Oxidative release of natural glycans for functional glycomics

Unraveling the complexity of glycosphingolipidome: the key role of mass spectrometry in the structural analysis of glycosphingolipids

Glycosphingolipids (GSL) are a highly heterogeneous class of lipids representing the majority of the sphingolipid category. GSL are fundamental constituents of cellular membranes that have key roles in various biological processes, such as cellular signaling, recognition, and adhesion. Understanding the structural complexity of GSL is pivotal for unraveling their functional significance in a biological context, specifically their crucial role in the pathophysiology of various diseases. Mass spectrometry (MS) has emerged as a versatile and indispensable tool for the structural elucidation of GSL enabling a deeper understanding of their complex molecular structures and their key roles in cellular dynamics and patholophysiology. Here, we provide a thorough overview of MS techniques tailored for the analysis of GSL, emphasizing their utility in probing GSL intricate structures to advance our understanding of the functional relevance of GSL in health and disease. The application of tandem MS using diverse fragmentation techniques, including novel ion activation methodologies, in studying glycan sequences, linkage positions, and fatty acid composition is extensively discussed. Finally, we address current challenges, such as the detection of low-abundance species and the interpretation of complex spectra, and offer insights into potential solutions and future directions by improving MS instrumentation for enhanced sensitivity and resolution, developing novel ionization techniques, or integrating MS with other analytical approaches for comprehensive GSL characterization.

[Applications of chromatography in glycomics]

Glycomics, an emerging "omics" technology that was developed after genomics and proteomics, is a discipline that studies the composition, structure, and functions of glycomes in cells, tissues, and organisms. Glycomics plays key roles in understanding the laws of major life activities, disease prevention and treatment, and drug quality control and development. At present, the structural analysis of glycans relies mainly on mass spectrometry. However, glycans have low abundance in biological samples. In addition, factors such as variable monosaccharide compositions, differences in glycosidic bond positions and modes, diverse branching structures, contribute to the complexity of the compositions and structures of glycans, posing great challenges to glycomics research. Liquid chromatography can effectively remove matrix interferences and enhance glycan separation to improve the mass spectrometric response of glycans. Thus, liquid chromatography and liquid chromatography coupled with mass spectrometry are important technical tools that have been actively applied to solve these problems; these technologies play indispensable roles in glycomics research. Different studies have highlighted similarities and differences in the applications of various types of liquid chromatography, which also reflects the versatility and flexibility of this technology. In this review, we first discuss the enrichment methods for glycans and their applications in glycomics research from the perspective of chromatographic separation mechanisms. We then compare the advantages and disadvantages of these methods. Some glycan-enrichment modes include affinity, hydrophilic interactions, size exclusion, and porous graphitized carbon adsorption. A number of newly developed materials exhibit excellent glycan-enrichment ability. We enumerate the separation mechanisms of reversed-phase high performance liquid chromatography (RP-HPLC), high performance anion-exchange chromatography (HPAEC), hydrophilic interaction chromatography (HILIC), and porous graphitic carbon (PGC) chromatography in the separation and analysis of glycans, and describe the applications of these methods in the separation of glycans, glycoconjugates, and glyco-derivatives. Among these methods, HILIC and PGC chromatography are the most widely used, whereas HPAEC and RP-HPLC are less commonly used. The HILIC and RP-HPLC modes are often used for the separation of derived glycans. The ionization efficiency and detectability of glycans are significantly improved after derivatization. However, the derivatization process is relatively cumbersome, and byproducts inevitably affect the accuracy and completeness of the detection results. HPAEC and PGC chromatography exhibit good separation effects on nonderivative glycans, but issues related to the detection integrity of low-abundance glycans owing to their poor detection effect continue to persist. Therefore, the appropriate analytical method for a specific sample or target analyte or mutual verification must be selected. Finally, we highlight the research progress in various chromatographic methods coupled with mass spectrometry for glycomics analysis. Significant progress has been made in glycomics research in recent years owing to advancements in the development of chromatographic separation techniques. However, several significant challenges remain. As the development of novel separation materials and methods continues, chromatographic techniques may be expected to play a critical role in future glycomics research.

O-GlycoIsoQuant: A Novel O-Glycome Quantitative Approach through Superbase Release and Isotopic Girard's P Labeling

Quantitative glycosylation analysis serves as an effective tool for detecting changes in glycosylation patterns in cancer and various diseases. However, compared with N-glycans, O-glycans present challenges in both qualitative and quantitative mass spectrometry analysis due to their low abundance, ease of peeling, lack of a universal enzyme, and difficult accessibility. To address this challenge, we developed O-GlycoIsoQuant, a novel O-glycome quantitative approach utilizing superbase release and isotopic Girard's P labeling. This method facilitates rapid and efficient nonreducing β-elimination to dissociate O-glycans from proteins using the organic superbase, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), combined with light and heavy isotopic Girard's reagent P (GP) labeling for relative quantification of O-glycans by mass spectrometry. Employing this method, labeled O-glycans exhibit a double peak with a mass difference of 5 Da, suitable for stable relative quantification. The O-GlycoIsoQuant method is characterized by its high labeling efficiency, excellent reproducibility (CV < 20%), and good linearity (R2 > 0.99), across a dynamic range spanning a 100-fold range. This method was applied to various complex sample types, including human serum, porcine spermatozoa, human saliva, and urinary extracellular vesicles, detecting 33, 39, 49, and 37 O-glycans, respectively, thereby demonstrating its broad applicability.

Labeling of Mucin-Type O-Glycans for Quantification Using Liquid Chromatography and Fluorescence Detection

O-glycosylation is a common post-translational modification that is essential for the defensive properties of mucus barriers. Incomplete and altered O-glycosylation is often linked to severe diseases, such as cancer, cystic fibrosis, and chronic obstructive pulmonary disease. Originating from a nontemplate-driven biosynthesis, mucin-type O-glycan structures are very complex. They are often present as heterogeneous mixtures containing multiple isomers. Therefore, the analysis of complex O-glycan mixtures usually requires hyphenation of orthogonal techniques such as liquid chromatography (LC), ion mobility spectrometry, and mass spectrometry (MS). However, MS-based techniques are mainly qualitative. Moreover, LC separation of O-glycans often lacks reproducibility and requires sophisticated data treatment and analysis. Here we present a mucin-type O-glycomics analysis workflow that utilizes hydrophilic interaction liquid chromatography for separation and fluorescence labeling for detection and quantification. In combination with mass spectrometry, a detailed analysis on the relative abundance of specific mucin-type O-glycan compositions and features, such as fucose, sialic acids, and sulfates, is performed. Furthermore, the average number of monosaccharide units of O-glycans in different samples was determined. To demonstrate universal applicability, the method was tested on mucins from different tissue types and mammals, such as bovine submaxillary mucins, porcine gastric mucins, and human milk mucins. To account for day-to-day retention time shifts in O-glycan separations and increase the comparability between different instruments and laboratories, we included fluorescently labeled dextran ladders in our workflow. In addition, we set up a library of glucose unit values for all identified O-glycans, which can be used to simplify the identification process of glycans in future analyses.

