Highly modified and immunoactive N-glycans of the canine heartworm

Glycans of parasitic nematodes - from glycomes to novel diagnostic tools and vaccines

Nematodes, commonly known as roundworms, are among the most prevalent and diverse multicellular organisms on Earth, belonging to the large phylum Nematoda. In addition to free-living species, many nematodes are parasitic, infecting plants, animals, and humans. Nematodes possess a wide array of genes responsible for carbohydrate metabolism and glycosylation. The glycosylation processes in parasitic nematodes often result in unique glycan modifications that are not present in their hosts. These distinct glycans can be highly immunogenic to mammalian hosts and play significant immunoregulatory roles during infection. This mini-review article summarises the glycosylation capabilities and characteristics of parasitic nematodes based on glycomic data. It also highlights recent research advances that explore the biological significance of nematode glycans and their potential for diagnostic and vaccine applications.

N-glycan core tri-fucosylation requires Golgi α-mannosidase III activity that impacts nematode growth and behavior

N-glycans with complex core chitobiose modifications are observed in various free-living and parasitic nematodes but are absent in mammals. Using Caenorhabditis elegans as a model, we demonstrated that the core N-acetylglucosamine (GlcNAc) residues are modified by three fucosyltransferases (FUTs), namely FUT-1, FUT-6, and FUT-8. Interestingly, FUT-6 can only fucosylate N-glycans lacking the α1,6-mannose upper arm, indicating that a specific α-mannosidase is required to generate substrates for subsequent FUT-6 activity. By analyzing the N-glycomes of aman-3 KOs using offline HPLC-MALDI-TOF MS/MS, we observed that the absence of aman-3 abolishes α1,3-fucosylation of the distal GlcNAc of N-glycans, which suggests that AMAN-3 is the relevant mannosidase on whose action FUT-6 depends. Enzymatic characterization of recombinant AMAN-3 and confocal microscopy studies using a knock-in strain (aman-3::eGFP) demonstrated a Golgi localization. In contrast to the classical Golgi α-mannosidase II (AMAN-2), AMAN-3 displayed a cobalt-dependent α1,6-mannosidase activity toward N-glycans. Using AMAN-3 and other C. elegans glycoenzymes, we were able to mimic nematode N-glycan biosynthesis in vitro by remodeling a fluorescein conjugated-glycan and generate a tri-fucosylated structure. In addition, using a high-content computer-assisted C. elegans analysis platform, we observed that aman-3 deficient worms display significant developmental delays, morphological, and behavioral alterations in comparison to the WT. Our data demonstrated that AMAN-3 is a Golgi α-mannosidase required for core fucosylation of the distal GlcNAc of N-glycans. This enzyme is essential for the formation of the unusual tri-fucosylated chitobiose modifications in nematodes, which may play important roles in nematode development and behavior.

Bioinformatic, Enzymatic, and Structural Characterization of Trichuris suis Hexosaminidase HEX-2

Hexosaminidases are key enzymes in glycoconjugate metabolism and occur in all kingdoms of life. Here, we have investigated the phylogeny of the GH20 glycosyl hydrolase family in nematodes and identified a β-hexosaminidase subclade present only in the Dorylaimia. We have expressed one of these, HEX-2 from Trichuris suis, a porcine parasite, and shown that it prefers an aryl β-N-acetylgalactosaminide in vitro. HEX-2 has an almost neutral pH optimum and is best inhibited by GalNAc-isofagomine. Toward N-glycan substrates, it displays a preference for the removal of GalNAc residues from LacdiNAc motifs as well as the GlcNAc attached to the α1,3-linked core mannose. Therefore, it has a broader specificity than insect fused lobe (FDL) hexosaminidases but one narrower than distant homologues from plants. Its X-ray crystal structure, the first of any subfamily 1 GH20 hexosaminidase to be determined, is closest to Streptococcus pneumoniae GH20C and the active site is predicted to be compatible with accommodating both GalNAc and GlcNAc. The new structure extends our knowledge about this large enzyme family, particularly as T. suis HEX-2 also possesses the key glutamate residue found in human hexosaminidases of either GH20 subfamily, including HEXD whose biological function remains elusive.

Serum antibody screening using glycan arrays

Humans and other animals produce a diverse collection of antibodies, many of which bind to carbohydrate chains, referred to as glycans. These anti-glycan antibodies are a critical part of our immune systems' defenses. Whether induced by vaccination or natural exposure to a pathogen, anti-glycan antibodies can provide protection against infections and cancers. Alternatively, when an immune response goes awry, antibodies that recognize self-glycans can mediate autoimmune diseases. In any case, serum anti-glycan antibodies provide a rich source of information about a patient's overall health, vaccination history, and disease status. Glycan microarrays provide a high-throughput platform to rapidly interrogate serum anti-glycan antibodies and identify new biomarkers for a variety of conditions. In addition, glycan microarrays enable detailed analysis of the immune system's response to vaccines and other treatments. Herein we review applications of glycan microarray technology for serum anti-glycan antibody profiling.

