Structural elucidation of zwitterionic carbohydrates derived from glycosphingolipids of the porcine parasitic nematode Ascaris suum

Recognition of Highly Branched N-Glycans of the Porcine Whipworm by the Immune System

Glycans are key to host-pathogen interactions, whereby recognition by the host and immunomodulation by the pathogen can be mediated by carbohydrate binding proteins, such as lectins of the innate immune system, and their glycoconjugate ligands. Previous studies have shown that excretory-secretory products of the porcine nematode parasite Trichuris suis exert immunomodulatory effects in a glycan-dependent manner. To better understand the mechanisms of these interactions, we prepared N-glycans from T. suis and both analyzed their structures and used them to generate a natural glycan microarray. With this array, we explored the interactions of glycans with C-type lectins, C-reactive protein, and sera from T. suis-infected pigs. Glycans containing LacdiNAc and phosphorylcholine-modified glycans were associated with the highest binding by most of these proteins. In-depth analysis revealed not only fucosylated LacdiNAc motifs with and without phosphorylcholine moieties but phosphorylcholine-modified mannose and N-acetylhexosamine-substituted fucose residues, in the context of maximally tetraantennary N-glycan scaffolds. Furthermore, O-glycans also contained fucosylated motifs. In summary, the glycans of T. suis are recognized by both the innate and adaptive immune systems and also exhibit species-specific features distinguishing its glycome from those of other nematodes.

Recognition of highly branched N-glycans of the porcine whipworm by the immune system

Glycans are key to host-pathogen interactions, whereby recognition by the host and immunomodulation by the pathogen can be mediated by carbohydrate binding proteins, such as lectins of the innate immune system, and their glycoconjugate ligands. Previous studies have shown that excretory-secretory products of the porcine nematode parasite Trichuris suis exert immunomodulatory effects in a glycan-dependent manner. To better understand the mechanisms of these interactions, we prepared N-glycans from T. suis and both analyzed their structures and used them to generate a natural glycan microarray. With this array we explored the interactions of glycans with C-type lectins, C-reactive protein and sera from T. suis infected pigs. Glycans containing LacdiNAc and phosphorylcholine-modified glycans were associated with the highest binding by most of these proteins. In-depth analysis revealed not only fucosylated LacdiNAc motifs with and without phosphorylcholine moieties, but phosphorylcholine-modified mannose and N-acetylhexosamine-substituted fucose residues, in the context of maximally tetraantennary N-glycan scaffolds. Furthermore, O-glycans also contained fucosylated motifs. In summary, the glycans of T. suis are recognized by both the innate and adaptive immune systems, and also exhibit species-specific features distinguishing its glycome from those of other nematodes.

Glycosphingolipids in human parasites

Glycosphingolipids (GSLs) are comprised of glycans (oligosaccharides) linked to a lipid containing a sphingosine moiety. They are major membrane components in cells of most animals, and importantly, they also occur in parasitic protozoans and worms that infect people. While the endogenous functions of the GSLs in most parasites are elusive, many of these GSLs are recognized by antibodies in infected human and animal hosts, and thus, their structures, biosynthesis, and functions are of great interest. Such knowledge of GSLs could lead to new drugs and diagnostics for treating infections, as well as novel vaccine strategies. The diversity of GSLs recently identified in such infectious organisms and aspects of their immune recognition are major topics of this review. It is not intended to be exhaustive but to highlight aspects of GSL glycans in human parasites.

Increasing Complexity of the N-Glycome During Caenorhabditis Development

Caenorhabditis elegans is a frequently employed genetic model organism and has been the object of a wide range of developmental, genetic, proteomic, and glycomic studies. Here, using an off-line MALDI-TOF-MS approach, we have analyzed the N-glycans of mixed embryos and liquid- or plate-grown L4 larvae. Of the over 200 different annotatable N-glycan structures, variations between the stages as well as the mode of cultivation were observed. While the embryonal N-glycome appears less complicated overall, the liquid- and plate-grown larvae differ especially in terms of methylation of bisecting fucose, α-galactosylation of mannose, and di-β-galactosylation of core α1,6-fucose. Furthermore, we analyzed the O-glycans by LC-electrospray ionization-MS following β-elimination; especially the embryonal O-glycomes included a set of phosphorylcholine-modified structures, previously not shown to exist in nematodes. However, the set of glycan structures cannot be clearly correlated with levels of glycosyltransferase transcripts in developmental RNA-Seq datasets, but there is an indication for coordinated expression of clusters of potential glycosylation-relevant genes. Thus, there are still questions to be answered in terms of how and why a simple nematode synthesizes such a diverse glycome.

MALDI-TOF mass spectrometry as a diagnostic tool in human and veterinary helminthology: a systematic review

BACKGROUND

Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS) has become a widely used technique for the rapid and accurate identification of bacteria, mycobacteria and certain fungal pathogens in the clinical microbiology laboratory. Thus far, only few attempts have been made to apply the technique in clinical parasitology, particularly regarding helminth identification.