Reusable glycan microarrays using a microwave assisted wet-erase (MAWE) process

Modern studies on binding of proteins to glycans commonly involve the use of synthetic glycans and their derivatives in which a small amount of the material is covalently printed onto a functionalized slide in a glycan microarray format. While incredibly useful to explore binding interactions with many types of samples, the common techniques involve drying the slides, which leads to irreversible association of the protein to the spots on slides to which they bound, thus limiting a microarray to a single use. We have developed a new technique which we term Microwave Assisted Wet-Erase (MAWE) glycan microarrays. In this approach we image the slides under wet conditions to acquire the data, after which the slides are cleaned of binding proteins by treatment with a denaturing SDS solution along with microwave treatment. Slides cleaned in this way can be reused multiple times, and an example here shows the reuse of a single array 15 times. We also demonstrate that this method can be used for a single-array per slide or multi-array per slide platforms. Importantly, the results obtained using this technique for a variety of lectins sequentially applied to a single array, are concordant to those obtained via the classical dry approaches on multiple slides. We also demonstrate that MAWE can be used for different types of samples, such as serum for antibody binding, and whole cells, such as yeast. This technique will greatly conserve precious glycans and prolong the use of existing and new glycan microarrays.

Integrated analysis of natural glycans using a versatile pyrazolone-type heterobifunctional tag ANPMP

Glycans mediate various biological processes through carbohydrate-protein interactions, and glycan microarrays have become indispensable tools for understanding these mechanisms. However, advances in functional glycomics are hindered by the absence of convenient and universal methods for obtaining natural glycan libraries with diverse structures from glycoconjugates. To address this challenge, we have developed an integrative approach that enables one-pot release and simultaneously capture, separation, structural characterization, and functional analysis of N/O-glycans. Using this approach, glycoconjugates are incubated with a pyrazolone-type heterobifunctional tag-ANPMP to obtain glycan-2ANPMP conjugates, which are then converted to glycan-AEPMP conjugates. We prepared a tagged glycan library from porcine gastric mucin, soy protein, human milk oligosaccharides, etc. Following derivatization by N-acetylation and permethylation, glycans were subjected to detailed structural characterization by ESI-MSn analysis, which revealed >83 highly pure glycan-AEPMPs containing various natural glycan epitopes. A shotgun microarray is constructed to study the fine details of glycan-bindings by proteins and antisera.

Development of mass spectrometric glycan characterization tags using acid-base chemistry and/or free radical chemistry

Despite recent advances in glycomics, glycan characterization still remains an analytical challenge. Accordingly, numerous glycan-tagging reagents with different chemistries were developed, including those involving acid-base chemistry and/or free radical chemistry. Acid-base chemistry excels at dissociating glycans into their constituent components in a systematic and predictable manner to generate cleavages at glycosidic bonds. Glycans are also highly susceptible to depolymerization by free radical processes, which is supported by results observed from electron-activated dissociation techniques. Therefore, the free radical activated glycan sequencing (FRAGS) reagent was developed so as to possess the characteristics of both acid-base and free radical chemistry, thus generating information-rich glycosidic bond and cross-ring cleavages. Alternatively, the free radical processes can be induced via photodissociation of the specific carbon-iodine bond which gives birth to similar fragmentation patterns as the FRAGS reagent. Furthermore, the methylated-FRAGS (Me-FRAGS) reagent was developed to eliminate glycan rearrangements by way of a fixed charged as opposed to a labile proton, which would otherwise yield additional, yet unpredictable, fragmentations including internal residue losses or multiple external residue losses. Lastly, to further enhance glycan enrichment and characterization, solid-support FRAGS was developed.

Synthetic Catalysts for Selective Glycan Cleavage from Glycoproteins and Cells

In situ modification of glycans requires extraordinary molecular recognition of highly complex and subtly different carbohydrates, followed by reactions at precise locations on the substrate. We here report synthetic catalysts that under physiological conditions cleave a predetermined oligosaccharide block such as a branched trimannose or the entire N-glycan of a glycoprotein, while nontargeted glycoproteins stay intact. The method also allows α2-6-sialylated galactosides to be removed preferentially over the α2-3-linked ones from cell surfaces, highlighting the potential of these synthetic glycosidases for glycan editing.

Simple Routes to Stable Isotope-Coded Native Glycans

Understanding the biological role of protein-linked glycans requires the reliable identification of glycans. Isomer separation and characterization often entail mass spectrometric detection preceded by high-performance chromatography on porous graphitic carbon. To this end, stable isotope-labeled glycans have emerged as powerful tools for retention time normalization. Hitherto, such standards were obtained by chemoenzymatic or purely enzymatic methods, which introduce, e.g., 13C-containing N-acetyl groups or galactose into native glycans. Glycan release with anhydrous hydrazine opens another route for heavy isotope introduction via concomitant de-N-acetylation. Here, we describe that de-N-acetylation can also be achieved with hydrazine hydrate, which is a more affordable and less hazardous reagent. Despite the slower reaction rate, complete conversion is achievable in 72 h at 100 °C for glycans with biantennary glycans with or without sialic acids. Shorter incubation times allow for the isolation of intermediate products with a defined degree of free amino groups, facilitating introduction of different numbers of heavy isotopes. Mass encoded glycans obtained by this versatile approach can serve a broad range of applications, e.g., as internal standards for isomer-specific studies of N-glycans, O-glycans, and human milk oligosaccharide by LC-MS on either porous graphitic carbon or─following permethylation─on reversed phase.

The functional roles of protein glycosylation in human maternal-fetal crosstalk

BACKGROUND

The establishment of maternal-fetal crosstalk is vital to a successful pregnancy. Glycosylation is a post-translational modification in which glycans (monosaccharide chains) are attached to an organic molecule. Glycans are involved in many physiological and pathological processes. Human endometrial epithelium, endometrial gland secretions, decidual immune cells, and trophoblasts are highly enriched with glycoconjugates and glycan-binding molecules important for a healthy pregnancy. Aberrant glycosylation in the placenta and uterus has been linked to repeated implantation failure and various pregnancy complications, but there is no recent review summarizing the functional roles of glycosylation at the maternal-fetal interface and their associations with pathological processes.

OBJECTIVE AND RATIONALE

This review aims to summarize recent findings on glycosylation, glycosyltransferases, and glycan-binding receptors at the maternal-fetal interface, and their involvement in regulating the biology and pathological conditions associated with endometrial receptivity, placentation and maternal-fetal immunotolerance. Current knowledge limitations and future insights into the study of glycobiology in reproduction are discussed.

SEARCH METHODS

A comprehensive PubMed search was conducted using the following keywords: glycosylation, glycosyltransferases, glycan-binding proteins, endometrium, trophoblasts, maternal-fetal immunotolerance, siglec, selectin, galectin, repeated implantation failure, early pregnancy loss, recurrent pregnancy loss, preeclampsia, and fetal growth restriction. Relevant reports published between 1980 and 2023 and studies related to these reports were retrieved and reviewed. Only publications written in English were included.

