Characterisation of the phosphorylcholine-containing N-linked oligosaccharides in the excretory-secretory 62 kDa glycoprotein of Acanthocheilonema viteae

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.

Mini Review: Structure and Function of Nematode Phosphorylcholine-Containing Glycoconjugates

An unusual aspect of the biology of nematodes is the covalent attachment of phosphorylcholine (PC) to carbohydrate in glycoconjugates. Investigation of the structure of these molecules by ever-increasingly sophisticated analytical procedures has revealed that PC is generally in phosphodiester linkage with C6 of N-acetylglucosamine (GlcNAc) in both N-type glycans and glycosphingolipids. Up to five PC groups have been detected in the former, being located on both antenna and core GlcNAc. The PC donor for transfer to carbohydrate appears to be phosphatidylcholine but the enzyme responsible for transfer remains to be identified. Work primarily involving the PC-containing Acanthocheilonema viteae secreted product ES-62, has shown that the PC attached to nematode N-glycans possesses a range of immunomodulatory properties, subverting for example, pro-inflammatory signalling in various immune system cell-types including lymphocytes, mast cells, dendritic cells and macrophages. This has led to the generation of PC-based ES-62 small molecule analogues (SMAs), which mirror the parent molecule in preventing the initiation or progression of disease in mouse models of a number of human conditions associated with aberrant inflammatory responses. These include rheumatoid arthritis, systemic lupus erythematosus and lung and skin allergy such that the SMAs are considered to have widespread therapeutic potential.

The Functional Parasitic Worm Secretome: Mapping the Place of Onchocerca volvulus Excretory Secretory Products

Nematodes constitute a very successful phylum, especially in terms of parasitism. Inside their mammalian hosts, parasitic nematodes mainly dwell in the digestive tract (geohelminths) or in the vascular system (filariae). One of their main characteristics is their long sojourn inside the body where they are accessible to the immune system. Several strategies are used by parasites in order to counteract the immune attacks. One of them is the expression of molecules interfering with the function of the immune system. Excretory-secretory products (ESPs) pertain to this category. This is, however, not their only biological function, as they seem also involved in other mechanisms such as pathogenicity or parasitic cycle (molting, for example). We will mainly focus on filariae ESPs with an emphasis on data available regarding Onchocerca volvulus, but we will also refer to a few relevant/illustrative examples related to other worm categories when necessary (geohelminth nematodes, trematodes or cestodes). We first present Onchocerca volvulus, mainly focusing on the aspects of this organism that seem relevant when it comes to ESPs: life cycle, manifestations of the sickness, immunosuppression, diagnosis and treatment. We then elaborate on the function and use of ESPs in these aspects.

Site-specific glycoproteomic characterization of ES-62: The major secreted product of the parasitic worm Acanthocheilonema viteae

ES-62 is the major secreted product of the parasitic filarial nematode Acanthocheilonema viteae and has potent anti-inflammatory activities as a consequence of posttranslational decoration by phosphorylcholine (PC). Previously, we showed that ES-62’s PC was attached to N-linked glycans, and using fast atom bombardment mass spectrometry, we characterized the structure of the glycans. However, it was unknown at this time which of ES-62’s four potential N-glycosylation sites carries the PC-modified glycans. In the present study, we now employ more advanced analytical tools—nano-flow liquid chromatography with high-definition electrospray mass spectrometry—to show that PC-modified glycans are found at all four potential N-glycosylation sites. Also, our earlier studies showed that up to two PC groups were detected per glycan, and we are now able to characterize N-glycans with up to five PC groups. The number per glycan varies in three of the four glycosylation sites, and in addition, for the first time, we have detected PC on the N-glycan chitobiose core in addition to terminal GlcNAc. Nevertheless, the majority of PC is detected on terminal GlcNAc, enabling it to interact with the cells and molecules of the immune system. Such expression may explain the potent immunomodulatory effects of a molecule that is considered to have significant therapeutic potential in the treatment of certain human allergic and autoimmune conditions.

Quantitative analysis of Northern bobwhite (Colinus virginianus) cytokines and TLR expression to eyeworm (Oxyspirura petrowi) and caecal worm (Aulonocephalus pennula) glycoproteins

Helminth parasites have been a popular research topic due to their global prevalence and adverse effects on livestock and game species. The Northern bobwhite (Colinus virginianus), a popular game bird in the USA, is one species subject to helminth infection and has been experiencing a decline of > 4% annually over recent decades. In the Rolling Plains Ecoregion of Texas, the eyeworm (Oxyspirura petrowi) and caecal worm (Aulonocephalus pennula) helminths are found to be highly prevalent in bobwhite. While there have been increasing studies on the prevalence, pathology, and phylogeny of the eyeworm and caecal worm, there is still a need to investigate the bobwhite immune response to infection. This study utilizes previously sequenced bobwhite cytokines and toll-like receptors to develop and optimize qPCR primers and measure gene expression in bobwhite intramuscularly challenged with eyeworm and caecal worm glycoproteins. For the challenge experiments, separate treatments of eyeworm and caecal worm glycoproteins were administered to bobwhite on day 1 and day 21. Measurements of primary and secondary immune responses were taken at day 7 and day 28, respectively. Using the successfully optimized qPCR primers for TLR7, IL1β, IL6, IFNα, IFNγ, IL10, and β-actin, the gene expression analysis from the challenge experiments revealed that there was a measurable immune reaction in bobwhite in response to the intramuscular challenge of eyeworm and caecal worm glycoproteins.

Anionic and zwitterionic moieties as widespread glycan modifications in non-vertebrates

Glycan structures in non-vertebrates are highly variable; it can be assumed that this is a product of evolution and speciation, not that it is just a random event. However, in animals and protists, there is a relatively limited repertoire of around ten monosaccharide building blocks, most of which are neutral in terms of charge. While two monosaccharide types in eukaryotes (hexuronic and sialic acids) are anionic, there are a number of organic or inorganic modifications of glycans such as sulphate, pyruvate, phosphate, phosphorylcholine, phosphoethanolamine and aminoethylphosphonate that also confer a 'charged' nature (either anionic or zwitterionic) to glycoconjugate structures. These alter the physicochemical properties of the glycans to which they are attached, change their ionisation when analysing them by mass spectrometry and result in different interactions with protein receptors. Here, we focus on N-glycans carrying anionic and zwitterionic modifications in protists and invertebrates, but make some reference to O-glycans, glycolipids and glycosaminoglycans which also contain such moieties. The conclusion is that 'charged' glycoconjugates are a widespread, but easily overlooked, feature of 'lower' organisms.

