Synthesis and conformational analysis of vicinally branched trisaccharide β-d-Galf-(1 → 2)-[β-d-Galf-(1 → 3)-]-α-Galp from Cryptococcus neoformans galactoxylomannan

The synthesis of a vicinally branched trisaccharide composed of two d-galactofuranoside residues attached viaβ-(1 → 2)- and β-(1 → 3)-linkages to the α-d-galactopyranoside unit has been performed for the first time. The reported trisaccharide represents the galactoxylomannan moiety first described in 2017, which is the capsular polysaccharide of the opportunistic fungal pathogen Cryptococcus neoformans responsible for life-threatening infections in immunocompromised patients. The NMR-data reported here for the synthetic model trisaccharide are in good agreement with the previously assessed structure of galactoxylomannan and are useful for structural analysis of related polysaccharides. The target trisaccharide as well as the constituent disaccharides were analyzed by a combination of computational and NMR methods to demonstrate good convergence of the theoretical and experimental results. The results suggest that the furanoside ring conformation may strongly depend on the aglycon structure. The reported conformational tendencies are important for further analysis of carbohydrate-protein interaction, which is critical for the host response toward C. neoformans infection.

Inhibition of glycosphingolipid biosynthesis reverts multidrug resistance by differentially modulating ABC transporters in chronic myeloid leukemias

Multidrug resistance (MDR) in cancer arises from cross-resistance to structurally- and functionally-divergent chemotherapeutic drugs. In particular, MDR is characterized by increased expression and activity of ATP-binding cassette (ABC) superfamily transporters. Sphingolipids are substrates of ABC proteins in cell signaling, membrane biosynthesis, and inflammation, for example, and their products can favor cancer progression. Glucosylceramide (GlcCer) is a ubiquitous glycosphingolipid (GSL) generated by glucosylceramide synthase, a key regulatory enzyme encoded by the UDP-glucose ceramide glucosyltransferase (UGCG) gene. Stressed cells increase de novo biosynthesis of ceramides, which return to sub-toxic levels after UGCG mediates incorporation into GlcCer. Given that cancer cells seem to mobilize UGCG and have increased GSL content for ceramide clearance, which ultimately contributes to chemotherapy failure, here we investigated how inhibition of GSL biosynthesis affects the MDR phenotype of chronic myeloid leukemias. We found that MDR is associated with higher UGCG expression and with a complex GSL profile. UGCG inhibition with the ceramide analog d-threo-1-(3,4,-ethylenedioxy)phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (EtDO-P4) greatly reduced GSL and monosialotetrahexosylganglioside levels, and co-treatment with standard chemotherapeutics sensitized cells to mitochondrial membrane potential loss and apoptosis. ABC subfamily B member 1 (ABCB1) expression was reduced, and ABCC-mediated efflux activity was modulated by competition with nonglycosylated ceramides. Consistently, inhibition of ABCC-mediated transport reduced the efflux of exogenous C₆-ceramide. Overall, UGCG inhibition impaired the malignant glycophenotype of MDR leukemias, which typically overcomes drug resistance through distinct mechanisms. This work sheds light on the involvement of GSL in chemotherapy failure, and its findings suggest that targeted GSL modulation could help manage MDR leukemias.

Functional Characterization of ABCC Proteins from Trypanosoma cruzi and Their Involvement with Thiol Transport

Chagas disease is a neglected disease caused by the protozoan Trypanosoma cruzi and affects 8 million people worldwide. The main chemotherapy is based on benznidazole. The efficacy in the treatment depends on factors such as the parasite strain, which may present different sensitivity to treatment. In this context, the expression of ABC transporters has been related to chemotherapy failure. ABC transporters share a well-conserved ABC domain, responsible for ATP binding and hydrolysis, whose the energy released is coupled to transport of molecules through membranes. The most known ABC transporters are ABCB1 and ABCC1, involved in the multidrug resistance phenotype in cancer, given their participation in cellular detoxification. In T. cruzi, 27 ABC genes were identified in the genome. Nonetheless, only four ABC genes were characterized: ABCA3, involved in vesicular trafficking; ABCG1, overexpressed in strains naturally resistant to benznidazole, and P-glycoprotein 1 and 2, whose participation in drug resistance is controversial. Considering P-glycoprotein genes are related to ABCC subfamily in T. cruzi according to the demonstration using BLASTP alignment, we evaluated both ABCB1-like and ABCC-like activities in epimastigote and trypomastigote forms of the Y strain. The transport activities were evaluated by the efflux of the fluorescent dyes Rhodamine 123 and Carboxyfluorescein in a flow cytometer. Results indicated that there was no ABCB1-like activity in both T. cruzi forms. Conversely, results demonstrated ABCC-like activity in both epimastigote and trypomastigote forms of T. cruzi. This activity was inhibited by ABCC transport modulators (probenecid, indomethacin, and MK-571), by ATP-depleting agents (sodium azide and iodoacetic acid) and by the thiol-depleting agent N-ethylmaleimide. Additionally, the presence of ABCC-like activity was supported by direct inhibition of the thiol-conjugated compound efflux with indomethacin, characteristic of ABCC subfamily members. Taken together, the results provide the first description of native ABCC-like activity in T. cruzi epimastigote and trypomastigote forms, indicating that the study of the biological role for that thiol transporter is crucial to reveal new molecular mechanisms for therapeutic approaches in the Chagas disease.

The trans-sialidase, the major Trypanosoma cruzi virulence factor: Three decades of studies

Chagas' disease is a potentially life-threatening disease caused by the protozoan parasite Trypanosoma cruzi. Since the description of Chagas'disease in 1909 extensive research has identified important events in the disease in order to understand the biochemical mechanism that modulates T. cruzi-host cell interactions and the ability of the parasite to ensure its survival in the infected host. Exactly 30 years ago, we presented evidence for the first time of a trans-sialidase activity in T. cruzi (T. cruzi-TS). This enzyme transfers sialic acid from the host glycoconjugates to the terminal β-galactopyranosyl residues of mucin-like molecules on the parasite's cell surface. Thenceforth, many articles have provided convincing data showing that T. cruzi-TS is able to govern relevant mechanisms involved in the parasite's survival in the mammalian host, such as invasion, escape from the phagolysosomal vacuole, differentiation, down-modulation of host immune responses, among others. The aim of this review is to cover the history of the discovery of T. cruzi-TS, as well as some well-documented biological effects encompassed by this parasite's virulence factor, an enzyme with potential attributes to become a drug target against Chagas disease.

Molecular and functional characterization of the ceramide synthase from Trypanosoma cruzi

In this study, we characterized ceramide synthase (CerS) of the protozoan parasite Trypanosoma cruzi at the molecular and functional levels. TcCerS activity was detected initially in a cell-free system using the microsomal fraction of epimastigote forms of T. cruzi, [(3)H]dihydrosphingosine or [(3)H]sphingosine, and fatty acids or acyl-CoA derivatives as acceptor or donor substrates, respectively. TcCerS utilizes both sphingoid long-chain bases, and its activity is exclusively dependent on acyl-CoAs, with palmitoyl-CoA being preferred. In addition, Fumonisin B(1), a broad and well-known acyl-CoA-dependent CerS inhibitor, blocked the parasite's CerS activity. However, unlike observations in fungi, the CerS inhibitors Australifungin and Fumonisin B(1) did not affect the proliferation of epimastigotes in culture, even after exposure to high concentrations or after extended periods of treatment. A search of the parasite genome with the conserved Lag1 motif from Lag1p, the yeast acyl-CoA-dependent CerS, identified a T. cruzi candidate gene (TcCERS1) that putatively encodes the parasite's CerS activity. The TcCERS1 gene was able to functionally complement the lethality of a lag1Δ lac1Δ double deletion yeast mutant in which the acyl-CoA-dependent CerS is not detectable. The complemented strain was capable of synthesizing normal inositol-containing sphingolipids and is 10 times more sensitive to Fumonisin B(1) than the parental strain.