OUTCOMES

The application of ultrasensitive mass spectrometry tools and lectin-based glycan profiling has enabled characterization of glycans present at the maternal-fetal interface and in maternal serum. The endometrial luminal epithelium is covered with highly glycosylated mucin that regulates blastocyst adhesion during implantation. In the placenta, fucose and sialic acid residues are abundantly presented on the villous membrane and are essential for proper placentation and establishment of maternal-fetal immunotolerance. Glycan-binding receptors, including selectins, sialic-acid-binding immunoglobulin-like lectins (siglecs) and galectins, also modulate implantation, trophoblast functions and maternal-fetal immunotolerance. Aberrant glycosylation is associated with repeated implantation failure, early pregnancy loss and various pregnancy complications. The current limitation in the field is that most glycobiological research relies on association studies, with few studies revealing the specific functions of glycans. Technological advancements in analytic, synthetic and functional glycobiology have laid the groundwork for further exploration of glycans in reproductive biology under both physiological and pathological conditions.

WIDER IMPLICATIONS

A deep understanding of the functions of glycan structures would provide insights into the molecular mechanisms underlying their involvement in the physiological and pathological regulation of early pregnancy. Glycans may also potentially serve as novel early predictive markers and therapeutic targets for repeated implantation failure, pregnancy loss, and other pregnancy complications.

Sialic acid O-acetylation patterns and glycosidic linkage type determination by ion mobility-mass spectrometry

O-acetylation is a common modification of sialic acids that has been implicated in a multitude of biological and disease processes. A lack of analytical methods that can determine exact structures of sialic acid variants is a hurdle to determine roles of distinct O-acetylated sialosides. Here, we describe a drift tube ion mobility-mass spectrometry approach that can elucidate exact O-acetylation patterns as well as glycosidic linkage types of sialosides isolated from complex biological samples. It is based on the use of a library of synthetic O-acetylated sialosides to establish intrinsic collision cross section (CCS) values of diagnostic fragment ions. The CCS values were used to characterize O-acetylated sialosides from mucins and N-linked glycans from biologicals as well as equine tracheal and nasal tissues. It uncovered contrasting sialic acid linkage types of acetylated and non-acetylated sialic acids and provided a rationale for sialic acid binding preferences of equine H7 influenza A viruses.

Mapping the Acetylamino and Carboxyl Groups on Glycans by Engineered α-Hemolysin Nanopores

Glycan is a crucial class of biological macromolecules with important biological functions. Functional groups determine the chemical properties of glycans, which further affect their biological activities. However, the structural complexity of glycans has set a technical hurdle for their direct identification. Nanopores have emerged as highly sensitive biosensors that are capable of detecting and characterizing various analytes. Here, we identified the functional groups on glycans with a designed α-hemolysin nanopore containing arginine mutations (M113R), which is specifically sensitive to glycans with acetamido and carboxyl groups. Molecular dynamics simulations indicated that the acetamido and carboxyl groups of the glycans produce unique electrical signatures by forming polar and electrostatic interactions with the M113R nanopores. Using these electrical features as the fingerprints, we mapped the length of the glycans containing acetamido and carboxyl groups at the monosaccharide, disaccharide, and trisaccharide levels. This proof-of-concept study provides a promising foundation for developing single-molecule glycan fingerprinting libraries and demonstrates the capability of biological nanopores in glycan sequencing.

Seamless Coupling of Chemical Glycan Release and Labeling for an Accelerated Protein N-Glycan Sample Preparation Workflow

Analytical methods fr direct quantitative N-glycan analysis require a sequence of sample preparation and clean-up steps that result in reduced glycan recovery. Therefore, we aimed to combine glycan release and labeling steps. Based on the hypothesis that the reaction mechanism for oxidative chemical glycan release comprises a stable glycan isocyanate intermediate, we investigated whether this could be exploited for the in-situ preparation of fluorescent glycan conjugates. ANTS-labeled N-glycans were derived from chicken ovalbumin via an in-situ chemical release/coupling approach and by standard Peptide-N-Glycosidase F (PNGase F) digestion/reductive amination. Synoptic fluorescence-assisted carbohydrate electrophoresis with UV detection (FACE-UV) analysis yielded matching patterns of fluorescent N-glycan bands in the expected electrophoretic mobility range between hexose units GU-5 and GU-11 of the standard. Anthranilamide (2-AB)-glycan conjugates prepared from a test glycoprotein carrying a predominant Core-F glycan gave single predominant peaks in hydrophilic interaction chromatography with fluorescence detection (HILIC-FLD) and electrospray ionization mass spectrometry (ESI-MS) spectra in agreement with sodiated triply charged Core-F-AB conjugates for both the standard and the in-situ coupling methods. The Core-F-AB conjugate prepared by the in-situ coupling approach had a slightly elevated retention time on HILIC-FLD and an ESI-MS m/z peak in line with a urea-bonded glycan-AB conjugate, with closed pyran ring structures on the glycan moiety. Glycan isocyanates intermittently formed during chemical glycan release, which could be utilized to prepare labeled glycan samples directly from glycoproteins and fluorescent dyes bearing a primary amine functional group.

Growing impact of sialic acid-containing glycans in future drug discovery

In nature, almost all cells are covered with a complex array of glycan chain namely sialic acids or nuraminic acids, a negatively charged nine carbon sugars which is considered for their great therapeutic importance since long back. Owing to its presence at the terminal end of lipid bilayer (commonly known as terminal sugars), the well-defined sialosides or sialoconjugates have served pivotal role on the cell surfaces and thus, the sialic acid-containing glycans can modulate and mediate a number of imperative cellular interactions. Understanding of the sialo-protein interaction and their roles in vertebrates in regard of normal physiology, pathological variance, and evolution has indeed a noteworthy journey in medicine. In this tutorial review, we present a concise overview about the structure, linkages in chemical diversity, biological significance followed by chemical and enzymatic modification/synthesis of sialic acid containing glycans. A more focus is attempted about the recent advances, opportunity, and more over growing impact of sialosides and sialoconjugates in future drug discovery and development.

Glycoproteins as a Platform for Making Proton-Conductive Free-Standing Biopolymers

Biopolymers are an attractive environmentally friendly alternative to common synthetic polymers, whereas primarily proteins and polysaccharides are the biomacromolecules that are used for making the biopolymer. Due to the breadth of side chains of such biomacromolecules capable of participating in hydrogen bonding, proteins and polysaccharide biopolymers were also used for the making of proton-conductive biopolymers. Here, we introduce a new platform for combining the merits of both proteins and polysaccharides while using a glycosylated protein for making the biopolymer. We use mucin as our starting point, whereas being a waste of the food industry, it is a highly available and low-cost glycoprotein. We show how we can use different chemical strategies to target either the glycan part or specific amino acids for both crosslinking between the different glycoproteins, thus making a free-standing biopolymer, as well as for introducing superior proton conductivity properties to the formed biopolymer. The resultant proton-conductive soft biopolymer is an appealing candidate for any soft bioelectronic application.

