A general approach to desalting oligosaccharides released from glycoproteins

Fucosylation and galactosylation in N-glycans of bovine intestinal alkaline phosphatase and their role in its enzymatic activity

Bovine intestinal alkaline phosphatase (biALP), a membrane-bound plasma metalloenzyme, maintains intestinal homeostasis, regulates duodenal surface pH, and protects against infections caused by pathogenic bacteria. The N-glycans of biALP regulate its enzymatic activity, protein folding, and thermostability, but their structures are not fully reported. In this study, the structures and quantities of the N-glycans of biALP were analyzed by liquid chromatography-electrospray ionization-high energy collision dissociation-tandem mass spectrometry. In total, 48 N-glycans were identified and quantified, comprising high-mannose [6 N-glycans, 33.1 % (sum of relative quantities of each N-glycan)], hybrid (6, 11.9 %), and complex (36, 55.0 %) structures [bi- (13, 26.1 %), tri- (16, 21.5 %), and tetra-antennary (7, 7.4 %)]. These included bisecting N-acetylglucosamine (33, 56.6 %), mono-to tri-fucosylation (32, 53.3 %), mono-to tri-α-galactosylation (16, 20.7 %), and mono-to tetra-β-galactosylation (36, 58.5 %). No sialylation was identified. N-glycans with non-bisecting GlcNAc (9, 10.3 %), non-fucosylation (10, 13.6 %), non-α-galactosylation (26, 46.2 %), and non-β-galactosylation (6, 8.4 %) were also identified. The activity (100 %) of biALP was reduced to 37.3 ± 0.2 % (by de-fucosylation), 32.7 ± 2.9 % (by de-α-galactosylation), and 0.2 ± 0.2 % (by de-β-galactosylation), comparable to inhibition by 10-4 to 101 mM EDTA, a biALP inhibitor. These results indicate that fucosylated and galactosylated N-glycans, especially β-galactosylation, affected the activity of biALP. This study is the first to identify 48 diverse N-glycan structures and quantities of bovine as well as human intestinal ALP and to demonstrate the importance of the role of fucosylation and galactosylation for maintaining the activity of biALP.

Structural identification and quantification of unreported sialylated N-glycans in bovine testicular hyaluronidase by LC-ESI-HCD-MS/MS

Bovine testicular hyaluronidase (BTH), which accelerates the absorption and dispersion of drugs by decomposing hyaluronan in subcutaneous tissues, has been used in medical applications, including local anesthesia, ophthalmology, and dermatosurgery. The requirement of N-glycans for the activity of human hyaluronidase has been reported, and BTH has greater activity than human hyaluronidase. However, the N-glycan characteristics of BTH are unclear. From a commercial BTH source containing additional proteins, purified BTH (pBTH) was obtained using size exclusion chromatography, and the structures and quantities of its N-glycans were analyzed using liquid chromatography (LC)-electrospray ionization-higher energy collisional dissociation (HCD)-tandem mass spectrometry (MS/MS). In pBTH, 32 N-glycans were identified, with 12 sialylations (39.0% of total N-glycan content), nine core-fucosylations (31.5%), six terminal galactosylations (14.6%), five high-mannosylations (13.7%), and four bisecting N-acetylglucosamine structures (7.8%). The presence of sialylated glycopeptides in pBTH was confirmed by nano-LC-HCD-MS/MS analysis. The absolute quantity of all N-glycans was calculated as 1.4 pmol (0.6 pmol for sialylation) in pBTH (1.0 pmol). The sialylation level (related to half-life, thermal stability, resistance to proteolysis, and solubility) was 24.4 times higher than that of human hyaluronidase. The hyaluronan degradation activity of de-sialylated pBTH decreased to 41.2 ± 4.2%, showing that sialylated N-glycans were required for pBTH activity as well. This is the first study to identify and quantify 32 N-glycans of pBTH and investigate their structural roles in its activity. The presence of larger amounts of sialylated N-glycans in pBTH than in human hyaluronidase suggests a greater utilization of pBTH.