Understanding the laminated layer of larval Echinococcus I: structure

Echinococcus larvae are protected by a massive carbohydrate-rich acellular structure, called the laminated layer. In spite of being widely considered the crucial element of these host-parasite interfaces, the laminated layer has been historically poorly understood. In fact, it is still often called 'chitinous', 'hyaline' or 'cuticular' layer, or said to be composed of polysaccharides. However, over the past few years the laminated layer was found to be comprised of mucins bearing defined galactose-rich carbohydrates, and accompanied, in the case of Echinococcus granulosus, by calcium inositol hexakisphosphate deposits. In this review, the architecture and biosynthesis of this unusual structure is discussed at depth in terms of what is known and what needs to be discovered.

Trypanosoma cruzi subverts host cell sialylation and may compromise antigen-specific CD8+ T cell responses

Upon activation, cytotoxic CD8(+) T lymphocytes are desialylated exposing beta-galactose residues in a physiological change that enhances their effector activity and that can be monitored on the basis of increased binding of the lectin peanut agglutinin. Herein, we investigated the impact of sialylation mediated by trans-sialidase, a specific and unique Trypanosoma transglycosylase for sialic acid, on CD8(+) T cell response of mice infected with T. cruzi. Our data demonstrate that T. cruzi uses its trans-sialidase enzyme to resialylate the CD8(+) T cell surface, thereby dampening antigen-specific CD8(+) T cell response that might favor its own persistence in the mammalian host. Binding of the monoclonal antibody S7, which recognizes sialic acid-containing epitopes on the 115-kDa isoform of CD43, was augmented on CD8(+) T cells from ST3Gal-I-deficient infected mice, indicating that CD43 is one sialic acid acceptor for trans-sialidase activity on the CD8(+) T cell surface. The cytotoxic activity of antigen-experienced CD8(+) T cells against the immunodominant trans-sialidase synthetic peptide IYNVGQVSI was decreased following active trans-sialidase-mediated resialylation in vitro and in vivo. Inhibition of the parasite's native trans-sialidase activity during infection strongly decreased CD8(+) T cell sialylation, reverting it to the glycosylation status expected in the absence of parasite manipulation increasing mouse survival. Taken together, these results demonstrate, for the first time, that T. cruzi subverts sialylation to attenuate CD8(+) T cell interactions with peptide-major histocompatibility complex class I complexes. CD8(+) T cell resialylation may represent a sophisticated strategy to ensure lifetime host parasitism.

Sorting of phosphoglucomutase to glycosomes in Trypanosoma cruzi is mediated by an internal domain

Trypanosoma cruzi relies on highly galactosylated molecules as virulence factors and the enzymes involved in sugar biosynthesis are potential therapeutic targets. The synthesis of UDP-galactose in T. cruzi requires the activity of phosphoglucomutase (PGM), the enzyme that catalyzes the interconversion of glucose-6-phosphate and glucose-1-phosphate. Several enzymes that participate in carbohydrate metabolism in trypanosomes are confined to specialized peroxisome-like organelles called glycosomes. The majority of glycosomal proteins contain peroxisome-targeting signals (PTS) at the COOH- or at the amino-terminus, which drive their transport to glycosomes. We had previously identified the T. cruzi PGM gene (TcPGM) and demonstrated that it encodes a functional enzyme. Here, we show that, in contrast to yeast and mammalian cells, TcPGM resides in glycosomes of the parasite. However, no classical PTS1 or PTS2 motif is present in its sequence. We investigated glycosomal targeting by generating T. cruzi cell lines expressing different domains of TcPGM fused to the green fluorescent protein (GFP). The analysis of the subcellular localization of fusion proteins revealed that an internal targeting signal of TcPGM, residing between amino acid residues 260 and 380, is capable of targeting GFP to glycosomes. These results demonstrate that, in T. cruzi, PGM import into glycosomes is mediated by a novel non-PTS domain that is located internally in the protein.

Endophytic colonization of rice (Oryza sativa L.) by the diazotrophic bacterium Burkholderia kururiensis and its ability to enhance plant growth

Burkholderia kururiensis is a diazotrophic bacterium originally isolated from a polluted aquifer environment and presents a high level of similarity with the rice endophyte "B. brasilensis" species. This work assessed the ability of B. kururiensis to endophytically colonize rice plantlets by monitoring different tissues of root-inoculated plants for the presence of bacterial growth in different media, electron microscopy and by 16S rDNA analysis. Observations of roots, stems and leaves of inoculated rice plantlets by electron microscopy revealed B. kururiensis colonization predominantly on root hair zones, demonstrating endophytic colonization primarily through the endodermis, followed by spreading into xylem vessels, a possible pathway leading to aerial parts. Although indifferent for the bacterial growth itself, addition of a nitrogen source was a limiting factor for endophytic colonization. As endophytic colonization was directly associated to an enhanced plant development, production of phytohormone auxin/indole-3-acetic acid by B. kururiensis was assayed with transgenic rice plantlets containing an auxin-responsive reporter (DR5-GUS). Our findings suggest the ability of auxin production by plant-associated B. kururiensis which may have a stimulatory effect on plant development, as evidenced by activation of DR5-GUS. We hereby demonstrate, for the first time, the ability of B. kururiensis to endophytically colonize rice, promoting both plant growth and rice grain yield.

Capsular polysaccharides galactoxylomannan and glucuronoxylomannan from Cryptococcus neoformans induce macrophage apoptosis mediated by Fas ligand

The effects of capsular polysaccharides, galactoxylomannan (GalXM) and glucuronoxylomannan (GXM), from acapsular (GXM negative) and encapsulate strains of Cryptococcus neoformans were investigated in RAW 264.7 and peritoneal macrophages. Here, we demonstrate that GalXM and GXM induced different cytokines profiles in RAW 264.7 macrophages. GalXM induced production of TNF-alpha, NO and iNOS expression, while GXM predominantly induced TGF-beta secretion. Both GalXM and GXM induced early morphological changes identified as autophagy and late macrophages apoptosis mediated by Fas/FasL interaction, a previously unidentified mechanism of virulence. GalXM was more potent than GXM at induction of Fas/FasL expression and apoptosis on macrophages in vitro and in vivo. These findings uncover a mechanism by which capsular polysaccharides from C. neoformans might compromise host immune responses.

Endothelial cell signalling induced by trans-sialidase from Trypanosoma cruzi

The protozoan responsible for Chagas' disease, Trypanosoma cruzi, expresses on its surface an unusual trans-sialidase enzyme thought to play an important role in host-parasite interactions. Trans-sialidase is the product of a multigene family encoding both active and inactive proteins. We have demonstrated that despite lacking enzymatic activity due to a single mutation, Tyr342-His, inactive trans-sialidase displays sialic acid binding activity, with identical specificity to that of its active analogue. In this work we demonstrate that binding of a recombinant inactive trans-sialidase to molecules containing alpha2,3-linked sialic acid on endothelial cell surface triggers NF-kappaB activation, expression of adhesion molecules and upregulation of parasite entry into host cells. Furthermore, inactive recombinant trans-sialidase blocks endothelial cell apoptosis induced by growth factor deprivation. These results suggest that inactive members of the trans-sialidase family play a role in endothelial cell responses to T. cruzi infection.

Toll-like receptor 4 (TLR4)-dependent proinflammatory and immunomodulatory properties of the glycoinositolphospholipid (GIPL) from Trypanosoma cruzi

We have demonstrated recently that the glycoinositolphospholipid (GIPL) molecule from the protozoan Trypanosoma cruzi is a TLR4 agonist with proinflammatory effects. Here, we show that GIPL-induced neutrophil recruitment into the peritoneal cavity is mediated by at least two pathways: one, where IL-1beta acts downstream of TNF-alpha, and a second, which is IL-1beta- and TNFRI-independent. Moreover, NKT cells participate in this proinflammatory cascade, as in GIPL-treated CD1d(-/-) mice, TNF-alpha and MIP-2 levels are reduced significantly. As a consequence of this inflammatory response, spleen and lymph nodes of GIPL-treated mice have an increase in the percentage of T and B cells expressing the CD69 activation marker. Cell-transfer experiments demonstrate that T and B cell activation by GIPL is an indirect effect, which relies on the expression of TLR4 by other cell types. Moreover, although signaling through TNFRI contributes to the activation of B and gammadelta+ T cells, it is not required for increasing CD69 expression on alphabeta+ T lymphocytes. It is interesting that T cells are also functionally affected by GIPL treatment, as spleen cells from GIPL-injected mice show enhanced production of IL-4 following in vitro stimulation by anti-CD3. Together, these results contribute to the understanding of the inflammatory properties of the GIPL molecule, pointing to its potential role as a parasite-derived modulator of the immune response during T. cruzi infection.

