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

The Glycan Structure of T. cruzi mucins Depends on the Host. Insights on the Chameleonic Galactose

Trypanosoma cruzi, the protozoa that causes Chagas disease in humans, is transmitted by insects from the Reduviidae family. The parasite has developed the ability to change the structure of the surface molecules, depending on the host. Among them, the mucins are the most abundant glycoproteins. Structural studies have focused on the epimastigotes and metacyclic trypomastigotes that colonize the insect, and on the mammal trypomastigotes. The carbohydrate in the mucins fulfills crucial functions, the most important of which being the accepting of sialic acid from the host, a process catalyzed by the unique parasite trans-sialidase. The sialylation of the parasite influences the immune response on infection. The O-linked sugars have characteristics that differentiate them from human mucins. One of them is the linkage to the polypeptide chain by the hexosamine, GlcNAc, instead of GalNAc. The main monosaccharide in the mucins oligosaccharides is galactose, and this may be present in three configurations. Whereas β-d-galactopyranose (β-Galp) was found in the insect and the human stages of Trypanosoma cruzi, β-d-galactofuranose (β-Galf) is present only in the mucins of some strains of epimastigotes and α-d-galactopyranose (α-Galp) characterizes the mucins of the bloodstream trypomastigotes. The two last configurations confer high antigenic properties. In this review we discuss the different structures found and we pose the questions that still need investigation on the exchange of the configurations of galactose.

Overview of the role of kinetoplastid surface carbohydrates in infection and host cell invasion: prospects for therapeutic intervention

Kinetoplastid parasites are responsible for serious diseases in humans and livestock such as Chagas disease and sleeping sickness (caused by Trypanosoma cruzi and Trypanosoma brucei, respectively), and the different forms of cutaneous, mucocutaneous and visceral leishmaniasis (produced by Leishmania spp). The limited number of antiparasitic drugs available together with the emergence of resistance underscores the need for new therapeutic agents with novel mechanisms of action. The use of agents binding to surface glycans has been recently suggested as a new approach to antitrypanosomal design and a series of peptidic and non-peptidic carbohydrate-binding agents have been identified as antiparasitics showing efficacy in animal models of sleeping sickness. Here we provide an overview of the nature of surface glycans in three kinetoplastid parasites, T. cruzi, T. brucei and Leishmania. Their role in virulence and host cell invasion is highlighted with the aim of identifying specific glycan-lectin interactions and carbohydrate functions that may be the target of novel carbohydrate-binding agents with therapeutic applications.

TcNST2encodes a Golgi-localized UDP-galactose transporter inTrypanosoma cruzi

Survival and infectivity of trypanosomatids rely on cell-surface and secreted glycoconjugates, many of which contain a variable number of galactose residues. Incorporation of galactose to proteins and lipids occurs along the secretory pathway from UDP-galactose (UDP-Gal). Before being used in glycosylation reactions, however, this activated sugar donor must first be transported across the endoplasmic reticulum and Golgi membranes by a specific nucleotide sugar transporter (NST). In this study, we identified an UDP-Gal transporter (named TcNST2 and encoded by the TcCLB.504085.60 gene) fromTrypanosoma cruzi, the etiological agent of Chagas disease. TcNST2 was identified by heterologous expression of selected putative nucleotide sugar transporters in a mutant Chinese Hamster Ovary cell line.TcNST2mRNA levels were detected in allT. cruzilife-cycle forms, with an increase in expression in axenic amastigotes. Confocal microscope analysis indicated that the transporter is specifically localized to the Golgi apparatus. A three-dimensional model of TcNST2 suggested an overall structural conservation as compared with members of the metabolite transporter superfamily and also suggested specific features that could be related to its activity. The identification of this transporter is an important step toward a better understanding of glycoconjugate biosynthesis and the role NSTs play in this process in trypanosomatids.

Theft and Reception of Host Cell's Sialic Acid: Dynamics of Trypanosoma Cruzi Trans-sialidases and Mucin-Like Molecules on Chagas' Disease Immunomodulation

The last decades have produced a plethora of evidence on the role of glycans, from cell adhesion to signaling pathways. Much of that information pertains to their role on the immune system and their importance on the surface of many human pathogens. A clear example of this is the flagellated protozoan Trypanosoma cruzi, which displays on its surface a great variety of glycoconjugates, including O-glycosylated mucin-like glycoproteins, as well as multiple glycan-binding proteins belonging to the trans-sialidase (TS) family. Among the latter, different and concurrently expressed molecules may present or not TS activity, and are accordingly known as active (aTS) and inactive (iTS) members. Over the last thirty years, it has been well described that T. cruzi is unable to synthesize sialic acid (SIA) on its own, making use of aTS to steal the host's SIA. Although iTS did not show enzymatic activity, it retains a substrate specificity similar to aTS (α-2,3 SIA-containing glycotopes), displaying lectinic properties. It is accepted that aTS members act as virulence factors in mammals coursing the acute phase of the T. cruzi infection. However, recent findings have demonstrated that iTS may also play a pathogenic role during T. cruzi infection, since it modulates events related to adhesion and invasion of the parasite into the host cells. Since both aTS and iTS proteins share structural substrate specificity, it might be plausible to speculate that iTS proteins are able to assuage and/or attenuate biological phenomena depending on the catalytic activity displayed by aTS members. Since SIA-containing glycotopes modulate the host immune system, it should not come as any surprise that changes in the sialylation of parasite's mucin-like molecules, as well as host cell glycoconjugates might disrupt critical physiological events, such as the building of effective immune responses. This review aims to discuss the importance of mucin-like glycoproteins and both aTS and iTS for T. cruzi biology, as well as to present a snapshot of how disturbances in both parasite and host cell sialoglycophenotypes may facilitate the persistence of T. cruzi in the infected mammalian host.

