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Summary Large-scale mapping of antigens and epitopes is pivotal for developing immunotherapies but challenging, especially for eukaryotic pathogens, owing to their large genomes. Here, we developed an integrated platform for genome phage display (gPhage) to show that unbiased libraries of the eukaryotic parasite Trypanosoma cruzi enable the identification of thousands of antigens recognized by serum samples from patients with Chagas disease. Because most of these antigens are hypothetical proteins, gPhage provides evidence of their expression during infection. We built and validated a comprehensive map of Chagas disease antibody response to show how linear and putative conformation epitopes, many rich in repetitive elements, allow the parasite to evade a buildup of neutralizing antibodies directed against protein domains that mediate infection pathogenesis. Thus, the gPhage platform is a reproducible and effective tool for rapid simultaneous identification of epitopes and antigens, not only in Chagas disease but perhaps also in globally emerging/reemerging acute pathogens., Graphical abstract, Highlights • Genomic shotgun phage display (gPhage) of eukaryotes is feasible and promising. • gPhage allows rapid antigen ID and epitope mapping, including 3D structures. • Conformation epitopes can be identified and validated by using the gPhage platform. • Most Chagas disease antigens are hypothetical proteins rich in repetitive elements., Parasitology; Sequence analysis; Systems biology

Trypanosoma cruzi is a flagellate protozoa being the etiological agent of Chagas disease, a neglected tropical disease, which still poses a public health problem worldwide. The intricate molecular changes during T. cruzi-host interaction have been explored using different largescale omics techniques. However, protein stability is largely unknown. Thermal proteome profiling (TPP) methodology has the potential to characterize proteome-wide stability highlighting key proteins during T. cruzi infection and life stage transition from the invertebrate to the mammalian host. In the present work, T. cruzi epimastigotes and trypomastigotes cell lysates were subjected to TPP workflow and analyzed by quantitative large-scale mass spectrometry-based proteomics to fit a melting profile for each protein. A total of 2884 proteins were identified and associated to 1741 melting curves being 1370 in trypomastigotes (TmAVG 53.53 °C) and 1279 in epimastigotes (TmAVG 50.89 °C). A total of 453 proteins were identified with statistically different melting profiles between the two life stages. Proteins associated to pathogenesis and intracellular transport had regulated melting temperatures. Membrane and glycosylated proteins had a higher average Tm in trypomastigotes compared to epimastigotes. This study represents the first large-scale comparison of parasite protein stability between life stages. Significance Trypanosoma cruzi, a unicellular flagellate parasite, is the etiological agent of Chagas disease, endemic in South America and affecting more that 7 million people worldwide. There is an intense research to identify novel chemotherapeutic and diagnostic targets of Chagas disease. Proteomic approaches have helped in elucidating the quantitative proteome and PTMs changes of T. cruzi during life cycle transition and upon different biotic and abiotic stimuli. However, a comprehensive knowledge of the protein-protein interaction and protein conformation is still missing. In order to fill this gap, this manuscript elucidates the T. cruzi Y strain proteome-wide thermal stability map in the epimastigote and trypomastigote life stages. Comparison between life stages showed a higher average melting temperature stability for trypomastigotes than epimastigotes indicating a host temperature adaptation. Both presented a selective thermal stability shift for cellular compartments, molecular functions and biological processes based on the T. cruzi life stage. Membrane and glycosylated proteins presented a higher thermal stability in trypomastigotes when compared to the epimastigotes.

Trypanosoma cruzi trypomastigotes adhere to extracellular matrix (ECM) to invade mammalian host cells regulating intracellular signaling pathways. Herein, resin-assisted enrichment of thiols combined with mass spectrometry were employed to map site-specific S-nitrosylated (SNO) proteins from T. cruzi trypomastigotes incubated (MTy) or not (Ty) with ECM. We confirmed the reduction of S-nitrosylation upon incubation with ECM, associated with a rewiring of the subcellular distribution and intracellular signaling pathways. Forty, 248 and 85 SNO-peptides were identified only in MTy, Ty or in both conditions, respectively. SNO proteins were enriched in ribosome, transport, carbohydrate and lipid metabolisms. Nitrosylation of histones H2B and H3 on Cys64 and Cys126, respectively, is described. Protein-protein interaction networks revealed ribosomal proteins, proteins involved in carbon and fatty acid metabolism to be among the enriched protein complexes. Kinases, phosphatases and enzymes involved in the metabolism of carbohydrates, lipids and amino acids were identified as nitrosylated and phosphorylated, suggesting a post-translational modifications crosstalk. In silico mapping of nitric oxide synthase (NOS) genes, previously uncharacterized, matched to four putative T. cruzi proteins expressing C-terminal NOS domain. Our results provide the first site-specific characterization of S-nitrosylated proteins in T. cruzi and their modulation upon ECM incubation before infection of the mammalian hosts. SIGNIFICANCE: Protein S-nitrosylation represents a major molecular mechanism for signal transduction by nitric oxide. We present for the first time a proteomic profile of S-nitrosylated proteins from infective forms of T. cruzi, showing a decrease in SNO proteins after incubation of the parasite with the extracellular matrix, a necessary step for the parasite invasion of the host mammalian cells. We also show for the first time nitrosylation of H2B (Cys64) and H3 (Cys126) histones, sites not conserved in higher eukaryotic cells, and suggest that some specific histone isoforms are sensitive to NO signaling. S-nitrosylation in H2B and H3 histones are more abundant in MTy. Moreover, proteins involved in translation, glycolytic pathway and fatty acid metabolism are enriched in the present dataset. Comparison of the SNO proteome and the phosphoproteome, obtained previously under the same experimental conditions, show that most of the proteins sharing both modifications are involved in metabolic pathways, transport and ribosome function. The data suggest that both PTMs are involved in reprogramming the metabolism of T. cruzi in response to environmental changes. Although NO synthesis was detected in T. cruzi, the identification of NOS remains elusive. Analysis in silico showed two genes similar in domains to NADPH-dependent cytochrome-P450 reductase and two putative oxidoreductases, but no oxygenase domain of NOS was mapped in the T. cruzi genome. It is tempting to speculate that NO synthase-like from T. cruzi and its early NO-mediated pathways triggered in response to host interaction constitute potential diagnostic and therapeutic targets.

Summary This protocol describes the genomic phage (gPhage) display platform, a large-scale antigen and epitope mapping technique. We constructed a gPhage display peptide library of a eukaryotic organism, Trypanosoma cruzi (causative agent of Chagas disease), to map the antibody response landscape against the parasite. Here, we used an organism with a relatively large but intronless genome, although future applications could include other prevalent or (re)emerging infectious organisms carrying genomes with a limited number of introns. For complete details on the use and execution of this protocol, please refer to Teixeira et al. (2021)., Graphical abstract, Highlights • A streamlined protocol to build genome shotgun phage display libraries • Scalable to different organisms, eukaryotes or prokaryotes • Optimizes key steps for high throughput identification of antibody antigens/epitopes • gPhage is also a platform to study conformational and difficult-to-validate antigens, This protocol describes the genomic phage (gPhage) display platform, a large-scale antigen and epitope mapping technique. We constructed a gPhage display peptide library of a eukaryotic organism, Trypanosoma cruzi (causative agent of Chagas disease), to map the antibody response landscape against the parasite. Here, we used an organism with a relatively large but intronless genome, although future applications could include other prevalent or (re)emerging infectious organisms carrying genomes with a limited number of introns.

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., Author summary T. cruzi, the etiological agent of Chagas’ disease, interacts with ECM in order to invade cells and establish the infection in the mammalian host. Studying this interaction, our group has recently described changes in the nitration profile of histones upon incubation of the parasite with ECM. Herein we used a proteomic approach to identify nitrated DNA binding proteins in T. cruzi. We also used ChIP-Seq to investigate whether the contact of the parasite with host ECM is capable of promoting changes in the DNA binding pattern of nitrated proteins. We observed significant alterations in the nitration levels and DNA binding profile of T. cruzi histones upon parasite incubation with ECM.