Expression of functional TLR4 confers proinflammatory responsiveness to Trypanosoma cruzi glycoinositolphospholipids and higher resistance to infection with T. cruzi

TLRs function as pattern recognition receptors in mammals and play an essential role in the recognition of microbial components. We found that the injection of glycoinositolphospholipids (GIPLs) from Trypanosoma cruzi into the peritoneal cavity of mice induced neutrophil recruitment in a TLR4-dependent manner: the injection of GIPL in the TLR4-deficient strain of mice (C57BL/10ScCr) caused no inflammatory response. In contrast, in TLR2 knockout mice, neutrophil chemoattraction did not differ significantly from that seen in wild-type controls. GIPL-induced neutrophil attraction and MIP-2 production were also severely affected in TLR4-mutant C3H/HeJ mice. The role of TLR4 was confirmed in vitro by testing genetically engineered mutants derived from TLR2-deficient Chinese hamster ovary (CHO)-K1 fibroblasts that were transfected with CD14 (CHO/CD14). Wild-type CHO/CD14 cells express the hamster TLR4 molecule and the mutant line, in addition, expresses a nonfunctional form of MD-2. In comparison to wild-type cells, mutant CHO/CD14 cells failed to respond to GIPLs, indicating a necessity for a functional TLR4/MD-2 complex in GIPL-induced NF-kappaB activation. Finally, we found that TLR4-mutant mice were hypersusceptible to T. cruzi infection, as evidenced by a higher parasitemia and earlier mortality. These results demonstrate that natural resistance to T. cruzi is TLR4 dependent, most likely due to TLR4 recognition of their GIPLs.

Heterogeneity in the biosynthesis of mucin O-glycans from Trypanosoma cruzi tulahuen strain with the expression of novel galactofuranosyl-containing oligosaccharides

Sialoglycoprotein from Trypanosoma cruzi strains participates in important biological functions in which the O-linked glycans play a pivotal role, and their structural diversity may be related to the parasite's virulence pattern. To provide supporting evidence for this idea, we have determined the structure of novel linear and branched alpha-O-GlcNAc-linked oligosaccharides present on the mucins of the T. cruzi Tulahuen strain. The O-glycans were isolated as oligosaccharide alditols by reductive beta-elimination, purified, and characterized by nuclear magnetic resonance spectroscopy and methylation analysis. Two core families were synthesized by the parasite: the Galfbeta1-->4GlcNAc and Galpbeta1-->4GlcNAc. The Galfbeta1-->4GlcNAc core yields three series of O-chain structures. In the first, the Galf residue is nonsubstituted, while in the other series it is elongated by the activity of galactopyranosyl or galactofuranosyl transferases giving rise to Galp-beta-(1-->2)-Galf-beta-(1-->4) or Galf-beta-(1-->2)-Galf-beta-(1-->4) substructures not previously observed. The three series can arise by further galactopyranosylation of the GlcNAc O-6 arm. Sialylation was the only observed elaboration of the Galpbeta1-->4GlcNAc core family. Thus the determination of the structures of the O-glycans from T. cruzi Tulahuen mucins confirms the strain specificity of the glycosylation and predicts a relationship between it and parasite pathogenicity and the epidemiology of Chagas' disease.

Influence of polarisation and differentiation on interaction of 43-kDa outer-membrane protein of Aeromonas caviae with human enterocyte-like Caco-2 cell line

It has been recognised that adherence and invasion to host cells are important steps in the pathogenesis of entero-pathogenic bacteria, including Aeromonas caviae. However, the virulence factors of A. caviae remain, for the most part, poorly known. This study examined the interaction of A. caviae isolates to Caco-2 cells in different polarisation and differentiation conditions. The adherence of A. caviae may be related to accessibility of host cell basolateral receptors. Aggregative A. caviae isolates, grown at 22 degrees C, were more adherent in both non-polarised and undifferentiated Caco-2 cells and EGTA-treated polarised and differentiated Caco-2 cells. Furthermore, monolayers pre-incubated with 43-kDa outer-membrane protein (OMP) or A. caviae strains pre-incubated with rabbit IgG anti-43-kDa OMP decreased adherence of some A. caviae strains to EGTA-treated polarised and differentiated Caco-2 cells, suggesting an interaction of 43-kDa OMP with basolateral cell receptors. Bacterial cells were observed adhering to microvilli and to plasma membrane on both the apical and basal surfaces of the monolayer. Pedestal-like formation with cytoskeletal rearrangement was also observed. The bacteria entered the Caco-2 cells and were observed enclosed in single and multiple membrane-bound vacuoles within the host cell cytoplasm. Furthermore, A. caviae were observed free in the cytosol of Caco-2 cells, suggesting escape form cytoplasmatic vacuoles.

Proinflammatory and cytotoxic effects of hexadecylphosphocholine (miltefosine) against drug-resistant strains of Trypanosoma cruzi

The increased resistance of the protozoan parasite Trypanosoma cruzi to nitro derivatives is one of the major problems for the successful treatment of Chagas' disease. In the present study, we have tested the effects of 1-O-hexadecylphosphocholine (miltefosine) against strains of T. cruzi that are partially resistant (strain Y) and highly resistant (strain Colombiana) to the drugs in clinical use. As expected, epimastigotes of strain Colombiana showed higher levels of resistance to benznidazole than those of strain Y. However, the level of resistance to miltefosine was the same for both strains. This alkylphospholipid was also extremely toxic against intracellular amastigotes of both strains. This ether-lipid analogue induced in a dose-dependent manner the production of tumor necrosis factor alpha and nitric oxide (NO) radicals by infected and noninfected macrophages, suggesting that miltefosine may activate macrophages in vitro. Nevertheless, the cytotoxic effect of miltefosine against intracellular amastigotes was independent of the amount of NO produced by the infected macrophages since the same dose-response curves for miltefosine were observed when the NO production was blocked by the NO synthase inhibitor N(G)-monomethyl-L-arginine monoacetate. Preliminary in vivo studies with BALB/c mice infected with strain Y indicated that oral miltefosine promoted survival and reduced the parasitemia to levels comparable to those observed when benznidazole was used. Four months after treatment, no parasites were detected in the blood or spleen tissue sections maintained in culture. Together, these results support the hypothesis that miltefosine may be used for the treatment of Chagas' disease, including cases caused by resistant strains of T. cruzi.

Molecular analysis of a novel family of complex glycoinositolphosphoryl ceramides from Cryptococcus neoformans: structural differences between encapsulated and acapsular yeast forms

Complex glycoinositolphosphoryl ceramides (GIPCs) have been purified from a pathogenic encapsulated wild-type (WT) strain of Cryptococcus neoformans var. neoformans and from an acapsular mutant (Cap67). The structures of the GIPCs were determined by a combination of tandem mass spectrometry, nuclear magnetic resonance spectroscopy, methylation analysis, gas chromatography-mass spectrometry, and chemical degradation. The main GIPC from the WT strain had the structure Manp(alpha1-3)[Xylp(beta1-2)] Manp(alpha1-4)Galp(beta1-6)Manp(alpha1-2)Ins-1-phosphoryl ceramide (GIPC A), whereas the compounds from the acapsular mutant were more heterogeneous in their glycan chains, and variants with Manp(alpha1-6) (GIPC B), Manp(alpha1-6) Manp(alpha1-6) (GIPC C), and Manp(alpha1-2)Manp(alpha1-6)Manp(alpha1-6) (GIPC D) substituents linked to the nonreducing terminal mannose residue found in the WT GIPC A were abundant. The ceramide moieties of C. neoformans GIPCs were composed of a C(18) phytosphingosine long-chain base mainly N-acylated with 2-hydroxy-tetracosanoic acid in the WT GIPC while in the acapsular Cap67 mutant GIPCs, as well as 2-hydroxy-tetracosanoic acid, the unusual 2,3-dihydroxy-tetracosanoic acid was characterized. In addition, structural analysis revealed that the amount of GIPC in the WT cells was fourfold less of that in the acapsular mutant.

