Anomalous N-glycan structures with an internal fucose branched to GlcA and GlcN residues isolated from a mollusk shell-forming fluid

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

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

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

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

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.

Immunotoxic effects of metal-based nanoparticles in fish and bivalves

There is a global research interest in metal nanoparticles (MNPs) due to their diverse applications, rapidly increasing use, and increased presence in the aquatic environment. Currently, most MNPs in the environment are at levels unlikely to cause overt toxicity. Sub-lethal effects that MNPs may induce, notable immunotoxicity, could however have significant health implications. Thus, deciphering the immunological interactions of MNPs with aquatic organisms constitutes a much-needed area of research. In this article, we critically assess the evidence for immunotoxic effects of MNPs in bivalves and fish, as key wildlife sentinels with widely differing ecological niches that are used as models in ecotoxicology. The first part of this review details the properties, fate, and fundamental physicochemical behavior of MNPs in the aquatic ecosystem. We then consider the toxicokinetics of MNP uptake, accumulation, and deposition in fish and bivalves. The main body of the review then focuses on immune reactions in response to MNPs exposure in bivalves and fish illustrating their immunotoxic potential. Finally, we identify major knowledge gaps in our current understanding of the implications of MNPs exposure for immunological functions and the associated health consequences for bivalves and fish, as well as the general lessons learned on the immunotoxic properties of the emerging class of nanoparticulate contaminants in fish and bivalves.

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.

Mollusc N-glycosylation: Structures, Functions and Perspectives

Molluscs display a sophisticated N-glycan pattern on their proteins, which is, in terms of involved structural features, even more diverse than that of vertebrates. This review summarises the current knowledge of mollusc N-glycan structures, with a focus on the functional aspects of the corresponding glycoproteins. Furthermore, the potential of mollusc-derived biomolecules for medical applications is addressed, emphasising the importance of mollusc research.

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.

Acidic Monosaccharides become Incorporated into Calcite Single Crystals*

Carbohydrates, along with proteins and peptides, are known to represent a major class of biomacromolecules involved in calcium carbonate biomineralization. However, in spite of multiple physical and biochemical characterizations, the explicit role of saccharide macromolecules (long chains of carbohydrate molecules) in mineral deposition is not yet understood. In this study, we investigated the influence of two common acidic monosaccharides (MSs), the two simplest forms of acidic carbohydrates, namely glucuronic and galacturonic acids, on the formation of calcite crystals in vitro. We show here that the size, morphology, and microstructure of calcite crystals are altered when they are grown in the presence of these MSs. More importantly, these MSs were found to become incorporated into the calcite crystalline lattice and induce anisotropic lattice distortions, a phenomenon widely studied for other biomolecules related to CaCO₃ biomineralization, but never before reported in the case of single MSs. Changes in the calcite lattice induced by MSs incorporation were precisely determined by high-resolution synchrotron powder X-ray diffraction. We believe that the results of this research may deepen our understanding of the interaction of saccharide polymers with an inorganic host and shed light on the implications of carbohydrates for biomineralization processes.

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.

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.

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.

Glycan-based biomarkers for diagnosis of cancers and other diseases: Past, present, and future

Glycans are essential biomolecules in regulating human physiology and pathology ranging from signal transduction to microbial infections. Developing complex human diseases, such as cancer, diabetes, and cardiovascular diseases, are a combination of genetic and environmental factors. Genetics dominates embryonic development and the passing of genes to the next generation whereas the information in glycans reflects the impact of internal and external environmental factors, such as diseases, lifestyle, and social factors, on a person's health and disease. The reason behind this is that glycans are not directly encoded in a genetic template. Instead, they are assembled dynamically by hundreds of enzymes organized in more than 10 complex biosynthetic pathways. Any environmental changes affecting enzymatic activities or the availability of high-energy monosaccharide donors in a specific location will disturb the final structure of glycans. The glycan structure-dependent biological activities subsequently enable or disable gene expressions, which partially explain that it is difficult to pinpoint specific genetic defects to aging-associated diseases. Glycan-based biomarkers are currently used for diagnosis of diabetes, cancers, and other complex diseases. We will recapitulate the discovery of glucose, glycated proteins, glycan-, and glycoprotein-based biomarkers followed by summarizing clinically used glycan/glycoprotein-based biomarkers. The potential serum/plasma-derived N- and O-linked glycans as biomarkers will also be discussed.