METHODS

We systematically reviewed the scientific literature on studies pertaining to MALDI-TOF MS as a diagnostic technique for helminths (cestodes, nematodes and trematodes) of medical and veterinary importance. Readily available electronic databases (i.e. PubMed/MEDLINE, ScienceDirect, Cochrane Library, Web of Science and Google Scholar) were searched from inception to 10 October 2018, without restriction on year of publication or language. The titles and abstracts of studies were screened for eligibility by two independent reviewers. Relevant articles were read in full and included in the systematic review.

RESULTS

A total of 84 peer-reviewed articles were considered for the final analysis. Most papers reported on the application of MALDI-TOF for the study of Caenorhabditis elegans, and the technique was primarily used for identification of specific proteins rather than entire pathogens. Since 2015, a small number of studies documented the successful use of MALDI-TOF MS for species-specific identification of nematodes of human and veterinary importance, such as Trichinella spp. and Dirofilaria spp. However, the quality of available data and the number of examined helminth samples was low.

CONCLUSIONS

Data on the use of MALDI-TOF MS for the diagnosis of helminths are scarce, but recent evidence suggests a potential role for a reliable identification of nematodes. Future research should explore the diagnostic accuracy of MALDI-TOF MS for identification of (i) adult helminths, larvae and eggs shed in faecal samples; and (ii) helminth-related proteins that are detectable in serum or body fluids of infected individuals.

The Eukaryotic Elongation Factor 1 Alpha (eEF1α) from the Parasite Leishmania infantum Is Modified with the Immunomodulatory Substituent Phosphorylcholine (PC)

Proteins and glycolipids have been found to be decorated with phosphorylcholine (PC) both in protozoa and nematodes that parasitize humans and animals. PC epitopes can provoke various effects on immune cells leading to an immunomodulation of the host’s immune system that allows long-term persistence of the parasites. So far, only a limited number of PC-modified proteins, mainly from nematodes, have been identified. Infections caused by Leishmania spp. (e.g., L. infantum in southern Europe) affect about 12 million people worldwide and are characterized by a wide spectrum of clinical forms in humans, ranging from cutaneous to fatal visceral leishmaniasis. To establish and maintain the infection, these protozoa are dependent on the secretion of effector molecules into the host for modulating their immune system. In this project, we analyzed the PC modification of L. infantum promastigotes by 2D-gel based proteomics. Western blot analysis with the PC-specific antibody TEPC-15 revealed one PC-substituted protein in this organism, identified as eEF1α. We could demonstrate that the binding of eEF1α to one of its downstream effectors is dependent on its PC-modification. In this study we provide evidence that in this parasite the modification of eEF1α with PC may be essential for its function as an important virulence factor.

Helminth glycomics - glycan repertoires and host-parasite interactions

Glycoproteins and glycolipids of parasitic helminths play important roles in biology and host-parasite interaction. This review discusses recent helminth glycomics studies that have been expanding our insights into the glycan repertoire of helminths. Structural data are integrated with biological and immunological observations to highlight how glycomics advances our understanding of the critical roles that glycans and glycan motifs play in helminth infection biology. Prospects and challenges in helminth glycomics and glycobiology are discussed.

Analysis of zwitterionic and anionic N-linked glycans from invertebrates and protists by mass spectrometry

Glycomic analyses over the years have revealed that non-vertebrate eukaryotes express oligosaccharides with inorganic and zwitterionic modifications which are either occurring in different contexts as compared to, or are absent from, mammals. Examples of anionic N-glycans (carrying sulphate or phosphate) are known from amoebae, fungi, molluscs and insects, while zwitterionic modifications by phosphorylcholine, phosphoethanolamine and aminoethylphosphonate occur on N-, O- and lipid-linked glycans from trichomonads, annelids, fungi, molluscs, insects, cestodes and nematodes. For detection of zwitterionic and anionic glycans, mass spectrometry has been a key method, but their ionic character affects the preparation and purification; therefore, as part of a glycomic strategy, the possibility of their presence must be considered in advance. On the other hand, their ionisation and fragmentation in positive and negative ion mode mass spectrometry as well as specific chemical or enzymatic treatments can prove diagnostic to their analysis. In our laboratory, we combine solid-phase extraction, reversed and normal phase HPLC, MALDI-TOF MS, exoglycosidase digests and hydrofluoric acid treatment to reveal N-glycans modified with anionic and zwitterionic moieties in a wide range of organisms. It is to be anticipated that, as more species are glycomically analysed, zwitterionic and anionic modifications of N-glycans will prove rather widespread. This knowledge is - in the longer term - then the basis for understanding the function of this cornucopia of glycan modifications.