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.

Analysis of Caenorhabditis Protein Glycosylation

Glycoproteins result from post-translational modification of proteins by glycans attached to certain side chains, with possible heterogeneity due to different structures being possible at the same glycosylation site.In contrast to the mammalian systems, analysis of invertebrate glycans presents a challenge in analysis as there exist unfamiliar epitopes and a high degree of structural and isomeric variation between different species-Caenorhabditis elegans is no exception. Simple screening using lectins and antibodies can yield hints regarding which glycan epitopes are present in wild-type and mutant strains, but detailed analysis is necessary for determining more exact glycomic information. Here, our analytical approach is to analyze N- and O-glycans involving "off-line" RP-HPLC MALDI-TOF MS/MS. Enrichment and labeling steps facilitate the analysis of single structures and provide isomeric separation. Thereby, the "simple" worm expresses over 200 N-glycan structures varying depending on culture conditions or the genetic background.

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.

Identification of Novel Glycans in the Mucus Layer of Shark and Skate Skin

The mucus layer covering the skin of fish has several roles, including protection against pathogens and mechanical damage. While the mucus layers of various bony fish species have been investigated, the composition and glycan profiles of shark skin mucus remain relatively unexplored. In this pilot study, we aimed to explore the structure and composition of shark skin mucus through histological analysis and glycan profiling. Histological examination of skin samples from Atlantic spiny dogfish (Squalus acanthias) sharks and chain catsharks (Scyliorhinus retifer) revealed distinct mucin-producing cells and a mucus layer, indicating the presence of a functional mucus layer similar to bony fish mucus albeit thinner. Glycan profiling using liquid chromatography-electrospray ionization tandem mass spectrometry unveiled a diverse repertoire of mostly O-glycans in the mucus of the two sharks as well as little skate (Leucoraja erinacea). Elasmobranch glycans differ significantly from bony fish, especially in being more sulfated, and some bear resemblance to human glycans, such as gastric mucin O-glycans and H blood group-type glycans. This study contributes to the concept of shark skin having unique properties and provides a foundation for further research into the functional roles and potential biomedical implications of shark skin mucus glycans.

N-glycan antennal modifications are altered in Caenorhabditis elegans lacking the HEX-4 N-acetylgalactosamine-specific hexosaminidase

Simple organisms are often considered to have simple glycomes, but plentiful paucimannosidic and oligomannosidic glycans overshadow the less abundant N-glycans with highly variable core and antennal modifications; Caenorhabditis elegans is no exception. By use of optimized fractionation and assessing wildtype in comparison to mutant strains lacking either the HEX-4 or HEX-5 β-N-acetylgalactosaminidases, we conclude that the model nematode has a total N-glycomic potential of 300 verified isomers. Three pools of glycans were analyzed for each strain: either PNGase F released and eluted from a reversed-phase C18 resin with either water or 15% methanol or PNGase Ar released. While the water-eluted fractions were dominated by typical paucimannosidic and oligomannosidic glycans and the PNGase Ar-released pools by glycans with various core modifications, the methanol-eluted fractions contained a huge range of phosphorylcholine-modified structures with up to three antennae, sometimes with four N-acetylhexosamine residues in series. There were no major differences between the C. elegans wildtype and hex-5 mutant strains, but the hex-4 mutant strains displayed altered sets of methanol-eluted and PNGase Ar-released pools. In keeping with the specificity of HEX-4, there were more glycans capped with N-acetylgalactosamine in the hex-4 mutants, as compared with isomeric chito-oligomer motifs in the wildtype. Considering that fluorescence microscopy showed that a HEX-4::enhanced GFP fusion protein colocalizes with a Golgi tracker, we conclude that HEX-4 plays a significant role in late-stage Golgi processing of N-glycans in C. elegans. Furthermore, finding more "parasite-like" structures in the model worm may facilitate discovery of glycan-processing enzymes occurring in other nematodes.

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.

An evolutionary molecular adaptation of an unusual stefin from the liver fluke Fasciola hepatica redefines the cystatin superfamily

Fasciolosis is a worldwide parasitic disease of ruminants and an emerging human disease caused by the liver fluke Fasciola hepatica. The cystatin superfamily of cysteine protease inhibitors is composed of distinct families of intracellular stefins and secreted true cystatins. FhCyLS-2 from F. hepatica is an unusual member of the superfamily, where our sequence and 3D structure analyses in this study revealed that it combines characteristics of both families. The protein architecture demonstrates its relationship to stefins, but FhCyLS-2 also contains the secretion signal peptide and disulfide bridges typical of true cystatins. The secretion status was confirmed by detecting the presence of FhCyLS-2 in excretory/secretory products, supported by immunolocalization. Our high-resolution crystal structure of FhCyLS-2 showed a distinct disulfide bridging pattern and functional reactive center. We determined that FhCyLS-2 is a broad specificity inhibitor of cysteine cathepsins from both the host and F. hepatica, suggesting a dual role in the regulation of exogenous and endogenous proteolysis. Based on phylogenetic analysis that identified several FhCyLS-2 homologues in liver/intestinal foodborne flukes, we propose a new group within the cystatin superfamily called cystatin-like stefins.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Recent Advances and Potential Future Applications of MALDI-TOF Mass Spectrometry for Identification of Helminths