The OX513A strain ofLa souche OX513A d'La cepa OX513A deتمثل سلالة OX513A منOX513A 类Вид комаров Aedes aegypti под названием OX513A, разработанный британской компанией Oxitec, экспрессирует ограничивающий популяцию своего носителя трансген, который препятствует развитию личинки во взрослую особь. В апреле 2014 года Бразильская национальная техническая комиссия по биобезопасности завершила оценку рисков OX513A и пришла к выводу, что этот вид не представляет новых биологических угроз для человека или окружающей среды и может быть выпущен в Бразилии. Тогда Бразилия стала первой страной, в которой был разрешен неограниченный выпуск генетически измененных комаров. В ходе оценки комиссия опубликовала исчерпывающий перечень предполагаемых рисков и провела их систематический анализ. Такие риски включали потенциальную способность комаров неполовозрелой стадии, несущих трансген, дожить до репродуктивного возраста в случае неудавшейся экспрессии трансгена или его подавления, вызванного воздействием достаточного количества тетрациклина на комаров во внешней среде. Среди других предполагаемых рисков — потенциальная аллергенность или токсичность белков, образующихся в результате экспрессии гена, возможность дрейфа генов или повышенного распространения болезнетворных организмов для человека и заселение свободных мест размножения другими видами переносчиков. На фоне эпидемии вируса Зика лица, ответственные за разработку стратегических решений, регулирующие органы, а также общественность увеличили внимание к роли Ae. Aegypti в качестве переносчиков и выразили большую обеспокоенность по поводу выпуска мужских особей вида OX513A. По этой причине авторы данной статьи провели повторную оценку потенциальных рисков. Была подтверждена безопасность и высокое потенциальное значение выпуска генетически измененных комаров для борьбы с распространяемыми Ae. aegypti заболеваниями, такими как чикунгунья, денге и болезнь, вызываемая вирусом Зика.

Trypanosoma cruzi, the etiological agent of Chagas’ disease, affects 8 million people predominantly living in socioeconomic underdeveloped areas. T. cruzi trypomastigotes (Ty), the classical infective stage, interact with the extracellular matrix (ECM), an obligatory step before invasion of almost all mammalian cells in different tissues. Here we have characterized the proteome and phosphoproteome of T. cruzi trypomastigotes upon interaction with ECM (MTy) and the data are available via ProteomeXchange with identifier PXD010970. Proteins involved with metabolic processes (such as the glycolytic pathway), kinases, flagellum and microtubule related proteins, transport-associated proteins and RNA/DNA binding elements are highly represented in the pool of proteins modified by phosphorylation. Further, important metabolic switches triggered by this interaction with ECM were indicated by decreases in the phosphorylation of hexokinase, phosphofructokinase, fructose-2,6-bisphosphatase, phosphoglucomutase, phosphoglycerate kinase in MTy. Concomitantly, a decrease in the pyruvate and lactate and an increase of glucose and succinate contents were detected by GC-MS. These observations led us to focus on the changes in the glycolytic pathway upon binding of the parasite to the ECM. Inhibition of hexokinase, pyruvate kinase and lactate dehydrogenase activities in MTy were observed and this correlated with the phosphorylation levels of the respective enzymes. Putative kinases involved in protein phosphorylation altered upon parasite incubation with ECM were suggested by in silico analysis. Taken together, our results show that in addition to cytoskeletal changes and protease activation, a reprogramming of the trypomastigote metabolism is triggered by the interaction of the parasite with the ECM prior to cell invasion and differentiation into amastigotes, the multiplicative intracellular stage of T. cruzi in the vertebrate host., Author summary Adhesion of Trypanosoma cruzi to distinct elements of ECM involving different surface proteins from the infective stage of the parasite has been described. Despite the relevance of ECM for T. cruzi infection, the signaling pathways triggered in trypomastigotes upon interactions with ECM are less well understood. In previous work we demonstrated the dephosphorylation of proteins, such as α-tubulin, paraflagellar rod proteins and ERK 1/2 in trypomastigotes incubated with either laminin or fibronectin. Further, we described changes in the S-nitrosylation and nitration pattern of proteins from trypomastigote incubated with ECM. To expand our knowledge on ECM triggered parasite signaling we applied quantitative proteomic and phosphoproteomic studies to trypomastigotes incubated with ECM (MTy) compared to controls (Ty). Our results indicate relevant changes in total protein and phosphoprotein profiles in MTy. The kinases implicated in the modifications were suggested by bioinformatic analyses, as well as the number of modifications and the frequency of amino acids per peptide that have been modified. Proteins involved in metabolic processes, including enzymes from the glycolytic pathway, phosphatases and kinases were the most representative groups among the proteins modified by phosphorylation. Quantification of metabolites in MTy and Ty also indicated that glucose metabolism is impaired in trypomastigotes incubated with ECM. The significant inhibition of hexokinase, pyruvate kinase and lactate dehydrogenase activities in MTy associated with phosphorylation levels, strongly suggests that trypomastigotes reprogram their metabolism in response to interaction with the extracellular matrix, an obligatory step prior to host cell invasion.

Trypanosoma cruzi, the protozoan that causes Chagas disease, has a complex life cycle involving insect and mammalian hosts and distinct developmental stages. During T. cruzi developmental stages, glycoproteins play important role in the host-parasite interaction, such as cellular recognition, host cell invasion and adhesion, and immune evasion. In this study, comprehensive glycoprofiling analysis was performed in the epimastigote and trypomastigote stages of T. cruzi using two glycopeptide enrichment strategies, lectin-based and hydrophilic interaction liquid chromatography, followed by high resolution LC-MS/MS. Following deglycosylation, a total of 1306 N-glycosylation sites in NxS/T/C motifs were identified from 690 T. cruzi glycoproteins. Among them, 170 and 334 glycoproteins were exclusively identified in epimastigotes and trypomastigotes, respectively. Besides, global site-specific characterization of the N- and O-linked glycan heterogeneity in the two life stages of T. cruzi was achieved by intact glycopeptide analysis, revealing 144/466 unique N-linked and 10/97 unique O-linked intact glycopeptides in epimastigotes/trypomastigotes, respectively. Conclusively, this study documents the significant T. cruzi stage-specific expression of glycoproteins that can help to better understand the T. cruzi phenotype and response caused by the interaction with different hosts during its complex life cycle. Biological significance Chagas disease caused by the protozoan Trypanosoma cruzi is a neglected disease which affects millions of people especially in Latin America. The absence of efficient drugs and vaccines against Chagas disease stimulates the search for novel targets. Glycoproteins are very attractive therapeutic candidate targets since they mediate key processes in the host-parasite interaction, such as cellular recognition, host cell invasion and adhesion, and immune evasion. This study aimed to provide an in depth characterization of the N-linked and O-linked glycoproteome of two T. cruzi life stages: epimastigotes and trypomastigotes. Mass spectrometry-based proteomics showed interesting stage-specific glycoproteome signatures that are valuable to better understand the importance of protein glycosylation in epimastigotes and trypomastigotes and to expand the repertoire of potential therapeutic targets against Chagas disease.

Different types of shed vesicles as, for example, exosomes, plasma-membrane-derived vesicles or microparticles, are the focus of intense research in view of their potential role in cell–cell communication and under the perspective that they might be good tools for immunotherapy, vaccination or diagnostic purposes. This review discusses ways employed by pathogenic trypanosomatids to interact with the host by shedding vesicles that contain molecules important for the establishment of infection, as opposed to previous beliefs considering them as a waste of cellular metabolism. Trypanosomatids are compared with Apicomplexa, which circulate parasite antigens bound to vesicles shed by host cells. The knowledge of the origin and chemical composition of these different vesicles might lead to the understanding of the mechanisms that determine their biological function.