Comparison of sialylated and fucosylated N-glycans attached to Asn 6 and Asn 41 with different roles in hyaluronan and proteoglycan link protein 1 (HAPLN1)

Hyaluronan and proteoglycan link protein 1 (HAPLN1) is an extracellular matrix protein stabilizing interactions between hyaluronan and proteoglycan. Although HAPLN1 is being investigated for various biological roles, its N-glycosylation is poorly understood. In this study, the structure of N-glycopeptides of trypsin-treated recombinant human HAPLN1 (rhHAPLN1) expressed from CHO cells were identified by nano-liquid chromatography-tandem mass spectrometry. A total of 66 N-glycopeptides were obtained, including 16 and 12 N-glycans at sites Asn 6 (located in the N-terminal region) and Asn 41 (located in the Ig-like domain, which interacts with proteoglycan), respectively. The quantities (%) of each N-glycan relative to the totals (100 %) at each site were calculated. Tri- and tetra-sialylation (to resist proteolysis and extend half-life) were more abundant at Asn 6, and di- (core- and terminal-) fucosylation (to increase binding affinity and stability) and sialyl-Lewis X/a epitope (a major ligand for E-selectin) were more abundant at Asn 41. These results indicate that N-glycans attached to Asn 6 (protecting HAPLN1) and Asn 41 (supporting molecular interactions) play different roles in HAPLN1. This is the first study of site-specific N-glycosylation in rhHAPLN1, which will be useful for understanding its molecular interactions in the extracellular matrix.

Evaluation of solid-phase extraction sorbents for purification of oligosaccharides and glycans derivatized by positively charged labels followed by capillary electrophoretic analysis

The sample preparation including labeling and clean-up represents a key analytical step in the analysis of oligosaccharides and glycans by either chromatographic or electrophoretic separation methods. Although the majority of labeling has been performed by neutral and/or negatively charged tags, the introduction of a positive charge into the saccharide molecule can significantly improve the analysis, especially with mass spectrometry detection. In this work, we present the evaluation of five solid-phase extraction sorbents differing in extraction chemistry for the clean-up and concentration of positively labeled maltooligosaccharides from the reaction mixtures. Maltooligosaccharides containing four to seven glucose units were labeled by cationic tags (2-aminoethyl)trimethylammonium chloride and (carboxymethyl)trimethylammonium chloride hydrazide and the extraction conditions were optimized followed by electrophoretic analysis with conductivity detection. The effects of the solid-phase extraction sorbent chemistry, extraction conditions, and sample composition are discussed. All tested sorbents were capable of cleaning up maltooligosaccharides from the reaction mixtures to some extent after optimization of the solid-phase extraction procedure (51.9%-98.9% recovery). The best-rated amide-based sorbent was used to process the sample of N-linked glycans enzymatically released from ribonuclease B.

Quantitative subcellular reconstruction reveals a lipid mediated inter-organelle biogenesis network

The structures and functions of organelles in cells depend on each other but have not been systematically explored. We established stable knockout cell lines of peroxisomal, Golgi and endoplasmic reticulum genes identified in a whole-genome CRISPR knockout screen for inducers of mitochondrial biogenesis stress, showing that defects in peroxisome, Golgi and endoplasmic reticulum metabolism disrupt mitochondrial structure and function. Our quantitative total-organelle profiling approach for focussed ion beam scanning electron microscopy revealed in unprecedented detail that specific organelle dysfunctions precipitate multi-organelle biogenesis defects, impair mitochondrial morphology and reduce respiration. Multi-omics profiling showed a unified proteome response and global shifts in lipid and glycoprotein homeostasis that are elicited when organelle biogenesis is compromised, and that the resulting mitochondrial dysfunction can be rescued with precursors for ether-glycerophospholipid metabolic pathways. This work defines metabolic and morphological interactions between organelles and how their perturbation can cause disease.