The PCome of Ascaris suum as a model system for intestinal nematodes: identification of phosphorylcholine-substituted proteins and first characterization of the PC-epitope structures

In multicellular parasites (e.g., nematodes and protozoa), proteins and glycolipids have been found to be decorated with phosphorylcholine (PC). PC can provoke various effects on immune cells leading to an immunomodulation of the host's immune system. This immunomodulation allows long-term persistence but also prevents severe pathology due to downregulation of cellular immune responses. PC-containing antigens have been found to interfere with key proliferative signaling pathways in B and T cells, development of dendritic cells and macrophages, and mast cell degranulation. These effects contribute to the observed modulated cytokine levels and impairment of lymphocyte proliferation. In contrast to glycosphingolipids, little is known about the PC-epitopes of proteins. So far, only a limited number of PC-modified proteins from nematodes have been identified. In this project, PC-substituted proteins and glycolipids in Ascaris suum have been localized by immunohistochemistry in specific tissues of the body wall, intestine, and reproductive tract. Subsequently, we investigated the PCome of A. suum by 2D gel-based proteomics and detection by Western blotting using the PC-specific antibody TEPC-15. By peptide-mass-fingerprint matrix-assisted laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), we could identify 59 PC-substituted proteins, which are in involved multiple cellular processes. In addition to membrane proteins like vitellogenin-6, we found proteins with structural (e.g., tubulins) and metabolic (e.g., pyruvate dehydrogenase) functions or which can act in the defense against the host's immune response (e.g., serpins). Initial characterization of the PC-epitopes revealed a predominant linkage of PC to the proteins via N-glycans. Our data form the basis for more detailed investigations of the PC-epitope structures as a prerequisite for comprehensive understanding of the molecular mechanisms of immunomodulation.

More Than Just Oligomannose: An N-glycomic Comparison of Penicillium Species

N-glycosylation is an essential set of post-translational modifications of proteins; in the case of filamentous fungi, N-glycans are present on a range of secreted and cell wall proteins. In this study, we have compared the glycans released by peptide/N-glycosidase F from proteolysed cell pellets of three Penicillium species (P. dierckxii, P. nordicum and P. verrucosum that all belong to the Eurotiomycetes). Although the major structures are all within the range Hex(5-11)HexNAc(2) as shown by mass spectrometry, variations in reversed-phase chromatograms and MS/MS fragmentation patterns are indicative of differences in the actual structure. Hydrofluoric acid and mannosidase treatments revealed that the oligomannosidic glycans were not only in part modified with phosphoethanolamine residues and outer chain och1-dependent mannosylation, but that bisecting galactofuranose was present in a species-dependent manner. These data are the first to specifically show the modification of N-glycans in fungi with zwitterionic moieties. Furthermore, our results indicate that mere mass spectrometric screening is insufficient to reveal the subtly complex nature of N-glycosylation even within a single fungal genus.

Detection and site localization of phosphorylcholine-modified peptides by NanoLC-ESI-MS/MS using precursor ion scanning and multiple reaction monitoring experiments

Phosphorylcholine (PC)-modified biomolecules like lipopolysaccharides, glycosphingolipids, and (glyco)proteins are widespread, highly relevant antigens of parasites, since this small hapten shows potent immunomodulatory capacity, which allows the establishment of long-lasting infections of the host. Especially for PC-modified proteins, structural data is rare because of the zwitterionic nature of the PC substituent, resulting in low sensitivities and unusual but characteristic fragmentation patterns. We have developed a targeted mass spectrometric approach using hybrid triple quadrupole/linear ion trap (QTRAP) mass spectrometry coupled to nanoflow chromatography for the sensitive detection of PC-modified peptides from complex proteolytic digests, and the localization of the PC-modification within the peptide backbone. In a first step, proteolytic digests are screened using precursor ion scanning for the marker ions of choline (m/z 104.1) and phosphorylcholine (m/z 184.1) to establish the presence of PC-modified peptides. Potential PC-modified precursors are then subjected to a second analysis using multiple reaction monitoring (MRM)-triggered product ion spectra for the identification and site localization of the modified peptides. The approach was first established using synthetic PC-modified synthetic peptides and PC-modified model digests. Following the optimization of key parameters, we then successfully applied the method to the detection of PC-peptides in the background of a proteolytic digest of a whole proteome. This methodological invention will greatly facilitate the detection of PC-substituted biomolecules and their structural analysis.

Bacillus thuringiensis-derived Cry5B has potent anthelmintic activity against Ascaris suum

Ascaris suum and Ascaris lumbricoides are two closely related geo-helminth parasites that ubiquitously infect pigs and humans, respectively. Ascaris suum infection in pigs is considered a good model for A. lumbricoides infection in humans because of a similar biology and tissue migration to the intestines. Ascaris lumbricoides infections in children are associated with malnutrition, growth and cognitive stunting, immune defects, and, in extreme cases, life-threatening blockage of the digestive tract and aberrant migration into the bile duct and peritoneum. Similar effects can be seen with A. suum infections in pigs related to poor feed efficiency and performance. New strategies to control Ascaris infections are needed largely due to reduced treatment efficacies of current anthelmintics in the field, the threat of resistance development, and the general lack of new drug development for intestinal soil-transmitted helminths for humans and animals. Here we demonstrate for the first time that A. suum expresses the receptors for Bacillus thuringiensis crystal protein and novel anthelmintic Cry5B, which has been previously shown to intoxicate hookworms and which belongs to a class of proteins considered non-toxic to vertebrates. Cry5B is able to intoxicate A. suum larvae and adults and triggers the activation of the p38 mitogen-activated protein kinase pathway similar to that observed with other nematodes. Most importantly, two moderate doses of 20 mg/kg body weight (143 nM/kg) of Cry5B resulted in a near complete cure of intestinal A. suum infections in pigs. Taken together, these results demonstrate the excellent potential of Cry5B to treat Ascaris infections in pigs and in humans and for Cry5B to work effectively in the human gastrointestinal tract.