N-glycomic Complexity in Anatomical Simplicity: Caenorhabditis elegans as a Non-model Nematode?

Caenorhabditis elegans is a genetically well-studied model nematode or "worm"; however, its N-glycomic complexity is actually baffling and still not completely unraveled. Some features of its N-glycans are, to date, unique and include bisecting galactose and up to five fucose residues associated with the asparagine-linked Man2-3GlcNAc2 core; the substitutions include galactosylation of fucose, fucosylation of galactose and methylation of mannose or fucose residues as well as phosphorylcholine on antennal (non-reducing) N-acetylglucosamine. Only some of these modifications are shared with various other nematodes, while others have yet to be detected in any other species. Thus, C. elegans can be used as a model for some aspects of N-glycan function, but its glycome is far from identical to those of other organisms and is actually far from simple. Possibly the challenges of its native environment, which differ from those of parasitic or necromenic species, led to an anatomically simple worm possessing a complex glycome.

A comprehensive Caenorhabditis elegans N-glycan shotgun array

Here we present a Caenorhabditis elegans N-glycan shotgun array. This nematode serves as a model organism for many areas of biology including but not limited to tissue development, host-pathogen interactions, innate immunity, and genetics. Caenorhabditis elegans N-glycans contain structural motifs that are also found in other nematodes as well as trematodes and lepidopteran species. Glycan binding toxins that interact with C. elegans glycoconjugates also do so with some agriculturally relevant species, such as Haemonchus contortus, Ascaris suum, Oesophagostomum dentatum and Trichoplusia ni. This situation implies that protein-carbohydrate interactions seen with C. elegans glycans may also occur in other species with related glycan structures. Therefore, this array may be useful to study these relationships in other nematodes as well as trematode and insect species. The array contains 134 distinct glycomers spanning a wide range of C. elegans N-glycans including the subclasses high mannose, pauci mannose, high fucose, mammalian-like complex and phosphorylcholine substituted forms. The glycans presented on the array have been characterized by two-dimensional separation, ion trap mass spectrometry, and lectin affinity. High fucose glycans were well represented and contain many novel core structures found in C. elegans as well as other species. This array should serve as an investigative platform for carbohydrate binding proteins that interact with N-glycans of C. elegans and over a range of organisms that contain glycan motifs conserved with this nematode.

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.

Parasite excretory-secretory products and their effects on metabolic syndrome

Obesity, one of the main causes of metabolic syndrome (MetS), is an increasingly common health and economic problem worldwide, and one of the major risk factors for developing type 2 diabetes and cardiovascular disease. Chronic, low-grade inflammation is associated with MetS and obesity. A dominant type 2/anti-inflammatory response is required for metabolic homoeostasis within adipose tissue: during obesity, this response is replaced by infiltrating, inflammatory macrophages and T cells. Helminths and certain protozoan parasites are able to manipulate the host immune response towards a TH2 immune phenotype that is beneficial for their survival, and there is emerging data that there is an inverse correlation between the incidence of MetS and helminth infections, suggesting that, as with autoimmune and allergic diseases, helminths may play a protective role against MetS disease. Within this review, we will focus primarily on the excretory-secretory products that the parasites produce to modulate the immune system and discuss their potential use as therapeutics against MetS and its associated pathologies.

The redefinition of Helicobacter pylori lipopolysaccharide O-antigen and core-oligosaccharide domains

Helicobacter pylori lipopolysaccharide promotes chronic gastric colonisation through O-antigen host mimicry and resistance to mucosal antimicrobial peptides mediated primarily by modifications of the lipid A. The structural organisation of the core and O-antigen domains of H. pylori lipopolysaccharide remains unclear, as the O-antigen attachment site has still to be identified experimentally. Here, structural investigations of lipopolysaccharides purified from two wild-type strains and the O-antigen ligase mutant revealed that the H. pylori core-oligosaccharide domain is a short conserved hexasaccharide (Glc-Gal-DD-Hep-LD-Hep-LD-Hep-KDO) decorated with the O-antigen domain encompassing a conserved trisaccharide (-DD-Hep-Fuc-GlcNAc-) and variable glucan, heptan and Lewis antigens. Furthermore, the putative heptosyltransferase HP1284 was found to be required for the transfer of the third heptose residue to the core-oligosaccharide. Interestingly, mutation of HP1284 did not affect the ligation of the O-antigen and resulted in the attachment of the O-antigen onto an incomplete core-oligosaccharide missing the third heptose and the adjoining Glc-Gal residues. Mutants deficient in either HP1284 or O-antigen ligase displayed a moderate increase in susceptibility to polymyxin B but were unable to colonise the mouse gastric mucosa. Finally, mapping mutagenesis and colonisation data of previous studies onto the redefined organisation of H. pylori lipopolysaccharide revealed that only the conserved motifs were essential for colonisation. In conclusion, H. pylori lipopolysaccharide is missing the canonical inner and outer core organisation. Instead it displays a short core and a longer O-antigen encompassing residues previously assigned as the outer core domain. The redefinition of H. pylori lipopolysaccharide domains warrants future studies to dissect the role of each domain in host-pathogen interactions. Also enzymes involved in the assembly of the conserved core structure, such as HP1284, could be attractive targets for the design of new therapeutic agents for managing persistent H. pylori infection causing peptic ulcers and gastric cancer.

Parasite molecules and host responses in cystic echinococcosis

Cystic echinococcosis is the infection by the larvae of cestode parasites belonging to the Echinococcus granulosus sensu lato species complex. Local host responses are strikingly subdued in relation to the size and persistence of these larvae, which develop within mammalian organs as 'hydatid cysts' measuring up to tens of cm in diameter. In a context in which helminth-derived immune-suppressive, as well as Th2-inducing, molecules garner much interest, knowledge on the interactions between E. granulosus molecules and the immune system lags behind. Here, we discuss what is known and what are the open questions on E. granulosus molecules and structures interacting with the innate and adaptive immune systems, potentially or in demonstrated form. We attempt a global biological approach on molecules that have been given consideration primarily as protective (Eg95) or diagnostic antigens (antigen B, antigen 5). We integrate glycobiological information, which traverses the discussions on antigen 5, the mucin-based protective laminated layer and immunologically active preparations from protoscoleces. We also highlight some less well-known molecules that appear as promising candidates to possess immune-regulatory activities. Finally, we point out gaps in the molecular-level knowledge of this infectious agent that hinder our understanding of its immunology.