Identification of O-Glcnacylated Proteins in Trypanosoma cruzi

Originally an anthropozoonosis in the Americas, Chagas disease has spread from its previous borders through migration. It is caused by the protozoan Trypanosoma cruzi. Differences in disease severity have been attributed to a natural pleomorphism in T. cruzi. Several post-translational modifications (PTMs) have been studied in T. cruzi, but to date no work has focused on O-GlcNAcylation, a highly conserved monosaccharide-PTM of serine and threonine residues mainly found in nucleus, cytoplasm, and mitochondrion proteins. O-GlcNAcylation is thought to regulate protein function analogously to protein phosphorylation; indeed, crosstalk between both PTMs allows the cell to regulate its functions in response to nutrient levels and stress. Herein, we demonstrate O-GlcNAcylation in T. cruzi epimastigotes by three methods: by using specific antibodies against the modification in lysates and whole parasites, by click chemistry labeling, and by proteomics. In total, 1,271 putative O-GlcNAcylated proteins and six modification sequences were identified by mass spectrometry (data available via ProteomeXchange, ID PXD010285). Most of these proteins have structural and metabolic functions that are essential for parasite survival and evolution. Furthermore, O-GlcNAcylation pattern variations were observed by antibody detection under glucose deprivation and heat stress conditions, supporting their possible role in the adaptive response. Given the numerous biological processes in which O-GlcNAcylated proteins participate, its identification in T. cruzi proteins opens a new research field in the biology of Trypanosomatids, improve our understanding of infection processes and may allow us to identify new therapeutic targets.

Identification of a Golgi-localized UDP-N-acetylglucosamine transporter in Trypanosoma cruzi

BACKGROUND

Nucleotide sugar transporters (NSTs) play an essential role in translocating nucleotide sugars into the lumen of the endoplasmic reticulum and Golgi apparatus to be used as substrates in glycosylation reactions. This intracellular transport is an essential step in the biosynthesis of glycoconjugates.

RESULTS

We have identified a family of 11 putative NSTs in Trypanosoma cruzi, the etiological agent of Chagas' disease. A UDP-N-acetylglucosamine transporter, TcNST1, was identified by a yeast complementation approach. Based on a phylogenetic analysis four candidate genes were selected and used for complementation assays in a Kluyveromyces lactis mutant strain. The transporter is likely expressed in all stages of the parasite life cycle and during differentiation of epimastigotes to infective metacyclics. Immunofluorescence analyses of a GFP-TcNST1 fusion protein indicate that the transporter is localized to the Golgi apparatus. As many NSTs are multisubstrate transporters, we also tested the capacity of TcNST1 to transport GDP-Man.

CONCLUSIONS

We have identified a UDP-N-acetylglucosamine transporter in T. cruzi, which is specifically localized to the Golgi apparatus and seems to be expressed, at the mRNA level, throughout the parasite life cycle. Functional studies of TcNST1 will be important to unravel the role of NSTs and specific glycoconjugates in T. cruzi survival and infectivity.

Golgi UDP-GlcNAc:polypeptide O-α-N-Acetyl-d-glucosaminyltransferase 2 (TcOGNT2) regulates trypomastigote production and function in Trypanosoma cruzi

All life cycle stages of the protozoan parasite Trypanosoma cruzi are enveloped by mucin-like glycoproteins which, despite major changes in their polypeptide cores, are extensively and similarly O-glycosylated. O-Glycan biosynthesis is initiated by the addition of αGlcNAc to Thr in a reaction catalyzed by Golgi UDP-GlcNAc:polypeptide O-α-N-acetyl-d-glucosaminyltransferases (ppαGlcNAcTs), which are encoded by TcOGNT1 and TcOGNT2. We now directly show that TcOGNT2 is associated with the Golgi apparatus of the epimastigote stage and is markedly downregulated in both differentiated metacyclic trypomastigotes (MCTs) and cell culture-derived trypomastigotes (TCTs). The significance of downregulation was examined by forced continued expression of TcOGNT2, which resulted in a substantial increase of TcOGNT2 protein levels but only modestly increased ppαGlcNAcT activity in extracts and altered cell surface glycosylation in TCTs. Constitutive TcOGNT2 overexpression had no discernible effect on proliferating epimastigotes but negatively affected production of both types of trypomastigotes. MCTs differentiated from epimastigotes at a low frequency, though they were apparently normal based on morphological and biochemical criteria. However, these MCTs exhibited an impaired ability to produce amastigotes and TCTs in cell culture monolayers, most likely due to a reduced infection frequency. Remarkably, inhibition of MCT production did not depend on TcOGNT2 catalytic activity, whereas TCT production was inhibited only by active TcOGNT2. These findings indicate that TcOGNT2 downregulation is important for proper differentiation of MCTs and functioning of TCTs and that TcOGNT2 regulates these functions by using both catalytic and noncatalytic mechanisms.

Discrimination of epimeric glycans and glycopeptides using IM-MS and its potential for carbohydrate sequencing

Mass spectrometry is the primary analytical technique used to characterize the complex oligosaccharides that decorate cell surfaces. Monosaccharide building blocks are often simple epimers, which when combined produce diastereomeric glycoconjugates indistinguishable by mass spectrometry. Structure elucidation frequently relies on assumptions that biosynthetic pathways are highly conserved. Here, we show that biosynthetic enzymes can display unexpected promiscuity, with human glycosyltransferase pp-α-GanT2 able to utilize both uridine diphosphate N-acetylglucosamine and uridine diphosphate N-acetylgalactosamine, leading to the synthesis of epimeric glycopeptides in vitro. Ion-mobility mass spectrometry (IM-MS) was used to separate these structures and, significantly, enabled characterization of the attached glycan based on the drift times of the monosaccharide product ions generated following collision-induced dissociation. Finally, ion-mobility mass spectrometry following fragmentation was used to determine the nature of both the reducing and non-reducing glycans of a series of epimeric disaccharides and the branched pentasaccharide Man3 glycan, demonstrating that this technique may prove useful for the sequencing of complex oligosaccharides.