Helminth infections caused by nematodes, trematodes, and cestodes are major neglected tropical diseases and of great medical and veterinary relevance. At present, diagnosis of helminthic diseases is mainly based on microscopic observation of different parasite stages, but microscopy is associated with limited diagnostic accuracy. Against this background, recent studies described matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry as a potential, innovative tool for helminth identification and differentiation. MALDI-TOF mass spectrometry is based on the analysis of spectra profiles generated from protein extracts of a given pathogen. It requires an available spectra database containing reference spectra, also called main spectra profiles (MSPs), which are generated from well characterized specimens. At present, however, there are no commercially available databases for helminth identification using this approach. In this narrative review, we summarize recent developments and published studies between January 2019 and September 2022 that report on the use of MALDI-TOF mass spectrometry for helminths. Current challenges and future research needs are identified and briefly discussed.

Negative-mode mass spectrometry in the analysis of invertebrate, fungal, and protist N-glycans

The approaches for analysis of N-glycans have radically altered in the last 20 years or so. Due to increased sensitivity, mass spectrometry has become the predominant method in modern glycomics. Here, we summarize recent studies showing that the improved resolution and detection by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has contributed greatly to the discovery of a large range of anionic and zwitterionic N-glycan structures across the different kingdoms of life, whereby MALDI-TOF MS in negative mode is less widely performed than in positive mode. However, its use enables the detection of key fragments indicative of certain sugar modifications such as sulfate, (methyl) phosphate, phosphoethanolamine, (methyl)aminoethylphosphonate, glucuronic, and sialic acid, thereby enabling certain isobaric glycan variations to be distinguished. As we also discuss in this review, complementary approaches such as negative-mode electrospray ionization-MS/MS, Fourier-transform ion cyclotron resonance MS, and ion mobility MS yield, respectively, cross-linkage fragments, high accuracy masses, and isomeric information, thus adding other components to complete the jigsaw puzzle when defining unusual glycan modifications from lower organisms.

Glyco-Engineering Plants to Produce Helminth Glycoproteins as Prospective Biopharmaceuticals: Recent Advances, Challenges and Future Prospects

Glycoproteins are the dominant category among approved biopharmaceuticals, indicating their importance as therapeutic proteins. Glycoproteins are decorated with carbohydrate structures (or glycans) in a process called glycosylation. Glycosylation is a post-translational modification that is present in all kingdoms of life, albeit with differences in core modifications, terminal glycan structures, and incorporation of different sugar residues. Glycans play pivotal roles in many biological processes and can impact the efficacy of therapeutic glycoproteins. The majority of biopharmaceuticals are based on human glycoproteins, but non-human glycoproteins, originating from for instance parasitic worms (helminths), form an untapped pool of potential therapeutics for immune-related diseases and vaccine candidates. The production of sufficient quantities of correctly glycosylated putative therapeutic helminth proteins is often challenging and requires extensive engineering of the glycosylation pathway. Therefore, a flexible glycoprotein production system is required that allows straightforward introduction of heterologous glycosylation machinery composed of glycosyltransferases and glycosidases to obtain desired glycan structures. The glycome of plants creates an ideal starting point for N- and O-glyco-engineering of helminth glycans. Plants are also tolerant toward the introduction of heterologous glycosylation enzymes as well as the obtained glycans. Thus, a potent production platform emerges that enables the production of recombinant helminth proteins with unusual glycans. In this review, we discuss recent advances in plant glyco-engineering of potentially therapeutic helminth glycoproteins, challenges and their future prospects.

Towards understanding the extensive diversity of protein N-glycan structures in eukaryotes

N-glycosylation is an important post-translational modification of proteins that has been highly conserved during evolution and is found in Eukaryota, Bacteria and Archaea. In eukaryotes, N-glycan processing is sequential, involving multiple specific steps within the secretory pathway as proteins travel through the endoplasmic reticulum and the Golgi apparatus. In this review, we first summarize the different steps of the N-glycan processing and further describe recent findings regarding the diversity of N-glycan structures in eukaryotic clades. This comparison allows us to explore the different regulation mechanisms of N-glycan processing among eukaryotic clades. Recent findings regarding the regulation of protein N-glycosylation are highlighted, especially the regulation of the biosynthesis of complex-type N-glycans through manganese and calcium homeostasis and the specific role of transmembrane protein 165 (TMEM165) for which homologous sequences have been identified in several eukaryotic clades. Further research will be required to characterize the function of TMEM165 homologous sequences in different eukaryotic clades.