Characterization of the N-glycans of female Angiostrongylus cantonensis worms

Glycoconjugates play a crucial role in the host-parasite relationships of helminthic infections, including angiostrongyliasis. It has previously been shown that the antigenicity of proteins from female Angiostrongylus cantonensis worms may depend on their associated glycan moieties. Here, an N-glycan profile of A. cantonensis is reported. A total soluble extract (TE) was prepared from female A. cantonensis worms and was tested by western blot before and after glycan oxidation or N- and O-glycosidase treatment. The importance of N-glycans for the immunogenicity of A. cantonensis was demonstrated when deglycosylation of the TE with PNGase F completely abrogated IgG recognition. The TE was also fractionated using various lectin columns [Ulex europaeus (UEA), concanavalin A (Con A), Arachis hypogaea (PNA), Triticum vulgaris (WGA) and Lycopersicon esculentum (LEA)], and then each fraction was digested with PNGase F. Released N-glycans were analyzed with matrix-assisted laser desorption ionization (MALDI)-time-of-flight (TOF)-mass spectrometry (MS) and MALDI-TOF/TOF-MS/MS. Complex-type, high mannose, and truncated glycan structures were identified in all five fractions. Sequential MALDI-TOF-TOF analysis of the major MS peaks identified complex-type structures, with a α1-6 fucosylated core and truncated antennas. Glycoproteins in the TE were labeled with BodipyAF558-SE dye for a lectin microarray analysis. Fluorescent images were analyzed with ProScanArray imaging software followed by statistical analysis. A total of 29 lectins showed positive binding to the TE. Of these, Bandeiraea simplicifolia (BS-I), PNA, and Wisteria floribunda (WFA), which recognize galactose (Gal) and N-acetylgalactosamine (GalNAc), exhibited high affinity binding. Taken together, our findings demonstrate that female A. cantonensis worms have characteristic helminth N-glycans.

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.

Sweet secrets of a therapeutic worm: mass-spectrometric N-glycomic analysis of Trichuris suis

Trichuris suis, a nematode parasite of pigs, has attracted attention as its eggs have been administered to human patients as a potential therapy for inflammatory diseases. The immunomodulatory factors remain molecularly uncharacterised, but in vitro studies suggest that glycans on the parasite's excretory/secretory proteins may play a role. Using an off-line LC-MS approach in combination with chemical and enzymatic treatments, we have examined the N-linked oligosaccharides of T. suis. In addition to the paucimannosidic and oligomannosidic N-glycans typical of many invertebrates, a number of glycans carry N,N'-diacetyllactosamine (LacdiNAc) modified by fucose and/or phosphorylcholine. Such antennal epitopes are similar to ones previously associated with immunomodulation by helminths; here we propose phosphorylcholine modifications predominantly of terminal N-acetylgalactosamine but also of subterminal α1,3-fucosylated N-acetylglucosamine. Exact knowledge of the glycome of T. suis will facilitate more targeted studies on glycan receptors in the host as well as the engineering of cell lines to produce correctly glycosylated recombinant forms of candidate proteins for future studies on immunomodulation.

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.

The highly conserved domain of unknown function 1792 has a distinct glycosyltransferase fold

More than 33,000 glycosyltransferases have been identified. Structural studies, however, have only revealed two distinct glycosyltransferase (GT) folds, GT-A and GT-B. Here we report a 1.34-Å resolution X-ray crystallographic structure of a previously uncharacterized 'domain of unknown function' 1792 (DUF1792) and show that the domain adopts a new fold and is required for glycosylation of a family of serine-rich repeat streptococcal adhesins. Biochemical studies reveal that the domain is a glucosyltransferase, and it catalyses the transfer of glucose to the branch point of the hexasaccharide O-linked to the serine-rich repeat of the bacterial adhesin, Fap1 of Streptococcus parasanguinis. DUF1792 homologues from both Gram-positive and Gram-negative bacteria also exhibit the activity. Thus, DUF1792 represents a new family of glycosyltransferases; therefore, we designate it as a GT-D glycosyltransferase fold. As the domain is highly conserved in bacteria and not found in eukaryotes, it can be explored as a new antibacterial target.

ES-62, a therapeutic anti-inflammatory agent evolved by the filarial nematode Acanthocheilonema viteae

Filarial nematodes cause long-term infections in hundreds of millions of people. A significant proportion of those affected develop a number of debilitating health problems but, remarkably, such infections are often unnoticed for many years. It is well known that parasitic worms modulate, yet do not completely inhibit, host immunological pathways, promoting their survival by limiting effective immune mechanisms. Such immunoregulation largely depends on molecules released by the worms, termed excretory-secretory products (ES). One of these products is the molecule ES-62, which is actively secreted by the rodent filarial nematode Acanthocheilonema viteae. ES-62 has been shown to exert anti-inflammatory actions thorough its phosphorylcholine (PC)-containing moiety on a variety of cells of the immune system, affecting intracellular signalling pathways associated with antigen receptor- and TLR-dependent responses. We summarise here how ES-62 modulates key signal transduction elements and how such immunomodulation confers protection to mice subjected to certain experimental models of inflammatory disease. Finally, we discuss recent results showing that it is possible to synthetise small molecule analogues (SMAs) that mimic the anti-inflammatory properties of ES-62, opening an exciting new drug development field in translational medicine.

Complicated N-linked glycans in simple organisms

Although countless genomes have now been sequenced, the glycomes of the vast majority of eukaryotes still present a series of unmapped frontiers. However, strides are being made in a few groups of invertebrate and unicellular organisms as regards their N-glycans and N-glycosylation pathways. Thereby, the traditional classification of glycan structures inevitably approaches its boundaries. Indeed, the glycomes of these organisms are rich in surprises, including a multitude of modifications of the core regions of N-glycans and unusual antennae. From the actually rather limited glycomic information we have, it is nevertheless obvious that the biotechnological, developmental and immunological relevance of these modifications, especially in insect cell lines, model organisms and parasites means that deciphering unusual glycomes is of more than just academic interest.