Addition of α-O-GlcNAc to threonine residues define the post-translational modification of mucin-like molecules in Trypanosoma cruzi

Trypanosoma cruzi, an intracellular protozoan etiologic agent of Chagas disease is covered by a dense coat of mucin-type glycoproteins, which is important to promote the parasite entry and persistence in the mammalian host cells. The O-glycosylation of T. cruzi mucins (Tc-mucins) is initiated by enzymatic addition of α-O-N-acetylglucosamine (GlcNAc) to threonine (Thr) by the UDP-GlcNAc:polypeptide α-N-acetylglucosaminyltransferase (pp-α-GlcNAcT) in the Golgi. The Tc-mucin is characterized by the presence of a high structural diversity of O-linked oligosaccharides found among different parasite strains, comprising two O-glycan Cores. In the Core 1, from strains principally associated with the domestic transmission cycle of Chagas disease, the GlcNAc O-4 is substituted with a β-galactopyranose (βGalp) unit, and in the most complex oligosaccharides the GlcNAc O-6 is further processed by the addition of β1 → 2-linked Galp residues creating a short linear Galp-containing chain. In the Core 2 structures, expressed by strains isolated from T. cruzi sylvatic hosts, the GlcNAc O-4 carries a β-galactofuranose (βGalf) unit and the GlcNAc O-6 can carry a branched Galpβ1 → 3[Galpβ1 → 2]Galpβ1 → 6 motif. The O-glycans carrying nonreducing terminal βGalp are available for sialylation by a surface T. cruzi trans-sialidase activity. Based on structural results, this review summarizes available data on the highly conserved process, which adds the GlcNAc unit in α-linkage to Thr residues the basis of the post-translational modification system in T. cruzi mucins. In addition, a mechanism unique employed by the parasite to transfer exogenous sialic acid residues to Tc-mucins is presented.

P-glycoprotein efflux pump plays an important role in Trypanosoma cruzi drug resistance

Drug resistance in protozoan parasites has been associated with the P-glycoprotein (Pgp), an energy-dependent efflux pump that transports substances across the membrane. Interestingly, the genes TcPGP1 and TcPGP2 have been described in Trypanosoma cruzi, although the function of these genes has not been fully elucidated. The main goal of this work was to investigate Pgp efflux pump activity and expression in T. cruzi lines submitted to in vitro induced resistance to the compounds 4-N-(2-methoxy styryl)-thiosemicarbazone (2-Meotio) and benznidazole (Bz) and to verify the stability of the resistant phenotypes during the parasite life cycle. We observed that the EC50 values for the treatment of epimastigotes with 2-Meotio or Bz were increased at least 4.7-fold in resistant lines, and this phenotype was maintained in metacyclic trypomastigotes, cell-derived trypomastigotes, and intracellular amastigotes. However, in epimastigotes, 2-Meotio resistance is reversible, but Bz resistance is irreversible. When compared with the parental line, the resistant lines exhibited higher Pgp efflux activity, reversion of the resistant phenotypes in the presence of Pgp inhibitors, cross-resistance with Pgp modulators, higher basal Pgp ATPase activity, and overexpression of the genes TcPGP1 and TcPGP2. In conclusion, the resistance induced in T. cruzi by the compounds 2-Meotio and Bz is maintained during the entire parasite life cycle. Furthermore, our data suggest the participation of the Pgp efflux pump in T. cruzi drug resistance.

Sialic acid: a sweet swing between mammalian host and Trypanosoma cruzi

Commonly found at the outermost ends of complex carbohydrates in extracellular medium or on outer cell membranes, sialic acids play important roles in a myriad of biological processes. Mammals synthesize sialic acid through a complex pathway, but Trypanosoma cruzi, the agent of Chagas’ disease, evolved to obtain sialic acid from its host through a trans-sialidase (TcTS) reaction. Studies of the parasite cell surface architecture and biochemistry indicate that a unique system comprising sialoglycoproteins and sialyl-binding proteins assists the parasite in several functions including parasite survival, infectivity, and host–cell recognition. Additionally, TcTS activity is capable of extensively remodeling host cell glycomolecules, playing a role as virulence factor. This review presents the state of the art of parasite sialobiology, highlighting how the interplay between host and parasite sialic acid helps the pathogen to evade host defense mechanisms and ensure lifetime host parasitism.

Structural features affecting trafficking, processing, and secretion of Trypanosoma cruzi mucins

Trypanosoma cruzi is wrapped by a dense coat of mucin-type molecules encoded by complex gene families termed TcSMUG and TcMUC, which are expressed in the insect- and mammal-dwelling forms of the parasite, respectively. Here, we dissect the contribution of distinct post-translational modifications on the trafficking of these glycoconjugates. In vivo tracing and characterization of tagged-variants expressed by transfected epimastigotes indicate that although the N-terminal signal peptide is responsible for targeting TcSMUG products to the endoplasmic reticulum (ER), the glycosyl phosphatidylinositol (GPI)-anchor likely functions as a forward transport signal for their timely progression along the secretory pathway. GPI-minus variants accumulate in the ER, with only a minor fraction being ultimately released to the medium as anchorless products. Secreted products, but not ER-accumulated ones, display several diagnostic features of mature mucin-type molecules including extensive O-type glycosylation, Galf-based epitopes recognized by monoclonal antibodies, and terminal Galp residues that become readily sialylated upon addition of parasite trans-sialidases. Processing of N-glycosylation site(s) is dispensable for the overall TcSMUG mucin-type maturation and secretion. Despite undergoing different O-glycosylation elaboration, TcMUC reporters yielded quite similar results, thus indicating that (i) molecular trafficking signals are structurally and functionally conserved between mucin families, and (ii) TcMUC and TcSMUG products are recognized and processed by a distinct repertoire of stage-specific glycosyltransferases. Thus, using the fidelity of a homologous expression system, we have defined some biosynthetic aspects of T. cruzi mucins, key molecules involved in parasite protection and virulence.