SUMMARYTrypanosoma cruziis a protozoan parasite that infects vertebrates, causing in humans a pathological condition known as Chagas’ disease. The infection of host cells byT. cruziinvolves a vast collection of molecules, including a family of 85 kDa GPI-anchored glycoproteins belonging to the gp85/trans-sialidase superfamily, which contains a conserved cell-binding sequence (VTVXNVFLYNR) known as FLY, for short. Herein, it is shown that BALB/c mice administered with a single dose (1μg/animal, intraperitoneally) of FLY-synthetic peptide are more susceptible to infection byT. cruzi, with increased systemic parasitaemia (2-fold) and mortality. Higher tissue parasitism was observed in bladder (7·6-fold), heart (3-fold) and small intestine (3·6-fold). Moreover, an intense inflammatory response and increment of CD4+T cells (1·7-fold) were detected in the heart of FLY-primed and infected animals, with a 5-fold relative increase of CD4+CD25+FoxP3+T (Treg) cells. Mice treated with anti-CD25 antibodies prior to infection, showed a decrease in parasitaemia in the FLY model employed. In conclusion, the results suggest that FLY facilitatesin vivoinfection byT. cruziand concurs with other factors to improve parasite survival to such an extent that might influence the progression of pathology in Chagas’ disease.

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 μM 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 β-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.

Chagas' disease is a chronic, debilitating and incapacitating illness, caused by the protozoan parasite Trypanosoma cruzi when infective trypomastigotes invade host cells. Although the mechanism of trypomastigotes interaction with mammalian cells has been intensively studied, a final and integrated picture of the signal transduction mechanisms involved still remains to be elucidated. Our group has previously shown that the conserved FLY domain (VTVXNVFLYNR), present in all members of the gp85/trans-sialidase glycoprotein family coating the surface of trypomastigotes, binds to cytokeratin 18 (CK18) on the surface of LLC-MK(2) epithelial cells, and significantly increases parasite entry into mammalian cells. Now it is reported that FLY, present on the surface of trypomastigotes or on latex beads binds to CK18, promotes dephosphorylation and reorganization of CK18 and activation of the ERK1/2 signaling cascade culminating in an increase of approximately 9-fold in the number of parasites/cell. Inhibition of ERK1/2 phosphorylation completely blocks the adhesion of FLY to cells and blocks by 57% the host cell infection by T. cruzi. Taken together our results indicate that the conserved FLY domain is an important tool that trypomastigotes have evolved to specific exploit the host cell machinery and guarantee a successful infection.

Both invasion of the host cell by T. cruzi and its establishment into the mammalian host are critical steps. In this review, the adhesion step and the intracellular survival in non-professional phagocytes are particularly focused on, with special emphasis on the role of Gp85/trans-sialidase (Gp85/TS) superfamily. Excellent reviews have been published lately, some covering other aspects of T. cruzi - host interaction and will be cited instead of the original articles due to limited number of listed references. IUBMB Life, 59: 274-279, 2007

Trypanosoma cruzi is the etiologic agent of Chagas disease. Two main distinct forms are present in the mammalian host: trypomastigote, an infective form, and the amastigote, a typical replicative form. Succeeding the host cell invasion, trypomastigotes differentiate to amastigotes, a process known as amastigogenesis. Amastigogenesis is characterized by parasite body remodeling, with drastic reduction of flagellum, and changes in protein profile and energetic metabolism. Our aim is to explore the role of nitric oxide as a signaling molecule during the amastigogenesis process, which must be strictly regulated. We report herein that acid pH (6.0) is essential for T. cruzi amastigogenesis. Also, during amastigogenesis there is a progressive solubilization of the paraflagellar protein, a flagellum marker. Moreover, the process is dependent on (•)NO concentration, since it is suppressed by 1mM SNAP, a (•)NO donor, and favored by 10mM L-NAME, a NOS inhibitor. Accordingly, S-nitrosylation of selective proteins occurs in amastigogenesis. Additionally, amastigogenesis is affected by IBMX (PDE inhibitor) treatment, suggesting the importance of cyclic nucleotides signaling. Furthermore, tubulin stability is also affected by the (•)NO availability. Along amastigogenesis, flagellum disassembling is accompanied by changes in a-tubulin tyrosylation and polyglutamylation levels. Taken together, these results suggest (•)NO participation in trypomastigote differentiation to amastigotes in T. cruzi.

Trypomastigote forms of Trypanosoma cruzi, the causative agent of Chagas Disease, shed extracellular vesicles (EVs) enriched with glycoproteins of the gp85/trans-sialidase (TS) superfamily and other α-galactosyl (α-Gal)-containing glycoconjugates, such as mucins. Here, purified vesicles from T. cruzi strains (Y, Colombiana, CL-14 and YuYu) were quantified according to size, intensity and concentration. Qualitative analysis revealed differences in their protein and α-galactosyl contents. Later, those polymorphisms were evaluated in the modulation of immune responses (innate and in the chronic phase) in C57BL/6 mice. EVs isolated from YuYu and CL-14 strains induced in macrophages higher levels of proinflammatory cytokines (TNF-α and IL-6) and nitric oxide via TLR2. In general, no differences were observed in MAPKs activation (p38, JNK and ERK 1/2) after EVs stimulation. In splenic cells derived from chronically infected mice, a different modulation pattern was observed, where Colombiana (followed by Y strain) EVs were more proinflammatory. This modulation was independent of the T. cruzi strain used in the mice infection. To test the functional importance of this modulation, the expression of intracellular cytokines after in vitro exposure was evaluated using EVs from YuYu and Colombiana strains. Both EVs induced cytokine production with the appearance of IL-10 in the chronically infected mice. A high frequency of IL-10 in CD4+ and CD8+ T lymphocytes was observed. A mixed profile of cytokine induction was observed in B cells with the production of TNF-α and IL-10. Finally, dendritic cells produced TNF-α after stimulation with EVs. Polymorphisms in the vesicles surface may be determinant in the immunopathologic events not only in the early steps of infection but also in the chronic phase.Keywords: Trypanosoma cruzi; extracellular vesicles; innate and chronic immunity; TLR2; α-galactosyl(Published: 26 November 2015)Citation: Journal of Extracellular Vesicles 2015, 4: 28734 - http://dx.doi.org/10.3402/jev.v4.28734

Trypanosoma cruzi trypomastigotes invade a great variety of mammalian cells, with several molecules being implicated in this complex event. Herein, the sequence GGIALAG present in prokineticin-2 receptor (PKR2), selected by phage display technology, is described as a new T. cruzi receptor for the Tc85 group of glycoproteins belonging to the gp85/TS superfamily and involved in cellular invasion of mammalian hosts. This finding is confirmed by the inhibitory activity of MCF10-A (human mammary) cell invasion by T. cruzi either by anti-PKR2 antibodies (77 %) or GGIALAG-synthetic peptide (42 %). Furthermore, interference RNA (iRNA) inhibition of PKR2 expression in MCF10-A cells reduces T. cruzi invasion by 50 %. The binding site of Tc85 to PKR2 was localized at the C-terminal end of the molecule, upstream of the conserved FLY sequence, previously implicated in parasite cell invasion. PKR2, a receptor formed by seven membrane-spanning α-helical segments, is mainly present in the central nervous system, peripheral organs, and mature blood cells. Due to its wide distribution, PKR2 could be a suitable receptor for T. cruzi natural infection, contributing to the parasite dissemination throughout the mammalian organism. These findings augment the number and diversity of possible in vivo receptors for T. cruzi and reassure the multiplicity of Tc85 binding sites to mammalian hosts.