Identification, quantification, and structural role of N-glycans in two highly purified isoforms of sheep testicular hyaluronidase

Animal-derived hyaluronidase, which hydrolyzes the polysaccharide hyaluronic acid, has been used in medical applications despite its limited purity. Additionally, the N-glycan characterization of sheep testicular hyaluronidase (STH) and its structural role remain poorly understood. In this study, STH was purified from the commercially available STH preparation (containing at least 14 impurity proteins) using heparin-affinity chromatography followed by size exclusion chromatography. The structure and quantity of N-glycans of STH were investigated using liquid chromatography-electrospray ionization-high energy collision dissociation-tandem mass spectrometry. Two isoforms, H3S1 and H3S2, of STH were obtained (purity >98 %) with a yield of 3.4 % and 5.1 %, respectively. Fourteen N-glycans, including nine core-fucosylated N-glycans (important for the stability and function of glycoproteins), were identified in both H3S1 and H3S2, with similar quantities of each N-glycan. The amino acid sequences of the proteolytic peptides of H3S1 and H3S2 were compared with those reported in STH. The hyaluronic acid-degrading activity of deglycosylated H3S1 and H3S2 was reduced to 70.8 % and 71.1 % compared to that (100 %) of H3S1 and H3S2, respectively. This is the first report of N-glycan characterization of two highly purified isoforms of STH. These H3S1 and H3S2 will be useful for medical use without unwanted effects of partially purified STH.

Contemporary human H3N2 influenza A viruses require a low threshold of suitable glycan receptors for efficient infection

Recent human H3N2 influenza A viruses have evolved to employ elongated glycans terminating in α2,6-linked sialic acid as their receptors. These glycans are displayed in low abundancies by (humanized) Madin-Darby Canine Kidney cells, which are commonly employed to propagate influenza A virus, resulting in low or no viral propagation. Here, we examined whether the overexpression of the glycosyltransferases β-1,3-N-acetylglucosaminyltransferase and β-1,4-galactosyltransferase 1, which are responsible for the elongation of poly-N-acetyllactosamines (LacNAcs), would result in improved A/H3N2 propagation. Stable overexpression of β-1,3-N-acetylglucosaminyltransferase and β-1,4-galactosyltransferase 1 in Madin-Darby Canine Kidney and "humanized" Madin-Darby Canine Kidney cells was achieved by lentiviral integration and subsequent antibiotic selection and confirmed by qPCR and protein mass spectrometry experiments. Flow cytometry and glycan mass spectrometry experiments using the β-1,3-N-acetylglucosaminyltransferase and/or β-1,4-galactosyltransferase 1 knock-in cells demonstrated increased binding of viral hemagglutinins and the presence of a larger number of LacNAc repeating units, especially on "humanized" Madin-Darby Canine Kidney-β-1,3-N-acetylglucosaminyltransferase cells. An increase in the number of glycan receptors did, however, not result in a greater infection efficiency of recent human H3N2 viruses. Based on these results, we propose that H3N2 influenza A viruses require a low number of suitable glycan receptors to infect cells and that an increase in the glycan receptor display above this threshold does not result in improved infection efficiency.

Protein glycosylation in urine as a biomarker of diseases

Human body fluids have become an indispensable resource for clinical research, diagnosis and prognosis. Urine is widely used to discover disease-specific glycoprotein biomarkers because of its recurrently non-invasive collection and disease-indicating properties. While urine is an unstable fluid in that its composition changes with ingested nutrients and further as it is excreted through micturition, urinary proteins are more stable and their abnormal glycosylation is associated with diseases. It is known that aberrant glycosylation can define tumor malignancy and indicate disease initiation and progression. However, a thorough and translational survey of urinary glycosylation in diseases has not been performed. In this article, we evaluate the clinical applications of urine, introduce methods for urine glycosylation analysis, and discuss urine glycoprotein biomarkers. We emphasize the importance of mining urinary glycoproteins and searching for disease-specific glycosylation in various diseases (including cancer, neurodegenerative diseases, diabetes, and viral infections). With advances in mass spectrometry-based glycomics/glycoproteomics/glycopeptidomics, characterization of disease-specific glycosylation will optimistically lead to the discovery of disease-related urinary biomarkers with better sensitivity and specificity in the near future.