Control of mucin-type O-glycosylation: a classification of the polypeptide GalNAc-transferase gene family

Glycosylation of proteins is an essential process in all eukaryotes and a great diversity in types of protein glycosylation exists in animals, plants and microorganisms. Mucin-type O-glycosylation, consisting of glycans attached via O-linked N-acetylgalactosamine (GalNAc) to serine and threonine residues, is one of the most abundant forms of protein glycosylation in animals. Although most protein glycosylation is controlled by one or two genes encoding the enzymes responsible for the initiation of glycosylation, i.e. the step where the first glycan is attached to the relevant amino acid residue in the protein, mucin-type O-glycosylation is controlled by a large family of up to 20 homologous genes encoding UDP-GalNAc:polypeptide GalNAc-transferases (GalNAc-Ts) (EC 2.4.1.41). Therefore, mucin-type O-glycosylation has the greatest potential for differential regulation in cells and tissues. The GalNAc-T family is the largest glycosyltransferase enzyme family covering a single known glycosidic linkage and it is highly conserved throughout animal evolution, although absent in bacteria, yeast and plants. Emerging studies have shown that the large number of genes (GALNTs) in the GalNAc-T family do not provide full functional redundancy and single GalNAc-T genes have been shown to be important in both animals and human. Here, we present an overview of the GalNAc-T gene family in animals and propose a classification of the genes into subfamilies, which appear to be conserved in evolution structurally as well as functionally.

Cloning, localization and differential expression of the Trypanosoma cruzi TcOGNT-2 glycosyl transferase

The surface of Trypanosoma cruzi is covered by a dense glycocalix which is characteristic of each stage of the life cycle. Its composition and complexity depend mainly on mucin-like proteins. A remarkable feature of O-glycan biosynthesis in trypanosomes is that it initiates with the addition of a GlcNAc instead of the GalNAc residue that is commonly used in vertebrate mucins. The fact that the interplay between trans-sialidase and mucin is crucial for pathogenesis, and both families have stage-specific members is also remarkable. Recently the enzyme that transfers the first GlcNAc from UDP-GlcNAc to a serine or threonine residue was kinetically characterized. The relevance of this enzyme is evidenced by its role as catalyzer of the first step in O-glycosylation. In this paper we describe how this gene is expressed differentially along the life cycle with a pattern that is very similar to that of trans-sialidases. Its localization was determined, showing that the protein predicted to be in the Golgi apparatus is also present in reservosomes. Finally our results indicate that this enzyme, when overexpressed, enhances T. cruzi infectivity.

Molecular diversity of the Trypanosoma cruzi TcSMUG family of mucin genes and proteins

The surface of the protozoan Trypanosoma cruzi is covered by a dense coat of mucin-type glycoconjugates, which make a pivotal contribution to parasite protection and host immune evasion. Their importance is further underscored by the presence of >1000 mucin-like genes in the parasite genome. In the present study we demonstrate that one such group of genes, termed TcSMUG L, codes for previously unrecognized mucin-type glycoconjugates anchored to and secreted from the surface of insect-dwelling epimastigotes. These features are supported by the in vivo tracing and characterization of endogenous TcSMUG L products and recombinant tagged molecules expressed by transfected parasites. Besides displaying substantial homology to TcSMUG S products, which provide the scaffold for the major Gp35/50 mucins also present in insect-dwelling stages of the T. cruzi lifecycle, TcSMUG L products display unique structural and functional features, including being completely refractory to sialylation by parasite trans-sialidases. Although quantitative real time-PCR and gene sequencing analyses indicate a high degree of genomic conservation across the T. cruzi species, TcSMUG L product expression and processing is quite variable among different parasite isolates.

Trans-sialidase and mucins of Trypanosoma cruzi: an important interplay for the parasite

A dense glycocalix covers the surface of Trypanosoma cruzi, the agent of Chagas disease. Sialic acid in the surface of the parasite plays an important role in the infectious process, however, T. cruzi is unable to synthesize sialic acid or the usual donor CMP-sialic acid. Instead, T. cruzi expresses a unique enzyme, the trans-sialidase (TcTS) involved in the transfer of sialic acid from host glycoconjugates to mucins of the parasite. The mucins are the major glycoproteins in the insect stage epimastigotes and in the infective trypomastigotes. Both, the mucins and the TcTS are anchored to the plasma membrane by a glycosylphosphatidylinositol anchor. Thus, TcTS may be shed into the bloodstream of the mammal host by the action of a parasite phosphatidylinositol-phospholipase C, affecting the immune system. The composition and structure of the sugars in the parasite mucins is characteristic of each differentiation stage, also, interstrain variations were described for epimastigote mucins. This review focus on the characteristics of the interplay between the trans-sialidase and the mucins of T. cruzi and summarizes the known carbohydrate structures of the mucins.

Molecular analysis of a UDP-GlcNAc:polypeptide alpha-N-acetylglucosaminyltransferase implicated in the initiation of mucin-type O-glycosylation in Trypanosoma cruzi

Trypanosoma cruzi, the causative agent of Chagas disease, is surrounded by a mucin coat that plays important functions in parasite survival/invasion and is extensively O-glycosylated by Golgi and cell surface glycosyltransferases. The addition of the first sugar, alpha-N-acetylglucosamine (GlcNAc) linked to Threonine (Thr), is catalyzed by a polypeptide alpha-GlcNAc-transferase (pp-alphaGlcNAcT) which is unstable to purification. Here, a comparison of the genomes of T. cruzi and Dictyostelium discoideum, an amoebazoan which also forms this linkage, identified two T. cruzi genes (TcOGNT1 and TcOGNT2) that might encode this activity. Though neither was able to complement the Dictyostelium gene, expression in the trypanosomatid Leishmania tarentolae resulted in elevated levels of UDP-[(3)H]GlcNAc:Thr-peptide GlcNAc-transferase activity and UDP-[(3)H]GlcNAc breakdown activity. The ectodomain of TcOGNT2 was expressed and the secreted protein was found to retain both activities after extensive purification away from other proteins and the endogenous activity. Product analysis showed that (3)H was transferred as GlcNAc to a hydroxyamino acid, and breakdown was due to hydrolysis. Both activities were specific for UDP-GlcNAc relative to UDP-GalNAc and were abolished by active site point mutations that inactivate a related Dictyostelium enzyme and distantly related animal pp-alphaGalNAcTs. The peptide preference and the alkaline pH optimum were indistinguishable from those of the native activity in T. cruzi microsomes. The results suggest that mucin-type O-glycosylation in T. cruzi is initiated by conserved members of CAZy family GT60, which is homologous to the GT27 family of animal pp-alphaGalNAcTs that initiate mucin-type O-glycosylation in animals.