Ascaris suum is an intestinal parasitic nematode of pigs that is very closely related to Ascaris lumbricoides, a major intestinal parasitic nematode of humans that infects more than one billion people worldwide. Because of reduced efficacy and the threat of resistance to the current small set of approved drugs to treat Ascaris infections, new treatments are needed. Here we test against A. suum infections the effectiveness of Cry5B, a nematode-killing protein made by the natural soil bacterium Bacillus thuringiensis and representing a promising new class of anthelmintics. We demonstrate for the first time that A. suum possesses the receptors to bind Cry5B and that Cry5B can kill A. suum larvae and adults in culture. Most importantly, we demonstrate that oral administration of Cry5B to pigs infected with A. suum larvae results in a near complete elimination of the infection. Given the similarities between A. suum and A. lumbricoides and the similarity between the pig and human gastrointestinal tracts, our data indicate that Cry5B has excellent potential to treat Ascaris infections in veterinary animals and in humans.

Variation of content of lipid classes, sterols and fatty acids in gonads and digestive glands of Scrobicularia plana in relation to environment pollution levels

Lipids are central for energy metabolism and their fate in bivalves is closely linked to environmental conditions and gametogenic cycle. In order to assess the pollution impact on lipid metabolism of bivalves, storage and structure lipids from samples of Scrobicularia plana were studied. These samples were collected during sexual maturity both from estuaries considered contaminated (Goyen and Blavet) and from a reference site (Bay of St Brieuc) for comparison. Lipids were extracted from the gonads and the digestive glands and further separated by column chromatography. Fatty acids and sterols were then analyzed by gas chromatography-mass spectrometry. Correlations were shown between dioxin-like compounds (Eq-TCDD) and triacyglycerol levels (TAG). In the same way, glycolipids and contamination by polycyclic aromatic hydrocarbons (PAH) and pollutants with estrogenic activity seem to be closely related. In a second time, lipid indices (ratio between storage and structure lipids) were evaluated. Whereas these indices are often used in fish to assess habitat quality with regards to differential anthropogenic pressure, the ratio TAG/sterols was not here significantly influenced by the site of origin of S. plana. Intersite fluctuations of the ratio TAG/phospholipids also remained very limited. This could be explained by the limited contamination level in studied sites but also by a contrasted response from organisms in different taxa (bivalves vs. fish). Environmental pollution is not the only factor able to induce changes in lipid classes. The trophic wealth seemed to be different between the reference site and contaminated estuaries, the total organic carbon content being higher in muddy estuarine sediments.

The N-glycans of Trichomonas vaginalis contain variable core and antennal modifications

Trichomonad species are widespread unicellular flagellated parasites of vertebrates which interact with their hosts through carbohydrate-lectin interactions. In the past, some data have been accumulated regarding their lipo(phospho)glycans, a major glycoconjugate on their cell surfaces; on the other hand, other than biosynthetic aspects, few details about their N-linked oligosaccharides are known. In this study, we present both mass spectrometric and high-performance liquid chromatography data about the N-glycans of different strains of Trichomonas vaginalis, a parasite of the human reproductive tract. The major structure in all strains examined is a truncated oligomannose form (Man(5)GlcNAc(2)) with α1,2-mannose residues, compatible with a previous bioinformatic examination of the glycogenomic potential of T. vaginalis. In addition, dependent on the strain, N-glycans modified by pentose residues, phosphate or phosphoethanolamine and terminal N-acetyllactosamine (Galβ1,4GlcNAc) units were found. The modification of N-glycans by N-acetyllactosamine in at least some strains is shared with the lipo(phospho)glycan and may represent a further interaction partner for host galectins, thereby playing a role in binding of the parasite to host epithelia. On the other hand, the variation in glycosylation between strains may be the result of genetic diversity within this species.

Glycomarkers in parasitic infections and allergy

Both helminth infections and contact with allergens result in development of a Th2 type of immune response in the affected individual. In this context, the hygiene hypothesis suggests that reduced prevalence of parasitic infections and successful vaccination strategies are causative for an increase of allergies in industrialized countries. It is therefore of interest to study glycans and their role as immunogenic structures in both parasitic infections and allergies. In the present paper we review information on the different types of glycan structure present in proteins from plant and animal food, insect venom and helminth parasites, and their role as diagnostic markers. In addition, the application of these glycan structures as immunomodulators in novel immunotherapeutic strategies is discussed.

