite's strategy for regulating gene expression during differentiation. This study contributes to the identification of relevant proteins involved in the metacyclogenesis process. The identification and molecular characterization of these proteins will render vital information about the steps of the parasite differentiation into the infective form.

The structure of chagasin in complex with a cysteine protease clarifies the binding mode and evolution of an inhibitor family

Protein inhibitors of proteolytic enzymes regulate proteolysis and prevent the pathological effects of excess endogenous or exogenous proteases. Cysteine proteases are a large family of enzymes found throughout the plant and animal kingdoms. Disturbance of the equilibrium between cysteine proteases and natural inhibitors is a key event in the pathogenesis of cancer, rheumatoid arthritis, osteoporosis, and emphysema. A family (I42) of cysteine protease inhibitors (http://merops.sanger.ac.uk) was discovered in protozoan parasites and recently found widely distributed in prokaryotes and eukaryotes. We report the 2.2 A crystal structure of the signature member of the I42 family, chagasin, in complex with a cysteine protease. Chagasin has a unique variant of the immunoglobulin fold with homology to human CD8alpha. Interactions of chagasin with a target protease are reminiscent of the cystatin family inhibitors. Protein inhibitors of cysteine proteases may have evolved more than once on nonhomologous scaffolds.

Sugar nucleotide pools of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major

The cell surface glycoconjugates of trypanosomatid parasites are intimately involved in parasite survival, infectivity, and virulence in their insect vectors and mammalian hosts. Although there is a considerable body of work describing their structure, biosynthesis, and function, little is known about the sugar nucleotide pools that fuel their biosynthesis. In order to identify and quantify parasite sugar nucleotides, we developed an analytical method based on liquid chromatography-electrospray ionization-tandem mass spectrometry using multiple reaction monitoring. This method was applied to the bloodstream and procyclic forms of Trypanosoma brucei, the epimastigote form of T. cruzi, and the promastigote form of Leishmania major. Five sugar nucleotides, GDP-alpha-d-mannose, UDP-alpha-d-N-acetylglucosamine, UDP-alpha-d-glucose, UDP-alpha-galactopyranose, and GDP-beta-l-fucose, were common to all three species; one, UDP-alpha-d-galactofuranose, was common to T. cruzi and L. major; three, UDP-beta-l-rhamnopyranose, UDP-alpha-d-xylose, and UDP-alpha-d-glucuronic acid, were found only in T. cruzi; and one, GDP-alpha-d-arabinopyranose, was found only in L. major. The estimated demands for each monosaccharide suggest that sugar nucleotide pools are turned over at very different rates, from seconds to hours. The sugar nucleotide survey, together with a review of the literature, was used to define the routes to these important metabolites and to annotate relevant genes in the trypanosomatid genomes.

Introducing histone modification in trypanosomes

Nuclear DNA is wrapped around histones. Vigorous research over the past decade has established a central role for histone post-translational modification in controlling the DNA-protein interactions that are required for successful growth and propagation. Recent work now provides a description of acetylated and methylated residues in the divergent trypanosome core histones. Future studies should provide insights into the genomic distribution of each modification and their roles in growth and pathogenesis.

Comparative rates of sialylation by recombinant trans-sialidase and inhibitor properties of synthetic oligosaccharides from Trypanosoma cruzi mucins-containing galactofuranose and galactopyranose

The mucin-like glycoproteins of Trypanosoma cruzi have novel O-linked oligosaccharides that are acceptors of sialic acid in the trans-sialidase (TcTS) reaction. The transference of sialic acid from host glycoconjugates to the mucins is involved in infection and pathogenesis. The O-linked chains may contain galactofuranose in addition to the acceptor galactopyranose units. Thus far, the galactofuranose form was found in the mucins of strains belonging to the less infective lineage. The acceptor properties of the chemically synthesized oligosaccharides were now studied in order to correlate their structure with the ability to act as substrates. Recombinant TcTS and sialyllactose as donor were used. The reactions were followed by HPAEC-PAD. The K(m) values were calculated for the free sugars, the sugar alditols and the benzyl glycosides. All the compounds showed to be good acceptors of sialic acid. Thus, the introduction of galactofuranose in the mucins of the strains of lineage 1 would not be responsible for the diminished virulence of the strains. The oligosaccharides and derivatives inhibited the transfer of sialic acid to the substrate N-acetyllactosamine with IC(50) values between 0.6 and 4 mM.

Trypanosoma cruzi: involvement of glycoinositolphospholipids in the attachment to the luminal midgut surface of Rhodnius prolixus

Trypanosoma cruzi epimastigotes adhere in vivo to the luminal surface of their triatomid vector digestive tract by molecular mechanisms, as yet, unknown. Here, we show that the administration of 0.5 microM epimastigote major surface glycoinositolphospholipids (GIPLs) to the infected bloodmeal inhibits up to 90% parasite infection in Rhodnius prolixus. The parasite behavior was investigated in vitro using fragments of the insect midgut. The addition of GIPLs in concentration as low as 50-100 nM impaired 95% the attachment of epimastigotes. Previous treatment of GIPLs with trifluoroacetic acid to remove the terminal beta-galactofuranosyl residues reversed 50% the epimastigote in vitro attachment. The binding sites of purified GIPLs on the luminal surface of the posterior midgut were exposed by immunofluorescence microscopy. These observations indicate that GIPLs are one of the components involved in the adhesion of T. cruzi to the luminal insect midgut surface and possibly one of the determinants of parasite infection in the insect vector.