Stage-specific expression and antigenicity of glycoprotein glycans isolated from the human liver fluke, Opisthorchis viverrini

Infection by Opisthorchis viverrini (liver fluke) is a major public health problem in southeastern Asia, resulting in hepatobiliary disease and cholangiocarcinoma. Fluke surface glycoconjugates are prominently presented to the host, thereby constituting a crucial immunological interface that can determine the parasite's success in establishing infection. Therefore, N- and O-linked glycoprotein glycan profiles of the infective metacercarial stage and of the mature adult were investigated by nanospray ionisation-linear ion trap mass spectrometry (NSI-MS(n)). Glycan immunogenicity was investigated by immunoblotting with serum from infected humans. Metacercariae and adult parasites exhibit similar glycan diversity, although the prevalence of individual glycans and glycan classes varies by stage. The N-glycans of the metacercaria are mostly high mannose and monofucosylated, truncated-type oligosaccharides (62.7%), with the remainder processed to complex and hybrid type glycans (37.3%). The N-linked glycan profile of the adult is also dominated by high mannose and monofucosylated, truncated-type oligosaccharides (80.0%), with a smaller contribution from complex and hybrid type glycans (20.0%). At both stages, complex and hybrid type glycans are detected as mono-, bi-, tri-, or tetra-antennary structures. In metacercariae and adults, O-linked glycans are detected as mono- to pentasaccharides. The mucin type core 1 structure, Galβ1-3GalNAc, predominates in both stages but is less prevalent in the adult than in the metacercaria. Immunogenic recognition of liver fluke glycoproteins is reduced after deglycosylation but infected human serum was unable to recognise glycans released from peptides. Therefore, the most potent liver fluke antigenic epitopes are mixed determinants, comprised of glycan and polypeptide elements.

How helminths use excretory secretory fractions to modulate dendritic cells

It is well known that helminth parasites have immunomodulatory effects on their hosts. They characteristically cause a skew toward T_H2 immunity, stimulate Treg cells while simultaneously inhibiting T_H1 and T_H17 responses. Additionally, they induce eosinophilia and extensive IgE release. The exact mechanism of how the worms achieve this effect have yet to be fully elucidated; however, parasite-derived secretions and their interaction with antigen presenting cells have been centrally implicated. Herein, we will review the effects of helminth excretory-secretory fractions on dendritic cells and discuss how this interaction is crucial in shaping the host response.

Galactosylated fucose epitopes in nematodes: increased expression in a Caenorhabditis mutant associated with altered lectin sensitivity and occurrence in parasitic species

The modification of α1,6-linked fucose residues attached to the proximal (reducing-terminal) core N-acetylglucosamine residue of N-glycans by β1,4-linked galactose ("GalFuc" epitope) is a feature of a number of invertebrate species including the model nematode Caenorhabditis elegans. A pre-requisite for both core α1,6-fucosylation and β1,4-galactosylation is the presence of a nonreducing terminal N-acetylglucosamine; however, this residue is normally absent from the final glycan structure in invertebrates due to the action of specific hexosaminidases. Previously, we have identified two hexosaminidases (HEX-2 and HEX-3) in C. elegans, which process N-glycans. In the present study, we have prepared a hex-2;hex-3 double mutant, which possesses a radically altered N-glycomic profile. Whereas in the double mutant core α1,3-fucosylation of the proximal N-acetylglucosamine was abolished, the degree of galactosylation of core α1,6-fucose increased, and a novel Galα1,2Fucα1,3 moiety attached to the distal core N-acetylglucosamine residue was detected. Both galactosylated fucose moieties were also found in two parasitic nematodes, Ascaris suum and Oesophagostomum dentatum. As core modifications of N-glycans are known targets for fungal nematotoxic lectins, the sensitivity of the C. elegans double hexosaminidase mutant was assessed. Although this mutant displayed hypersensitivity to the GalFuc-binding lectin CGL2 and the N-acetylglucosamine-binding lectin XCL, the mutant was resistant to CCL2, which binds core α1,3-fucose. Thus, the use of C. elegans mutants aids the identification of novel N-glycan modifications and the definition of in vivo specificities of nematotoxic lectins with potential as anthelmintic agents.

Mass spectrometric analysis of the immunodominant glycan epitope of Echinococcus granulosus antigen Ag5

In previous work we showed that Ag5, a major diagnostic antigen from the metacestode of Echinococcus granulosus, possesses a dominant sugar epitope that upon removal results in abolition of most of the antigen immunoreactivity with patient sera. Analysis of this glycan modification has now been performed by western blotting and mass spectrometry. Reactivity to both a specific monoclonal antibody (TEPC15) and human C-reactive protein as well as the presence of a modification of 165 mass units, as detected by mass spectrometry of both glycopeptides and released N-glycans, indicated that the immunodominant sugar epitope of the Ag5 38 kDa subunit is a biantennary structure modified by phosphorylcholine. We believe this is the first time that such a modification has been proven in cestodes and provides the structural basis for understanding the antigenicity of this major E. granulosus component.

Receptor usage by the Acanthocheilonema viteae-derived immunomodulator, ES-62

ES-62 is an immunomodulatory phosphorylcholine (PC)-containing glycoprotein secreted by the rodent filarial nematode Acanthocheilonema viteae. Previously, the use of knockout mice has revealed the effects of ES-62 on macrophages and dendritic cells to be dependent on TLR4. However, it is possible that ES-62 may interact with additional proteins on the surfaces of target cells and hence that cells may vary with respect to receptor usage. In this study, we identified by molecular weight, proteins that interact with ES-62 and found differences amongst the immune system cells studied. Thus, whereas lymphocytes appear to have two major interacting proteins of ∼135 and ∼82 kDa, U937 monocytes only contain an ES-62-binding protein of the latter molecular weight. Binding to the proteins on B cells and U937 cells was blocked by PC, suggesting a critical role for this ES-62 moiety in facilitating interaction. Finally, ES-62 binding is followed by internalization in both macrophages and B cells but only in the former was absence of TLR4 found to block internalization. These findings are consistent with differences in receptor usage by ES-62 amongst different cell-types.