Mass spectrometric and glycan microarray-based characterization of the filarial nematode Brugia malayi glycome reveals anionic and zwitterionic glycan antigens

Millions of people worldwide are infected with filarial nematodes, responsible for lymphatic filariasis (LF) and other diseases causing chronic disablement. Elimination programs have resulted in a substantial reduction of the rate of infection in certain areas creating a need for improved diagnostic tools to establish robust population surveillance and avoid LF resurgence. Glycans from parasitic helminths are emerging as potential antigens for use in diagnostic assays. However, despite its crucial role in host–parasite interactions, filarial glycosylation is still largely, structurally, and functionally uncharacterized. Therefore, we investigated the glycan repertoire of the filarial nematode Brugia malayi. Glycosphingolipid and N-linked glycans were extracted from several life-stages using enzymatic release and characterized using a combination of MALDI-TOF-MS and glycan sequencing techniques. Next, glycans were purified by HPLC and printed onto microarrays to assess the host anti-glycan antibody response. Comprehensive glycomic analysis of B. malayi revealed the presence of several putative antigenic motifs such as phosphorylcholine and terminal glucuronic acid. Glycan microarray screening showed a recognition of most B. malayi glycans by immunoglobulins from rhesus macaques at different time points after infection, which permitted the characterization of the dynamics of anti-glycan immunoglobulin G and M during the establishment of brugian filariasis. A significant level of IgG binding to the parasite glycans was also detected in infected human plasma, while IgG binding to glycans decreased after anthelmintic treatment. Altogether, our work identifies B. malayi glycan antigens and reveals antibody responses from the host that could be exploited as potential markers for LF.

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Antigenic B. malayi N-linked and GSL glycans were structurally defined.

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IgG/IgM is induced to a subset of B. malayi glycans upon infection of rhesus macaques.

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Preferential IgG response to B. malayi glycans observed in chronically infected humans.

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Marked drop of anti-glycan IgG following treatment of individuals with anthelminthic.

Using Caenorhabditis elegans to produce functional secretory proteins of parasitic nematodes

The expression of antigens in their immunologically-active form remains a challenge, both in the analysis of regulatory pathways exploited by parasitic nematodes or in the development of vaccines. Despite the success of native proteins to induce protective immunity, recombinant proteins expressed in bacteria, yeast or insect cells offer only limited protective capacities, presumably due to incorrect folding or missing complex posttranslational modifications. The present study investigates the feasibility of using the free-living nematode Caenorhabditis elegans as an alternative expression system for proteins found in the secretome of parasitic nematodes. Exemplified by the expression of the extracellular superoxide dismutase from Haemonchus contortus (HcSODe) and the extracellular and glycosylated glutathione S-transferase from the filarial parasite Onchocerca volvulus (OvGST1), we continue our efforts to improve production and purification of recombinant proteins expressed in C. elegans. We demonstrate that sufficient quantities of functional proteins can be expressed in C. elegans for subsequent immunological and biochemical studies.

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.

Profiling the glycome of Cardicola forsteri, a blood fluke parasitic to bluefin tuna

Infections by blood flukes (Cardicola spp.) are considered the most significant health issue for ranched bluefin tuna, a major aquaculture industry in Japan and Australia. The host-parasite interfaces of trematodes, namely their teguments, are particularly rich in carbohydrates, which function both in evasion and modulation of the host immune system, while some are primary antigenic targets. In this study, histochemistry and mass spectrometry techniques were used to profile the glycans of Cardicola forsteri. Fluorescent lectin staining of adult flukes indicates the presence of oligomannose (Concanavalin A-reactive) and fucosylated (Pisum sativum agglutinin-reactive) N-glycans. Additionally, reactivity of succinylated wheat germ agglutinin (s-WGA) was localised to several internal organs of the digestive and monoecious reproductive systems. Glycan structures were further investigated with tandem mass spectrometry, which revealed structures indicated by lectin reactivity. While O-glycans from these adult specimens were not detectable by mass spectrometry, several oligomannose, paucimannosidic, and complex-type N-glycans were identified, including some carrying hexuronic acid and many carrying core xylose. This is, to our knowledge, the first glycomic characterisation of a marine platyhelminth, with broader implications for research into other trematodes.