Immunomodulation by phosphocholine--biosynthesis, structures and immunological implications of parasitic PC-epitopes

Phosphocholine (PC) as a small haptenic molecule present on antigens of parasites can provoke various effects on immune cells leading to immunomodulation of the host's immune system. This immunomodulation not only allows long-term persistence but also prevents severe pathology due to down-regulation of cellular immune responses. Additionally, PC plays an important role for development and fertility of the parasites. To fully understand the mechanisms of immunomodulation the detailed knowledge of the biosynthesis of the PC-epitopes, their molecular structure and biological function has to be elucidated. The implication of parasite-specific transferases in the biosynthesis of the PC-epitopes and the sensitivity of parasites towards disruption of the choline metabolism offers new perspectives for the development of anti-parasitic drugs and therapies. Furthermore, the immunomodulation provoked by PC-epitopes preventing inflammatory reactions may be useful in the treatment of inflammatory diseases. This review summarizes the current knowledge on the biosynthesis of PC-epitopes, their structures and immunological implications.

A novel fucosyl glycosphingolipid of brine shrimp that is highly sensitive to endoglycoceramidase

Endoglycoceramidase (EGCase; EC 3.2.1.123) is a glycohydrolase that hydrolyzes the glycosidic linkage between the oligosaccharide and ceramide of various glycosphingolipids. We previously reported that hydra produced EGCase to digest glycosphingolipids of brine shrimp (Artemia salina), a type of aquatic crustacean used as a diet for the culture of hydra (Horibata Y, Sakaguchi K, Okino N, Iida H, Inagaki M, Fujisawa T, Hama Y, Ito M. 2004. J Biol Chem. 279:33379-33389). We report here that a major glycosphingolipid of brine shrimp is unique in structure and highly sensitive to EGCase. The glycosphingolipid was extracted from freshly hatched brine shrimp by Folch's partition, followed by mild alkaline hydrolysis and purification with a Sep-Pak plus silica cartridge. The structure of brine shrimp glycosphingolipid was determined by gas chromatography, gas chromatography-mass spectrometry, fast-atom bombardment mass spectrometry, and (1)H-NMR spectrometry to be GlcNAcalpha1-2Fucalpha1-3Manbeta1-4Glcbeta1-1'Cer. Two major molecular species of the glycosphingolipid were identified; the sugar and sphingoid base of each were the same but the major fatty acid was C22:0 and 2-hydroxy C22:0, respectively. This is the first report describing the glycosphingolipid that has an internal fucosyl residue substituted with alpha1-2 N-acetylglucosaminyl residue. This study also suggests the biological relevance of the glycosphingolipid as a dietary source of hydra which possesses EGCase as a digestion enzyme.

Vaccination-induced IgG response to Galalpha1-3GalNAc glycan epitopes in lambs protected against Haemonchus contortus challenge infection

Lambs vaccinated with Haemonchus contortus excretory/secretory (ES) glycoproteins in combination with the adjuvant Alhydrogel are protected against H. contortus challenge infection. Using glycan micro-array analysis we showed that serum from such vaccinated lambs contains IgG antibodies that recognise the glycan antigen Galalpha1-3GalNAc-R and GalNAcbeta1-4(Fucalpha1-3)GlcNAc-R. Our studies revealed that H. contortus glycoproteins contain Galalpha1-3Gal-R as well as significant levels of Galalpha1-3GalNAc-R, which has not been previously reported. Extracts from H. contortus adult worms contain a galactosyltransferase acting on glycan substrates with a terminal GalNAc, indicating that the worms possess the enzymatic potential to synthesise terminal Gal-GalNAc moieties. These data illustrate that glycan micro-arrays constitute a promising technology for fast and specific analysis of serum anti-glycan antibodies in vaccination studies. In addition, this approach facilitates the discovery of novel, antigenic parasite glycan antigens that may have potential for developing glycoconjugate vaccines or utilization in diagnostics.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2003-2004

This review is the third update of the original review, published in 1999, on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings the topic to the end of 2004. Both fundamental studies and applications are covered. The main topics include methodological developments, matrices, fragmentation of carbohydrates and applications to large polymeric carbohydrates from plants, glycans from glycoproteins and those from various glycolipids. Other topics include the use of MALDI MS to study enzymes related to carbohydrate biosynthesis and degradation, its use in industrial processes, particularly biopharmaceuticals and its use to monitor products of chemical synthesis where glycodendrimers and carbohydrate-protein complexes are highlighted.