Sensitive and robust MALDI-TOF-MS glycomics analysis enabled by Girard's reagent T on-target derivatization (GTOD) of reducing glycans

Sensitive glycomics analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is of great importance but significantly hampered by their low ionization efficiency and labile sialic acid moieties. Chemical derivatization offers a viable way to improve both the ionization efficiency and analytical sensitivity of the glycans in MS analysis by altering their hydrophobicity or charge property. Here we employed Girard's reagent T (GT) for on-target derivatization (GTOD) of reducing glycan under mild acid condition to form stable hydrazones at room temperature, allowing rapid and sensitive identification of neutral and sialylated glycans in positive-ion mode as only permanently positive charged molecular ions without multiple ion adducts by MALDI-TOF-MS. The MS signal intensities of lactose, sialylated N-glycans derived from bovine fetuin and neutral N-glycans derived from RNaseB and ovalbumin were boosted by 7.44, 9.13, 12.96 and 13.47 folds on average (n = 3), respectively. More importantly, after GTOD strategy, unwanted desialylation of sialylated glycans during MS was suppressed. The detection limit of the assay is desirable since the nanogram of N-glycans derived from 0.16 μg ovalbumin could be detected. The assay demonstrated good stability (RSD≤2.95%, within 10 days), reliable reproducibility (RSD = 2.96%, n = 7) and a desirable linear dynamic range from 78 nmol/mL to 10 μmol/mL. The strategy has been successfully applied to MS analysis of reducing glycans from human milks, neutral and sialylated O-, N-glycans from glycoproteins, and reducing glycans derived from glycosphingolipids, presenting neater [M]⁺ signals which allow detection of more low-abundance glycans and assignation of Neu5Ac vs. Neu5Gc or fucose vs. hexose in glycans due to the absence of the ambiguous interpretation from multiple peaks (ion adducts [M+Na]⁺ and [M+K]⁺). Moreover, the GTOD assay prevents desialylation during MALDI-TOF-MS profiling and enables distinct linkage-specific characterization of terminal sialic acids of N-glycans derived from human serum protein when combines with an esterification.

Quantum Chemistry Meets Deep Learning for Complex Carbohydrate and Glycopeptide Species I

Carbohydrate complexes are crucial in many various biological and medicinal processes. The impacts of N-acetyl on the glycosidic linkage flexibility of methyl β-D-glucopyranose, and of the glycoamino acid β-D-glucopyranose-asparagine are poorly understood at the electronic level. Furthermore, the effect of D- and L-isomers of asparagine in the complexes of N-acetyl-β-D-glucopyranose-(L)-asparagine and N-acetyl-β-D-glucopyranose-(D)-asparagine is unknown. In this study, we performed density functional theory calculations of methyl β-D-glucopyranose, methyl N-acetyl-β-D-glucopyranose, and of glycoamino acids β-D-glucopyranose-asparagine, N-acetyl-β-D-glucopyranose-(L)-asparagine and N-acetyl-β-D-glucopyranose-(D)-asparagine for studying their linkage flexibilities, total solvated energies, thermochemical properties and intra-molecular hydrogen bond formations in an aqueous solution environment using the COnductor-like Screening MOdel (COSMO) for water. We linked these density functional theory calculations to deep learning via estimating the total solvated energy of each linkage torsional angle value. Our results show that deep learning methods accurately estimate the total solvated energies of complex carbohydrate and glycopeptide species and provide linkage flexibility trends for methyl β-D-glucopyranose, methyl N-acetyl-β-D-glucopyranose, and of glycoamino acids β-D-glucopyranose-asparagine, N-acetyl-β-D-glucopyranose-(L)-asparagine and N-acetyl-β-D-glucopyranose-(D)-asparagine in agreement with density functional theory results. To the best of our knowledge, this study represents the first application of density functional theory along with deep learning for complex carbohydrate and glycopeptide species in an aqueous solution medium. In addition, this study shows that a few thousands of optimization frames from DFT calculations are enough for accurate estimations by deep learning tools.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