O-linked N-acetylglucosamine is present on the extracellular domain of notch receptors

Rare types of glycosylation often occur in a domain-specific manner and are involved in specific biological processes. In particular, O-fucose glycans are reported to regulate the functions of EGF domain-containing proteins such as Notch receptors. In the course of mass spectrometric analysis of O-glycans displayed on Drosophila Notch receptors expressed in S2 cells, we found an unusual O-linked N-acetylhexosamine (HexNAc) modification which occurs at a site distinct from those of O-fucose and O-glucose glycosylations. Modification site mapping by mass spectrometry and amino acid substitution studies revealed that O-HexNAc modification occurs on a serine or threonine located between the fifth and sixth cysteines within the EGF domain. This modification occurs simultaneously along with other closely positioned O-glycosylations. This modification was determined to be O-beta-GlcNAc by galactosyltransferase labeling and beta-N-acetyl-hexosaminidase digestion experiments and by immunoblotting with a specific antibody. O-GlcNAc modification occurs at multiple sites on Notch epidermal growth factor repeats. O-GlcNAc modification was also found on the extracellular domain of Delta, a ligand for Notch receptors. Although the O-GlcNAc modification is known to regulate a wide range of cellular processes, the list of known modified proteins has previously been limited to intracellular proteins in animals. Thus, the finding of O-GlcNAc modification in extracellular environments predicts a distinct glycosylation process that might be associated with a novel regulatory mechanism for Notch receptor activity.

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

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

Trypanosoma cruzi surface mucins: host-dependent coat diversity

The surface of the protozoan parasite Trypanosoma cruzi is covered in mucins, which contribute to parasite protection and to the establishment of a persistent infection. Their importance is highlighted by the fact that the approximately 850 mucin-encoding genes comprise approximately 1% of the parasite genome and approximately 6% of all predicted T. cruzi genes. The coordinate expression of a large repertoire of mucins containing variable regions in the mammal-dwelling stages of the T. cruzi life cycle suggests a possible strategy to thwart the host immune response. Here, we discuss the expression profiling of T. cruzi mucins, the mechanisms leading to the acquisition of mucin diversity and the possible consequences of a mosaic surface coat in the interplay between parasite and host.

Cloning and characterization of the phosphoglucomutase of Trypanosoma cruzi and functional complementation of a Saccharomyces cerevisiae PGM null mutant

Trypanosoma cruzi is the etiological agent of Chagas' disease, a chronic illness characterized by progressive cardiomyopathy and/or denervation of the digestive tract. The parasite surface is covered with glycoconjugates, such as mucin-type glycoproteins and glycoinositolphospholipids (GIPLs), whose glycans are rich in galactopyranose (Galp) and/or galactofuranose (Galf) residues. These molecules have been implicated in attachment of the parasite to and invasion of mammalian cells and in modulation of the host immune responses during infection. In T. cruzi, galactose (Gal) biosynthesis depends on the conversion of uridine diphosphate (UDP)-glucose (UDP-Glc) into UDP-Gal by an NAD-dependent reduction catalyzed by UDP-Gal 4-epimerase. Phosphoglucomutase (PGM) is a key enzyme in this metabolic pathway catalyzing the interconversion of Glc-6-phosphate (Glc-6-P) and Glc-1-P which is then converted into UDP-Glc. We here report the cloning of T. cruzi PGM, encoding T. cruzi PGM, and the heterologous expression of a functional enzyme in Saccharomyces cerevisiae. T. cruzi PGM is a single copy gene encoding a predicted protein sharing 61% amino acid identity with Leishmania major PGM and 43% with the yeast enzyme. The 59-trans-splicing site of PGM RNA was mapped to a region located at 18 base pairs upstream of the start codon. Expression of T. cruzi PGM in a S. cerevisiae null mutant-lacking genes encoding both isoforms of PGM (pgm1Delta/pgm2Delta) rescued the lethal phenotype induced upon cell growth on Gal as sole carbon source.

Kinetic analysis of a Golgi UDP-GlcNAc:polypeptide-Thr/Ser N-acetyl-alpha-glucosaminyltransferase from Dictyostelium

Mucin-type O-glycosylation in Dictyostelium is initiated in the Golgi by a UDP-GlcNAc:polypeptide-Thr/Ser N-acetyl-alpha-glucosaminyltransferase (Dd-pp alphaGlcNAcT2) whose sequence is distantly related to the sequences of animal polypeptide-Thr/Ser N-acetyl-alpha-galactosaminyltransferases, such as murine Mm-pp alphaGalNAcT1. To evaluate the significance of this similarity, highly purified Dd-pp alphaGlcNAcT2 was assayed using synthetic peptides derived from known substrates. Dd-pp alphaGlcNAcT2 strongly prefers UDP-GlcNAc over UDP-GalNAc, preferentially modifies the central region of the peptide, and modifies Ser in addition to Thr residues. Initial velocity measurements performed over a matrix of UDP-GlcNAc donor and peptide acceptor concentrations indicate that the substrates bind to the enzyme in ordered fashion before the chemical conversion. Substrate inhibition exerted by a second peptide, and the pattern of product inhibition exerted by UDP, suggest that UDP-GlcNAc binds first and the peptide binds second, consistent with data reported for Mm-pp alphaGalNAcT1. Two selective competitive inhibitors of Mm-pp alphaGalNAcT1, retrieved from a screen of neutral-charge uridine derivatives, also inhibit Dd-pp alphaGlcNAcT1 competitively with only slightly less efficacy. Inhibition is specific for Dd-pp alphaGlcNAcT2 relative to two other Dictyostelium retaining glycosyltransferases. These data support a phylogenetic model in which the alphaGlcNAcT function in unicellular eukaryotes converted to an alphaGalNAcT function in the metazoan ortholog while conserving a similar reaction mechanism and active site architecture.