Parasitic helminths: a pharmacopeia of anti-inflammatory molecules

Infection with parasitic helminths takes a heavy toll on the health and well-being of humans and their domestic livestock, concomitantly resulting in major economic losses. Analyses have consistently revealed bioactive molecules in extracts of helminths or in their excretory/secretory products that modulate the immune response of the host. It is our view that parasitic helminths are an untapped source of immunomodulatory substances that, in pure form, could become new drugs (or models for drug design) to treat disease. Here, we illustrate the range of immunomodulatory molecules in selected parasitic trematodes, cestodes and nematodes, their impact on the immune cells in the host and how the host may recognize these molecules. There are many examples of the partial characterization of helminth-derived immunomodulatory molecules, but these have not yet translated into new drugs, reflecting the difficulty of isolating and fully characterizing proteins, glycoproteins and lipid-based molecules from small amounts of parasite material. However, this should not deter the investigator, since analytical techniques are now being used to accrue considerable structural information on parasite-derived molecules, even when only minute quantities of tissue are available. With the introduction of methodologies to purify and structurally-characterize molecules from small amounts of tissue and the application of high throughput immunological assays, one would predict that an assessment of parasitic helminths will yield a variety of novel drug candidates in the coming years.

Structural studies on the neutral glycosphingolipids of Manduca sexta

Glycosphingolipids (GSLs) have been implicated as playing major roles in cellular interactions and control of cell proliferation in muticellular organisms. Moreover GSLs and other sphingolipids such as sphingomyelins, ceramides and sphingosines serve a variety of roles in signal transduction. Hence, identification of structures of GSLs in different biota will shed light in understanding their physiological role. During this study, the major glycosphingolipid component present in the extracts of stage-12 and stage-17/18 metamorphosing adults of Manduca sexta was identified as mactosyl ceramide. We report the isolation of several ceramide disaccharides, a ceramide trisaccharide and a ceramide tetrasaccharide. The GSL structures were confirmed by high-resolution mass spectrometry and tandem mass spectrometry. The identity of the monosaccharides was proved using exoglycosidases. The predominant sphingosine chain-length varied from C-14 (tetradecasphing-4-enine) to C-16 (hexadecasphing-4-enine) in these GSLs. Sphingosines of both chain lengths were accompanied by their doubly unsaturated counterparts tetradecasphinga-4,6-diene and hexadecasphinga-4,6-diene. It is also interesting to note the presence of tetradecasphinganine and hexadecasphinganine in minute amounts in the form of a GSL in the extracts of M. sexta. The varying degrees of unsaturation in the sphingosine moiety of GSLs in M. sexta may be biologically significant in insect metamorphosis. The ceramide trisaccharides and ceramide tetrasaccharide belong to the arthro-series, The observation of fucose in the M. sexta GSLs is the first report of the presence of fucose in an arthroseries GSL.

N-glycans of the porcine nematode parasite Ascaris suum are modified with phosphorylcholine and core fucose residues

In recent years, the glycoconjugates of many parasitic nematodes have attracted interest due to their immunogenic and immunomodulatory nature. Previous studies with the porcine roundworm parasite Ascaris suum have focused on its glycosphingolipids, which were found, in part, to be modified by phosphorylcholine. Using mass spectrometry and western blotting, we have now analyzed the peptide N-glycosidase A-released N-glycans of adults of this species. The presence of hybrid bi- and triantennary N-glycans, some modified by core alpha1,6-fucose and peripheral phosphorylcholine, was demonstrated by LC/electrospray ionization (ESI)-Q-TOF-MS/MS, as was the presence of paucimannosidic N-glycans, some of which carry core alpha1,3-fucose, and oligomannosidic oligosaccharides. Western blotting verified the presence of protein-bound phosphorylcholine and core alpha1,3-fucose, whereas glycosyltransferase assays showed the presence of core alpha1,6-fucosyltransferase and Lewis-type alpha1,3-fucosyltransferase activities. Although, the unusual tri- and tetrafucosylated glycans found in the model nematode Caenorhabditis elegans were not found, the vast majority of the N-glycans found in A. suum represent a subset of those found in C. elegans; thus, our data demonstrate that the latter is an interesting glycobiological model for parasitic nematodes.

First identification of a phosphorylcholine-substituted protein from Caenorhabditis elegans: isolation and characterization of the aspartyl protease ASP-6

Caenorhabditis elegans is a widely accepted model system for parasitic nematodes, drug screening and developmental studies. Similar to parasitic worms, C. elegans expresses glycosphingolipids and glycoproteins carrying, in part, phosphorylcholine (PCho) substitutions, which might play important roles in nematode development, fertility and, at least in the case of parasites, survival within the host. With the exception of a major secretory/excretory product from Acanthocheilonema viteae (ES-62), no protein carrying this epitope has been studied in detail yet. Here we report on the identification, characterization and localization of the aspartyl protease ASP-6 of C. elegans, which is excreted by the nematode in a PCho-substituted form. Within the worm, most prominent expression of the protein is observed in the intestine, while muscle and epithelial cells express asp-6 to a lesser extent. In animals harboring an ASP-6::GFP fusion protein, diffuse fluorescence throughout the body cavity of adult worms indicates that the chimeric protein is secreted.

Strategies for analysis of glycoprotein glycosylation

Glycoproteins are known to exhibit multiple biological functions. In order to assign distinct functional properties to defined structural features, detailed information on the respective carbohydrate moieties is required. Chemical and biochemical analyses, however, are often impeded by the small amounts of sample available and the vast structural heterogeneity of these glycans, thus necessitating highly sensitive and efficient methods for detection, separation and structural investigation. The aim of this article is to briefly review suitable strategies for characterization of glycosylation at the levels of intact proteins, glycopeptides and free oligosaccharides. Furthermore, methods commonly used for isolation, fractionation and carbohydrate structure analysis of liberated glycoprotein glycans are discussed in the context of potential applications in glycoproteomics.