Serum glycoprotein-derived N- and O-linked glycans as cancer biomarkers

Early detection of cancer is the key to improving survival. Since most clinically used serum cancer biomarkers are either glycoproteins or glycan structures that can be recognized by specific monoclonal antibodies, developing glycan structure-based biomarkers from human serum/plasma glycoproteins through mass spectrometry (MS) analysis are active research field during the past decades. Numerous studies have shown that changes in serum/plasma glycan structures occur during cancer initiation, progression, and treatment. This review describes N- and O-linked glycan structures identified from serum/plasma glycoprotein (s) by MS analysis with focus on alterations associated with different types of human cancers. The global changes in serum N- and O-linked glycan structures, especially the glycans that are not made by cancer cells such as B lymphocyte-derived IgG and liver-synthesized haptoglobin and α1 acid glycoprotein, suggest that glycans might be the long sought diagnostic biomarkers associated with system malfunction in the blood circulation of cancer patients. Therefore, N- and O-linked glycan structures have great potential to serve as cancer diagnosis, prognosis, and treatment monitoring biomarkers to facilitate personalized medicine.

Interactions of cationic polystyrene nanoparticles with marine bivalve hemocytes in a physiological environment: Role of soluble hemolymph proteins

The bivalve Mytilus galloprovincialis has proven as a suitable model invertebrate for evaluating the potential impact of nanoparticles (NPs) in the marine environment. In particular, in mussels, the immune system represents a sensitive target for different types of NPs. In environmental conditions, both NP intrinsic properties and those of the receiving medium will affect particle behavior and consequent bioavailability/uptake/toxicity. However, the evaluation of the biological effects of NPs requires additional understanding of how, once within the organism, NPs interact at the molecular level with cells in a physiological environment. In mammalian systems, different NPs associate with serum soluble components, organized into a "protein corona", which affects particle interactions with target cells. However, no information is available so far on the interactions of NPs with biological fluids of aquatic organisms. In this work, the influence of hemolymph serum (HS) on the in vitro effects of amino modified polystyrene NPs (PS-NH2) on Mytilus hemocytes was investigated. Hemocytes were incubated with PS-NH2 suspensions in HS (1, 5 and 50µg/mL) and the results were compared with those obtained in ASW medium. Cell functional parameters (lysosomal membrane stability, oxyradical production, phagocytosis) were evaluated, and morphological changes were investigated by TEM. The activation state of the signalling components involved in Mytilus immune response (p38 MAPK and PKC) was determined. The results show that in the presence of HS, PS-NH2 increased cellular damage and ROS production with respect to ASW medium. The effects were apparently mediated by disregulation of p38 MAPK signalling. The formation of a PS-NH2-protein corona in HS was investigated by centrifugation, and 1D- gel electrophoresis and nano-HPLC-ESI-MS/MS. The results identified the Putative C1q domain containing protein (MgC1q6) as the only component of the PS-NH2 hard protein corona in Mytilus hemolymph. These data represent the first evidence for the formation of a NP bio-corona in aquatic organisms and underline the importance of the recognizable biological identity of NPs in physiological exposure medium when testing their potential impact environmental model organisms. Although the results obtained in vitro do not entirely reflect a realistic exposure scenario and the more complex formation of a bio-corona that is likely to occur in vivo, these data will contribute to a better understanding of the effects of NPs in marine invertebrates.