Glycoinositol phospholipids from Trypanosoma cruzi transmit signals to the cells of the host immune system through both ceramide and glycan chains

Chagas' disease is a chronic disease affecting millions of people in Latin America. The cell surface of Trypanosoma cruzi, the etiological agent, is covered by a glycocalyx whose components play important roles in parasite survival and infectivity. The most abundant surface component is a glycolipid (glycoinositol phospholipid, GIPL) related in structure to glycosylphosphatidyl inositol anchors. In this review, we describe the biological effects of highly purified native GIPLs and their glycan or lipid moities on cells of the host immune system.

Costimulation of host T lymphocytes by a trypanosomal trans-sialidase: involvement of CD43 signaling

Trans-sialidase is a membrane-bound and shed sialidase from Trypanosoma cruzi, the protozoan parasite responsible for Chagas disease. We investigated the role of soluble trans-sialidase on host CD4+ T cell activation. Trans-sialidase activated naive CD4+ T cells in vivo. Both enzymatically active and inactive recombinant trans-sialidases costimulated CD4+ T cell activation in vitro. Costimulation resulted in increased mitogen-activated protein kinase activation, proliferation, and cytokine synthesis. Furthermore, active and inactive trans-sialidases blocked activation-induced cell death in CD4+ T cells from T. cruzi-infected mice. By flow cytometry, inactive trans-sialidase bound the highly sialylated surface Ag CD43 on host CD4+ T cells. Both costimulatory and antiapoptotic effects of trans-sialidases required CD43 signaling. These results suggest that trans-sialidase family proteins are involved in exacerbated host T lymphocyte responses observed in T. cruzi infection.

Involvement of fungal cell wall components in adhesion of Sporothrix schenckii to human fibronectin

Systemic sporotrichosis is an emerging infection potentially fatal for immunocompromised patients. Adhesion to extracellular matrix proteins is thought to play a crucial role in invasive fungal diseases. Here we report studies of the adhesion of Sporothrix schenckii to the extracellular protein fibronectin (Fn). Both yeast cells and conidia of S. schenckii were able to adhere to Fn as detected by enzyme-linked immunosorbent binding assays. Adhesion of yeast cells to Fn is dose dependent and saturable. S. schenckii adheres equally well to 40-kDa and 120-kDa Fn proteolytic fragments. While adhesion to Fn was increased by Ca(2+), inhibition assays demonstrated that it was not RGD dependent. A carbohydrate-containing cell wall neutral fraction blocked up to 30% of the observed adherence for the yeast cells. The biochemical nature of this fraction suggests the participation of cell surface glycoconjugates in binding by their carbohydrate or peptide moieties. These results provide new data concerning S. schenckii adhesion mechanisms, which could be important in host-fungus interactions and the establishment of sporotrichosis.

Characterization of novel structures of mannosylinositolphosphorylceramides from the yeast forms of Sporothrix schenckii

Novel structures of glycoinositolphosphorylceramide (GIPC) from the infective yeast form of Sporothrix schenckii were determined by methylation analysis, mass spectrometry and NMR spectroscopy. The lipid portion was characterized as a ceramide composed of C-18 phytosphingosine N-acylated by either 2-hydroxylignoceric acid (80%), lignoceric (15%) or 2,3-dihydroxylignoceric acids (5%). The ceramide was linked through a phosphodiester to myo-inositol (Ins) which is substituted on position O-6 by an oligomannose chain. GIPC-derived Ins oligomannosides were liberated by ammonolysis and characterized as: Manpalpha1-->6Ins; Manpalpha1-->3Manpalpha1-->6Ins; Manpalpha1-->6Manpalpha1-->3Manpalpha1-->3Manpalpha1-->6Ins; Manpalpha1-->2Manpalpha1-->6Manpalpha1-->3Manpalpha1-->3Manpalpha1-->6Ins. These structures comprise a novel family of fungal GIPC, as they contain the Manpalpha1-->6Ins substructure, which has not previously been characterized unambigously, and may be acylated with a 2,3 dihydroxylignoceric fatty acid, a feature hitherto undescribed in fungal lipids.

Isolation and characterization of the Golgi complex of the protozoan Trypanosoma cruzi

In this study the Golgi complex of the epimastigote forms of Trypanosoma cruzi were isolated and characterized. Using well-controlled sonication to rupture the cells and centrifugation on a discontinuous sucrose density gradient, a highly enriched Golgi fraction was obtained. The Golgi fraction contained most of the beta-galactosyltransferase (beta-Gal transferase) and UDP-N-acetyl-glucosamine: polypeptide-alpha-N-acetyl-glucosaminyltransferase (O-alpha-GlcNAc transferase) activities with minimal contamination of other organelles, as observed by enzymatic assays and electron microscopy analysis. To characterize the Golgi from T. cruzi cells further, it was incubated with a monoclonal antibody against a 58 kDa protein involved in the association of the Golgi complex with microtubules in mammalian cells. Immunofluorescence microscopy showed that the 58 kDa protein is localized in the T. cruzi Golgi region, a result confirmed by high resolution scanning electron microscopy immunocytochemistry. Thus, our results show, for the first time, that the beta-Gal transferase, the O-alpha-GlcNAc transferase and the 58 kDa protein are present in the Golgi complex of T. cruzi and are novel biochemical markers which can be used in the characterization of this organelle in T. cruzi.

Structure of an acidic exopolysaccharide produced by the diazotrophic endophytic bacterium Burkholderia brasiliensis

The structure of an exopolysaccharide (EPS) produced by Burkholderia brasiliensis, a diazotrophic endophytic organism originally isolated from rice roots, has been determined. The bacterium was grown in a synthetic medium, containing mannitol and glutamate, which favours the expression of two anionic EPSs, which were separated by anion-exchange chromatography. The structure of the repeat unit of EPS A, eluted at higher ionic strength, was determined by a combination of methylation analysis, partial hydrolysis, chemical degradations, and NMR spectroscopic studies, and shown to be the linear O-acetylated pentasaccharide: -->4)-alpha-D-Glcp-(1-->2)-alpha-L-Rhap-(1-->4)-alpha-D-GlcpA-(1-->3)-beta-L-Rhap[2OAc]-(1-->4)-beta-D-Glcp-(1-->.

Corynebacterium diphtheriae surface proteins as adhesins to human erythrocytes

Corynebacterium diphtheriae strains express non-fimbrial surface proteins able to recognize and bind to specific host cells receptors. Protein extracts were obtained from bacterial cells by mechanical process and ammonium sulfate precipitation at 25 and 45% (w/v) saturation. SDS-PAGE analysis of the extracts detected two polypeptide bands of 67 and 72 kDa, named 67-72 p. The 67-72 p, rabbit anti-67-72 p IgG antibodies as well as human gastric mucin, N-acetylneuraminic acid and N-acetyl D-glucosamine molecules were able to inhibit bacterial hemagglutination. Hemagglutination assays using 67-72 p-coated latex beads and Western blot analysis of biotin-labeled 67-72 p and erythrocyte receptors demonstrated the binding of 67-72 p to human erythrocyte membranes. Immunolabeled colloidal gold-A protein transmission electron microscopy using anti-67-72 p revealed a diffuse distribution of non-fimbrial 67-72 p on the surface of C. diphtheriae strains of both sucrose-fermenting and non-fermenting biotypes. Non-fimbrial lectin-like surface 67-72 p may play a role as adhesins in bacterial attachment thereby facilitating the early steps in pathogenesis of both toxigenic and non-toxigenic C. diphtheriae.