Investigation of the Protective Effect for GcMAF by a Glycosidase Inhibitor and the Glycan Structure of Gc Protein

O-linked α-N-acetylgalactosamine (α-GalNAc) in the Gc protein is essential for macrophage activation; thus, the GalNAc-attached form of Gc protein is called Gc macrophage activating factor (GcMAF). O-linked glycans in Gc proteins from human plasma mainly consist of trisaccharides. GcMAF is produced when glycans on the Gc protein are hydrolyzed by α-Sia-ase and β-Gal-ase, leaving an α-GalNAc. Upon hydrolysis of α-GalNAc present on GcMAF, the protein loses the macrophage-activating effect. In contrast, our synthesized pyrrolidine-type iminocyclitol possessed strong in vitro α-GalNAc-ase inhibitory activity. In this study, we examined the protective effects of iminocyclitol against GcMAF via inhibition of α-GalNAc-ase activity. Detailed mass spectrometric analyses revealed the protective effect of the inhibitor on GcMAF. Furthermore, structural information regarding the glycosylation site and glycan structure was obtained using tandem mass spectrometric (MS/MS) analysis of the glycosylated peptides after tryptic digestion.

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.

Dysregulation and prometastatic function of glycosyltransferase C1GALT1 modulated by cHP1BP3/ miR-1-3p axis in bladder cancer

Background

Abnormal glycosylation in a variety of cancer types is involved in tumor progression and chemoresistance. Glycosyltransferase C1GALT1, the key enzyme in conversion of Tn antigen to T antigen, is involved in both physiological and pathological conditions. However, the mechanisms of C1GALT1 in enhancing oncogenic phenotypes and its regulatory effects via non-coding RNA are unclear.

Methods

Abnormal expression of C1GALT1 and its products T antigen in human bladder cancer (BLCA) were evaluated with BLCA tissue, plasma samples and cell lines. Effects of C1GALT1 on migratory ability and proliferation were assessed in YTS-1 cells by transwell, CCK8 and colony formation assay in vitro and by mouse subcutaneous xenograft and trans-splenic metastasis models in vivo. Dysregulated circular RNAs (circRNAs) and microRNAs (miRNAs) were profiled in 3 pairs of bladder cancer tissues by RNA-seq. Effects of miR-1-3p and cHP1BP3 (circRNA derived from HP1BP3) on modulating C1GALT1 expression were investigated by target prediction program, correlation analysis and luciferase reporter assay. Functional roles of miR-1-3p and cHP1BP3 on migratory ability and proliferation in BLCA were also investigated by in vitro and in vivo experiments. Additionally, glycoproteomic analysis was employed to identify the target glycoproteins of C1GALT1.

Results

In this study, we demonstrated upregulation of C1GALT1 and its product T antigen in BLCA. C1GALT1 silencing suppressed migratory ability and proliferation of BLCA YTS-1 cells in vitro and in vivo. Subsets of circRNAs and miRNAs were dysregulated in BLCA tissues. miR-1-3p, which is reduced in BLCA tissues, inhibited transcription of C1GALT1 by binding directly to its 3′-untranslated region (3′-UTR). miR-1-3p overexpression resulted in decreased migratory ability and proliferation of YTS-1 cells. cHP1BP3 was upregulated in BLCA tissues, and served as an miR-1-3p “sponge”. cHP1BP3 was shown to modulate migratory ability, proliferation, and colony formation of YTS-1 cells, and displayed tumor-suppressing activity in BLCA. Target glycoproteins of C1GALT1, including integrins and MUC16, were identified.