Antibody responses to Ascaris-derived proteins and glycolipids: the role of phosphorylcholine

In addition to proteins, glycolipids can be targets of antibody responses and contribute to host-pathogen interaction. Following the structural analysis of Ascaris lumbricoides-derived glycolipids, the antibody responses of a group of children with no, light and heavy infections were analysed. The role of the phosphorylcholine moiety, present on Ascaris glycoproteins and glycolipids, in antibody reactivity of these infected individuals was determined. Children carrying heavy infections showed highest IgG reactivity to glycolipids compared to lightly or non-infected children. Substantial IgG antibody reactivity to both (glyco)proteins and glycolipids was found to be directed to the phosphorylcholine moiety as determined by either removal of this group or a competition assay. This was most pronounced for glycolipids, where removal of the phosphorylcholine moieties by hydrofluoric acid treatment abrogated IgG antibody reactivity. Measurement of IgG4 and IgE isotypes showed no IgG4 reactivity to Ascaris glycolipids, but raised IgE responses were detected in subjects with light or no Ascaris infections, suggesting that IgE responses to glycolipids may play a role in controlling parasite burden. Differences found in antibody profiles to glycolipids and (glyco)proteins, indicate that these different classes of compounds may have distinct roles in shaping of and interacting with humoral immune responses.

Proteomic analysis of glycosylation: structural determination of N- and O-linked glycans by mass spectrometry

This review summarizes the methods, mainly based on mass spectrometry, for the structural determination of N- and O-linked carbohydrates that are post-translationally attached to a large number of proteins and which play a key role in determining the function and biophysical properties of these compounds. Analysis of these carbohydrates has proved difficult in the past due to their structural complexity. However, modern analytical methods such as mass spectrometry have the ability to elucidate most structural details at the concentration levels required for proteomics. This review describes methods for direct examination of glycoproteins by mass spectrometry, the release of N- and O-linked glycans from glycoproteins separated in sodium dodecyl sulfate polyacrylamide electrophoresis gels, and the analysis of these compounds by techniques such as matrix-assisted laser desorption/ionization and electrospray ionization mass spectrometry. Matrix-assisted laser desorption/ionization mass spectrometry provides the most rapid method for comparing glycan profiles and is probably most appropriate for clinical studies. One of the most promising techniques for determining the structures of N-glycans in proteomic studies is negative ion fragmentation of electrosprayed ions. This technique combines high throughput with ease of structural interpretation and provides structural details that are difficult to obtain by classical methods.

Identification and Characterization of Keyhole Limpet Hemocyanin N-Glycans Mediating Cross-reactivity with Schistosoma mansoni

Keyhole limpet hemocyanin (KLH) of the mollusc Megathura crenulata is known to serologically cross-react with Schistosoma mansoni glycoconjugates in a carbohydrate-dependent manner. To elucidate the structural basis for this cross-reactivity, KLH glycans were released from tryptic glycopeptides and fluorescently labeled. Cross-reacting glycans were identified using a polyclonal antiserum reacting with soluble S. mansoni egg antigens, isolated by a three-dimensional fractionation scheme and analyzed by different mass spectrometric techniques as well as linkage analysis and exoglycosidase treatment. The results revealed that cross-reacting species comprise approximately 4.5% of released glycans. They all represent novel types of N-glycans with a Fuc(alpha1-3)GalNAc(beta1-4)[Fuc(alpha1-3)]GlcNAc motif, which is known to occur also in schistosomal glycoconjugates. The tetrasaccharide unit is attached to the 3-linked antenna of a trimannosyl core, which can be further decorated by galactosyl residues, a xylose residue in 2-position of the central mannose and/or a fucose at the innermost N-acetylglucosamine. This study provides for the first time detailed structural data on the KLH carbohydrate entities responsible for cross-reactivity with glycoconjugates from S. mansoni.

The Drosophila melanogaster homologue of the human histo-blood group Pk gene encodes a glycolipid-modifying alpha1,4-N-acetylgalactosaminyltransferase

Insects express arthro-series glycosphingolipids, which contain an alpha1,4-linked GalNAc residue. To determine the genetic basis for this linkage, we cloned a cDNA (CG17223) from Drosophila melanogaster encoding a protein with homology to mammalian alpha1,4-glycosyltransferases and expressed it in the yeast Pichia pastoris. Culture supernatants from the transformed yeast were found to display a novel UDP-GalNAc:GalNAcbeta1,4GlcNAcbeta1-R alpha-N-acetylgalactosaminyltransferase activity when using either a glycolipid, p-nitrophenylglycoside or an N-glycan carrying one or two terminal beta-N-acetylgalactosamine residues. NMR and MS in combination with glycosidase digestion and methylation analysis indicate that the cloned cDNA encodes an alpha1,4-N-acetylgalactosaminyltransferase. We hypothesize that this enzyme and its orthologues in other insects are required for the biosynthesis of the N5a and subsequent members of the arthro-series of glycolipids as well as of N-glycan receptors for Bacillus thuringiensis crystal toxin Cry1Ac.