Worms to the rescue: can worm glycans protect from autoimmune diseases?

Autoimmune and autoinflammatory diseases represent a significant health burden, especially in Western societies. For the majority of these diseases, no cure exists. Recently, research on parasitic worms (helminths) has demonstrated great potential for whole worms, their eggs or their excretory/secretory proteins in down-regulating inflammatory responses both in vitro and in vivo, in various disease models and, in some cases, even in clinical trials. The worms are thought to induce Th2 and regulatory T cells, interfere with Toll-like receptor (TLR) signaling and to down-regulate Th17 and Th1 responses. The molecular mechanisms underlying the worms' ability to modulate the host immune response are not well understood, and many hypotheses have been proposed to explain the observed immune modulation. Increasing evidence suggests that carbohydrate structures (glycans), for example, phosphorylcholine-modified glycans or Galbeta1-4(Fucalpha1-3)GlcNAc- (Lewis X, Le(X)) containing glycans, expressed by the worms contribute to these modulating properties by their interaction with antigen presenting cells. Helminths express a broad variety of protein- and lipid-linked glycans on their surface and on secretory products. These glycans differ in amount and composition and several of these structures are species specific. However, worms also express glycan antigens that are found in a wide variety of different species. Some of these "common" worm glycans are particularly interesting with regard to regulating host responses, because they have the potential to interact with C-type lectins on dendritic cells and thereby may interfere with T-cell polarization. Helminths and helminth-derived molecules form a novel and promising group of therapeutics for autoinflammatory diseases. However, much has to be learned about the molecular mechanisms behind the helminth-mediated antiinflammatory properties. This review will describe some of the emerging evidence in selected disease areas as well as discuss the putative role of glycans in helminth-mediated immunosuppression.

Mass spectrometric analysis of mutant mice

Mass spectrometry (MS) has proven to be the preeminent tool for the rapid, high-sensitivity analysis of the primary structure of glycans derived from diverse biological sources including cells, fluids, secretions, tissues, and organs. These analyses are anchored by matrix-assisted laser desorption ionization time of flight (MALDI-TOF) analysis of permethylated derivatives of glycan pools released from the samples, to produce glycomic mass fingerprints. The application of complimentary techniques, such as chemical and enzymatic digestions, GC-MS linkage analysis, and tandem mass spectrometry (MS/MS) utilizing both electrospray (ES) and MALDI-TOF/TOF, together with bioinformatic tools allows the elucidation of incrementally more detailed structural information from the sample(s) of interest. The mouse as a model organism offers many advantages in the study of human biology, health, and disease; it is a mammal, shares 99% genetic homology with humans and its genome supports targeted mutagenesis in specific genes to produce knockouts efficiently and precisely. Glycomic analyses of tissues and organs from mice genetically deficient in one or more glycosylation gene and comparison with data collected from wild-type samples enables the facile identification of changes and perturbations within the glycome. The Consortium for Functional Glycomics (CFG) has been applying such MS-based glycomic analyses to a range of murine tissues from both wild-type and glycosylation-knockout mice in order to provide a repository of structural data for the glycobiology community. In this chapter, we describe in detail the methodologies used to prepare, derivatize, purify, and analyze glycan pools from mouse organs and tissues by MS. We also present a summary of data produced from the CFG systematic structural analysis of wild-type and knockout mouse tissues, together with a detailed example of a glycomic analysis of the Mgat4a knockout mouse.

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.

Glycan gimmickry by parasitic helminths: a strategy for modulating the host immune response?

Parasitic helminths (worms) co-evolved with vertebrate immune systems to enable long-term survival of worms in infected hosts. Among their survival strategies, worms use their glycans within glycoproteins and glycolipids, which are abundant on helminth surfaces and in their excretory/ secretory products, to regulate and suppress host immune responses. Many helminths express unusual and antigenic (nonhost-like) glycans, including those containing polyfucose, tyvelose, terminal GalNAc, phosphorylcholine, methyl groups, and sugars in unusual linkages. In addition, some glycan antigens are expressed that share structural features with those in their intermediate and vertebrate hosts (host-like glycans), including Le(X) (Galbeta1-4[Fucalpha1-3]GlcNAc-), LDNF (GalNAcbeta1-4[Fucalpha1-3]GlcNAc-), LDN (GalNAcbeta1-4GlcNAc-), and Tn (GalNAcalpha1-O-Thr/Ser) antigens. The expression of host-like glycan determinants is remarkable and suggests that helminths may gain advantages by synthesizing such glycans. The expression of host-like glycans by parasites previously led to the concept of "molecular mimicry," in which molecules are either derived from the pathogen or acquired from the host to evade recognition by the host immune system. However, recent discoveries into the potential of host glycan-binding proteins (GBPs), such as C-type lectin receptors and galectins, to functionally interact with various host-like helminth glycans provide new insights. Host GBPs through their interactions with worm-derived glycans participate in shaping innate and adaptive immune responses upon infection. We thus propose an alternative concept termed "glycan gimmickry," which is defined as an active strategy of parasites to use their glycans to target GBPs within the host to promote their survival.

Identification of a novel mammalian post-translational modification, phosphocholine, on placental secretory polypeptides

Placental neurokinin B appears to be post-translationally modified by phosphocholine (PC) attached to the aspartyl side chain at residue 4 of the mature peptide. Corticotrophin releasing factor (CRF) was found to be expressed by the rat placenta with the main secreted forms being phosphocholinated proCRF+/- one or two polysaccharide moieties. A combination of high-pressure liquid chromatography (HPLC) and two-site immunometric analysis suggested that PC was also attached to the placental precursors of adrenocorticotrophin, hemokinin, activin and follistatin. However, the fully processed forms of rat placental activin and CRF were free of PC. Formerly, the parasitic filarial nematodes have used PC as a post-translational modification, attached via the polysaccharide moiety of certain secretory glycoproteins to attenuate the host immune system allowing parasite survival, but it is the PC group itself which endows the carrier with the biological activity. The fact that treatment of proCRF peptides with phospholipase C but not endoglycosidase destroyed PC immunoreactivity suggested a simpler mode of attachment of PC to placental peptides than that used by nematodes. Thus, it is possible that by analogy the placenta uses its secreted phosphocholinated hormones to modulate the mother's immune system and help protect the placenta from rejection.