A Rapid Protocol for Preparing 8-Aminopyrene-1,3,6-Trisulfonate-Labeled Glycans for Capillary Electrophoresis-Based Enzyme Assays

Purified glycan standards are required for glycan arrays, characterizing substrate specificities of glycan-active enzymes, and to serve as retention-time or mobility standards for various separation techniques. This chapter describes a method for the rapid separation, and subsequent desalting, of glycans labeled with the highly fluorescent fluorophore 8-aminopyrene-1,3,6-trisulfonate (APTS). By using fluorophore-assisted carbohydrate electrophoresis (FACE) on polyacrylamide gels, a technique amenable to equipment readily available in most molecular biology laboratories, many APTS-labeled glycans can be simultaneously resolved. Excising specific gel bands containing the desired APTS-labeled glycans, followed by glycan elution from the gel by simple diffusion and subsequent solid-phase extraction (SPE)-based desalting, affords a single glycan species free of excess labeling reagents and buffer components. The described protocol also offers a simple, rapid method for the simultaneous removal of excess APTS and unlabeled glycan material from reaction mixtures. This chapter describes a FACE/SPE procedure ideal for preparing glycans for capillary electrophoresis (CE)-based enzyme assays, as well as for the purification of rare, commercially unavailable glycans from tissue culture samples.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth 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 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of 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. Most of the applications are 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. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

An Efficient and Economical N-Glycome Sample Preparation Using Acetone Precipitation

Due to the critical role of the glycome in organisms and its close connections with various diseases, much time and effort have been dedicated to glycomics-related studies in the past decade. To achieve accurate and reliable identification and quantification of glycans extracted from biological samples, several analysis methods have been well-developed. One commonly used methodology for the sample preparation of N-glycomics usually involves enzymatic cleavage by PNGase F, followed by sample purification using C18 cartridges to remove proteins. PNGase F and C18 cartridges are very efficient both for cleaving N-glycans and for protein removal. However, this method is most suitable for a limited quantity of samples. In this study, we developed a sample preparation method focusing on N-glycome extraction and purification from large-scale biological samples using acetone precipitation. The N-glycan yield was first tested on standard glycoprotein samples, bovine fetuin and complex biological samples, and human serum. Compared to C18 cartridges, most of the sialylated N-glycans from human serum were detected with higher abundance after acetone precipitation. However, C18 showed a slightly higher efficiency for protein removal. Using the unfiltered human serum as the baseline, around 97.7% of the proteins were removed by acetone precipitation, while more than 99.9% of the proteins were removed by C18 cartridges. Lastly, the acetone precipitation was applied to N-glycome extraction from egg yolks to demonstrate large-scale glycomics sample preparation.

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 in demystifying O-glycosylation in health and disease

O-Glycosylation is one of the most common protein post-translational modifications (PTM) and plays an essential role in the pathophysiology of diseases. However, the complexity of O-glycosylation and the lack of specific enzymes for the processing of O-glycans and their O-glycopeptides make O-glycosylation analysis challenging. Recently, research on O-glycosylation has received attention owing to technological innovation and emerging O-glycoproteases. Several serine/threonine endoproteases have been found to specifically cleave O-glycosylated serine or threonine, allowing for the systematic analysis of O-glycoproteins. In this review, we first assessed the field of protein O-glycosylation over the past decade and used bibliometric analysis to identify keywords and emerging trends. We then summarized recent advances in O-glycosylation, covering several aspects: O-glycan release, site-specific elucidation of intact O-glycopeptides, identification of O-glycosites, characterization of different O-glycoproteases, mass spectrometry (MS) fragmentation methods for site-specific O-glycosylation assignment, and O-glycosylation data analysis. Finally, the role of O-glycosylation in health and disease was discussed.

Activation of Neutrophils by Mucin–Vaterite Microparticles

Nano- and microparticles enter the body through the respiratory airways and the digestive system, or form as biominerals in the gall bladder, salivary glands, urinary bladder, kidney, or diabetic pancreas. Calcium, magnesium, and phosphate ions can precipitate from biological fluids in the presence of mucin as hybrid nanoparticles. Calcium carbonate nanocrystallites also trap mucin and are assembled into hybrid microparticles. Both mucin and calcium carbonate polymorphs (calcite, aragonite, and vaterite) are known to be components of such biominerals as gallstones which provoke inflammatory reactions. Our study was aimed at evaluation of neutrophil activation by hybrid vaterite–mucin microparticles (CCM). Vaterite microparticles (CC) and CCM were prepared under standard conditions. The diameter of CC and CCM was 3.3 ± 0.8 µm and 5.8 ± 0.7 µm, with ƺ-potentials of −1 ± 1 mV and −7 ± 1 mV, respectively. CC microparticles injured less than 2% of erythrocytes in 2 h at 1.5 mg mL−1, and no hemolysis was detected with CCM; this let us exclude direct damage of cellular membranes by microparticles. Activation of neutrophils was analyzed by luminol- and lucigenin-dependent chemiluminescence (Lum-CL and Luc-CL), by cytokine gene expression (IL-6, IL-8, IL-10) and release (IL-1β, IL-6, IL-8, IL-10, TNF-α), and by light microscopy of stained smears. There was a 10-fold and higher increase in the amplitude of Lum-CL and Luc-CL after stimulation of neutrophils with CCM relative to CC. Adsorption of mucin onto prefabricated CC microparticles also contributed to activation of neutrophil CL, unlike mucin adsorption onto yeast cell walls (zymosan); adsorbed mucin partially suppressed zymosan-stimulated production of oxidants by neutrophils. Preliminary treatment of CCM with 0.1–10 mM NaOCl decreased subsequent activation of Lum-CL and Luc-CL of neutrophils depending on the used NaOCl concentration, presumably because of the surface mucin oxidation. Based on the results of ELISA, incubation of neutrophils with CCM downregulated IL-6 production but upregulated that of IL-8. IL-6 and IL-8 gene expression in neutrophils was not affected by CC or CCM according to RT2-PCR data, which means that post-translational regulation was involved. Light microscopy revealed adhesion of CC and CCM microparticles onto the neutrophils; CCM increased neutrophil aggregation with a tendency to form neutrophil extracellular traps (NETs). We came to the conclusion that the main features of neutrophil reaction to mucin–vaterite hybrid microparticles are increased oxidant production, cell aggregation, and NET-like structure formation, but without significant cytokine release (except for IL-8). This effect of mucin is not anion-specific since particles of powdered kidney stone (mainly calcium oxalate) in the present study or calcium phosphate nanowires in our previous report also activated Lum-CL and Luc-CL response of neutrophils after mucin sorption.

Release of protein N-glycans by effectors of a Hofmann carboxamide rearrangement

Background: Chemical methods for glycan release have gained traction because of their cost efficiency, accelerated reaction time and ability to release glycans not amenable to enzymatic cleavage. Oxidative chemical glycan release via hypochlorite treatment has been shown to be a convenient and efficient method that yields N-glycans similar to classical PNGase F digestion. We observed that the initial steps of the suggested mechanism for the oxidative release of glycans from glycoproteins by hypohalites showed similarities to the initiating steps of the classical Hofmann rearrangement of carboxamides. Therefore, we investigated the ability of different stable effectors of a Hofmann-type carboxamide rearrangement to efficiently and selectively release N-glycans from glycoproteins.