Impact of Protein Glycosylation on the Design of Viral Vaccines

Glycans play crucial roles in various biological processes such as cell proliferation, cell-cell interactions, and immune responses. Since viruses co-opt cellular biosynthetic pathways, viral glycosylation mainly depends on the host cell glycosylation machinery. Consequently, several viruses exploit the cellular glycosylation pathway to their advantage. It was shown that viral glycosylation is strongly dependent on the host system selected for virus propagation and/or protein expression. Therefore, the use of different expression systems results in various glycoforms of viral glycoproteins that may differ in functional properties. These differences clearly illustrate that the choice of the expression system can be important, as the resulting glycosylation may influence immunological properties. In this review, we will first detail protein N- and O-glycosylation pathways and the resulting glycosylation patterns; we will then discuss different aspects of viral glycosylation in pathogenesis and in vaccine development; and finally, we will elaborate on how to harness viral glycosylation in order to optimize the design of viral vaccines. To this end, we will highlight specific examples to demonstrate how glycoengineering approaches and exploitation of different expression systems could pave the way towards better self-adjuvanted glycan-based viral vaccines.

Effector and regulator: Diverse functions of C. elegans C-type lectin-like domain proteins

In C. elegans, 283 clec genes encode a highly diverse family of C-type lectin-like domain (CTLD) proteins. Since vertebrate CTLD proteins have characterized functions in defense responses against pathogens and since expression of C. elegans clec genes is pathogen-dependent, it is generally assumed that clec genes function in C. elegans immune defenses. However, little is known about the relative contribution and exact function of CLEC proteins in C. elegans immunity. Here, we focused on the C. elegans clec gene clec-4, whose expression is highly upregulated by pathogen infection, and its paralogs clec-41 and clec-42. We found that, while mutation of clec-4 resulted in enhanced resistance to the Gram-positive pathogen Bacillus thuringiensis MYBt18247 (Bt247), inactivation of clec-41 and clec-42 by RNAi enhanced susceptibility to Bt247. Further analyses revealed that enhanced resistance of clec-4 mutants to Bt247 was due to an increase in feeding cessation on the pathogen and consequently a decrease in pathogen load. Moreover, clec-4 mutants exhibited feeding deficits also on non-pathogenic bacteria that were in part reflected in the clec-4 gene expression profile, which overlapped with gene sets affected by starvation or mutation in nutrient sensing pathways. However, loss of CLEC-4 function only mildly affected life-history traits such as fertility, indicating that clec-4 mutants are not subjected to dietary restriction. While CLEC-4 function appears to be associated with the regulation of feeding behavior, we show that CLEC-41 and CLEC-42 proteins likely function as bona fide immune effector proteins that have bacterial binding and antimicrobial capacities. Together, our results exemplify functional diversification within clec gene paralogs.

C-type lectin-like domain (CTLD) containing proteins fulfill various and fundamental tasks in the human and mouse immune system. Genes encoding CTLD proteins are present in all animal genomes, in some cases in very large numbers and highly diversified. While the function of several vertebrate CTLD proteins is well characterized, experimental evidence of an immune function of most invertebrate CTLD proteins is missing, although their role in immunity is usually assumed. We here explore the immune function of three related CTLD proteins in the model nematode Caenorhabditis elegans. We find that they play diverse roles in C. elegans immunity, functioning as antimicrobial immune effector proteins that are important for defense against pathogen infection and probably directly interact with bacteria, but also regulators of feeding behavior that more indirectly affect C. elegans pathogen resistance. Such insight into the functional consequence of invertebrate CTLD protein diversification contributes to our understanding of the evolution of innate and invertebrate immune systems.

A mass spectrometry-based glycotope-centric cellular glycomics is the more fruitful way forward to see the forest for the trees

The nature of protein glycosylation renders cellular glycomics a very challenging task in having to deal with all the disparate glycans carried on membrane glycoproteins. Rapid mapping by mass spectrometry analysis provides only a coarse sketch of the glycomic complexity based primarily on glycosyl compositions, whereby the missing high-resolution structural details require a combination of multi-mode separations and multi-stages of induced fragmentation to gain sufficiently discriminative precision, often at the expenses of throughput and sensitivity. Given the available technology and foreseeable advances in the near future, homing in on resolving the terminal fucosylated, sialylated and/or sulfated structural units, or glycotopes, maybe a more pragmatic and ultimately more rewarding approach to gain insights into myriad biological processes mediated by these terminal coding units carried on important glycoproteins, to be decoded by a host of endogenous glycan-binding proteins and antibodies. A broad overview of recent technical advances and limitations in cellular glycomics is first provided as a backdrop to the propounded glycotope-centric approach based on advanced nanoLC-MS2/MS3 analysis of permethylated glycans. To prioritize analytical focus on the more tangible glycotopes is akin to first identifying the eye-catching and characteristic-defining flowers and fruits of the glyco-forest, to see the forest for the trees. It has the best prospects of attaining the much-needed balance in sensitivity, structural precision and analytical throughput to match advances in other omics.