Filarial nematode secreted product ES-62 is an anti-inflammatory agent: therapeutic potential of small molecule derivatives and ES-62 peptide mimetics

1. The 'hygiene hypothesis' postulates that the recent increased incidence of allergic or autoimmune diseases (e.g. asthma, type I diabetes) in the West reflects an absence of appropriate priming of the immune response by infectious agents, such as parasitic worms, during childhood. 2. Consistent with this, it has long been recognized that several autoimmune disorders, such as rheumatoid arthritis (RA), a T helper (Th) 1-mediated autoimmune disease characterized by excess production of pro-inflammatory cytokines, such as tumour necrosis factor-alpha, exhibit reduced incidence and severity in geographical regions with high parasite load, suggesting that environmental factors may subtly alter disease progression. 3. Infection with worms also appears to suppress Th2-biased inflammatory disorders, such as asthma, because there also appears to be an inverse correlation between parasite load and atopy. This is perhaps more surprising, given that helminths often induce strong Th2-type immune responses characterized by release of specific cytokines, such as interleukin (IL)-4, IL-5 and IL-13. 4. Therefore, these findings suggest that the co-evolution of helminths with hosts, which has resulted in the ability of worms to modulate inflammatory responses in order to promote parasite survival, may also have generated a predisposition for the host to develop autoimmunity and allergy in the absence of infection. 5. The mechanisms underlying such immunomodulation are not clear, but appear to involve the release of parasite-derived molecules that allow the worms to modulate or evade the host immune response by a number of mechanisms, including skewing of cytokine responses and the induction of T regulatory cells. 6. In the present review we discuss the properties of one such filarial nematode-derived immunomodulatory molecule, namely ES-62, its anti-inflammatory action and the therapeutic potential of small molecule derivatives and peptides that mimic its action.

Antibodies elicited by the bovine lungworm, Dictyocaulus viviparus, cross-react with platelet-activating factor

Parasite N-glycans may play an important role in helminth infections. As antibodies from Dictyocaulus viviparus-infected calves strongly react with N-glycans, we investigated the characteristics of the major immunodominant glycoprotein (GP300) of this parasite. Probing of worm extracts with various lectins demonstrated unique binding of GP300 to wheat germ agglutinin. Analysis of lectin-purified GP300 revealed that the glycan was substituted with phosphorylcholine and reacted with the phosphorylcholine-specific antibody TEPC-15. Competitive enzyme-linked immunosorbent assay with GP300-coated plates and GP300-specific immunoglobulin G (IgG) in conjunction with free phosphorylcholine or TEPC-15 demonstrated that antibodies from infected calves recognized phosphorylcholine on GP300. Additional assays showed that these antibodies cross-reacted with the phosphorylcholine moiety present on platelet-activating factor (PAF; 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine), a proinflammatory mediator of the host. Heavily infected calves contained high levels of serum GP300-specific IgG1 but low levels of IgA and IgG2 and showed a reduced influx of eosinophils in the lungs, all consistent with a neutralization of PAF activity. In conclusion, we demonstrated that D. viviparus infection elicits GP300-specific antibodies that cross-react with PAF and may neutralize PAF function, thus limiting the development of a protective response as well as parasite-induced host pathology.

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.

O-methylated glycans from Toxocara are specific targets for antibody binding in human and animal infections

The parasitic helminth Toxocara canis is a widely distributed nematode of mammals. Larval parasites, which infect a wide range of hosts including mice and humans, export glycosylated macromolecules bearing novel methylated oligosaccharide structures, similar to the mammalian blood group antigen H but bearing one or two O-methylated substitutions on the terminal fucose and subterminal galactose residues. We have studied the reactivity of synthetic forms of these glycans to parasite-specific antibodies and mammalian immune system lectins. Murine antibodies, generated to T. canis infection, predominantly recognise the mono-O-methylated form with the beta-configuration of the GalNAc residue (MoMbeta), and antibodies are entirely IgM isotype. The mAb Tcn-2 reproduces this pattern, and shows little reactivity to either the alpha isomer (MoMalpha) or the di-O-methylated form (DiM). Antibodies generated to helminth infections other than T. canis were unreactive with the glycans, except antibodies to other members of the Toxocara genus. Hence, the carbohydrate structures represent immunogenic, genus-specific antigens. Antibodies from human toxocariasis patients are reactive with the same sugars, although preferentially towards DiM. Sera from unrelated helminth infections do not react, confirming the status of these structures as Toxocara-specific glycans. The human dendritic cell lectin, DC-SIGN, was found to bind both Toxocara excretory/secretory products and mammalian blood group antigen H3. However, DC-SIGN did not bind the synthetic glycans, indicating additional non-methylated carbohydrates may also play a role in the interaction between T. canis and its host.

A deletion in the golgi alpha-mannosidase II gene of Caenorhabditis elegans results in unexpected non-wild-type N-glycan structures

The processing of N-linked oligosaccharides by alpha-mannosidases in the endoplasmic reticulum and Golgi is a process conserved in plants and animals. After the transfer of a GlcNAc residue to Asn-bound Man(5)GlcNAc(2) by N-acetylglucosaminyltransferase I, an alpha-mannosidase (EC 3.2.1.114) removes one alpha1,3-linked and one alpha1,6-linked mannose residue. In this study, we have identified the relevant alpha-mannosidase II gene (aman-2; F58H1.1) from Caenorhabditis elegans and have detected its activity in both native and recombinant forms. For comparative studies, the two other cDNAs encoding class II mannosidases aman-1 (F55D10.1) and aman-3 (F48C1.1) were cloned; the corresponding enzymes are, respectively, a putative lysosomal alpha-mannosidase and a Co(II)-activated alpha-mannosidase. The analysis of the N-glycan structures of an aman-2 mutant strain demonstrates that the absence of alpha-mannosidase II activity results in a shift to structures not seen in wild-type worms (e.g. N-glycans with the composition Hex(5-7)HexNAc(2-3)Fuc(2)Me) and an accumulation of hybrid oligosaccharides. Paucimannosidic glycans are almost absent from aman-2 worms, indicative also of a general lack of alpha-mannosidase III activity. We hypothesize that there is a tremendous flexibility in the glycosylation pathway of C. elegans that does not impinge, under standard laboratory conditions, on the viability of worms with glycotypes very unlike the wild-type pattern.