Methods: Released glycans obtained from different experimental chemical release approaches were analyzed by HILIC-FLD, BHZ-FACE and ESI-MS and evaluated with respect to electrophoretic mobility, retention time and integrated peak area for resolved glycans.

Results: We show that the known Hoffmann catalysts 1,3-dichloro-5,5-dimethylhydantoin, the hypervalent organoiodine (III) compound diacetoxy-iodobenzene as well as in-situ hypobromite generation using Oxone^® and potassium bromide are all capable of releasing protein-bound N-glycans in good yield. Among the compounds investigated, diacetoxy-iodobenzene was capable of releasing glycans in the absence of alkali. Detailed investigations of the bromide/Oxone^® method revealed a dependence of N-glycan release efficiency from the temporal order of bromide addition to the reaction mix as well as from a molar excess of bromide over Oxone^®. Conclusions. These findings suggest that the oxidative release of N-glycans occurs via the initiating steps of a Hofmann carboxamide rearrangement. Hypervalent organoiodine compounds hold the promise of releasing glycans in the absence of alkali. The in-situ generation of hypobromite by bromide/Oxone^® produces a consistent defined amount of reagent for rapid N-glycan release for both analytical and preparative purposes.

Rapid oxidative release of fungal mannan for detection by immunoassay

Detection of fungal cells in infected tissue by procedures such as KOH microscopy and histopathology are well-established methods in medical mycology. However, microscopy requires skilled personnel, specialized equipment, and may take considerable time to a result. An alternative approach is immunoassay for detection of fungal mannans in tissue as a biomarker for the presence of fungal cells. However, mannan is a component of the fungal cell wall, and detection of mannan would require a facile means for mannan extraction prior to detection by immunoassay. In this study we evaluated a broad spectrum of extraction reagents using Trichophyton rubrum mycelia and Saccharomyces cerevisiae Mnn2 blastoconidia as model fungi. Oxidative release by treatment with dilute bleach proved to be a novel and highly effective procedure. Complete extraction occurred in as little as 2-4 min. Detergents, chaotropes and acid were ineffective. Strong base released mannan but was less efficient than oxidative release and required the use of highly corrosive reagents. Oxidative release of cell wall mannans from fungal mycelia and blastoconidia may be an effective first step in immunodetection of fungi in tissues from infected humans, animals or plants that could be done at or near the diagnostic point of need.

Tools for mammalian glycoscience research

Cellular carbohydrates or glycans are critical mediators of biological function. Their remarkably diverse structures and varied activities present exciting opportunities for understanding many areas of biology. In this primer, we discuss key methods and recent breakthrough technologies for identifying, monitoring, and manipulating glycans in mammalian systems.

Qualitative and quantitative mass spectrometry comparison of characteristic galactosyl lactose isomers from goat milk at different lactation stages

Galactooligosaccharides are composed mainly of galactosyl lactose, which is important for infant growth and as a functional food additive. Although galactosyl lactose is abundant in goat milk, its complex structure has hindered the separation and analysis of its isomers. In this study, 5 isomers of goat milk galactosyl lactose were separated by HPLC: β6'-galactosyl lactose (β6'-GL), α6'-galactosyl lactose (α6'-GL), β4'-galactosyl lactose (β4'-GL), α3'-galactosyl lactose (α3'-GL), and β3'-galactosyl lactose (β3'-GL). This composition differs from that of commercial galactooligosaccharide products, which comprise mainly β-configuration oligosaccharides. The isomers were then qualitatively and quantitatively compared at different lactation stages using online HPLC-mass spectrometry. Relative quantitative analysis showed that the total content of the 5 galactosyl lactose isomers was highest in transitional goat milk. Specifically, β3'-GL was the main isomer in colostrum and α3'-GL was the main isomer in transitional and mature milk. β6'-Galactosyl lactose and β4'-GL tended to increase and then decrease during lactation. Moreover, α3'-GL content was 2 times higher than in colostrum and 10 times higher in transitional milk than in mature milk; in contrast, for β3'-GL, the values were 5 and 2 times higher, respectively. Absolute quantitative analysis revealed that β3'-GL was the most abundant isomers in colostrum (32.3 mg/L), and α3'-GL was the most abundant in transitional milk (88.1 mg/L) and mature milk (36.3 mg/L). These findings provide an important quantitative basis for understanding the relationship between structure and function of galactosyl lactose in goat milk, as well as its exploitation as a functional food.

Regeneration of Free Reducing Glycans from Reductive Amination-Tagged Glycans by Oxone

Glycans are usually fluorescently tagged by reductive amination for analytic tools. However, free reducing glycan regeneration is sometimes important and necessary for further structural or functional studies. Here, we introduce a new method for efficiently removing fluorescent tags from glycoconjugates by a simple treatment with Oxone. This method is proven to be fast and general after being tested on a series of common saccharides and widely used tags. We successfully achieved N-glycopeptide synthesis by using the regenerated glycans.

Recent advances and trends in sample preparation and chemical modification for glycan analysis

Growing significance of glycosylation in protein functions has accelerated the development of methodologies for detection, identification, and characterization of protein glycosylation. In the past decade, glycobiology research has been advanced by innovative techniques with further progression in the post-genome era. Although significant technical progress has been made in terms of analytical throughput, comprehensiveness, and sensitivity, most methods for glycosylation analysis still require laborious and time-consuming sample preparation tasks. Additionally, sample preparation methods that are focused on specific glycan(s) require an in-depth understanding of various issues in glycobiology. In this review, modern sample preparation and chemical modification methods for the structural and quantitative glycan analyses together with the challenges and advantages of recent sample preparation methods are summarized. The techniques presented herein can facilitate the exploration of biomarkers, understanding of unknown glycan functions, and development of biopharmaceuticals.

Profiling of glycosphingolipids with SCDase digestion and HPLC-FLD-MS

Lipid components of cells and tissues feature a large diversity of structures that present a challenging problem for molecular analysis. Glycolipids from mammalian cells contain glycosphingolipids (GSLs) as their major glycolipid component, and these structures vary in the identity of the glycan headgroup as well as the structure of the fatty acid and sphingosine (Sph) tails. Analysis of intact GSLs is challenging due to the low abundance of these species. Here, we develop a new strategy for the analysis of lyso-GSL (l-GSL), GSL that retain linkage of the glycan headgroup with the Sph base. The analysis begins with digestion of a GSL sample with sphingolipid ceramide N-deacylase (SCDase), followed by labelling with an amine-reactive fluorophore. The sample was then analyzed by HPLC-FLD-MS and quantitated by addition of an external standard. This method was compared to analysis of GSL glycans after cleavage by an Endoglycoceramidase (EGCase) enzyme and labeling with a fluorophore (2-anthranilic acid, 2AA). The two methods are complementary, with EGCase providing improved signal (due to fewer species) and SCDase providing analysis of lyso-GSL. Importantly the SCDase method provides Sph composition of GSL species. We demonstrate the method on cultured human cells (Jurkat T cells) and tissue homogenate (porcine brain).