Glycomics, Glycoproteomics, and Glycogenomics: An Inter-Taxa Evolutionary Perspective

Glycosylation is a highly diverse set of co- and posttranslational modifications of proteins. For mammalian glycoproteins, glycosylation is often site-, tissue-, and species-specific and diversified by microheterogeneity. Multitudinous biochemical, cellular, physiological, and organismic effects of their glycans have been revealed, either intrinsic to the carrier proteins or mediated by endogenous reader proteins with carbohydrate recognition domains. Furthermore, glycans frequently form the first line of access by or defense from foreign invaders, and new roles for nucleocytoplasmic glycosylation are blossoming. We now know enough to conclude that the same general principles apply in invertebrate animals and unicellular eukaryotes-different branches of which spawned the plants or fungi and animals. The two major driving forces for exploring the glycomes of invertebrates and protists are (i) to understand the biochemical basis of glycan-driven biology in these organisms, especially of pathogens, and (ii) to uncover the evolutionary relationships between glycans, their biosynthetic enzyme genes, and biological functions for new glycobiological insights. With an emphasis on emerging areas of protist glycobiology, here we offer an overview of glycan diversity and evolution, to promote future access to this treasure trove of glycobiological processes.

The Two Faces of Nematode Infection: Virulence and Immunomodulatory Molecules From Nematode Parasites of Mammals, Insects and Plants

Helminths stage a powerful infection that allows the parasite to damage host tissue through migration and feeding while simultaneously evading the host immune system. This feat is accomplished in part through the release of a diverse set of molecules that contribute to pathogenicity and immune suppression. Many of these molecules have been characterized in terms of their ability to influence the infectious capabilities of helminths across the tree of life. These include nematodes that infect insects, known as entomopathogenic nematodes (EPN) and plants with applications in agriculture and medicine. In this review we will first discuss the nematode virulence factors, which aid parasite colonization or tissue invasion, and cause many of the negative symptoms associated with infection. These include enzymes involved in detoxification, factors essential for parasite development and growth, and highly immunogenic ES proteins. We also explore how these parasites use several classes of molecules (proteins, carbohydrates, and nucleic acids) to evade the host's immune defenses. For example, helminths release immunomodulatory molecules in extracellular vesicles that may be protective in allergy and inflammatory disease. Collectively, these nematode-derived molecules allow parasites to persist for months or even years in a host, avoiding being killed or expelled by the immune system. Here, we evaluate these molecules, for their individual and combined potential as vaccine candidates, targets for anthelminthic drugs, and therapeutics for allergy and inflammatory disease. Last, we evaluate shared virulence and immunomodulatory mechanisms between mammalian and non-mammalian plant parasitic nematodes and EPNs, and discuss the utility of EPNs as a cost-effective model for studying nematode-derived molecules. Better knowledge of the virulence and immunomodulatory molecules from both entomopathogenic nematodes and soil-based helminths will allow for their use as beneficial agents in fighting disease and pests, divorced from their pathogenic consequences.

Characterization of glycan determinants that mediate recognition of the major Wuchereria bancrofti circulating antigen by diagnostic antibodies

The Global Program to Eliminate Lymphatic Filariasis (GPELF) relies heavily on a rapid diagnostic test (RDT) to a Wuchereria bancrofti circulating filarial antigen (Wb-CFA) to identify endemic areas and for determining when mass drug administration can stop. The antigen contains a carbohydrate epitope that is recognized by monoclonal antibody AD12. Og4C3, a monoclonal antibody that is used in a commercial ELISA for Wb-CFA recognizes the same moiety. Despite its diagnostic importance, little is known about the structure and function of this "AD12 epitope". It is also present on other W. bancrofti glycoproteins and on glycoproteins of other filarial worms, but such antigens are not detected in the sera of individuals with most other filarial infections. We report here functional and biochemical analyses that shed light on the interaction between filarial glycoproteins and AD12 and/or Og4C3. Binding of these monoclonal antibodies to a mammalian glycan array suggests the reactive moiety has structural similarity to terminal β-d-glucuronic acid in a 1-3 linkage to other hexoses. However, sera collected from individuals with patent W. bancrofti infection had very low or undetectable serum antibodies to the GlcA-containing array glycans. Unlike other filarial glycoproteins, the Wb-CFA is relatively resistant to protease digestion by pronase and trypsin and completely resistant to the mucinase O-sialoglycoprotein endopeptidase (OSGE). The protease resistance of the Wb-CFA may contribute to its consistent detection in Wb-infected sera.