Conclusions

This study reveals the pro-metastatic and proliferative function of upregulated glycosyltransferase C1GLAT1, and provides preliminary data on mechanisms underlying dysregulation of C1GALT1 via miR-1-3p / cHP1BP3 axis in BLCA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02438-7.

High sensitivity glycomics in biomedicine

Many analytical challenges in biomedicine arise from the generally high heterogeneity and complexity of glycan- and glycoconjugate-containing samples, which are often only available in minute amounts. Therefore, highly sensitive workflows and detection methods are required. In this review mass spectrometric workflows and detection methods are evaluated for glycans and glycoproteins. Furthermore, glycomic methodologies and innovations that are tailored for enzymatic treatments, chemical derivatization, purification, separation, and detection at high sensitivity are highlighted. The discussion is focused on the analysis of mammalian N-linked and GalNAc-type O-linked glycans.

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.

Green Extraction Processes for Complex Samples from Vegetable Matrices Coupled with On-Line Detection System: A Critical Review

The detection of analytes in complex organic matrices requires a series of analytical steps to obtain a reliable analysis. Sample preparation can be the most time-consuming, prolonged, and error-prone step, reducing the reliability of the investigation. This review aims to discuss the advantages and limitations of extracting bioactive compounds, sample preparation techniques, automation, and coupling with on-line detection. This review also evaluates all publications on this topic through a longitudinal bibliometric analysis, applying statistical and mathematical methods to analyze the trends, perspectives, and hot topics of this research area. Furthermore, state-of-the-art green extraction techniques for complex samples from vegetable matrices coupled with analysis systems are presented. Among the extraction techniques for liquid samples, solid-phase extraction was the most common for combined systems in the scientific literature. In contrast, for on-line extraction systems applied for solid samples, supercritical fluid extraction, ultrasound-assisted extraction, microwave-assisted extraction, and pressurized liquid extraction were the most frequent green extraction techniques.

Quality Markers of Dendrobium officinale by “Oligosaccharide-Spectrum-Effect” Relationships

Dendrobium officinale Kimura et Migo has been used as a traditional Chinese medicine (TCM) and a functional food for thousands of years. Carbohydrate is one of the most important effective substances and indicative components in D. officinale. However, since the qualitative and quantitative analysis of polysaccharides in D. officinale remains a challenge and limitation, herein, an oligosaccharide-quality marker approach was newly developed for quality assessment of D. officinale by spectrum–effect relationships between high performance liquid chromatographic (HPLC) fingerprints and anti-inflammatory effects. The HPLC fingerprints of 48 batches of oligosaccharides from D. officinale (DOOS) were developed and analyzed with similarity analysis (SA) and hierarchical cluster analysis (HCA), and eight common peaks were identified. In vitro screening experiment indicated that DOOS potentially inhibited nitric oxide (NO) production and effectively reduced the release of inflammatory cytokines, such as TNF-α, IL-6, and IL-1β in RAW 264.7 cells, thereby reducing the inflammatory response of cells. Finally, the HPLC fingerprint of different batches of DOOS was combined with in vitro anti-inflammatory activity to assess the spectrum–effect relationships of DOOS by gray correlation analysis (GCA), in addition, the purified oligosaccharide components were identified and validated for NO inhibitory activity. Our results showed four DOOS (maltotetraose, maltopentaose, maltohexaose, and mannohexaose) were relevant to anti-inflammatory effects and could be as quality markers for the quality control of D. officinale. It suggests that the “oligosaccharide-spectrum-effect” relationships approach is a simple and reliable method for the quality control of herb medicines or nutritious foods.