This present work reports on development of an amperometric immunosensor for the diagnosis of Chagas’ disease using a specific glycoprotein of the trypomastigote surface, which belongs to the Tc85-11 protein family of Trypanosoma cruzi (T. cruzi). An atomically flat gold surface on a silicon substrate and gold screen-printed electrodes were functionalized with cystamine and later activated with glutaraldehyde (GA), which was used to form covalent bonds with the purified recombinant antigen (Tc85-11). The antigen reacts with the antibody from the serum, and the affinity reaction was monitored directly using atomic force microscopy or amperometry through a secondary antibody tagged to peroxidase (HRP). Surface imaging allowed to us to differentiate the modification steps and antigen–antibody interaction allowed to distinguish the affinity reactions. In the amperometric immunosensor, peroxidase catalyses the L2 formation in the presence of hydrogen peroxide and potassium iodide, and the reduction current intensity was measured at a given potential with screen-printed electrodes. The immunosensor was applied to sera of chagasic patients and patients having different systemic diseases.

Trypanosoma cruzi proteins from epimastigote membranes, herein referred as antigens, have been used for the construction of an amperometric immunosensor for serological diagnosis of Chagas’ disease. The proteins used had a molecular mass ranging from 30 to 100 kDa. The gold electrode was treated with cysteamine and glutaraldehyde prior to antigen immobilization. Antibodies present in the serum of patients with Chagas’ disease were captured by the immobilized antigens and the affinity interaction was monitored by chronoamperometry at a potential of −400 mV (versus Ag pseudo-reference electrode) using peroxidase-labeled IgG conjugate and hydrogen peroxide, iodide substrate. The incubation time to allow maximum antigen–antibody and antibody–peroxidase-labeled IgG interactions was 20 min with a reactivity threshold at −0.104 μA.

Chagas' disease is a zoonosis caused by the parasite Trypanosoma cruzi, a haematic protozoan, transmitted by insects from the Reduviidae family. This constitutes a relevant health and socio-economic problem in the Americas, with 11 - 18 million people infected, and approximately 100 million people at risk. The therapeutic possibilities rely into two drugs, nifurtimox and benznidazole, that were discovered more than thirty years ago, and are mainly successful during the acute phase of the disease. In the majority of the cases the disease is diagnosed in the chronic phase, when the therapy is inefficient and the probability of cure is low. In addition, these drugs are highly toxic, with systemic side effects on patients. Trypanosoma cruzi has a metabolism largely based on the consumption of amino acids, mainly proline, aspartate and glutamate, which constitute the main carbon and energy sources in the insect stage of the parasite life cycle. These amino acids also participate in the differentiation process of the replicative non-infective form (epimastigote) to the non-replicative infective form (trypomastigote). In particular, the participation of proline in the intracellular differentiation cycle, which occurs in the mammalian host, was recently demonstrated. In addition, an arginine kinase has been described in T. cruzi and T. brucei, which converts free arginine to phosphoarginine, a phosphagen with a role as an energy reservoir. Arginine kinase seems to be an essential component of energy management during stress conditions. Taken together, these data indicate that amino acid metabolism may provide multiple as yet unexplored targets for therapeutic drugs.

Trypanosoma cruzi expresses a set of glycoproteins encoded by the gp85/trans-sialidase gene superfamily. In this report a structure model is proposed for a cloned member of the superfamily, the Tc85-11 protein. The structure consists of an N-terminus beta-propeller and a C-terminus beta-sandwich interconnected by an alpha-helix. The recombinant protein, corresponding to the N-domain (Tc85-N), binds to laminin in a selective manner. Six synthetic 20-mer peptides from the N-domain adhere onto the surface of LLC-MK(2) cells and two of these peptides specifically inhibit the Tc85-N/laminin interaction, indicating that they are the laminin-binding sites of the molecule. Thus, Tc85-11 and other related members of the family appear to be good candidates to play an important role in T. cruzi infection via a laminin mediated host-parasite interaction.

The "amino acid/auxin permeases" is probably the most represented family of transporters in the Trypanosoma cruzi genome. Using a high-throughput searching routine and preliminary data from the T. cruzi genome project, more than 15,000 sequences were iteratively assembled into contigs, and 60 open reading frames corresponding to different putative amino acid transporters, clustered in 12 groups, were detected and characterized in silico. T. cruzi genomic organization of such sequences showed that these putative amino acid transporter genes are in an unusually large number and arranged in repeat clusters comprising about 0.2% of the genome. These data suggest that the family has evolved following tandem duplication events and constitutes a novel family of variable proteins in protozoan organisms. The mRNA expression of the predicted genes was demonstrated in infective and non-infective parasite forms. Orthologous sequences were also identified in other unicellular parasites such as Leishmania spp., Plasmodium spp., and Trypanosoma brucei.

Summary Using as the host cell, a proline-requiring mutant of Chinese hamster ovary cell (CHO-K1), it was possible to arrest the differentiation of amastigote forms of Trypanosoma cruzi at the intermediate intracellular epimastigote-like stage. Complete differentiation to the trypomastigote stage was obtained by addition of L -proline to the medium. This effect was more pro- nounced using the T. cruzi CL-14 clone that differen- tiates fully at 33 ∞ ∞ ∞ C (permissive temperature) and poorly at 37 ∞ C (restrictive temperature). A synchro- nous differentiation of T. cruzi inside the host-cell is then possible by temperature switching in the pres- ence of proline. It was found that differentiation of intracellular epimastigotes and trypomastigote burst- ing were proline concentration dependent. The intra- cellular concentration of proline was measured as well as the transport capacity of proline by each stage of the parasite. Amastigotes have the highest concen- tration of free proline (8.09 ± 1.46 mM) when com- pared to trypomastigotes (3.81 ± 1.55) or intracellular epimastigote-like forms (0.45 ± 0.06 mM). In spite of having the lowest content of intracellular free proline, intracellular epimastigotes maintained the highest levels of L -proline transport compared to trypomas- tigotes and intracellular amastigotes, providing evi- dence for a high turnover for the L -proline pool in that parasite stage. This is the first report to establish a relationship between proline concentration and intra- cellular differentiation of Trypanosoma cruzi in the mammalian host.

The synthesis of mutual prodrugs of nitrofurazone with primaquine, using specific and nonspecific spacer groups, has been previously attempted seeking selective antichagasic agents. The intermediate reaction product, hydroxymethylnitrofurazone (NFOH-121), was isolated and tested in LLC-MK(2) culture cells infected with trypomastigotes forms of Trypanosoma cruzi showing higher trypanocidal activity than nitrofurazone and benznidazol in all stages. The mutagenicity tests showed that the prodrug was less toxic than the parent drug. Degradation assays were carried out in pH 1.2 and 7.4.

The aim of the present study was to demonstrate the presence of alpha-L-fucosidase in Trypanosoma cruzi. Immunocytochemical and biochemical techniques were used to localize and characterize a membrane-associated, neutral-pH-optimum, alpha-L-fucosidase from the parasite. Light and electron microscopy localized the alpha-L-fucosidase specifically on the surface of the parasite and on membranes in the posterior region of the epimastigote stage. Although much less intense, labeling was also detected on the surface of trypomastigotes. At least 50% of the alpha-L-fucosidase activity was associated with epimastigote membrane solubilized with 1 M NaCl or 1% Triton X-100, suggesting that alpha-L-fucosidase is peripherally associated with membranes. The enzyme from epimastigotes had a neutral pH optimum (near 7) but displayed low specific activity when p-nitrophenyl-alpha-L-fucoside was employed as substrate (0.028 U/mg protein for epimastigotes and 0.015 U/mg protein for tissue culture-derived trypomastigotes). Polyacrylamide gel electrophoresis and Western blotting analysis both showed an expected 50-kDa polypeptide which was immunoreactive with anti-alpha-L-fucosidase antibodies.