The intriguing world of prothrombin activators from snake venom

Activation of prothrombin to mature thrombin occurs by the proteolytic action of the prothrombinase complex consisting of a serine proteinase factor Xa, and cofactors factor Va, Ca(2+) ions and phospholipids. Several exogenous prothrombin activators are found in snake venom. They are classified into four groups based on their cofactor requirements. Group A and B prothrombin activators are metalloproteinases whereas group C and D prothrombin activators are serine proteinases. Group C prothrombin activators resemble the mammalian factor Xa-factor Va complex, while Group D activators are structurally and functionally similar to factor Xa. This review provides a detailed description of the current knowledge on all prothrombin activators and highlights several intriguing questions that are yet to be answered.

Characterization of the inositol phosphorylceramide synthase activity from Trypanosoma cruzi

IPC (inositol phosphorylceramide) synthase is an enzyme essential for fungal viability, and it is the target of potent antifungal compounds such as rustmicin and aureobasidin A. Similar to fungi and some other lower eukaryotes, the protozoan parasite Trypanosoma cruzi is capable of synthesizing free or protein-linked glycoinositolphospholipids containing IPC. As a first step towards understanding the importance and mechanism of IPC synthesis in T. cruzi, we investigated the effects of rustmicin and aureobasidin A on the proliferation of different life-cycle stages of the parasite. The compounds did not interfere with the axenic growth of epimastigotes, but aureobasidin A decreased the release of trypomastigotes from infected murine peritoneal macrophages and the number of intracellular amastigotes in a dose-dependent manner. We have demonstrated for the first time that all forms of T. cruzi express an IPC synthase activity that is capable of transferring inositol phosphate from phosphatidylinositol to the C-1 hydroxy group of C6-NBD-cer {6-[N-(7-nitro-2,1,3-benzoxadiazol-4-yl)-amino]hexanoylceramide} to form inositol phosphoryl-C6-NBD-cer, which was purified and characterized by its chromatographic behaviour on TLC and HPLC, sensitivity to phosphatidylinositol-specific phospholipase C and resistance to mild alkaline hydrolysis. Unlike the Saccharomyces cerevisiae IPC synthase, the T. cruzi enzyme is stimulated by Triton X-100 but not by bivalent cations, CHAPS or fatty-acid-free BSA, and it is not inhibited by rustmicin or aureobasidin A, or the two in combination. Further studies showed that aureobasidin A has effects on macrophages independent of the infecting T. cruzi cells. These results suggest that T. cruzi synthesizes its own IPC, but by a mechanism that is not affected by rustmicin and aureobasidin A.

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.

The Surface Coat of the Mammal-dwelling Infective Trypomastigote Stage of Trypanosoma cruzi Is Formed by Highly Diverse Immunogenic Mucins

A thick coat of mucin-like glycoproteins covers the surface of Trypanosoma cruzi and plays a crucial role in parasite protection and infectivity and host immunomodulation. The appealing candidate genes coding for the mucins of the mammal-dwelling stages define a heterogeneous family termed TcMUC, which comprises up to 700 members, thus precluding a genetic approach to address the protein core identity. Here, we demonstrate by multiple approaches that the TcMUC II genes code for the majority of trypomastigote mucins. These molecules display a variable, non-repetitive, highly O-glycosylated central domain, followed by a short conserved C terminus and a glycosylphosphatidylinositol anchor. A simultaneous expression of multiple TcMUC II gene products was observed. Moreover, the C terminus of TcMUC II mucins, but not their central domain, elicited strong antibody responses in patients with Chagas' disease and T. crusi infected animals. This highly diverse coat of mucins may represent a refined parasite strategy to elude the mammalian host immune system.

Sialyl-Tn antigen expression and O-linked GalNAc-Thr synthesis by Trypanosoma cruzi

Most Trypanosoma cruzi O-glycans are linked to Thr/Ser residues via N-acetylglucosamine. We report that the mucin-type carcinoma-associated sialyl-Tn antigen (NeuAc-GalNAc-O-Ser/Thr) is expressed by T. cruzi. A specific MAb allowed us to localize the antigen on the surface of epimastigotes and to identify reactive components in parasite lysates (32, 60, and 94kDa). In addition, ppGalNAc-T activity was characterized in epimastigotes, and direct evidence was obtained for the in vitro incorporation of GalNAc to a synthetic peptide derived from a T. cruzi mucin. These results add an as yet unknown complexity to the pathways of O-glycan biosynthesis in this protozoan parasite.

Initiation of Mucin-type O-Glycosylation in Dictyostelium Is Homologous to the Corresponding Step in Animals and Is Important for Spore Coat Function