Identification and quantification of sialylated and core-fucosylated N-glycans in human transferrin by UPLC and LC-MS/MS

Sialylated and core-fucosylated N-glycans in human transferrin (HTF) are used as glycan biomarkers due to their increased or decreased characteristics in certain diseases. However, their absolute quantities remain unclear. In this study, N-glycans of HTF were identified by UPLC and LC-MS/MS using fluorescence tags [2-aminobenzamide (AB) and procainamide (ProA)] and columns [HILIC and anion exchange chromatography-HILIC (AXH)]. The structures of 14 (including five core-fucosylated) N-glycans in total comprising two non-, six mono-, four di-, and two tri-sialylated N-glycans were identified. The quantities (%) of each N-glycan relative to the total N-glycans (100%) were obtained. HILIC and AXH were better for peak identification and separability except for desialylation, respectively. Specifically, sialylated (in ProA-HILIC and ProA-AXH by UPLC or LC-MS/MS) and core-fucosylated (in AB-HILIC and ProA-AXH by UPLC) N-glycans were efficiently identified. Seven neuraminidase-treated (including three core-fucosylated) N-glycans were efficiently identified in ProA-AXH, even their poor separation. Additionally, ProA-AXH was more efficient for the estimation of the absolute quantities of N-glycans from the results of fluorescence intensity (by UPLC) and relative quantity (by LC-MS/MS). These results first demonstrate that ProA is useful for identifying and quantifying sialylated, core-fucosylated, and neuraminidase-treated desialylated N-glycans in HTF using AXH by UPLC and LC/MS.

Characterization of novel nonacid glycosphingolipids as biomarkers of human gastric adenocarcinoma

Changes in glycosphingolipid structures have been shown to occur during the development of several types of human cancers, generating cancer-specific carbohydrate structures that could be used as biomarkers for diagnosis and therapeutic targeting. In this study, we characterized nonacid glycosphingolipids isolated from a human gastric adenocarcinoma by mass spectrometry, enzymatic hydrolysis, and by binding with a battery of carbohydrate-recognizing ligands. We show that the majority of the complex nonacid glycosphingolipids had type 2 (Galβ4GlcNAc) core chains (neolactotetraosylceramide, the Le^x, H type 2, x₂, and the P1 pentaosylceramides, and the Le^y, A type 2, and neolacto hexaosylceramides). We also found glycosphingolipids with type 1 (Galβ3GlcNAc) core (lactotetraosylceramide and the H type 1 pentaosylceramide) and globo (GalαGal) core chains (globotriaosylceramide and globotetraosylceramide). Interestingly, we characterized two complex glycosphingolipids as a P1 heptaosylceramide (Galα4Galβ4GlcNAcβ3Galβ4GlcNAcβ3Gal β4Glcβ1Cer) and a branched P1 decaosylceramide (Galα4Gal β4GlcNAcβ3(Galα4Galβ4GlcNAcβ6)Galβ4GlcNAcβ3Galβ4Glc β1Cer). These are novel glycosphingolipid structures and the first reported cases of complex glycosphingolipids larger than pentaosylceramide carrying the P1 trisaccharide. We propose that these P1 glycosphingolipids may represent potential biomarkers for the early diagnosis of gastric cancer.

Surface Shave: Revealing the Apical-Restricted Uroglycome

This study aimed to investigate the highly differentiated urothelial apical surface glycome. The functions of the mammalian urothelium, lining the majority of the urinary tract and providing a barrier against toxins in urine, are dependent on the correct differentiation of urothelial cells, relying on protein expression, modification, and complex assembly to regulate the formation of multiple differentiated cell layers. Protein glycosylation, a poorly studied aspect of urothelial differentiation, contributes to the apical glycome and is implicated in the development of urothelial diseases. To enable surface glycome characterization, we developed a method to collect tissue apical surface N- and O-glycans. A simple, novel device using basic laboratory supplies was developed for enzymatic shaving of the luminal bladder urothelial surface, with subsequent release and mass spectrometric analysis of apical surface O- and N-glycans, the first normal mammalian urothelial N-glycome to be defined. Trypsinization of superficial glycoproteins was tracked using immunolabeling of the apically expressed uroplakin 3a protein to optimize enzymatic release, without compromising the integrity of the superficial urothelial layer. The approach developed for releasing apical tissue surface glycans allowed for comparison with the N-glycome of the total porcine bladder urothelial cells and thus identification of apical surface glycans as candidates implicated in the urothelial barrier function. Data are available in MassIve: MSV000087851.