Gold nanoparticle (AuNP) bioconjugates have been used as therapeutic and diagnostic tools; however, in vivo biocompatibility and cytotoxicity continue to be two fundamental issues. The effect of AuNPs (20 nm) conjugated with antibody [immunoglobulin G (IgG)], albumin, protein A, PEG4000, and citrate (cit) were evaluated in vitro using primary human cells of the vascular system. AuNP bioconjugates did not cause lysis of human erythrocytes, apoptosis or necrosis of human leukocytes, and endothelial cells in vitro, although AuNPs had been internalized and detected in the cytoplasm. Moreover, the influence of AuNPs on rheological parameters, blood and vessel wall characteristics was investigated in vivo by intravital microscopy assay using male Wistar rats mesentery microcirculation as model. Intravenous injection of AuNP-IgG or cit-AuNP did not cause hemorrhage, hemolysis or thrombus formation, instead suppressed the leukocyte adhesion to postcapillary vessel walls, an early stage of an inflammatory process. Furthermore, AuNP-IgG abrogated the expression of platelet-endothelial cell adhesion molecule-1, chemotaxis, and oxidative burst activation on neutrophils after leukotriene B4 stimulation, a membrane receptor-dependent stimulus, thus confirming their anti-inflammatory effects in vitro. The expression of oxidative burst activation was also suppressed after stimulating AuNP-IgG-treated neutrophils with lipid-soluble phorbol myristate acetate (PMA), confirming the direct intracellular action of AuNP-IgG on the inflammatory process in vitro. Our in vitro and in vivo experimental approaches highlighted the great potentiality of AuNP bioconjugates for therapeutic and diagnostic applications by parenteral routes.

A monoclonal antibody, 1E7, raised against tissue culture-derived trypomastigotes of Trypanosoma cruzi reacted with proteins located at the perinuclear region of the parasite as detected by immunofluorescence and immunogold electron microscopy. The antibody also recognized antigens in all trypanosomatids tested, including T. cruzi epimastigotes, as well as in many mammalian cells. Five principal antigens of 140-270 kDa soluble in 1 M NaCl were recognized by the monoclonal antibody, suggesting that the epitope may belong to more than one polypeptide since the same bands appeared even when the samples were treated with high concentrations of denaturing agents. The antibody reacted in Western blots with muscle myosin. Bacterial clones expressing fast skeletal muscle myosin head or tail cDNAs upon IPTG induction were used to demonstrate that 1E7 monoclonal antibody recognizes an epitope present in the tail region of the myosin heavy chain. This result adds to the on-going discussion related to the possible existence of an auto-immune component in the immunopathogenesis of Chagas' disease due to cross-reactive epitopes shared by the parasite and cardiac myosin.

The infective trypomastigote stage ofTrypanosoma cruzi expresses a set of surface glycoproteins that are known collectively as Tc85 and belong to the gp85/trans-sialidase supergene family. A member of this family, Tc85–11, with adhesive properties to laminin and cell surfaces was recently cloned. In this report, the Tc85–11 domain for cell binding and its corresponding receptor on epithelial cell LLC-MK2are described. Using synthetic peptides corresponding to the Tc85–11 carboxyl-terminal segment, we show that the mammalian cell-binding domain colocalizes to the most conserved motif of the trypanosome gp85/trans-sialidase supergene family (VTVXNVFLYNR). Even though Tc85–11 binds to laminin, the 19-residue cell-binding peptide (peptide J) does not contain the laminin-binding site, because it does not bind to laminin or inhibit cell binding to this glycoprotein. The host cell receptor for the peptide was characterized as cytokeratin 18. Addition of anti-cytokeratin antibodies to the culture medium significantly inhibited the infection of epithelial cells byT. cruzi. Tc85–11 is a multiadhesive glycoprotein, encoding at least two different binding sites, one for laminin and one for cytokeratin 18, that allow the parasite to overcome the barriers imposed by cell membranes, extracellular matrices, and basal laminae to reach the definitive host cell. This is the first description of a direct interaction between cytokeratin and a protozoan parasite.

Tryparedoxin peroxidase has recently been identified as a constituent of the complex peroxidase system in the trypanosomatid Crithidia fasciculata [Nogoceke E, Gommel DU, Kiess M, Kalisz HM, Flohe L (1997) Biol Chem 378: 827-836]. In trypanosomatids, hydroperoxides are reduced at the expense of NADPH by means of a cascade of three oxidoreductases: the flavoprotein trypanothione reductase, tryparedoxin and tryparedoxin peroxidase. Inhibitors of these enzymes are presumed to be trypanocidal drugs. Here, we present the heterologous expression of a putative tryparedoxin peroxidase gene of Trypanosoma cruzi (accession no AJ012101) as an N-terminally His-tagged protein (TcH6TXNPx). The product was purified with a high yield (8.75 mg from 11 fermentation broth of A(600)2.1) from the cytosolic fraction of sonified Escherichia coli BL21(DE3)[pET22b( + )/TcH6TXNPx] by metal-chelating chromatography. TcH6TXNPx proved to be fully active when tested with heterologous tryparedoxins of C. fasciculata (His-tagged TXN1H6 and TXN2H6). TcH6TXNPx displayed ping-pong kinetics with a k(cat) of 1.7 s(-1) and limiting Km values of 51.8 microM and 1.7 microM for t-butyl hydroperoxide and CfTXN2H6, respectively.

Hydroperoxide metabolism in Crithidia fasciculata has recently been shown to be catalyzed by a cascade of three oxidoreductases comprising trypanothione reductase (TR), tryparedoxin (TXN1), and tryparedoxin peroxidase (TXNPx) (Nogoceke et al., Biol. Chem. 378, 827-836, 1997). The existence of this metabolic system in the human pathogen Trypanosoma cruzi is supported here by immunohistochemistry. Epimastigotes of T. cruzi display strong immunoreactivity with antibodies raised against TXN1 and TXNPx of C. fasciculata. In addition, a full-length open reading frame presumed to encode a peroxiredoxin-type protein in T. cruzi (Acc. Nr. AJ 012101) was heterologously expressed in Escherichia coli and shown to exhibit tryparedoxin peroxidase activity. With TXN, TXNPx, trypanothione and TR, T. cruzi possesses all components constituting the crithidial peroxidase system. It is concluded that the antioxidant defense of T. cruzi also depends on the NADPH-fuelled, trypanothione-mediated enzymatic hydroperoxide metabolism.

Trypomastigote forms of Trypanosoma cruzi were metabolically labeled with [14C]-ethanolamine and [3H]-palmitic acid. Lipids shed to the culture medium were analyzed and compared with the parasite components. Phosphatidylcholine and lysophosphatidylcholine accounted for 53% of the total incorporated precursor. Interestingly, phosphatidylethanolamine and its lyso derivative lysophosphatidylethanolamine, although present in significant amounts in the parasites, could not be detected in the shed material. Shed lipids were highly enriched in the desaturated fatty acids C16:1 and C18:1 when compared to the total fatty acid pool isolated from the parasites.