Core-6 fucose and the oligomerization of the 1918 pandemic influenza viral neuraminidase

The 1918 H1N1 influenza virus was responsible for one of the most deadly pandemics in human history. Yet to date, the structure component responsible for its virulence is still a mystery. In order to search for such a component, the neuraminidase (NA) antigen of the virus was expressed, which led to the discovery of an active form (tetramer) and an inactive form (dimer and monomer) of the protein due to different glycosylation. In this report, the N-glycans from both forms were released and characterized by mass spectrometry. It was found that the glycans from the active form had 26% core-6 fucosylated, while the glycans from the inactive form had 82% core-6 fucosylated. Even more surprisingly, the stalk region of the active form was almost completely devoid of core-6-linked fucose. These findings were further supported by the results obtained from in vitro incorporation of azido fucose and (3)H-labeled fucose using core-6 fucosyltransferase, FUT8. In addition, the incorporation of fucose did not change the enzymatic activity of the active form, implying that core-6 fucose is not directly involved in the enzymatic activity. It is postulated that core-6 fucose prohibits the oligomerization and subsequent activation of the enzyme.

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

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

Multistep Fractionation and Mass Spectrometry Reveal Zwitterionic and Anionic Modifications of the N- and O-glycans of a Marine Snail

Various studies in the past have revealed that molluscs can produce a wide range of rather complex N-glycan structures, which vary from those occurring in other invertebrate animals; particularly methylated glycans have been found in gastropods, and there are some reports of anionic glycans in bivalves. Due to the high variability in terms of previously described structures and methodologies, it is a major challenge to establish glycomic workflows that yield the maximum amount of detailed structural information from relatively low quantities of sample. In this study, we apply differential release with peptide:N-glycosidases F and A followed by solid-phase extraction on graphitized carbon and reversed-phase materials to examine the glycome of Volvarina rubella (C. B. Adams, 1845), a margin snail of the clade Neogastropoda. The resulting four pools of N-glycans were fractionated on a fused core RP-HPLC column and subject to MALDI-TOF MS and MS/MS in conjunction with chemical and enzymatic treatments. In addition, selected N-glycan fractions, as well as O-glycans released by β-elimination, were analyzed by porous graphitized carbon-LC-MS and MS(n). This comprehensive approach enabled us to determine a number of novel modifications of protein-linked glycans, including N-methyl-2-aminoethylphosphonate on mannose and N-acetylhexosamine residues, core β1,3-linked mannose, zwitterionic moieties on core Galβ1,4Fuc motifs, additional mannose residues on oligomannosidic glycans, and bisubstituted antennal fucose; furthermore, typical invertebrate N-glycans with sulfate and core fucose residues are present in this gastropod.

Dual modifications strategy to quantify neutral and sialylated N-glycans simultaneously by MALDI-MS

Differences in ionization efficiency among neutral and sialylated glycans prevent direct quantitative comparison by their respective mass spectrometric signals. To overcome this challenge, we developed an integrated chemical strategy, Dual Reactions for Analytical Glycomics (DRAG), to quantitatively compare neutral and sialylated glycans simultaneously by MALDI-MS. Initially, two glycan samples to be compared undergo reductive amination with 2-aminobenzoic acid and 2-¹³[C₆]-aminobenzoic acid, respectively. The different isotope-incorporated glycans are then combined and subjected to the methylamidation of the sialic acid residues in one mixture, homogenizing the ionization responses for all neutral and sialylated glycans. By this approach, the expression change of relevant glycans between two samples is proportional to the ratios of doublet signals with a static 6 Da mass difference in MALDI-MS and the change in relative abundance of any glycan within samples can also be determined. The strategy was chemically validated using well-characterized N-glycans from bovine fetuin and IgG from human serum. By comparing the N-glycomes from a first morning (AM) versus an afternoon (PM) urine sample obtained from a single donor, we further demonstrated the ability of DRAG strategy to measure subtle quantitative differences in numerous urinary N-glycans.