SARS-CoV-2 and other coronaviruses bind to phosphorylated glycans from the human lung

SARS-CoV, MERS-CoV, and potentially SARS-CoV-2 emerged as novel human coronaviruses following cross-species transmission from animal hosts. Although the receptor binding characteristics of human coronaviruses are well documented, the role of carbohydrate binding in addition to recognition of proteinaceous receptors has not been fully explored. Using natural glycan microarray technology, we identified N-glycans in the human lung that are recognized by various human and animal coronaviruses. All viruses tested, including SARS-CoV-2, bound strongly to a range of phosphorylated, high mannose N-glycans and to a very specific set of sialylated structures. Examination of two linked strains, human CoV OC43 and bovine CoV Mebus, reveals shared binding to the sialic acid form Neu5Gc (not found in humans), supporting the evidence for cross-species transmission of the bovine strain. Our findings, revealing robust recognition of lung glycans, suggest that these receptors could play a role in the initial stages of coronavirus attachment and entry.

Mass Spectrometry Imaging for Glycome in the Brain

Glycans are diverse structured biomolecules that play crucial roles in various biological processes. Glycosylation, an enzymatic system through which various glycans are bound to proteins and lipids, is the most common and functionally crucial post-translational modification process. It is known to be associated with brain development, signal transduction, molecular trafficking, neurodegenerative disorders, psychopathologies, and brain cancers. Glycans in glycoproteins and glycolipids expressed in brain cells are involved in neuronal development, biological processes, and central nervous system maintenance. The composition and expression of glycans are known to change during those physiological processes. Therefore, imaging of glycans and the glycoconjugates in the brain regions has become a “hot” topic nowadays. Imaging techniques using lectins, antibodies, and chemical reporters are traditionally used for glycan detection. However, those techniques offer limited glycome detection. Mass spectrometry imaging (MSI) is an evolving field that combines mass spectrometry with histology allowing spatial and label-free visualization of molecules in the brain. In the last decades, several studies have employed MSI for glycome imaging in brain tissues. The current state of MSI uses on-tissue enzymatic digestion or chemical reaction to facilitate successful glycome imaging. Here, we reviewed the available literature that applied MSI techniques for glycome visualization and characterization in the brain. We also described the general methodologies for glycome MSI and discussed its potential use in the three-dimensional MSI in the brain.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth 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 2016. 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. 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. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Chemoenzymatic modular assembly of O-GalNAc glycans for functional glycomics

O-GalNAc glycans (or mucin O-glycans) play pivotal roles in diverse biological and pathological processes, including tumor growth and progression. Structurally defined O-GalNAc glycans are essential for functional studies but synthetic challenges and their inherent structural diversity and complexity have limited access to these compounds. Herein, we report an efficient and robust chemoenzymatic modular assembly (CEMA) strategy to construct structurally diverse O-GalNAc glycans. The key to this strategy is the convergent assembly of O-GalNAc cores 1-4 and 6 from three chemical building blocks, followed by enzymatic diversification of the cores by 13 well-tailored enzyme modules. A total of 83 O-GalNAc glycans presenting various natural glycan epitopes are obtained and used to generate a unique synthetic mucin O-glycan microarray. Binding specificities of glycan-binding proteins (GBPs) including plant lectins and selected anti-glycan antibodies towards these O-GalNAc glycans are revealed by this microarray, promoting their applicability in functional O-glycomics. Serum samples from colorectal cancer patients and healthy controls are assayed using the array reveal higher bindings towards less common cores 3, 4, and 6 than abundant cores 1 and 2, providing insights into O-GalNAc glycan structure-activity relationships.

Comprehensive analysis of glycosphingolipid glycans by lectin microarrays and MALDI-TOF mass spectrometry

Glycosphingolipids (GSLs) are ubiquitous glycoconjugates present on the cell membrane; they play significant roles in many bioprocesses such as cell adhesion, embryonic development, signal transduction and carcinogenesis. Analyzing such amphiphilic molecules is a major challenge in the field of glycosphingolipidomics. We provide a step-by-step protocol that uses a lectin microarray to analyze GSL glycans from cultured cells. The procedure describes (i) extraction of GSLs from cell pellets, (ii) N-monodeacylation using sphingolipid ceramide N-deacylase digestion to form lyso-GSLs, (iii) fluorescence labeling at the newly exposed amine group, (iv) preparation of a lectin microarray, (v) GSL-glycan analysis by a lectin microarray, (vi) complementary mass spectrometry analysis and (vii) data acquisition and analysis. This method is high-throughput, low cost and easy to conduct, and it provides detailed information about glycan linkages. This protocol takes ~10 d.

Comparative Analysis of Different N-glycan Preparation Approaches and Development of Optimized Solid-Phase Permethylation Using Mass Spectrometry

Protein N-glycosylation characterization is challenging due to structural micro- and macro-heterogeneity. Although various N-glycan preparation strategies, including purification and derivatization, have been previously developed prior to mass spectrometric analysis, systematic evaluation still needs to be performed. This study compared the different N-glycan purification strategies, including filter-aided sample preparation, de-N-glycosylated protein precipitation, and trypsin digestion followed by reversed phase-based solid-phase extraction, and derivatization approaches, such as solid-phase permethylation, reductive amination, and reduction. With the comparative analysis, an optimized solid-phase permethylation (OSPP) workflow was developed for mass spectrometric N-glycomics, showing simplified analysis for N-glycan compositions and high yields using etanercept. The N-glycan samples released from trastuzumab and adalimumab were utilized to test OSPP to obtain their N-glycan profiles using mass spectrometry. Based on different standard procedures across laboratories, this study provides the reference for analysts to select an appropriate N-glycan preparation method with their research purposes.

Sweet systems: technologies for glycomic analysis and their integration into systems biology

Found in virtually every organism, glycans are essential molecules that play important roles in almost every aspect of biology. The composition of glycome, the repertoire of glycans in an organism or a biological sample, is often found altered in many diseases, including cancer, infectious diseases, metabolic and developmental disorders. Understanding how glycosylation and glycomic changes enriches our knowledge of the mechanisms of disease progression and sheds light on the development of novel therapeutics. However, the inherent diversity of glycan structures imposes challenges on the experimental characterization of glycomes. Advances in high-throughput glycomic technologies enable glycomic analysis in a rapid and comprehensive manner. In this review, we discuss the analytical methods currently used in high-throughput glycomics, including mass spectrometry, liquid chromatography and lectin microarray. Concomitant with the technical advances is the integration of glycomics into systems biology in the recent years. Herein we elaborate on some representative works from this recent trend to underline the important role of glycomics in such integrated approaches to disease.