Although Chagas disease has been discovered90 years ago, only after 1970 substantial progresshas been made in the knowledge of molecular as-pects of the host-parasite interaction. The amountof information gathered in the past 30 years wasconsiderable, making it virtually impossible tocover all aspects of the biochemistry and molecu-lar biology of the Trypanosoma cruzi , the etiologicagent of the disease. T. cruzi colonizes differenthabitats, from the intestinal tract of an insect to thecytoplasm of a mammalian cell, with a brief pas-sage by the blood of the vertebrate host. An adap-tation of the parasite to these different environmentsshould occur and, consequently, differences in thecomposition of the plasma membrane should beexpected among the parasite stages. In fact, in eachparasite stage, molecules belonging to the surfacemembrane are the ones most probably involved ininteraction with the hosts. In the vertebrate side ofthe infective cycle, the parasite has to leave theblood by crossing the capillary walls, the basallaminae and the extracellular matrix before encoun-tering receptors located on the host cell plasmamembrane. In the invertebrate phase of the cycle,epimastigotes must attach to the perimicrovillarmembrane of the reduviid intestine in order to getprepared to differentiate to metacyclic trypo-mastigotes.This review will cover mainly the evolution ofknowledge which occurred with the parasite mac-romolecular structures residing in the plasma mem-brane and originally described by our laboratory.In fact, by extracting epimastigote forms with phe-nol it was possible to separate in polyacrylamidegels four bands developed by the Schiff reagentthat were called bands A, B, C, and D (Alves &Colli 1975). Band D was baptized as lipopeptidophosphoglycan (LPPG) (Lederkremer et al. 1976),and more recently T. cruzi Type-1 GIPL (Ferguson1997), and bands A, B, C have been shown to becompounds which are the main sialic acid accep-tors on T. cruzi membranes, including the now wellstudied mucins (Acosta Serrano et al. 1995). Inaddition, trypomastigotes have on their surface afamily of glycoproteins (Abuin et al. 1989) prob-ably involved in parasite interiorization (Alves etal. 1986) and adhesion (Giordano et al. 1994, 1999,Alves 1996) which have been collectively calledTc-85 (Katzin & Colli 1983).Excellent reviews on related issues were re-cently published on surface receptors and trans-porters of trypanosomatids, including the glucosetransporter (Tetaud et al. 1997, Borst & Fairlamb1998) and trans-sialidase (Cross & Takle 1993,Colli 1993, Schenkman et al. 1994).

□ American trypanosomiasis (Chagas’ disease) is an endemic parasitic disease afflicting more than 20 million people in Latin America. Currently , therapy is unsatisfactory and only two drugs are available. Primaquine, an antimalarial drug, has trypanocidal activity. Dipeptide derivatives of primaquine, Phe-Arg-PQ, Lys-Arg-PQ, and Phe-Ala-PQ, were synthesized. The choice of the peptides was based on the primary specificity of cruzipain, the major cysteine proteinase from T cruzi. The prodrugs obtained were tested on the LLC-MK 2 cell culture infected with trypomastigotes forms of T. cruzi Phe-Arg-PQ, Lys-Arg-PQ, and Phe-Ala-PQ were active in all stages.

In trypanosomatids, little is known about the biosynthetic pathways involved in the metabolism of ethanolamine. In an attempt to clarify this point, an exhaustive analysis of the chloroform:methanol extract of T. cruzi trypomastigotes metabolically labeled with [14C]ethanolamine, in comparison with the lipids from [3H]palmitic acid-incorporated parasites, was performed. In both cases, phosphatidylethanolamine and lysophosphatidylethanolamine were detected, while phosphatidylcholine and lysophosphatidylcholine were only labeled with the fatty acid precursor. However, dimethylphosphatidylethanolamine was isolated from parasites labeled with the base precursor, indicating the ability of trypanosomes to methylate phosphatidylethanolamine to dimethylphosphatidylethanolamine. Fatty acids of the labeled phospholipids were analyzed by reverse-phase thin-layer chromatography and fluorography. Interestingly, phospholipids from the trypomastigote stage show palmitic acid (C16:0) and stearic acid (C18:0) as the only labeled components. The same saturated fatty acids were found free and as components of the radioactive triglycerides. No unsaturated fatty acids were detected, in accordance with the results obtained with inositolphospholipids. Conversely, when the fatty acids of phospholipids purified from nonlabeled parasites were analyzed by gas-liquid chromatography and gas-liquid chromatography-mass spectrometry, C18:1 was also detected. A striking finding was the presence of a considerable amount of free lignoceric acid (C24:0). Also, the C24:0 fatty acid was identified in the triglyceride fraction and as a component of phosphatidylcholine. The limited capacity of trypomastigote forms to elongate fatty acids was determined. In contrast with the results reported for other noninfective forms of the parasite, the absence of unsaturated fatty acids due to a low activity of desaturases was observed.

Trypanosoma cruzi strains show distinctive characteristics as genetic polymorphism and infectivity. Large repertoires of molecules, such as the Gp85 glycoproteins, members of the Gp85/Trans-sialidase superfamily, as well as multiple signaling pathways, are associated with invasion of mammalian cells by the parasite. Due to the large number of expressed members, encoded by more than 700 genes, the research focused on this superfamily conserved sequences is discussed. Binding sites to laminin have been identified at the N-terminus of the Gp85 molecules. Interestingly, the T. cruzi protein phosphorylation profile is changed upon parasite binding to laminin (or fibronectin), particularly the cytoskeletal proteins such as those from the paraflagellar rod and the tubulins, which are both markedly dephosphorylated. Detailed analysis of the signaling cascades triggered upon T. cruzi binding to extracellular matrix (ECM) proteins revealed the involvement of the MAPK/ERK pathway in this event. At the C-terminus, the conserved FLY sequence is a cytokeratin-binding domain and is involved in augmented host cell invasion in vitro and high levels of parasitemia in vivo. FLY, which is associated to tissue tropism and preferentially binds to the heart vasculature may somehow be correlated with the severe cardiac form, an important clinical manifestation of chronic Chagas’ disease.

Parasite infections are largely dependent on interactions between pathogen and different host cell populations to guarantee a successful infectious process. This is particularly true for obligatory intracellular parasites as Plasmodium, Toxoplasma, and Leishmania, to name a few. Adhesion to and entry into the cell are essential steps requiring specific parasite and host cell molecules. The large amount of possible involved molecules poses additional difficulties for their identification by the classical biochemical approaches. In this respect, the search for alternative techniques should be pursued. Among them two powerful methodologies can be employed, both relying upon the construction of highly diverse combinatorial libraries of peptides or oligonucleotides that randomly bind with high affinity to targets on the cell surface and are selectively displaced by putative ligands. These are, respectively, the peptide-based phage display and the oligonucleotide-based aptamer techniques. The phage display technique has been extensively employed for the identification of novel ligands in vitro and in vivo in different areas such as cancer, vaccine development, and epitope mapping. Particularly, phage display has been employed in the investigation of pathogen–host interactions. Although this methodology has been used for some parasites with encouraging results, in trypanosomatids its use is, as yet, scanty. RNA and DNA aptamers, developed by the SELEX process (Systematic Evolution of Ligands by Exponential Enrichment), were described over two decades ago and since then contributed to a large number of structured nucleic acids for diagnostic or therapeutic purposes or for the understanding of the cell biology. Similarly to the phage display technique scarce use of the SELEX process has been used in the probing of parasite–host interaction. In this review, an overall survey on the use of both phage display and aptamer technologies in different pathogenic organisms will be discussed. Using these techniques, recent results on the interaction of Trypanosoma cruzi with the host will be highlighted focusing on members of the 85 kDa protein family, a subset of the gp85/TS superfamily.

In vivo labeling experiments with [3H]palmitic acid, [3H]inositol, and [3H]glucose allowed the identification of two main classes of inositolphospholipids (IPLs) from the trypomastigote stage of Trypanosoma cruzi. Purification of these compounds was achieved by ion-exchange chromatography, high performance liquid chromatography and thin layer chromatography. Specific phosphatidyl-inositol phospholipase C digestion, dephosphorylation and acid methanolysis showed a ceramide structure for the lower migrating IPL1. Palmitoyldihydrosphingosine and palmitoylsphingosine were detected by reverse-phase thin-layer chromatography. On the other hand, IPL2 showed to be a mixture of diacylglycero- and alkylacylglycero-phospholipids in a 1:1 ratio. After PI-PLC digestion, the lipids were separated by preparative TLC and individually analysed. The diacylglycerol contained mainly C18:0 fatty acid together with a low amount of C16:0. Hexadecylglycerol esterified with the C18:0 fatty acid was the only alkylacylglycerol detected. The C18:2 and C18:1 fatty acids, preponderant in the PI molecules of epimastigote forms, were not detected in trypomastigote forms. This is the first report on inositol phospholipids, putative precursors of lipid anchors in the infective stage of T. cruzi.