Protein glycosylation in Parelaphostrongylus tenuis--first description of the Galalpha1-3Gal sequence in a nematode

The white-tailed deer is the definitive host of the parasitic nematode Parelaphostrongylus tenuis. This parasite also infects a wide variety of domesticated livestock, causing a debilitating neurologic disease. Glycoconjugates are becoming increasingly implicated in nematode strategies to maintain persistent infections in immunologically competent hosts. In this study, we have carried out detailed mass spectrometric analysis together with classical biochemical techniques, including western blotting and immunohistochemical staining with anticarbohydrate monoclonal antibodies and have shown that P. tenuis contains complex-type N-glycans with the antennae capped with Galalpha1-3Galbeta1-4GlcNAc sequence. By mimicking a vertebrate glycan, Galalpha1-3Gal may aid the parasite in evading immunological detection by the host. This is the first report of the Galalpha1-3Gal sequence in a nematode.

Glycomic profiling of cells and tissues by mass spectrometry: fingerprinting and sequencing methodologies

Over the past decade, rapid, high-sensitivity mass spectrometric strat-egies have been developed and optimized for screening for the types of N- and O-glycans present in a diverse range of biological material, including secretions, cell lines, tissues, and organs. These glycomic strategies are based on matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass fingerprinting of permethylated derivatives, combined with electrospray (ES) or MALDI tandem mass spectrometry (MS/MS) sequencing and gas chromatography (GC)-MS linkage analysis, complemented by chemical and enzymatic degradations. Protocols for these methods are described in the first part of this chapter. Glycomic experiments yield large volumes of MS data, and interpretation of the resulting spectra remains a time-consuming bottleneck in the process. In the second part of this chapter, we describe the use and operation of a mass spectral viewer program capable of displaying and automatically labeling spectra arising from MALDI fingerprinting of N-glycans.

Lack of immunological cross-reactivity between parasite-derived and recombinant forms of ES-62, a secreted protein of Acanthocheilonema viteae

The longevity of filarial nematodes is dependent on secreted immunomodulatory products. Previous investigation of one such product, ES-62, has suggested a critical role for post-translationally attached phosphorylcholine (PC) moieties. In order to further investigate this, ES-62 lacking PC was produced, using the Pichia pastoris recombinant gene expression system. Unlike parasite-derived ES-62, which is tetrameric the recombinant material was found to consist of a mixture of apparently stable tetramers, dimers and monomers. Nevertheless, the recombinant protein was considered to be an adequate PC-free ES-62 as it was recognized by existing antisera against the parasite-derived protein. However, subsequent to this, recognition of parasite-derived ES-62 by antibodies produced against the recombinant protein was found to be absent. In an attempt to explain this, recombinant ES-62 was subjected to structural analysis and was found to (i) contain 3 changes in amino acid composition; (ii) demonstrate significant alterations in glycosylation; (iii) show major differences in protein secondary structure. The effects of these alterations in relation to the observed change in immunogenicity were investigated and are discussed. The data presented clearly show that recognition by existing antibodies is insufficient proof that recombinant proteins can be used to mimic parasite-derived material in studies on nematode immunology and vaccination.

The immunogenicity of Echinococcus granulosus antigen 5 is determined by its post-translational modifications

Since its early introduction as a marker for the immunodiagnosis of hydatid disease, antigen 5 (Ag5) has been regarded as one of the more relevant antigens of Echinococcus granulosus, and it is still widely used in different confirmation techniques. In this work we prepared 2 recombinant forms of the antigen, namely, rAg5 (corresponding to the unprocessed polypeptide chain of the antigen) and rAg5-38s (corresponding to its 38 kDa subunit). Their antigenicities were compared to that of the native antigen using a human serum collection. There was a major drop in the reactivity of the sera, particularly against rAg5-38s, which was confirmed by analysis of the cross-reactivity of 2 panels of monoclonal antibodies specific for rAg5-38s and the native antigen. Using the chemically deglycosylated native antigen, we demonstrated that the reduced antigenicity of the recombinants is due to the loss of the sugar determinants, and not to their misfolding. Inhibition experiments using phosphorylcholine confirmed that this moiety also contributes to the reactivity of the antigen, but to a much lesser extent. The presence of immunodominant highly cross-reactive glycan moieties in the Ag5 molecule may involve a parasite evasion mechanism.

Searching new targets for anthelminthic strategies: Interference with glycosphingolipid biosynthesis and phosphorylcholine metabolism affects development of Caenorhabditis elegans

Nematode infections are amongst the most abundant diseases of man and animals. They are characterised by a low mortality but high morbidity, thus reflecting the adaptation of these parasites to their hosts. Resistance as well as severe side-effects and efficacies restricted to distinct larval stages or parasites of the anthelmithics used at present require the urgent development of new and more nematode-specific drugs, targeting enzymes of parasite restricted biosynthetic routes. Caenorhabditis elegans has been found to be a good model system for parasitic nematodes, drug screening and developmental studies. Structural analyses have revealed nematode-specific glycosphingolipid structures of the arthro-series, carrying in part, phosphorylcholine substituents. These biomolecules appear to play important roles in nematode development, fertility and survival within the host and are, therefore, good target-candidates for the development of new anthelminthic strategies. Here we show that RNAi experiments targeting enzymes of glycosphingolipid biosynthesis or choline metabolism result, in part, in a drastic reduction of fertility. We further tested various chemical inhibitors of these pathways and found significant effects on the development of the worms, resulting in developmental arrest, sterility and, in part, lethality. Such inhibitors can, therefore, help to define new classes of anthelminthics.

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.