Identification of a 43-kDa outer-membrane protein as an adhesin in Aeromonas caviae

Aeromonas spp. are associated with intestinal and extra-intestinal infections. However, the virulence factors of A. caviae remain, for the most part, poorly known. This study examined the interactions involved in the adherence of A. caviae isolates Ae56, Ae391 and Ae398 to HEp-2 cells. All strains expressed high levels of aggregative adherence. Maximum adhesion occurred with bacteria grown at 22 degrees C, but transmission electron microscopy did not reveal the presence of fimbrial structures on the bacterial cell surface. Outer-membrane proteins (OMPs) extracted from isolate Ae398, grown at 22 degrees C and 37 degrees C, showed similar SDS-PAGE protein profiles. Most proteins were < 60 kDa. A major 43-kDa protein was seen only in the boiled OMP extract. The biotinylated 43-kDa protein bound specifically to HEp-2 cells. Microbeads coated with the 43-kDa protein were also adherent to HEp-2 cells, and anti-43-kDa protein antibody blocked adherence of 43-kDa protein-coated latex beads. These data suggest that the 43-kDa OMP functions as an adhesin in A. caviae.

Structure of O-glycosidically linked oligosaccharides from glycoproteins of Trypanosoma cruzi CL-Brener strain: evidence for the presence of O-linked sialyl-oligosaccharides

Glycoproteins on the cell surface of Trypanosoma cruzi are known to play important roles in the interaction of the parasite with the host cells. We previously determined the structures of the O-glycan chains from the sialoglycoproteins (mucin-like molecules) of the G- and Y-strains and observed significant differences between them. We now report the structures of the sialylated and nonsialylated O-linked oligosaccharides isolated from the cell surface glycoproteins of the myotropic CL-Brener strain grown in the presence of fetal calf serum. The structures of the O-linked oligosaccharide alditols obtained by reductive beta-elimination of the sialoglycoprotein were determined by a combination of methylation analysis, fast atom bombardment-mass spectrometry and nuclear magnetic resonance spectroscopy. The presence of a beta-galactopyranose substituent on the N-acetylglucosamine O-4 position shows that these O-linked oligosaccharides from CL-Brener strain belong to the same family as those isolated from mucins expressed by T. cruzi Y strain, a reticulotropic strain. In addition, novel O-glycans, including alpha2-3 mono-sialylated species are described.

Glycoinositolphospholipids from Trypanosoma cruzi induce B cell hyper-responsiveness in vivo

The surface of the protozoan Trypanosoma cruzi, the etiologic agent of Chagas' disease, is covered by a dense glycolipid layer, composed mainly by a structurally related family of glycoinositolphospholipids (GIPLs). In the present study we evaluated the in vivo effects of the GIPL on B cell function and immunoglobulin (Ig) secretion. We observed that GIPL injection led to a sustained increase in circulating IgM levels. B cells from GIPL injected mice showed higher response when activated in vitro with either LPS or dextran-conjugated anti-IgD antibodies or purified cytokines. GIPL purified from T. cruzi also showed an adjuvant effect, since this glycophospholipid boosted a polysaccharide-(TNP-Ficoll) induced IgG response. Taken together, our data indicate that T. cruzi-derived GIPL could be at least partially responsible for the remarkable B cell activation observed during T. cruzi acute infection in vivo.

NMR assignments for glucosylated and galactosylated N-acetylhexosaminitols: oligosaccharide alditols related to O-linked glycans from the protozoan parasite Trypanosoma cruzi

We report full 1H and 13C NMR assignments for 13 gluco- or galacto-pyranosylated derivatives of GlcNAc-ol, GalNAc-ol or ManNAc-ol, many of which have been prepared by enzymatic methods. These spectra are reference data to aid the structural analysis by NMR spectroscopy of glycosylated alditols derived from the mucin of the protozoan parasite Trypanosoma cruzi. A series of structural reporter groups for the derivatives from this unusual series of O-glycans are described.

The structure of a complex glycosylphosphatidyl inositol-anchored glucoxylan from the kinetoplastid protozoan Leptomonas samueli

The structure of a glycosylphosphatidyl inositol-anchored glucoxylan (GPI-glucoxylan) synthesized by the monogenetic trypanosomatid Leptomonas samueli has been determined. The glucoxylan is anchored to the membrane by phytoceramide and an oligosaccharide core, the structure of which is identical to glycoinositolphospholipids (GIPLs) expressed by this protozoan. The glucoxylan chain is linear, containing -->4Glcalpha1-->, -->4Xylbeta1--> and -->3Xylbeta1--> residues. A well defined sequence heterogeneity was analysed in terms of a series of overlapping trisaccharide substructures. A proportion of the chains are capped with a GlcAalpha1-->3Glcalpha1--> sequence. While an average GlcA-capped chain contained 10 Glc and 16 Xyl residues, uncapped chains have a higher molecular mass with an average of 30 Glc and 50 Xyl per chain. We propose a mode of biosynthesis based on the observed structural heterogeneity.

Trans-sialidase from Trypanosoma cruzi catalyzes sialoside hydrolysis with retention of configuration

The trans -sialidase from Trypanosoma cruzi is a member of the sialidase superfamily that functions as a sialidase in the absence of a carbohydrate acceptor. We have used(1)H nuclear magnetic resonance (NMR) spectroscopy to investigate the stereospecificity of the hydrolysis of two substrates, namely, 4-methyl-umbelliferyl- N -acetylneur-aminic acid and alpha(2-3)-sialyllactose, catalyzed by a recombinant T.cruzi trans -sialidase. We demonstrate that, in aqueous solution, the thermodynamically less stable alpha-form of N -acetylneuraminic acid is the initial product of the hydrolysis; subsequent mutarotation leads eventually to an equilibrium mixture of the alpha and beta forms, in molar ratio 8:92. In a mixed water/methanol solution, the hydrolysis reaction produces also the alpha-methyl sialoside but not its beta-methyl counterpart. We also show that 4-methyl-umbelliferyl- N -acetylneuraminic acid is a significantly better substrate for the sialidase than alpha(2-3)-sialyllactose. Prolonged incubation of alpha(2-3)-sialyllactose with an excess of trans -sialidase produced a trace of 2-deoxy-2,3-didehydro- N -acetylneuraminic acid, as identified by NMR spectroscopy and by gas liquid chromatography/mass spectro-metry. In conclusion, this study shows that the stereo-selectivity of the sialidase activity of T.cruzi trans -sialidase is identical to that of bacterial, viral, and mammalian sialidases, suggesting a similar active-site architecture.

Modulation of B-lymphocyte and NK cell activities by glycoinositolphospholipid purified from Trypanosoma cruzi

Glycoinositolphospholipids (GIPLs) are some of the major glycolipids of the Trypanosoma cruzi surface that were previously shown to activate B cells. In the present study, we investigated whether (i) T. cruzi GIPLs could induce immunoglobulin secretion from B cells in the absence of T cells and NK cells and whether (ii) NK cells are also stimulated by the GIPLs. B cells purified from mice deficient in both T and NK cells (CD3epsilon transgenic mice) secreted immunoglobulin in response to the GIPL. This response was increased by coculture with a murine NK cell line. The T. cruzi GIPL also increased the NK cell (interleukin-2 induced) proliferative response. Our data indicate that the T. cruzi GIPL has a direct stimulatory effect on NK cells and induces immunoglobulin secretion in the absence of T lymphocytes and NK cells. These findings suggest that this T. cruzi-derived molecule may be one of the stimulators that lead to NK cell activation during T. cruzi infection.

Costimulatory action of glycoinositolphospholipids from Trypanosoma cruzi: increased interleukin 2 secretion and induction of nuclear translocation of the nuclear factor of activated T cells 1

The effects of the glycoinositolphospholipids (GIPLs) fromTrypanosoma cruzi on T lymphocyte activation were investigated in a mouse T cell hybridoma (DO-11.10). Purified GIPLs from T. cruzi strains Y and G markedly increased IL-2 mRNA transcripts and IL-2 secretion induced by mitogenic anti-CD3 and anti-Thy1 mAbs. This costimulatory function was also revealed by the induction of IL-2 secretion after the simultaneous addition of the T. cruzi GIPLs and either the calcium ionophore A23187 or phorbol ester. The capacity of the GIPL molecule to induce an increase in cytoplasmic calcium levels was also demonstrated. After exposure of T cell hybridoma to GIPL, the nuclear transcription factor NFAT1 became partially dephosphorylated, and its nuclear localization was demonstrated both in the T cell hybridoma and in Balb/c CD3(+) cells. These results demonstrate that T. cruzi GIPL molecules are capable of signaling to T cells and therefore could be valuable tools for the study of T cell activation, besides playing a potential role in subverting the T lymphocyte immune response during T. cruzi infection.