Tc-85, an 85-kDa surface glycoprotein specific for the trypomastigote stage of Trypanosoma cruzi, has been implicated in the invasion of host cells by the parasite. Radioactive palmitic acid was incorporated into Tc-85 immunoprecipitated from the culture medium with the H1A10 monoclonal antibody, suggesting that shedding occurs with Tc-85 bearing its GPI anchor. In contrast to the glycoprotein remaining in the parasites, the glycosylphosphatidylinositol moiety in shed Tc-85 is resistant to phosphatidylinositol phospholipase C and becomes susceptible to the enzyme following alkali treatment. An alkylglycerol was identified by thin layer chromatography of an ether extract after the enzymatic reaction. Resistance to cleavage by phospholipase C is due to fatty acid esterification of the inositol residue in shed Tc-85. This is the first example of inositol modification in anchors from a glycoprotein of Trypanosoma cruzi.

Galactofuranose has been characterized in glycoinositolphospholipid (GIPL) anchor-like structures having a glycerolipid or a ceramide, as in lipopeptidophosphoglycan (LPPG) of Trypanosoma cruzi, in the oligosaccharide core of lipopeptidophosphoglycan (LPG) of Leishmania species, and also modifying high-mannose chains of trypanosomatid glycoproteins. Galactofuranose is usually present linked beta 1-->3 to Man, either as a terminal non-reducing unit, like in LPPG, or in the middle of the oligosaccharide core, as in LPG. The presence in protozoan parasites of galactose in the furanose configuration is a feature which deserves further attention since the mammalian hosts do not appear to produce glycoconjugates containing this structural unit. For that reason, hosts produce antibodies against galactofuranose, which may turn out to be important in understanding the pathogenesis and in the development of diagnostic methods. The metabolic pathways involved in the attachment to or removal of galactofuranose from glycoconjugates have not yet been elucidated. This is an area of incipient research, but of growing importance, since it will foster the design of inhibitors which may prove to be useful for the treatment of disease.

BACKGROUND: The unicellular parasite Trypanosoma cruzi is the causative agent of Chagaś disease in humans. Adherence of the infective stage to elements of the extracellular matrix (ECM), as laminin and fibronectin, is an essential step in host cell invasion. Although members of the gp85/TS, as Tc85, were identified as laminin and fibronectin ligands, the signaling events triggered on the parasite upon binding to these molecules are largely unexplored. METHODOLOGY/PRINCIPAL FINDINGS: Viable infective parasites were incubated with laminin, fibronectin or bovine serum albumin for different periods of time and the proteins were separated by bidimensional gels. The phosphoproteins were envisaged by specific staining and the spots showing phosphorylation levels significantly different from the control were excised and identified by MS/MS. The results of interest were confirmed by immunoblotting or immunoprecipitation and the localization of proteins in the parasite was determined by immunofluorescence. Using a host cell-free system, our data indicate that the phosphorylation contents of T. cruzi proteins encompassing different cellular functions are modified upon incubation of the parasite with fibronectin or laminin. CONCLUSIONS/SIGNIFICANCE: Herein it is shown, for the first time, that paraflagellar rod proteins and α-tubulin, major structural elements of the parasite cytoskeleton, are predominantly dephosphorylated during the process, probably involving the ERK1/2 pathway. It is well established that T. cruzi binds to ECM elements during the cell infection process. The fact that laminin and fibronectin induce predominantly dephosphorylation of the main cytoskeletal proteins of the parasite suggests a possible correlation between cytoskeletal modifications and the ability of the parasite to internalize into host cells.

Successful infection of mammalian host by trypomastigotes of Trypanosoma cruzi is a complex event, involving host receptors and parasite ligands. Interaction of the trypomastigote stage with laminin, a component of specialized extracellular matrices, as basement membranes, is studied in this report. Binding of 125I-laminin to trypomastigotes is specific and 2−5 × 103 laminin binding sites were calculated to be present on the surface of live trypomastigotes. Antilaminin antibodies were able to inhibit the invasion of cultured cells by trypomastigotes (75-62%), suggesting that laminin may be involved in the adhesion of the parasite to host cells. By affinity chromatography, an 85-kDa glycoprotein was isolated (laminin binding glycoprotein, LBG) from trypomastigote lysates, but not from epimastigote lysates. It is suggested that at least fragment E8 (but not E1′) from laminin could be involved in the reaction which is independent of the carbohydrate moieties from both ligand and receptor, as suggested by glycosidase or tunicamycin treatments. It is also shown that LBG is an acidic component of the polymorphic Tc-85 protein family, a trypomastigote-specific surface membrane glycoprotein which contains several polypeptides recognized by the monoclonal antibody H1A10, and previously related with the invasion process of the parasite.

Antiserum to LPPG, a lipopeptidophosphoglycan originally described on the surface of Trypanosoma cruzi epimastigotes of the Y strain, and antibodies to furanoic galactose (galf) were obtained in rabbits. A micromethod for the extraction and purification of LPPG from a limited amount of parasites is described. Analysis by Western blots of the purified glycoconjugate probed with both antisera confirmed the presence of galf-containing LPPG-like molecules in 10 different strains and clones of T. cruzi. An analogous approach indicated that trypomastigotes also contain LPPG-like components. Quantitation experiments allowed to calculate an average value of 1.0 x 10(7) LPPG molecules per epimastigote cell and 0.16 x 10(7) LPPG-like molecules per trypomastigote cell. Immunoelectron microscopy has shown a homogenous distribution of LPPG on the surface of epimastigotes. The trypomastigote population, however, is highly heterogenous with no more than 15% of the parasites being labeled by the anti-LPPG serum. Intense labeling has also been found in vesicles inside the epimastigote and trypomastigote forms. The distribution of galf epitopes among glycoconjugates of epimastigotes and trypomastigotes was further investigated. It was shown that galf units in epimastigotes are bound to low molecular mass compounds which co-migrate with LPPG whereas in trypomastigotes they have been found in both low molecular mass LPPG-like molecules and glycoproteins of 80-90 kDa. Direct chemical evidence for the presence of galf residues in the N-linked oligosaccharide chains of these surface glycoproteins has been obtained. Finally, the natural antigenicity of LPPG and galf in chronic Chagas' disease was investigated. It was found that all chronic chagasic sera investigated recognize this glycoconjugate and that an important part of such recognition can be attributed to galf residues. Furthermore, no correlation among reactivity to LPPG, strain zymodeme and clinical forms of the disease was found.

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., Author Summary 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.

1. Nifurtimox uptake and metabolism by epimastigote forms of three strains of Trypanosoma cruzi (Basileu, Y, YuYu) with different drug responsiveness in mice experimental infections were compared. 2. Statistical analysis of the results demonstrated no correlation between the ability of the strains to catalyze nifurtimox redox-cycling (Basileu = Y = YuYu) nor nifurtimox multiple electron reduction (Basileu = Y greater than Y) and drug susceptibility (Basileu greater than Y greater than YuYu). 3. A partial correlation however, was observed between drug responsiveness and nifurtimox uptake (Basileu greater than Y = YuYu). 4. The results suggest that drug uptake may be more important than drug metabolism in modulating resistance to nifurtimox in T. cruzi strains.