Like animal cells, many unicellular eukaryotes modify mucin-like domains of secretory proteins with multiple O-linked glycans. Unlike animal mucin-type glycans, those of some microbial eukaryotes are initiated by alpha-linked GlcNAc rather than alpha-GalNAc. Based on sequence similarity to a recently cloned soluble polypeptide hydroxyproline GlcNAc-transferase that modifies Skp1 in the cytoplasm of the social ameba Dictyostelium, we have identified an enzyme, polypeptide alpha-N-acetylglucosaminyltransferase (pp alpha-GlcNAc-T2), that attaches GlcNAc to numerous secretory proteins in this organism. Unlike the Skp1 GlcNAc-transferase, pp alpha-GlcNAc-T2 is predicted to be a type 2 transmembrane protein. A highly purified, soluble, recombinant fragment of pp alpha-GlcNAc-T2 efficiently transfers GlcNAc from UDP-GlcNAc to synthetic peptides corresponding to mucin-like domains in two proteins that traverse the secretory pathway. pp alpha-GlcNAc-T2 is required for addition of GlcNAc to peptides in cell extracts and to the proteins in vivo. Mass spectrometry and Edman degradation analyses show that pp alpha-GlcNAc-T2 attaches GlcNAc in alpha-linkage to the Thr residues of all the synthetic mucin repeats. pp alpha-GlcNAc-T2 is encoded by the previously described modB locus defined by chemical mutagenesis, based on sequence analysis and complementation studies. This finding establishes that the many phenotypes of modB mutants, including a permeability defect in the spore coat, can now be ascribed to defects in mucin-type O-glycosylation. A comparison of the sequences of pp alpha-GlcNAc-T2 and the animal pp alpha-GalNAc-transferases reveals an ancient common ancestry indicating that, despite the different N-acetylhexosamines involved, the enzymes share a common mechanism of action.

Cloning and characterisation of the UDP-glucose 4′-epimerase of Trypanosoma cruzi

Trypanosoma cruzi incorporates galactose into many of its cell-surface glycoconjugates but it is unable to transport this sugar through its hexose transporter. Epimerisation of UDP-glucose to UDP-galactose by UDP-glucose 4'-epimerase may be the only way that the parasites can obtain galactose. Here, we describe cloning the T. cruzi UDP-Glc 4'-epimerase (TcGALE) gene and show that it is functional by complementing an Escherichia coli epimerase-deficient strain. The T. cruzi GALE gene encodes a 42.4 kDa protein and the recombinant protein expressed in E. coli is a homodimer in solution with a specific activity of 3.8 U mg(-1) and K(m) for UDP-Gal of 114 microM. Unlike the human epimerase, T. cruzi UDP-Glc 4'-epimerase is unable to inter-convert UDP-N-acetylglucosamine and UDP-N-acetylgalactosamine. This may explain why T. cruzi initiates O-glycosylation of its abundant GPI-anchored surface mucins via GlcNAcalpha1-O-Thr/Ser rather than the GalNAcalpha1-O-Thr/Ser linkage that is common for mucins from many other eukaryotes.

Occurrence of O-linked Xyl-GlcNAc and Xyl-Glc disaccharides in trocarin, a factor Xa homolog from snake venom

Trocarin is a 46515-Da group D prothrombin-activating glycoprotein from the venom of the Australian elapid, Tropidechis carinatus. Amino acid sequencing and functional characterization of trocarin demonstrated that it is a structural and functional homolog of mammalian blood coagulation factor (F)Xa. In this study we show that, in contrast to mammalian Xa, which is not glycosylated, trocarin contains an O-linked carbohydrate moiety in its light chain and an N-linked carbohydrate oligosaccharide in its heavy chain. Mass spectrometry and sugar compositional analysis indicate that the O-linked carbohydrate moiety is a mixture of Xyl-GlcNAc-, GlcNAc-, Xyl-Glc- and Glc- structures linked to Ser 52. The N-linked carbohydrate on Asn 45 of the heavy chain is a sialylated, diantennary oligosaccharide that is located at the lip of the active site of the prothrombin activator.

Plasmodium falciparum merozoite surface protein 1

In addition to the major carbohydrate moieties of the glycosylphosphatidylinositol (GPI) anchor, we report that Plasmodium falciparum merozoite surface protein 1 (MSP-1) bears O-GlcNAc modifications predominantly in beta-anomeric configuration, in both the C- and N-terminal portions of the protein. Subcellular fractionation of parasitized erythrocytes in the late trophozoite/schizont stage reveals that GPI-anchored C-terminal fragments of MSP-1 are recovered in Triton X-100 resistant, low-density membrane fractions. Our results suggest that O-GlcNAc-modified MSP-1 N-terminal fragments tend to localize within the parasitophorous vacuolar membrane while GPI-anchored MSP-1 C-terminal fragments associate with low-density, Triton X-100 resistant membrane domains (rafts), redistribute in the parasitized erythrocyte and are eventually shed as membrane vesicles that also contain the endogenous, GPI-linked CD59.

Molecular Cloning and Expression of a UDP-N-acetylglucosamine (GlcNAc):Hydroxyproline Polypeptide GlcNAc-transferase That Modifies Skp1 in the Cytoplasm ofDictyostelium

Skp1 is a ubiquitous eukaryotic protein found in several cytoplasmic and nuclear protein complexes, including the SCF-type E3 ubiquitin ligase. In Dictyostelium, Skp1 is hydroxylated at proline 143, which is then modified by a pentasaccharide chain. The enzyme activity that attaches the first sugar, GlcNAc, was previously shown to copurify with the GnT51 polypeptide whose gene has now been cloned using a proteomics approach based on a quadrupole/time-of-flight hybrid mass spectrometer. When expressed in Escherichia coli, recombinant GnT51 exhibits UDP-GlcNAc:hydroxyproline Skp1 GlcNAc-transferase activity. Based on amino acid sequence alignments, GnT51 defines a new family of microbial polypeptide glycosyltransferases that appear to be distantly related to the catalytic domain of mucin-type UDP-GalNAc:Ser/Thr polypeptide alpha-GalNAc-transferases expressed in the Golgi compartment of animal cells. This relationship is supported by the effects of site-directed mutagenesis of GnT51 amino acids associated with its predicted DXD-like motif, DAH. In contrast, GnT51 lacks the N-terminal signal anchor sequence present in the Golgi enzymes, consistent with the cytoplasmic localization of the Skp1 acceptor substrate and the biochemical properties of the enzyme. The first glycosylation step of Dictyostelium Skp1 is concluded to be mechanistically similar to that of animal mucin type O-linked glycosylation, except that it occurs in the cytoplasm rather than the Golgi compartment of the cell.