Glycan chip based on structure-switchable DNA linker for on-chip biosynthesis of cancer-associated complex glycans

On-chip glycan biosynthesis is an effective strategy for preparing useful complex glycan sources and for preparing glycan-involved applications simultaneously. However, current methods have some limitations when analyzing biosynthesized glycans and optimizing enzymatic reactions, which could result in undefined glycan structures on a surface, leading to unequal and unreliable results. In this work, a glycan chip is developed by introducing a pH-responsive i-motif DNA linker to control the immobilization and isolation of glycans on chip surfaces in a pH-dependent manner. On-chip enzymatic glycosylations are optimized for uniform biosynthesis of cancer-associated Globo H hexasaccharide and its related complex glycans through stepwise quantitative analyses of isolated products from the surface. Successful interaction analyses of the anti-Globo H antibody and MCF-7 breast cancer cells with on-chip biosynthesized Globo H-related glycans demonstrate the feasibility of the structure-switchable DNA linker-based glycan chip platform for on-chip complex glycan biosynthesis and glycan-involved applications.

Glycoproteins as diagnostic and prognostic biomarkers for neurodegenerative diseases: A glycoproteomic approach

Neurodegenerative diseases (NDs) are incurable and can develop progressively debilitating disorders, including dementia and ataxias. Alzheimer's disease and Parkinson's disease are the most common NDs that mainly affect the elderly people. There is an urgent need to develop new diagnostic tools so that patients can be accurately stratified at an early stage. As a common post-translational modification, protein glycosylation plays a key role in physiological and pathological processes. The abnormal changes in glycosylation are associated with the altered biological pathways in NDs. The pathogenesis-related proteins, like amyloid-β and microtubule-associated protein tau, have altered glycosylation. Importantly, specific glycosylation changes in cerebrospinal fluid, blood and urine are valuable for revealing neurodegeneration in the early stages. This review describes the emerging biomarkers based on glycoproteomics in NDs, highlighting the potential applications of glycoprotein biomarkers in the early detection of diseases, monitoring of the disease progression, and measurement of the therapeutic responses. The mass spectrometry-based strategies for characterizing glycoprotein biomarkers are also introduced.

Mass Spectrometry-Based Methods for Immunoglobulin G N-Glycosylation Analysis

Mass spectrometry and its hyphenated techniques enabled by the improvements in liquid chromatography, capillary electrophoresis, novel ionization, and fragmentation modes are truly a cornerstone of robust and reliable protein glycosylation analysis. Boost in immunoglobulin G (IgG) glycan and glycopeptide profiling demands for both applied biomedical and research applications has brought many new advances in the field in terms of technical innovations, sample preparation, improved throughput, and confidence in glycan structural characterization. This chapter summarizes mass spectrometry basics, focusing on IgG and monoclonal antibody N-glycosylation analysis on several complexity levels. Different approaches, including antibody enrichment, glycan release, labeling, and glycopeptide preparation and purification, are covered and illustrated with recent breakthroughs and examples from the literature omitting excessive theoretical frameworks. Finally, selected highly popular methodologies in IgG glycoanalytics such as liquid chromatography-mass spectrometry and matrix-assisted laser desorption ionization are discussed more thoroughly yet in simple terms making this text a practical starting point either for the beginner in the field or an experienced clinician trying to make sense out of the IgG glycomic or glycoproteomic dataset.

Meta-heterogeneity: Evaluating and Describing the Diversity in Glycosylation Between Sites on the Same Glycoprotein

Mass spectrometry-based glycoproteomics has gone through some incredible developments over the last few years. Technological advances in glycopeptide enrichment, fragmentation methods, and data analysis workflows have enabled the transition of glycoproteomics from a niche application, mainly focused on the characterization of isolated glycoproteins, to a mature technology capable of profiling thousands of intact glycopeptides at once. In addition to numerous biological discoveries catalyzed by the technology, we are also observing an increase in studies focusing on global protein glycosylation and the relationship between multiple glycosylation sites on the same protein. It has become apparent that just describing protein glycosylation in terms of micro- and macro-heterogeneity, respectively, the variation and occupancy of glycans at a given site, is not sufficient to describe the observed interactions between sites. In this perspective we propose a new term, meta-heterogeneity, to describe a higher level of glycan regulation: the variation in glycosylation across multiple sites of a given protein. We provide literature examples of extensive meta-heterogeneity on relevant proteins such as antibodies, erythropoietin, myeloperoxidase, and a number of serum and plasma proteins. Furthermore, we postulate on the possible biological reasons and causes behind the intriguing meta-heterogeneity observed in glycoproteins.

Integrated glycomics strategy for the evaluation of glycosylation alterations in salivary proteins associated with type 2 diabetes mellitus

Glycosylation is involved in several biological processes, and its alterations can reflect the process of certain diseases. Type 2 diabetes mellitus (T2DM) has attained the status of a global pandemic; however, the difference in salivary protein glycosylation between healthy subjects and patients with T2DM has not been fully understood. In the present study, salivary specimens from patients with T2DM (n = 72) and healthy volunteers (HVs, n = 80) were enrolled and divided into discovery and validation cohorts. A method combining the lectin microarray and lectin blotting was employed to investigate and confirm the altered glycopatterns in salivary glycoproteins. Then, lectin-mediated affinity capture of glycoproteins and MALDI-TOF/TOF-MS were performed to obtain the precise structural information of the altered glycans. As a result, the glycopatterns recognized by 5 lectins (LEL, VVA, Jacalin, RCA120 and DSA) showed significant alteration in the saliva of T2DM patients. Notably, the glycopattern of Galβ-1,4GlcNAc (LacNAc) recognized by LEL exhibited a significant increase in T2DM patients compared to HVs in both discovery and validation cohorts. The MALDI-TOF/TOF-MS results indicated that there were 10 and 7 LacNAc-containing N/O-glycans (e.g. m/z 1647.586, 11 688.613 and 1562.470) that were identified only in T2DM patients. Besides, the relative abundance of 3 LacNAc-containing N-glycans and 10 LacNAc-containing O-glycans showed an increase in the glycopattern in T2DM patients. These results indicated that the glycopattern of LacNAc is increased in salivary glycoproteins from T2DM patients, and an increase in LacNAc-containing N/O-glycans may contribute to this alteration. Our findings provide useful information to understand the complex physiological changes in the T2DM patients.

A streamlined pipeline for multiplexed quantitative site-specific N-glycoproteomics

Regulation of protein N-glycosylation is essential in human cells. However, large-scale, accurate, and site-specific quantification of glycosylation is still technically challenging. We here introduce SugarQuant, an integrated mass spectrometry-based pipeline comprising protein aggregation capture (PAC)-based sample preparation, multi-notch MS3 acquisition (Glyco-SPS-MS3) and a data-processing tool (GlycoBinder) that enables confident identification and quantification of intact glycopeptides in complex biological samples. PAC significantly reduces sample-handling time without compromising sensitivity. Glyco-SPS-MS3 combines high-resolution MS2 and MS3 scans, resulting in enhanced reporter signals of isobaric mass tags, improved detection of N-glycopeptide fragments, and lowered interference in multiplexed quantification. GlycoBinder enables streamlined processing of Glyco-SPS-MS3 data, followed by a two-step database search, which increases the identification rates of glycopeptides by 22% compared with conventional strategies. We apply SugarQuant to identify and quantify more than 5,000 unique glycoforms in Burkitt’s lymphoma cells, and determine site-specific glycosylation changes that occurred upon inhibition of fucosylation at high confidence.