Trypanosoma cruzi, the agent of Chagas' disease, alternates between different morphogenetic stages that face distinct physiological conditions in their invertebrate and vertebrate hosts, likely in the availability of glucose. While the glucose transport is well characterized in epimastigotes of T. cruzi, nothing is known about how the mammalian stages acquire this molecule. Herein glucose transport activity and expression were analyzed in the three developmental stages present in the vertebrate cycle of T. cruzi. The infective trypomastigotes showed the highest transport activity (Vmax = 5.34 ± 0.54 nmol/min per mg of protein; Km = 0.38 ± 0.01 mM) when compared to intracellular epimastigotes (Vmax =2 .18± 0.20 nmol/min per mg of protein; Km = 0.39 ± 0.01 mM). Under the conditions employed no transport activity could be detected in amastigotes. The gene of the glucose transporter is expressed at the mRNA level in trypomastigotes and in intracellular epimastigotes but not in amastigotes, as revealed by real-time PCR. In both trypomastigotes and intracellular epimastigotes protein expression could be detected by Western blot with an antibody raised against the glucose transporter correlating well with the transport activity measured experimen- tally. Interestingly, anti-glucose transporter antibodies showed a strong reactivity with glycosome and reservosome organelles. A comparison between proline and glucose transport among the intracellular differentiation forms is presented. The data suggest that the regulation of glucose transporter reflects different energy and carbon requirements along the intracellular life cycle of T. cruzi. © 2009 Elsevier B.V. All rights reserved.

Trypanosoma cruzi trypomastigotes continuously shed into the medium plasma membrane fragments sealed as vesicles enriched in glycoproteins of the gp85 and trans-sialidase (TS) superfamily and α-galactosyl-containing glycoconjugates. Injection of a vesicle fraction into BALB/c mice prior to T. cruzi infection led to 40% of deaths on the 16th day post-infection and 100% on day 20th whereas 20% of untreated animals survived for more than 30 days. The vesicle-treated animals developed severe heart pathology, with intense inflammatory reaction and higher number of amastigote nests. Analysis of the inflammatory infiltrates 15 days after infection showed predominance of TCD4+ lymphocytes and macrophages, but not of TCD8+ cells, as well as a decrease of areas labeled with anti-iNOS antibodies as compared to the control. Higher levels of IL-4 and IL-10 mRNAs were found in the hearts and higher IL-10 and lower NO levels in splenocytes of vesicles pretreated animals. Treatment of mice with neutralizing anti-IL-10 or anti-IL-4 antibodies precluded the effects of pre-inoculation of membrane vesicles on infection. These results indicate that T. cruzi shed membrane components increase tissue parasitism and inflammation by stimulation of IL-4 and IL-10 synthesis and thus may play a central role in the pathogenesis of Chagas’ disease acute phase.

Background Chagas' disease, caused by the protozoan parasite Trypanosoma cruzi, is a disease that affects millions of people most of them living in South and Central Americas. There are few treatment options for individuals with Chagas' disease making it important to understand the molecular details of parasite infection, so novel therapeutic alternatives may be developed for these patients. Here, we investigate the interaction between host cell intermediate filament proteins and the T. cruzi gp85 glycoprotein superfamily with hundreds of members that have long been implicated in parasite cell invasion. Methodology/Principal Findings An in silico analysis was utilized to identify peptide motifs shared by the gp85 T. cruzi proteins and, using phage display, these selected peptide motifs were screened for their ability to bind to cells. One peptide, named TS9, showed significant cell binding capacity and was selected for further studies. Affinity chromatography, phage display and invasion assays revealed that peptide TS9 binds to cytokeratins and vimentin, and prevents T. cruzi cell infection. Interestingly, peptide TS9 and a previously identified binding site for intermediate filament proteins are disposed in an antiparallel β-sheet fold, present in a conserved laminin-G-like domain shared by all members of the family. Moreover, peptide TS9 overlaps with an immunodominant T cell epitope. Conclusions/Significance Taken together, the present study reinforces previous results from our group implicating the gp85 superfamily of glycoproteins and the intermediate filament proteins cytokeratin and vimentin in the parasite infection process. It also suggests an important role in parasite biology for the conserved laminin-G-like domain, present in all members of this large family of cell surface proteins., Author Summary Chagas' disease affects millions of people worldwide and is caused by a microorganism called Trypanosoma cruzi. Treatment options for patients with Chagas' disease is still limited to a small number of drugs, all of them very toxic with important side effects that can be debilitating for the health of patients. Understanding the molecular details of how T. cruzi infects humans is an important step toward the development of new drugs for this disease. As part of its life cycle, T. cruzi has to invade cells in order to replicate and produce new parasites. This is a complex event, which involves different proteins produced by both the parasite and the human host cells. Among them, there is a large family of highly polymorphic T. cruzi proteins important to guide the parasite to the target cells. Here we show that notwithstanding their differences, all members of this family share a small region comprised of nine amino acids that is important for cell recognition and infection by the parasite. Exploring these findings may provide researchers with new insights on how to prevent T. cruzi cell invasion and lead to novel therapeutic alternative for this debilitating disease.

Background Adhesion of the Trypanosoma cruzi trypomastigotes, the causative agent of Chagas' disease in humans, to components of the extracellular matrix (ECM) is an important step in host cell invasion. The signaling events triggered in the parasite upon binding to ECM are less explored and, to our knowledge, there is no data available regarding •NO signaling. Methodology/Principal Findings Trypomastigotes were incubated with ECM for different periods of time. Nitrated and S-nitrosylated proteins were analyzed by Western blotting using anti-nitrotyrosine and S-nitrosyl cysteine antibodies. At 2 h incubation time, a decrease in NO synthase activity, •NO, citrulline, arginine and cGMP concentrations, as well as the protein modifications levels have been observed in the parasite. The modified proteins were enriched by immunoprecipitation with anti-nitrotyrosine antibodies (nitrated proteins) or by the biotin switch method (S-nitrosylated proteins) and identified by MS/MS. The presence of both modifications was confirmed in proteins of interest by immunoblotting or immunoprecipitation. Conclusions/Significance For the first time it was shown that T. cruzi proteins are amenable to modifications by S-nitrosylation and nitration. When T. cruzi trypomastigotes are incubated with the extracellular matrix there is a general down regulation of these reactions, including a decrease in both NOS activity and cGMP concentration. Notwithstanding, some specific proteins, such as enolase or histones had, at least, their nitration levels increased. This suggests that post-translational modifications of T. cruzi proteins are not only a reflex of NOS activity, implying other mechanisms that circumvent a relatively low synthesis of •NO. In conclusion, the extracellular matrix, a cell surrounding layer of macromolecules that have to be trespassed by the parasite in order to be internalized into host cells, contributes to the modification of •NO signaling in the parasite, probably an essential move for the ensuing invasion step., Author Summary Interaction of Trypanosoma cruzi with the extracellular matrix (ECM) is an essential step in the invasion of mammalian cells. However, the nature of the signaling triggered in the parasite is poorly understood. Herein the key role of nitric oxide in T. cruzi signaling is described, using an ECM preparation, in the absence of host cells. Inhibition of NOS activity, with the expected decrease in •NO production, as well as decrease in cGMP concentration were observed by the incubation of T. cruzi trypomastigotes with ECM. Additionally, lower levels of protein S-nitrosylation and nitration were detected. These post-translational modifications have been analyzed by biotin-switch and protein immunoprecipitation approaches coupled to mass spectrometry. The presence of both modifications was confirmed for specific proteins, as mucin II (S-nitrosylation), histones, enolase and tubulins. To our knowledge, decrease in the •NO signaling pathway upon T. cruzi trypomastigotes adhesion to ECM, affecting both the canonical pathway (•NO-soluble guanylyl cyclase-cGMP) and protein S-nitrosylation and nitration is described for the first time in this parasite.