From the cell biology to the development of new chemotherapeutic approaches against trypanosomatids: dreams and reality

Members of the Trypanosomatidae family comprise a large number of species that are causative agents of important diseases such as sleeping sickness, Chagas' disease and Leishmaniasis. These organisms are also of biological interest since they are able to change the morphology according to the environment where they live, through a process of reversible cell transformation, and possess structures and organelles that are not found in mammalian cells. This review analyses the process of transformation, which takes place during the life cycle of Trypanosoma cruzi in the vertebrate and invertebrate hosts. Special attention is given to the interaction of the parasite with vertebrate cells. In addition, the present knowledge of structures and organelles such as the nucleus, the plasma membrane, the sub-pellicular microtubules, the flagellum, the kinetoplast-mitochondrion complex, the peroxisome (glycosome), the acidocalcisome and the structures and organelles involved in the endocytic pathway, is reviewed from a cell biology perspective. The possible use of available data for the development of new anti parasite drugs is also discussed.

Protein glycosylation: nature, distribution, enzymatic formation, and disease implications of glycopeptide bonds

Formation of the sugar-amino acid linkage is a crucial event in the biosynthesis of the carbohydrate units of glycoproteins. It sets into motion a complex series of posttranslational enzymatic steps that lead to the formation of a host of protein-bound oligosaccharides with diverse biological functions. These reactions occur throughout the entire phylogenetic spectrum, ranging from archaea and eubacteria to eukaryotes. It is the aim of this review to describe the glycopeptide linkages that have been found to date and specify their presence on well-characterized glycoproteins. A survey is also made of the enzymes involved in the formation of the various glycopeptide bonds as well as the site of their intracellular action and their affinity for particular peptide domains is evaluated. This examination indicates that 13 different monosaccharides and 8 amino acids are involved in glycoprotein linkages leading to a total of at least 41 bonds, if the anomeric configurations, the phosphoglycosyl linkages, as well as the GPI (glycophosphatidylinositol) phosphoethanolamine bridge are also considered. These bonds represent the products of N- and O-glycosylation, C-mannosylation, phosphoglycation, and glypiation. Currently at least 16 enzymes involved in their formation have been identified and in many cases cloned. Their intracellular site of action varies and includes the endoplasmic reticulum, Golgi apparatus, cytosol, and nucleus. With the exception of the Asn-linked carbohydrate and the GPI anchor, which are transferred to the polypeptide en bloc, the sugar-amino acid linkages are formed by the enzymatic transfer of an activated monosaccharide directly to the protein. This review also deals briefly with glycosidases, which are involved in physiologically important cleavages of glycopeptide bonds in higher organisms, and with a number of human disease states in which defects in enzymatic transfer of saccharides to protein have been implicated.

Secretory pathway of trypanosomatid parasites

The Trypanosomatidae comprise a large group of parasitic protozoa, some of which cause important diseases in humans. These include Trypanosoma brucei (the causative agent of African sleeping sickness and nagana in cattle), Trypanosoma cruzi (the causative agent of Chagas' disease in Central and South America), and Leishmania spp. (the causative agent of visceral and [muco]cutaneous leishmaniasis throughout the tropics and subtropics). The cell surfaces of these parasites are covered in complex protein- or carbohydrate-rich coats that are required for parasite survival and infectivity in their respective insect vectors and mammalian hosts. These molecules are assembled in the secretory pathway. Recent advances in the genetic manipulation of these parasites as well as progress with the parasite genome projects has greatly advanced our understanding of processes that underlie secretory transport in trypanosomatids. This article provides an overview of the organization of the trypanosomatid secretory pathway and connections that exist with endocytic organelles and multiple lytic and storage vacuoles. A number of the molecular components that are required for vesicular transport have been identified, as have some of the sorting signals that direct proteins to the cell surface or organelles in the endosome-vacuole system. Finally, the subcellular organization of the major glycosylation pathways in these parasites is reviewed. Studies on these highly divergent eukaryotes provide important insights into the molecular processes underlying secretory transport that arose very early in eukaryotic evolution. They also reveal unusual or novel aspects of secretory transport and protein glycosylation that may be exploited in developing new antiparasite drugs.

A novel endo-beta-galactosidase from Clostridium perfringens that liberates the disaccharide GlcNAcalpha 1-->Gal from glycans specifically expressed in the gastric gland mucous cell-type mucin

We found that commercially available sialidases prepared from Clostridium perfringens ATCC10543 were contaminated with an endoglycosidase capable of releasing the disaccharide GlcNAcalpha1-->4Gal from glycans expressed in the gastric gland mucous cell-type mucin. We have isolated this enzyme in electrophoretically homogeneous form from the culture supernatant of this organism by ammonium sulfate precipitation followed by affinity chromatography using a Sephacryl S-200 HR column. The enzyme was specifically retained by and eluted from the column with methyl-alpha-Glc. By NMR spectroscopy, the structure of the disaccharide released from porcine gastric mucin by this enzyme was established to be GlcNAcalpha1-->4Gal. The specificity of this enzyme as an endo-beta-galactosidase was established by analyzing the liberation of GlcNAcalpha1-->4Gal from GlcNAcalpha1-->4Galbeta1-->4GlcNAcbeta1-->6(GlcNAcalpha1--> 4Galbeta1-->3)GalNAc-ol by mass spectrometry. Because this novel endo-beta-galactosidase specifically releases the GlcNAcalpha1-->4Gal moiety from porcine gastric mucin, we propose to call this enzyme a GlcNAcalpha1-->4Gal-releasing endo-beta-galactosidase (Endo-beta-Gal(GnGa)). Endo-beta-Gal(GnGa) was found to remove the GlcNAcalpha1-->4Gal epitope expressed in gastric adenocarcinoma AGS cells transfected with alpha1,4-N-acetylglucosaminyltransferase cDNA. Endo-beta-Gal(GnGa) should become useful for studying the structure and function of glycoconjugates containing the terminal GlcNAcalpha1-->4Gal epitope.

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.

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.