Characterization of surface saccharides in two Corynebacterium diphtheriae strains

Two Corynebacterium diphtheriae strains were analyzed by assays employing a battery of highly purified fluorescent lectins. From 22 lectins tested only seven with affinity to receptor molecules containing N-acetylglucosamine (D-GlcNAc), N-acetylgalactosamine (D-GalNAc), galactose (D-Gal), mannose-like (D-Man-like) and sialic acid residues showed positive fluorescent labeling. A higher reactivity of Triticum vulgaris (WGA), which binds to sialic acid and/or beta-D-GlcNAc-containing residues, and Bandeiraea simplicifolia II (BS-II), which recognizes alpha and beta-D-GlcNAc units, was shown by the sucrose-fermenting strain. Ricinus communis (RCA-I), which recognizes D-Gal units in addition to both Glycine max (SBA) and Artocarpus integrifolia (Jacaline) agglutinins that bind to D-GalNAc-containing residues, reacted preferentially with the sucrose-negative strain. Canavalia ensiformis (Con A), which recognizes D-Man-like receptors, reacted with both sucrose-fermenting and non-sucrose-fermenting C. diphtheriae biotypes. However, higher interaction was observed with the non-sucrose-fermenting strain. Fluorescence of WGA binding was significantly decreased by neuraminidase treatment suggesting the presence of an exposed sialic acid moiety on C. diphtheriae surfaces. Binding assay using radiolabeled [125I]WGA essentially confirmed the lectin fluorescence studies. N-Acetylneuraminic acid moieties were detected in whole cell hydrolysates as assessed by thin-layer and gas-liquid chromatography. The data indicate differences on the cell surface saccharide ligands between the sucrose-fermenting and the non-sucrose-fermenting C. diphtheriae strains.

Proapoptotic activity of a Trypanosoma cruzi ceramide-containing glycolipid turned on in host macrophages by IFN-gamma

The effects of glycoinositolphospholipid (GIPL), from the pathogenic protozoan Trypanosoma cruzi, and its isolated glycan and lipid (dihydroceramide) components, were investigated in J774 cells and primary macrophages. Isolated GIPL ceramide, but not intact GIPL or its glycan, induced intense fluid phase endocytosis when added exogenously. In the presence of the cytokine IFN-gamma, GIPL ceramide induced marked apoptosis in J774 cells and macrophages, independent of nitric oxide secretion. When cells were preincubated with the GIPL-derived glycan chain, addition of intact GIPL induced macrophage apoptosis in the presence of IFN-gamma. Synthetic C2-dihydroceramide also induced apoptosis in the presence of IFN-gamma. Induction of apoptosis in T. cruzi-infected macrophages by GIPL ceramide plus IFN-gamma led to increased parasite release compared with IFN-gamma treatment alone. Viable parasites released comprised both infective trypomastigote and spheromastigote forms. These results identify a novel pathway by which T. cruzi glycosylphosphatidylinositol family molecules affect host macrophages, with implications for the infectious process.

Biosynthesis of O-N-acetylglucosamine-linked glycans in Trypanosoma cruzi. Characterization of the novel uridine diphospho-N-acetylglucosamine:polypeptide N-acetylglucosaminyltransferase-catalyzing formation of N-acetylglucosamine alpha1-->O-threonine

In this study, we have characterized the activity of a uridine diphospho-N-acetylglucosamine:polypeptide-alpha-N-acetylglucosaminylt ransferase (O-alpha-GlcNAc-transferase) from Trypanosoma cruzi. The activity is present in microsomal membranes and is responsible for the addition of O-linked alpha-N-acetylglucosamine to cell surface proteins. This preparation adds N-acetylglucosamine to a synthetic peptide KPPTTTTTTTTKPP containing the consensus threonine-rich dodecapeptide encoded by T. cruzi MUC gene (Di Noia, J. M., Sánchez D. O., and Frasch, A. C. C. (1995) J. Biol. Chem. 270, 24146-24149). Incorporation of N-[3H]acetylglucosamine is linearly dependent on incubation time and concentration of enzyme and substrate. The transferase activity has an optimal pH of 7.5- 8.5, requires Mn2+, is unaffected by tunicamycin or amphomycin, and is strongly inhibited by UDP. The optimized synthetic peptide acceptor for the cytosolic O-GlcNAc-transferase (YSDSPSTST) (Haltiwanger, R. S., Holt, G. D., and Hart, G. W. (1990) J. Biol. Chem. 265, 2563-2568) is not a substrate for this enzyme. The glycosylated KPPTTTTTTTTKPP product is susceptible to base-catalyzed beta-elimination, and the presence of N-acetylglucosamine alpha-linked to threonine is supported by enzymatic digestion and nuclear magnetic resonance data. These results describe a unique biosynthetic pathway for T. cruzi surface mucin-like molecules, with potential chemotherapeutic implications.

Glycoinositol phospholipids from Endotrypanum species express epitopes in common with saccharide side chains of the lipophosphoglycan from Leishmania major

We have characterized glycoinositol phospholipids (GIPLs) from three strains of the trypanosomatid parasites Endotrypanum schaudinni and Endotrypanum monterogeii. Methanolysis of the intact GIPLs liberated methyl esters of tetracosanoic acid, docosanoic acid, octadecanoic acid and hexadecanoic acid and C20 and C21 phytosphingosines. Phosphoinositol oligosaccharides were released from the GIPLs by mild base treatment, and their structures were determined by compositional analysis, fast-atom-bombardment MS and NMR spectroscopy. Similar compounds were detected in all three strains, although their relative proportions varied. The predominant components in E. schaudinni strain LV59 and E. monterogeii LV88 were Galpbeta1-3Galpbeta1-3Manalpha1-3Manalpha1-4G lcNalpha1-6Ins-1-P and Arapbeta1-2Ga lpbeta1-3Galpbeta1-3Manalpha1-3Manalpha1-4Glc Nalpha1-6Ins-1-P, and the major phosphoinositol oligosaccharide in E. schaudinni LV58 was the hybrid-type GIPL Manalpha1-2(EtNP-6)Manalpha1-6(Galpbeta1-3Man alpha1-3)Manalpha1-4GlcN alpha1-6Ins-1-P (where EtNP is ethanolamine phosphate). Several minor oligosaccharides containing additional galactose and/or arabinose residues were also detected.

Leishmania adleri, a lizard parasite, expresses structurally similar glycoinositolphospholipids to mammalian Leishmania

Glycoinositolphospholipids (GIPLs) were isolated from promastigotes of the lizard parasites Leishmania adleri by phenol/water extraction. Phosphoinositol oligosaccharides were liberated by mild alkaline hydrolysis, purified by gel filtration and high pH anion exchange chromatography, and characterized by methylation analysis, fast atom bombardment mass spectrometry, and nuclear magnetic resonance spectroscopy. The four major compounds (I-IV) from L. adleri were linked to alkylacyl glycerol, and their glycan moieties had the following structures: Man alpha(1-2)Man alpha(1-6)[Man alpha(1-3)] Man alpha(1-4)GlcN alpha(1-6)Ins-1-PO4 (I), Galp alpha(1-6) Galp alpha(1-3)Galf beta(1-3)Man alpha(1-3)Man alpha(1-4)GlcN alpha(1-6)Ins-1-PO4 (II), Galp alpha(1-3)Galf beta(1-3)Man alpha(1-3) Man alpha(1-4)GlcN alpha(1-6)Ins-1-PO4 (III), Man alpha(1-2)[EtNP(-6)]Man alpha(1-6)[Man alpha(1-3)] Man alpha(1-4)GlcN alpha(1-6)Ins-1-PO4 (IV). These compounds are analogous to the previously characterized GIPLs from New and Old World leishmanial parasites of mammals designated iM4 (identical to compound I), GIPLs 3 and 2 (identical to compounds II and III, respectively), and EPiM4 (identical to compound IV), which is consistent with a close phylogenetic relationship between lizard and mammalian Leishmania. However, in contrast to the mammalian parasites, the abundant surface glycoconjugate known as lipophosphoglycan was either absent or confined to the flagellar pocket region in L. adleri.