Comprehensive quantitative profiling of intact glycopeptides remains technically challenging. To address this, the authors here develop an integrated quantitative glycoproteomic workflow, including optimized sample preparation, multiplexed quantification and a dedicated data processing tool.

Recent advances in the mass spectrometric analysis of glycosphingolipidome - A review

Aberrant expression of glycosphingolipids has been implicated in a myriad of diseases, but our understanding of the strucural diversity, spatial distribution, and biological function of this class of biomolecules remains limited. These challenges partly stem from a lack of sensitive tools that can detect, identify, and quantify glycosphingolipids at the molecular level. Mass spectrometry has emerged as a powerful tool poised to address most of these challenges. Here, we review the recent developments in analytical glycosphingolipidomics with an emphasis on sample preparation, mass spectrometry and tandem mass spectrometry-based structural characterization, label-free and labeling-based quantification. We also discuss the nomenclature of glycosphingolipids, and emerging technologies like ion mobility spectrometry in differentiation of glycosphingolipid isomers. The intrinsic advantages and shortcomings of each method are carefully critiqued in line with an individual's research goals. Finally, future perspectives on analytical sphingolipidomics are stated, including a need for novel and more sensive methods in isomer separation, low abundance species detection, and profiling the spatial distribution of glycosphingolipid molecular species in cells and tissues using imaging mass spectrometry.

Intestinal epithelial glycosylation in homeostasis and gut microbiota interactions in IBD

Inflammatory bowel disease (IBD) affects 6.8 million people globally. A variety of factors have been implicated in IBD pathogenesis, including host genetics, immune dysregulation and gut microbiota alterations. Emerging evidence implicates intestinal epithelial glycosylation as an underappreciated process that interfaces with these three factors. IBD is associated with increased expression of truncated O-glycans as well as altered expression of terminal glycan structures. IBD genes, glycosyltransferase mislocalization, altered glycosyltransferase and glycosidase expression and dysbiosis drive changes in the glycome. These glycan changes disrupt the mucus layer, glycan-lectin interactions, host-microorganism interactions and mucosal immunity, and ultimately contribute to IBD pathogenesis. Epithelial glycans are especially critical in regulating the gut microbiota through providing bacterial ligands and nutrients and ultimately determining the spatial organization of the gut microbiota. In this Review, we discuss the regulation of intestinal epithelial glycosylation, altered epithelial glycosylation in IBD and mechanisms for how these alterations contribute to disease pathobiology. We hope that this Review provides a foundation for future studies on IBD glycosylation and the emergence of glycan-inspired therapies for IBD.

Fmoc N-hydroxysuccinimide ester: A facile and multifunctional role in N-glycan analysis

N-glycans that are fluorescently tagged by glycosylamine acylation have become a promising way for glycan biomarker discovery. Here, we describe a simple and rapid method using Fmoc N-hydroxysuccinimide ester (Fmoc-OSu) to label N-glycans by reacting with their corresponding intermediate glycosylamines produced by microwave-assisted deglycosylation. After optimizing reaction conditions, this derivatization reaction can be effectively achieved under 40 °C for 1 h. Moreover, the comparison of fluorescent intensities for Fmoc-OSu, Fmoc-Cl and 2-AA labeling strategies were also performed. Among which, the fluorescent intensities of Fmoc-OSu labeled glycan derivatives were approximately 5 and 13 times higher than that labeled by Fmoc-Cl and 2-AA respectively. Furthermore, the developed derivatization strategy has also been applied for analyzing serum N-glycans, aiming to screen specific biomarkers for early diagnosis of lung squamous cell cancer. More interestingly, the preparation of free reducing N-glycan standards have been achieved by the combination of HPLC fraction of Fmoc labeled glycan derivatives and Fmoc releasing chemistry. Overall, this proposed method has the potential to be used in functional glycomic study.

Synthetic lectins for selective binding of glycoproteins in water

Although synthetic mimics of lectins can be extremely useful in biological and biomedical research, molecular recognition of carbohydrates has been hampered by their strong solvation in water and subtle structural differences among analogues. Molecularly imprinted nanoparticle receptors were prepared with glycans directly cleaved from glycoproteins. Functionalized with boroxole groups in the binding sites, these water-soluble synthetic lectins bound the parent glycoproteins selectively in water with an association constant of Ka = 104-105 M-1. The strong binding enabled the receptors to protect the targeted glycans from enzymatic cleavage. When clicked onto magnetic nanoparticles, the receptors enabled facile isolation of glycoproteins from a mixture.

Strategy for Isolation, Preparation, and Structural Analysis of Chondroitin Sulfate Oligosaccharides from Natural Sources

The structure of chondroitin sulfate oligosaccharides (CSOs), especially their sulfation pattern, has been found to be closely related with many biological pathways and diseases. However, detailed functional analysis such as their interaction with glycan binding proteins (GBPs) has been lagging, presumably due to the unavailability of well-defined, diverse structures. Besides challenging chemical and enzymatic synthesis, this is also due to the challenges in their purification at the isomer level and structural analysis owing to their instability, structural complexity, and low mass spectrometry detection sensitivity. Herein, we first used recycling preparative HPLC to separate and purify shark CS tetrasaccharide component labeled by a bifunctional fluorescent linker 2-amino-N-(2-aminoethyl)benzamide (AEAB) at the isomer level. Then, each isomer was derivatized through a multistage procedure including N-acetylation, carboxyl amidation, permethylation, and desulfation with silylating reagent. Structural analysis of each derivatized isomer was performed with ESI-MSⁿ in positive ion mode. A total of 16 isomers of CSO-AEAB were isolated, with a minimum mass component of 0.007 mg and a maximum mass component of 17.53 mg, of which 10 isomers (>90 μg) were structurally analyzed. This preparation and structure analysis of CSOs lay the foundation for further study of the structure-activity relationship of CSOs.

Purification of natural neutral N-glycans by using two-dimensional hydrophilic interaction liquid chromatography × porous graphitized carbon chromatography for glycan-microarray assay

Glycan microarray for studying carbohydrate-protein interactions requires diverse classes of well-defined glycan standards. In this study, a purification strategy was established based on two-dimensional hydrophilic interaction liquid chromatography and porous graphitized carbon chromatography (HILIC × PGC) for the acquisition of neutral N-glycan standards from natural source. A total of thirty-one N-glycan compounds including seven pairs of isomers with the amounts from 0.7 to 230.0 nmol were isolated from ovalbumin as the model glycoconjugate. The purified N-glycans covered high-mannose, hybrid as well as multi-antenna asymmetric complex types. The purity of majority of these N-glycans was higher than 90%. Detailed structures of the N-glycan compounds were verified via negative ion tandem MS analysis, in which specific diagnostic ions including D- and E-ions were used to identify isomeric and terminal fine structures. The tag-free glycan compounds with well-defined structures, purity and amounts were finally assembled on the glass slide through neoglycolipid technology. Microarray binding assay of purified glycans with WGA lectin indicated the potential of the established strategy in glycan library expansion and functional glycomics.