Structure and synthesis of nematode phosphorylcholine-containing glycoconjugates

Infection with filarial nematodes produces a chronic, long-lasting illness with adult worms able to survive within human hosts for up to 15 years. A contributor to the longevity of these parasites is the presence of phosphorylcholine (PC) on components of the worms' molecular secretions (ES). PC on ES modulates host immune responses towards an anti-inflammatory phenotype thereby generating an environment favourable for parasite survival. PC is attached to nematode ES via a covalent association with carbohydrate, which, although well-documented in bacteria and fungi, is absent from humans, making it an ideal target for the development of novel drugs. In order to produce such drugs it is first necessary to understand the structure and synthesis of nematode PC-glycans. ES-62 is the major PC-ES-product ofAcanthocheilonema viteaeand is a homologue of PC-ES found in human filarial nematodes. We have studied the structure and biosynthesis of PC-glycans of ES-62 by a combination of pulse-chase experiments, experiments involving the use of inhibitors of each of intracellular trafficking, oligosaccharide processing and phospholipid biosynthesis and various forms of mass spectrometry. Our indications indicate that PC is transferred in the lumen of the medial Golgi to an N-type glycan consisting of a trimannosyl core with or without core fucosylation bearing between 1 and 4 N-acetyl glucosamine residues. The structure of the PC-N-glycans found in ES-62 appears to be conserved amongst filarial nematodes in that it has additionally been identified inOnchocerca volvulusandO. gibsoni. Also, similar structures have been found in non-filarial parasitic nematodes and in the free-living nematodeCaenorhabditis elegans. Finally, PC has also been recently found attached to the carbohydrate moieties of nematode glycosphingolipids and the structure of these will also be considered.

ES-62, a filarial nematode-derived immunomodulator with anti-inflammatory potential

Arthropod-transmitted filarial nematodes can survive for in excess of a decade via modulation of the vertebrate host immune system. Although human infection can result in very severe pathology, most infected individuals show remarkably little evidence of this. Analysis of the anti-nematode response indicates that apparently pathology-free individuals have an anti-inflammatory immunological phenotype and it has been suggested that this favours maintenance of host good health. It is considered that parasite-derived molecular secretions contribute to the anti-inflammatory phenotype and we have thus investigated the properties of a filarial nematode glycoprotein secreted in some abundance, ES-62. This molecule shows a plethora of immunomodulatory activities that can be classified as anti-inflammatory. It has been observed in a number of studies that several autoimmune disorders including rheumatoid arthritis (RA) exhibit reduced incidence and severity in geographic regions in which filarial nematodes are transmitted to humans. Furthermore, it has been speculated that these two observations are linked although molecular explanations for such an association have not been forthcoming. Although the aetiology of RA remains unknown a majority of data are consistent with it being mediated via excess pro-inflammatory cytokine production. Given that ES-62 is anti-inflammatory, we hypothesised that it might be able to counter the pathology associated with diseases like RA. Indeed, we found that exposure to ES-62 prevented initiation of collagen-induced arthritis (CIA) in a murine model and also suppressed progression of established disease. Ex vivo analyses demonstrated that these effects correlated with inhibition of TNF-alpha production and inhibition of collagen-specific TH-1 responses. The nematode product was also able to suppress pro-inflammatory cytokine release in vitro in synovial cells derived from RA patients. ES-62 thus constitutes a pathogen-derived immunomodulator with significant therapeutic potential.

Biosynthesis in vitro of Caenorhabditis elegans phosphorylcholine oligosaccharides

The biosynthesis in vitro of phosphorylcholine oligosaccharides in Caenorhabditis elegans has been investigated. Here we show that extracts of C. elegans' microsomes transfer phosphorylcholine from L-alpha-dipalmitoyl phosphatidylcholine to hybrid and complex type N-linked oligosaccharides containing mannose residues disubstituted with N-acetylglucosamine. The reaction products are consistent with structures reported for C. elegans as well those found in the filarial nematodes Acanthocheilonema viteae, Onchocerca volvulus, and Brugia malayi, strongly supporting the concept that the phosphorylcholine oligosaccharide biosynthetic enzymes are conserved in this group of organisms. Because it is thought that phosphorylcholine substitution of oligosaccharides modulates host immune response in filarial infections, this in vitro system may help in gaining an understanding of the basis for this response.

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

Carbohydrates substituted with phosphocholine (PC) and phosphoethanolamine (PE) were released from zwitterionic glycosphingolipids of the pig parasitic nematode Ascaris suum by treatment with endoglycoceramidase. Individual glycans were obtained by HPLC on porous graphitic carbon followed by high-pH anion-exchange chromatography. In addition to the known pentasaccharides Gal alpha 3GalNAc beta 4[PC6]GlcNAc beta 3Man beta 4Glc and Gal alpha 3GalNAc beta 4[PC6]GlcNAc beta 3[PE6]Man beta 4Glc, the corresponding tri- and tetra-saccharides, as well as components with elongated structures, could be identified by matrix-assisted laser-desorption ionization-time-of-flight MS, methylation analysis, 1H- and 13C-NMR spectroscopy, exoglycosidase cleavage and electrospray ionization ion-trap MS. The extended components comprised novel structural motifs such as di-substituted alpha-galactose carrying two beta-linked galactosyl residues, which were found to bear, in part, further fucose, galactose, N -acetylgalactosamine and/or N -acetylglucosamine moieties. Furthermore, additional fucosylation of the PC-substituted N -acetylglucosamine and a non-terminal fucosyl motif were detected. In conclusion, this study contributes significant new information on the glycome of nematodes.

The fine structure of Caenorhabditis elegans N-glycans

We report the fine structure of a nearly contiguous series of N-glycans from the soil nematode Caenorhabditis elegans. Five major classes are revealed including high mannose, mammalian-type complex, hybrid, fuco-pausimannosidic (five mannose residues or fewer substituted with fucose), and phosphocholine oligosaccharides. The high mannose, complex, and hybrid N-glycan series show a high degree of conservation with the mammalian biosynthetic pathways. The fuco-pausimannosidic glycans contain a novel terminal fucose substitution of mannose. The phosphocholine oligosaccharides are high mannose type and are multiply substituted with phosphocholine. Although phosphocholine oligosaccharides are known immunomodulators in human nematode and trematode infections, C. elegans is unique as a non-parasitic nematode containing phosphocholine N-glycans. Therefore, studies in C. elegans should aid in the elucidation of the biosynthetic pathway(s) of this class of biomedically relevant compounds. Results presented here show that C. elegans has a functional orthologue for nearly every known enzyme found to be deficient in congenital disorders of glycosylation types I and II. This nematode is well characterized genetically and developmentally. Therefore, elucidation of its N-glycome, as shown in this report, may place it among the useful systems used to investigate human disorders of glycoconjugate synthesis such as the congenital disorders of glycosylation syndromes.