Structure of the repeating oligosaccharide from the lipopolysaccharide of the nitrogen-fixing bacterium Acetobacter diazotrophicus strain PAL 5

Acetobacter diazotrophicus is an acid-tolerant nitrogen-fixing bacterium found in roots, rhizosphere, stems, and leaves of sugar cane (Saccharum officinarum) cultivated in Brazil. The O-polysaccharide from the lipopolysaccharide of the root isolate strain PAL 5 has been determined by a combination of methylation analysis and two-dimensional high field NMR spectroscopy. The pentasaccharide repeat has the structure: [formula: see text] Minor resonances in the NMR spectra are consistent with the presence of a proportion of repeating units which lack the beta-D-Glc side-chain.

High diversity in mucin genes and mucin molecules in Trypanosoma cruzi

Mucins are highly O-glycosylated molecules which in mammalian cells accomplish essential functions, like cytoprotection and cell-cell interactions. In the protozoan parasite Trypanosoma cruzi, mucin-related glycoproteins have been shown to play a relevant role in the interaction with and invasion of host cells. We have previously reported a family of mucin-like genes in T. cruzi whose overall structure resembled that of mammalian mucin genes. We have now analyzed the relationship between these genes and mucin proteins. A monoclonal antibody specific for a mucin sugar epitope and a polyclonal serum directed to peptide epitopes in a MUC gene-encoded recombinant protein, detected identical bands in three out of seven strains of T. cruzi. Immunoprecipitation experiments confirmed these results. When expressed in eukaryotic cells, the MUC gene product is post-translationally modified, most likely, through extensive O-glycosylation. Gene sequencing showed that the central domains encoding the repeated sequences with the consensus T8KP2, varies in number from 1 to 10, and the number of Thr residues in each repeat could be 7, 8, or 10. A run of 16 to 18 Thr residues was present in some, but not all, MUC gene-derived sequences. Direct compositional analysis of mucin core proteins showed that Thr residues are much more frequent than Ser residues. The same fact occurs in MUC gene-derived protein sequences. Molecular mass determinations of the 35-kDa glycoproteins further extend the heterogeneity of the family to the natural mucin molecules. Difficulties in assigning each of the several MUC genes identified to a mucin product arise from the high diversity and partial sequence conservation of the members of this family.

Structural variation in the glycoinositolphospholipids of different strains of Trypanosoma cruzi

The structures of the glycoinositolphospholipids (GIPLs) from five strains of the protozoan parasite Trypanosoma cruzi have been determined. Two series of structures were identified, all but one containing the same Man4(AEP)GlcN-Ins-PO4 core. Series 1 oligosaccharides are substituted at the third mannose distal to inositol (Man 3) by ethanolamine-phosphate or 2-aminoethylphosphonic acid, as are some glycosyl-phosphatidylinositol-protein anchors of T. cruzi. The core can be further substituted by terminal (1-3)-linked beta-galactofuranose units. In contrast, Series 2 oligosaccharides do not have additional phosphorus-containing groups attached to Man 3, the latter being substituted instead by a single side chain unit of beta-galactofuranose. Series 1 oligosaccharides are present in all strains (G, G-645, Tulahuen CL, and Y) whereas Series 2 structures are present mainly in CL and Y strains. The lipid moiety in the GIPLs from the G, G-645 and Tulahuen strains is predominantly ceramide, as reported for the Y strain, whilst that from the CL strain is a mixture of ceramide and alkylacylglycerol species. The lipid moiety of the GIPLs, and probably also the phosphoinositol-oligosaccharide structures may play an important immunomodulatory role in infection by T. cruzi.

Glycoinositolphospholipids purified from Trypanosoma cruzi stimulate Ig production in vitro

We have investigated the effects of glycoinositolphospholipid (GIPL) purified from Trypanosoma cruzi on murine B cell activation. The GIPL neither stimulated any proliferative response by itself, nor affected the blastogenesis induced by surface IgD cross-linking or LPS. On the other hand, the GIPL significantly stimulated both low and high density B cells to secrete IgM in vitro. The GIPL induced B cells to produce IgM when added in the presence of either the surface Ig cross-linker, anti-delta-dextran, or a combination of IL-4 and IL-5. The T. cruzi-derived GIPL also stimulated Ig class switch to IgG1 in cultures stimulated with GIPL, IL-4, and IL-5. The IgG1 secretion was comparable to that induced by LPS plus IL-4. Production of IgG3 was also detected and the GIPL also potentiated the IgG3 production induced by LPS. The stimulatory effect of the T. cruzi-derived GIPL was mediated mainly by its oligosaccharide moiety. This isolated fraction induced a potent IgM secretory response, compared with a much lower response induced by the isolated GIPL ceramide. Taken together, our data suggest that the stimulatory effect of the T. cruzi-derived GIPL on B cell activation could play a role on the conspicuous Ig production observed during infection of the host with T. cruzi.

Glycoinositolphospholipids purified from Trypanosoma cruzi stimulate Ig production in vitro

We have investigated the effects of glycoinositolphospholipid (GIPL) purified from Trypanosoma cruzi on murine B cell activation. The GIPL neither stimulated any proliferative response by itself, nor affected the blastogenesis induced by surface IgD cross-linking or LPS. On the other hand, the GIPL significantly stimulated both low and high density B cells to secrete IgM in vitro. The GIPL induced B cells to produce IgM when added in the presence of either the surface Ig cross-linker, anti-delta-dextran, or a combination of IL-4 and IL-5. The T. cruzi-derived GIPL also stimulated Ig class switch to IgG1 in cultures stimulated with GIPL, IL-4, and IL-5. The IgG1 secretion was comparable to that induced by LPS plus IL-4. Production of IgG3 was also detected and the GIPL also potentiated the IgG3 production induced by LPS. The stimulatory effect of the T. cruzi-derived GIPL was mediated mainly by its oligosaccharide moiety. This isolated fraction induced a potent IgM secretory response, compared with a much lower response induced by the isolated GIPL ceramide. Taken together, our data suggest that the stimulatory effect of the T. cruzi-derived GIPL on B cell activation could play a role on the conspicuous Ig production observed during infection of the host with T. cruzi.

Structure of the N-linked oligosaccharide of the main diagnostic antigen of the pathogenic fungus Paracoccidioides brasiliensis

The major diagnostic antigen of Paracoccidioides brasiliensis is the exocellularly secreted 43,000 Da glycoprotein (gp43) which contains a single N-linked oligosaccharide chain. This oligosaccharide, although poorly immunogenic in man, is responsible for the cross-reactivity of the gp43 with sera from patients with histoplasmosis, and may have a role in fungal virulence. It contains a neutral high-mannose core (Man7GlcNAc2) to which a (1-->6)-linked alpha-D-Manp chain of variable length, substituted at the 2-O positions by single alpha-D-Manp residues, is attached. A terminal unit of beta-D-galactofuranose is (1-->6)-linked to one of the (1-->2)-linked mannosyl residues, either in the C or in the A arm of the oligosaccharide. The heterogeneity of the oligosaccharide is determined by the different sizes of the A arm and the sites of insertion of the beta-galactofuranosyl unit. The complete structure was determined by methylation analysis, 1H-NMR, mass spectrometry, acetolysis and mannosidase degradation. Electrospray mass spectrometry showed that the oligosaccharide comprises several subtypes ranging from Hex18GlcNAc2 to Hex10GlcNAc2 which accounts for the diffuse migration of the gp43 in polyacrylamide gels. The average size of the most frequent subtype is Hex13.6GlcNAc2. Dilute acid treatment to remove beta-D-Galf reduced the molecular masses of the majority of the subtypes by a single sugar unit.