NEGATIVE ION MASS SPECTROMETRY FOR THE ANALYSIS OF N-LINKED GLYCANS

N-glycans from glycoproteins are complex, branched structures whose structural determination presents many analytical problems. Mass spectrometry, usually conducted in positive ion mode, often requires extensive sample manipulation, usually by derivatization such as permethylation, to provide the necessary structure-revealing fragment ions. The newer but, so far, lesser used negative ion techniques, on the contrary, provide a wealth of structural information not present in positive ion spectra that greatly simplify the analysis of these compounds and can usually be conducted without the need for derivatization. This review describes the use of negative ion mass spectrometry for the structural analysis of N-linked glycans and emphasises the many advantages that can be gained by this mode of operation. Biosynthesis and structures of the compounds are described followed by methods for release of the glycans from the protein. Methods for ionization are discussed with emphasis on matrix-assisted laser desorption/ionization (MALDI) and methods for producing negative ions from neutral compounds. Acidic glycans naturally give deprotonated species under most ionization conditions. Fragmentation of negative ions is discussed next with particular reference to those ions that are diagnostic for specific features such as the branching topology of the glycans and substitution positions of moieties such as fucose and sulfate, features that are often difficult to identify easily by conventional techniques such as positive ion fragmentation and exoglycosidase digestions. The advantages of negative over positive ions for this structural work are emphasised with an example of a series of glycans where all other methods failed to produce a structure. Fragmentation of derivatized glycans is discussed next, both with respect to derivatives at the reducing terminus of the molecules, and to methods for neutralization of the acidic groups on sialic acids to both stabilize them for MALDI analysis and to produce the diagnostic fragments seen with the neutral glycans. The use of ion mobility, combined with conventional mass spectrometry is described with emphasis on its use to extract clean glycan spectra both before and after fragmentation, to separate isomers and its use to extract additional information from separated fragment ions. A section on applications follows with examples of the identification of novel structures from lower organisms and tables listing the use of negative ions for structural identification of specific glycoproteins, glycans from viruses and uses in the biopharmaceutical industry and in medicine. The review concludes with a summary of the advantages and disadvantages of the technique. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Macrobrachium rosenbergii nodavirus virus-like particles attach to fucosylated glycans in the gills of the giant freshwater prawn

The Macrobrachium rosenbergii nodavirus (MrNV), the causative agent of white-tail disease (WTD) in many species of shrimp and prawn, has been shown to infect hemocytes and tissues such as the gills and muscles. However, little is known about the host surface molecules to which MrNV attach to initiate infection. Therefore, the present study investigated the role of glycans as binding molecules for virus attachment in susceptible tissues such as the gills. We established that MrNV in their virus-like particle (MrNV-VLP) form exhibited strong binding to gill tissues and lysates, which was highly reduced by the glycan-reducing periodate and PNGase F. The broad, fucose-binding Aleuria Aurantia lectin (AAL) highly reduced MrNV-VLPs binding to gill tissue sections and lysates, and efficiently disrupted the specific interactions between the VLPs and gill glycoproteins. Furthermore, mass spectroscopy revealed the existence of unique fucosylated LacdiNAc-extended N-linked and O-linked glycans in the gill tissues, whereas beta-elimination experiments showed that MrNV-VLPs demonstrated a binding preference for N-glycans. Therefore, the results from this study highly suggested that MrNV-VLPs preferentially attach to fucosylated N-glycans in the susceptible gill tissues, and these findings could lead to the development of strategies that target virus-host surface glycan interactions to reduce MrNV infections.

Unique glycan and lipid composition of helminth-derived extracellular vesicles may reveal novel roles in host-parasite interactions

Although the study of helminth-derived extracellular vesicles (EVs) is in its infancy, proteomic studies of EVs from representatives of nematodes, cestodes and trematodes have identified homologs of mammalian EV proteins including components of the endosomal sorting complexes required for transport and heat-shock proteins, suggesting conservation of pathways of EV biogenesis and cargo loading between helminths and their hosts. However, parasitic helminth biology is unique and this is likely reflected in helminth EV composition and biological activity. This opinion article highlights two exceptional studies that identified EVs released by Heligmosomoides polygyrus and Fasciola hepatica which display differential lipid and glycan composition, respectively, when compared with EVs derived from mammalian cells. Furthermore, we discuss the potential implications of helminth EV lipid and glycan composition upon helminth infection and host pathology. Future studies, focusing on the unique composition and functional properties of helminth EVs, may prove crucial to the understanding of host-parasite communication.

Zwitterionic Phosphodiester-Substituted Neoglycoconjugates as Ligands for Antibodies and Acute Phase Proteins

Zwitterionic modifications of glycans, such as phosphorylcholine and phosphoethanolamine, are known from a range of prokaryotic and eukaryotic species and are recognized by mammalian antibodies and pentraxins; however, defined saccharide ligands modified with these zwitterionic moieties for high-throughput studies are lacking. In this study, we prepared and tested example mono- and disaccharides 6-substituted with either phosphorylcholine or phosphoethanolamine as bovine serum albumin neoglycoconjugates or printed in a microarray format for subsequent assessment of their binding to lectins, pentraxins, and antibodies. C-Reactive protein and anti-phosphorylcholine antibodies bound specifically to ligands with phosphorylcholine, but recognition by concanavalin A was abolished or decreased as compared with that to the corresponding nonzwitterionic compounds. Furthermore, in array format, the phosphorylcholine-modified ligands were recognized by IgG and IgM in sera of either non-infected or nematode-infected dogs and pigs. Thereby, these new compounds are defined ligands which allow the assessment of glycan-bound phosphorylcholine as a target of both the innate and adaptive immune systems in mammals.