Non-conventional flow cytometry approaches to detect anti-Trypanosoma cruzi immunoglobulin G in the clinical laboratory

We have recently developed a flow cytometric approach to detect anti-live trypomastigote and anti-fixed epimastigote IgG antibodies (FC-ALTA and FC-AFEA) in sera from individuals infected by Trypanosoma cruzi. Here, we present the first evaluation of the applicability of FC-AFEA-IgG as a diagnostic tool for Chagas disease. Performance analysis demonstrated that FC-AFEA-IgG has a sensitivity of 82% and a specificity of 100%. The assessment for prognosis performed by FC-ALTA-IgG1 and FC-AFEA-IgG, after classification of chagasic patients as belonging to indeterminate (IND), cardiac (CARD) or digestive (DIG) clinical forms, showed that most of IND have higher amounts of IgG than individuals' carrying CARD or DIG Chagas disease. FC-AFEA-IgG was also evaluated as a method to monitor chemotherapy efficacy in individuals classified into three distinct categories: not treated (NT), treated but not cured (TNC), and treated and cured (TC). Performance analysis demonstrated that FC-AFEA-IgG has an extraordinary capacity as a serological criterion to assess cure after therapeutic intervention in Chagas disease. These results represent a great advance in the application of serological techniques for clinical investigations on Chagas disease, and they clearly define new directions and perspectives. We intend to continue this field research focusing our attention on the influence of the degree of clinical damage on the FC-ALTA-IgG1 and FC-AFEA-IgG reactivity.

Characterization of glycosomal RING finger proteins of trypanosomatids

The glycosomes of trypanosomatids are essential organelles that are evolutionarily related to peroxisomes of other eukaryotes. The peroxisomal RING proteins-PEX2, PEX10 and PEX12-comprise a network of integral membrane proteins that function in the matrix protein import cycle. Here, we describe PEX10 and PEX12 in Trypanosoma brucei, Leishmania major, and Trypanosoma cruzi. We expressed GFP fusions of each T. brucei coding region in procyclic form T. brucei, where they localized to glycosomes and behaved as integral membrane proteins. Despite the weak transmembrane predictions for TbPEX12, protease protection assays demonstrated that both the N and C termini are cytosolic, similar to mammalian PEX12. GFP fusions of T. cruzi PEX10 and L. major PEX12 also localized to glycosomes in T. brucei indicating that glycosomal membrane protein targeting is conserved across trypanosomatids.

Post-translational modifications of Trypanosoma cruzi histone H4

Histone tails provide sites for a variety of post-translational modifications implicated in the control of gene expression and chromatin assembly. As both histones and control of gene expression in trypanosomes are highly divergent compared to most eukaryotes, post-translational modifications of Trypanosoma cruzi histones were investigated. After in vivo incubation of live parasites with radiolabeled precursors, histone H4 mainly incorporates [(3)H]-acetyl, and to a lesser extent [(3)H]-methyl residues. In contrast, histone H3 preferentially incorporates [(3)H]-methyl residues. The modifications of histone H4 were further characterized by mass spectrometry. MALDI-TOF-TOF-MS analysis revealed that peptides from histone H4 amino-terminus, obtained by either endoproteinase Glu-C or endoproteinase Arg-C digestion, contain isoforms with 14 and 42Da additions, suggesting the presence of simultaneous acetylations and/or methylations. Tandem mass spectrometry analysis demonstrated that the N-terminal alanine is methylated, and lysine residues at positions 4, 10, 14 and 57 are acetylated; lysine at position 18 is mono-methylated, while arginine at position 53 is dimethylated. Immunoblotting analyses using specific antibodies raised against synthetic and acetylated peptides of T. cruzi histone H4 indicate that lysine 4 is acetylated in the majority of histone H4, while other acetylations at the N-terminus portion of histone H4 are less abundant.

Evaluation of a prototype Trypanosoma cruzi antibody assay with recombinant antigens on a fully automated chemiluminescence analyzer for blood donor screening

BACKGROUND

Chagas disease is caused by Trypanosoma cruzi, a protozoan parasite that can be transmitted by transfusion. The diagnosis of chronic T. cruzi infection is generally made by detecting specific antibodies that bind to parasite antigens. The aim of this study was to assess the sensitivity and specificity of a new serologic assay for antibodies to T. cruzi on a fully automated analyzer (PRISM, Abbott Laboratories).

STUDY DESIGN AND METHODS

A prototype chemiluminescent immunoassay based on chimeric recombinant antigens and run on the automated PRISM system was developed for detecting antibodies to T. cruzi in human serum and plasma. Assay specificity was evaluated by testing samples from random blood donors and from a diverse group of specimens from persons with diseases or conditions often associated with false-positive reactions in T. cruzi assays. Sensitivity was determined by testing 377 geographically diverse T. cruzi antibody-positive specimens.

RESULTS

Six of 7911 samples (0.08%) from random donors were repeatedly reactive in the prototype PRISM Chagas assay. One of these was reactive in three other tests, including the radioimmune precipitation assay and was presumed to be a true positive. Hence, the specificity was 99.94 percent (7905/7910) in the negative donor group studied. All 377 T. cruzi antibody-positive specimens were positive in the prototype assay and thus the sensitivity was 100 percent.

CONCLUSION

The results obtained to date, in terms of sensitivity as well as specificity, strongly suggest that the PRISM Chagas assay should function well as a tool for screening blood for serologic evidence of T. cruzi infection.