Identification of phosphorylcholine substituted peptides by their characteristic mass spectrometric fragmentation

Phosphorylcholine (PC) substituted biomolecules are wide-spread, highly relevant antigens of parasites, since this small hapten has been found to be a potent immunomodulatory component which allows the establishment of long lasting infections of the host. Structural data, especially of protein bound PC-substituents, are still rare due to the observation that mass spectrometric analyses are mostly hampered by this zwitterionic substituent resulting in low sensitivities and unusual but characteristic fragmentation patterns. Here we investigated the fragmentation behaviour of synthetic PC-substituted peptides by matrix-assisted laser desorption/ionization mass spectrometry and electrospray ionization ion trap mass spectrometry. We could show that the predominant neutral loss of a trimethylamine unit (Hoffmann elimination) leads to cyclic phosphate derivatives which prevent further fragmentation of the peptide backbone by stabilizing the positive charge at this particular side chain. Knowledge of this PC-specific fragmentation might help to identify PC-substituted biomolecules and facilitate their structural analysis.

Molecular Basis of Anti-horseradish Peroxidase Staining in Caenorhabditis elegans

Cross-reactivity with anti-horseradish peroxidase antiserum is a feature of many glycoproteins from plants and invertebrates; indeed staining with this reagent has been used to track neurons in Drosophila melanogaster and Caenorhabditis elegans. Although in insects the evidence indicates that the cross-reaction results from the presence of core alpha1,3-fucosylated N-glycans, the molecular basis for anti-horseradish peroxidase staining in nematodes has been unresolved to date. By using Western blots of wild-type and mutant C. elegans extracts in conjunction with specific inhibitors, we show that the cross-reaction is due to core alpha1,3-fucosylation. Of the various mutants examined, one with a deletion of the fut-1 (K08F8.3) gene showed no reaction to anti-horseradish peroxidase; the molecular phenotype was rescued by injection of either the K08F8 cosmid or the fut-1 open reading frame under control of the let-858 promoter. Furthermore, expression of fut-1 cDNA in Pichia and insect cells in conjunction with antibody staining, high pressure liquid chromatography, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry analyses showed that FUT-1 is a core alpha1,3-fucosyltransferase with an unusual substrate specificity. It is the only core fucosyltransferase in plants and animals described to date that does not require the prior action of N-acetylglucosaminyltransferase I.

Structural elucidation of novel phosphocholine-containing glycosylinositol-phosphoceramides in filamentous fungi and their induction of cell death of cultured rice cells

Novel ZGLs (zwitterionic glycosphingolipids) have been found in and extracted from the mycelia of filamentous fungi ( Acremonium sp.) isolated from soil. Five ZGLs (ZGL1-ZGL5) were structurally elucidated by sugar compositional analysis, methylation analysis, periodate oxidation, matrix-assisted laser-desorption ionization-time-of-flight MS, (1)H-NMR spectroscopy and fast-atom bombardment MS. Their chemical structures were as follows: GlcN(alpha1-2)Ins1-P-1Cer (ZGL1), Man(alpha1-6)GlcN(alpha1-2)Ins1-P-1Cer (ZGL2), Man(alpha1-6)Man(alpha1-6)GlcN(alpha1-2)Ins1-P-1Cer (ZGL3), PC-->6Man(alpha1-6)GlcN(alpha1-2)Ins1- P -1Cer (ZGL4), and PC-->6Man(alpha1-6)Man(alpha1-6)GlcN(alpha1-2)Ins1-P-1Cer (ZGL5) (where Cer is ceramide and PC is phosphocholine). In addition, one acidic glycosphingolipid, which was the precursor of ZGLs, was also characterized as inositol-phosphoceramide. The core structure of the ZGLs, GlcN(alpha1-2)Ins1- P, is rather different from those found in other fungi, such as Man(alpha1-2)Ins1- P and Man(alpha1-6)Ins1- P. Interestingly, the terminal mannose residue of ZGL4 and ZGL5 was modified further with a PC group. The presence of PC-containing glycosylinositol-phosphoceramides has not been reported previously in any organism. The ceramide constituents of both ZGLs and acidic glycosphingolipid were essentially the same, and consisted of a 4-hydroxyoctadecasphinganine (phytosphingosine) as the sole sphingoid base and 2-hydroxytetracosanoic acid (>90%) as the major fatty acid. ZGLs were found to cause cell death in suspensions of cultured rice cells. The cell death-inducing activity of ZGLs is probably due to the characteristic glycan moiety of Man(alpha1-6)GlcN, and PC-containing ZGLs had high activity. This study is the first to demonstrate that fungal glycosylinositol-phosphoceramides induce cell death in cultured rice cells.