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.

Tissue-specific glycosylation in the honeybee: Analysis of the N-glycomes of Apis mellifera larvae and venom

BACKGROUND

Previous glycophylogenetic comparisons of dipteran and lepidopteran species revealed variations in the anionic and zwitterionic modifications of their N-glycans; therefore, we wished to explore whether species- and order-specific glycomic variations would extend to the hymenoptera, which include the honeybee Apis mellifera, an agriculturally- and allergologically-significant social species.

METHODS

In this study, we employed an off-line liquid chromatography/mass spectrometry approach, in combination with enzymatic and chemical treatments, to analyse the N-glycans of male honeybee larvae and honeybee venom in order to facilitate definition of isomeric structures.

RESULTS

The neutral larval N-glycome was dominated by oligomannosidic and paucimannosidic structures, while the neutral venom N-glycome displayed more processed hybrid and complex forms with antennal N-acetylgalactosamine, galactose and fucose residues including Lewis-like epitopes; the anionic pools from both larvae and venom contained a wide variety of glucuronylated, sulphated and phosphoethanolamine-modified N-glycans with up to three antennae. In comparison to honeybee royal jelly, there were more fucosylated and fewer Man_4/5-based hybrid glycans in the larvae and venom samples as well as contrasting antennal lengths.

CONCLUSIONS

Combining the current data on venom and larvae with that we previously published on royal jelly, a total honeybee N-glycomic repertoire of some 150 compositions can be proposed in addition to the 20 previously identified on specific venom glycoproteins.

SIGNIFICANCE

Our data are indicative of tissue-specific modification of the core and antennal regions of N-glycans in Apis mellifera and reinforce the concept that insects are capable of extensive processing to result in rather complex anionic oligosaccharide structures.

Persistence of pulmonary endarteritis in canine heartworm infection 10 months after the eradication of adult parasites of Dirofilaria immitis

Pulmonary endarteritis caused by Dirofilaria immitis and pulmonary hypertension (PH) are closely linked and the determination of PH could be validated to assess the severity and chronicity of the vascular damage, i.e. by the use of the Right Pulmonary Artery Distensibility (RPAD) Index. The aim was to evaluate the RPAD Index in dogs 10 months after the last dose of adulticide. The study included 23 client-owned dogs with heartworm brought for adulticide treatment. Echocardiographic exam was carried out to estimate worm burden, RPAD Index as well as other routine echocardiographic values on day 0 (diagnosis), day 120 (discharge), and 10 months after the last dose of adulticide. No significant differences were observed in the RPAD Index over time, neither when microfilaremic status and parasite burden were evaluated. An RPAD Index <29% was found in 52.2% of the dogs on day 0, day 120, and 10 months after the last dose of adulticide. Regarding other echocardiographic parameters, only significant differences were observed on tricuspid annular plane systolic excursion (TAPSE) values between day 0:day 120 (p = 0.008), and day 0:end of the study (p = 0.037). There was not significant improvement in pulmonary damage 10 months after the elimination of the parasites (p = 0.296), suggesting that, once the endarteritis has developed, the vascular changes are chronic and may not be reversible. The modifications of the TAPSE value suggest an improvement in the systolic function of the right ventricle after the disappearance of the worms, independently of the presence of PH. The endarteritis causes a decrease in the elasticity in the pulmonary vasculature and an increase in the resistance that, chronically, and depending on the severity, will cause the development of PH and later right heart failure. This complication of the disease is one of the most damaging and frequent, so it is necessary to adequately monitor PH in dogs undergoing adulticide treatment. Furthermore, knowing the pulmonary status could provide valuable information to help provide an objective prognosis and help assess the need to add additional treatments, once the worms have been eliminated.

Comparisons of N-glycans across invertebrate phyla

Many invertebrates are either parasites themselves or vectors involved in parasite transmission; thereby, the interactions of parasites with final or intermediate hosts are often mediated by glycans. Therefore, it is of interest to compare the glycan structures or motifs present across invertebrate species. While a typical vertebrate modification such as sialic acid is rare in lower animals, antennal and core modifications of N-glycans are highly varied and range from core fucose, galactosylated fucose, fucosylated galactose, methyl groups, glucuronic acid and sulphate through to addition of zwitterionic moieties (phosphorylcholine, phosphoethanolamine and aminoethylphosphonate). Only in some cases are the enzymatic bases and the biological function of these modifications known. We are indeed still in the phase of discovering invertebrate glycomes primarily using mass spectrometry, but molecular biology and microarraying techniques are complementary to the determination of novel glycan structures and their functions.

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.