Down-regulation of T lymphocyte activation in vitro and in vivo induced by glycoinositolphospholipids from Trypanosoma cruzi. Assignment of the T cell-suppressive determinant to the ceramide domain

The major surface glycoinositolphospholipid (GIPL) from Trypanosoma cruzi was purified and assessed in mouse T cell function assays. Purified GIPLs from T. cruzi strains Y and G, but not from a plant trypanosomatid (Phytomonas serpens), markedly blocked in vitro CD4+ and CD8+ T cell mitogenesis induced by bacterial superantigen and anti-TCR;CD3 Abs. Secretion of IL-2, but not of IL-4, bioactivity, was reduced by GIPLs. T. cruzi, but not P. serpens, GIPL also blocked recall cellular responses to T. cruiz. GIPLs from T. cruzi, but not from P. serpens, blocked in vivo regional lymph node T cell activation induced by anti-CD3 mAb. Blockage led to loss of IL-2 responsiveness, with inhibition of CD25 expression on both CD4+ and CD8+ subsets. Isolated phosphoinositol oligosaccharides from GIPLs had no effect on in vitro CD4+ T cell mitogenesis. Isolated ceramide from T. cruzi GIPLs contained mainly N-lignoceroyldihydrosphingosine and blocked CD4+ T cell activation in vitro with the same potency as the intact GIPL. Standard N-palmitoylsphingosine, but not N-palmitoyldihydrosphingosine, blocked CD4+ T cell mitogenesis. A longer fatty acid chain, such as in standard N-lignoceroyldihydrosphingosine, or in the natural trypanosomal GIPL-derived ceramide, however, conferred full inhibitory effects on CD4+ T cells. These results demonstrate that T. cruzi GIPL has T cell immunomodulatory activity in vitro and in vivo, and that this novel activity maps to the ceramide domain. These findings could have implications for immunologic disturbances induced in the host by the causative agent of Chagas' disease.

Down-regulation of T lymphocyte activation in vitro and in vivo induced by glycoinositolphospholipids from Trypanosoma cruzi. Assignment of the T cell-suppressive determinant to the ceramide domain

The major surface glycoinositolphospholipid (GIPL) from Trypanosoma cruzi was purified and assessed in mouse T cell function assays. Purified GIPLs from T. cruzi strains Y and G, but not from a plant trypanosomatid (Phytomonas serpens), markedly blocked in vitro CD4+ and CD8+ T cell mitogenesis induced by bacterial superantigen and anti-TCR;CD3 Abs. Secretion of IL-2, but not of IL-4, bioactivity, was reduced by GIPLs. T. cruzi, but not P. serpens, GIPL also blocked recall cellular responses to T. cruiz. GIPLs from T. cruzi, but not from P. serpens, blocked in vivo regional lymph node T cell activation induced by anti-CD3 mAb. Blockage led to loss of IL-2 responsiveness, with inhibition of CD25 expression on both CD4+ and CD8+ subsets. Isolated phosphoinositol oligosaccharides from GIPLs had no effect on in vitro CD4+ T cell mitogenesis. Isolated ceramide from T. cruzi GIPLs contained mainly N-lignoceroyldihydrosphingosine and blocked CD4+ T cell activation in vitro with the same potency as the intact GIPL. Standard N-palmitoylsphingosine, but not N-palmitoyldihydrosphingosine, blocked CD4+ T cell mitogenesis. A longer fatty acid chain, such as in standard N-lignoceroyldihydrosphingosine, or in the natural trypanosomal GIPL-derived ceramide, however, conferred full inhibitory effects on CD4+ T cells. These results demonstrate that T. cruzi GIPL has T cell immunomodulatory activity in vitro and in vivo, and that this novel activity maps to the ceramide domain. These findings could have implications for immunologic disturbances induced in the host by the causative agent of Chagas' disease.

Differentiation of capsular polysaccharides from Acetobacter diazotrophicus strains isolated from sugarcane

Capsular polysaccharides (CPSs) from six representative strains of Acetobacter diazotrophicus were isolated and fractionated by gel filtration and anion-exchange chromatography. Purified CPSs obtained in the non-adsorbed fraction of a DEAE-Sephadex A-25 column were qualitatively and quantitatively analyzed for sugar composition. Uronic acid and amino sugars were not detected in all purified CPSs. Basically the CPSs of A. diazotrophicus are composed of rhamnose, mannose, galactose and glucose. The presence of fucose was only observed in the CPS of strains PR2 and PAL3. Based on these results, the six strains of A. diazotrophicus could be divided into four groups according to the sugar content of their capsules: (i) fucose-containing capsules (PR2 and PAL3, localized in roots), (ii) mannose-rich capsule (PAL5, localized in root), (iii) capsules with a high ratio of hexose to rhamnose (PR4 and PR20, localized in stems) and (iv) capsules with a low ratio of hexose to rhamnose (PR14, localized in rhizosphere). For all CPSs, sodium dodecy sulfate-polyacrylamide gel electrophoresis showed diffuse bands of slow mobility in silver-stained gels. The different CPS migration patterns could not be correlated with sugar composition. The purified CPS of strain PAL3 was found to be immunogenic and immunochemically similar to the CPS of strain PR2. The serological specificity to CPS of strains PAL3 and PR2 correlated well with the presence of focuse, indicating that this deoxyhexose is immunodominant.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural characterization of the major glycosylphosphatidylinositol membrane-anchored glycoprotein from epimastigote forms of Trypanosoma cruzi Y-strain

We have investigated the structure of the glycosylphosphatidylinositol (GPI) anchor and the O-linked glycan chains of the 40/45-kDa glycoprotein from the cell surface of the protozoan parasite Trypanosoma cruzi. This glycoconjugate is the major acceptor for sialic acid transferred by trans-sialidase of T. cruzi Y-strain, epimastigote form. The GPI anchor was liberated by treatment with hot alkali, and the phosphoinositol-oligosaccharide moiety was characterized and shown to have the following structure. [formula: see text] Unusually the glucosamine was 6-O-substituted with 2-aminoethylphosphonate, and 2-aminoethylphosphonate was also present on the third mannose residue distal to glucosamine, partially replacing the ethanolamine phosphate. The beta-eliminated reduced oligosaccharide chains showed that two novel classes of O-linked N-acetylglucosamine oligosaccharide were present. The first series had the structures Galp beta 1-3GlcNAc-ol; Galp beta 1-6(Galp beta 1-3)GlcNAc-ol; and Galp beta 1-2Galp beta 1-6(Galp beta 1-3)GlcNAc-ol, whereas the other series had a 1-4 linkage to N-acetylglucosaminitol and had structures Galp beta 1-4GlcNAc-ol, Galp beta 1-6(Galp beta 1-4)GlcNAc-ol, and Galp beta 1-2Galp beta 1-6(Galp beta 1-4)GlcNAc-ol. We have also investigated the kinetics of in vitro sialylation of these O-linked oligosaccharides by the T. cruzi transsialidase and have shown that incorporation of one molecule of sialic acid hinders entry of a second molecule when two potential acceptor sites are present.

Chemical characterisation of glycosylinositolphospholipids of Herpetomonas samuelpessoai

The structure of two glycosylinositolphospholipids of the cell surface of the monoxenic protozoan Herpetomonas samuelpessoai have been deduced by methylation analysis, fast-atom bombardment mass spectrometry and two dimensional nuclear magnetic resonance spectroscopy. These glycolipids have features in common with the glycoinositolphospholipids of both Leishmania and Trypanosoma cruzi, resembling the former by the presence of the hybrid type core sequence Man alpha 1-->3(Man alpha 1-->6)Man alpha 1-->4GlcN alpha 1-->6 myo-inositol-1-PO4-lipid, while the 2-aminoethylphosphonate substituent on 0-6 of glucosamine and the presence of ceramide in place of glycerol lipids is more reminiscent of T. cruzi. Possible phylogenetic implications of these observations are discussed.