Characterization and Analysis of Food-Sourced Carbohydrates

Food carbohydrates are macronutrients that are found in fruits, grains, vegetables, and milk products. These organic compounds are present in foods in the form of sugars, starches, and fibers and are composed of carbon, hydrogen, and oxygen. These wide ranging macromolecules can be classified according to their chemical structure into three major groups: low molecular weight mono- and disaccharides, intermediate molecular weight oligosaccharides, and high molecular weight polysaccharides. Notably, the digestibility of specific carbohydrate components differ and nondigestible carbohydrates can reach the large intestine intact where they act as food sources for beneficial bacteria. In this review, we give an overview of advances made in food carbohydrate analysis. Overall, this review indicates the importance of carbohydrate analytical techniques in the quest to identify and isolate health-promoting carbohydrates to be used as additives in the functional foods industry.

Probing serum N-glycan patterns for rapid and precise detection of Crohn's disease

Serum N-glycan patterns from 50 Crohn's disease (CD) patients and 50 healthy controls were acquired using a carbon matrix, from which eight N-glycans with significant difference were screened out to reveal remarkale performance for CD diagnosis. This research is expected to help future glycan-based disease detection not limited to CD.

A single sulfatase is required to access colonic mucin by a gut bacterium

Humans have co-evolved with a dense community of microbial symbionts that inhabit the lower intestine. In the colon, secreted mucus creates a barrier that separates these microorganisms from the intestinal epithelium1. Some gut bacteria are able to utilize mucin glycoproteins, the main mucus component, as a nutrient source. However, it remains unclear which bacterial enzymes initiate degradation of the complex O-glycans found in mucins. In the distal colon, these glycans are heavily sulfated, but specific sulfatases that are active on colonic mucins have not been identified. Here we show that sulfatases are essential to the utilization of distal colonic mucin O-glycans by the human gut symbiont Bacteroides thetaiotaomicron. We characterized the activity of 12 different sulfatases produced by this species, showing that they are collectively active on all known sulfate linkages in O-glycans. Crystal structures of three enzymes provide mechanistic insight into the molecular basis of substrate specificity. Unexpectedly, we found that a single sulfatase is essential for utilization of sulfated O-glycans in vitro and also has a major role in vivo. Our results provide insight into the mechanisms of mucin degradation by a prominent group of gut bacteria, an important process for both normal microbial gut colonization2 and diseases such as inflammatory bowel disease3.

In-depth characterization of non-human sialic acid (Neu5Gc) in human serum using label-free ZIC-HILIC/MRM-MS

Sialic acid Neu5Gc, a non-human glycan, is recognized as a new harmful substance that can cause vascular disease and cancer. Humans are unable to synthesize Neu5Gc due to a genetic defect that converts Neu5Ac to Neu5Gc, but Neu5Gc is often observed in human biological samples. Therefore, the demand for accurately measuring the amount of Neu5Gc present in human blood or tissues is rapidly increasing, but there is still no method to reliably quantify trace amounts of a non-human sugar. In particular, selective isolation and detection of Neu5Gc from human serum is analytically challenging due to the presence of excess sialic acid Neu5Ac, which has physicochemical properties very similar to Neu5Gc. Herein, we developed the label-free approach based on ZIC-HILIC/MRM-MS that can enrich sialic acids released from human serum and simultaneously monitor Neu5Ac and Neu5Gc. The combination of complete separation of Neu5Gc from abundant Neu5Ac by hydrophilic and electrostatic interactions with selective monitoring of structure-specific cross-ring cleavage ions generated by negative CID-MS/MS was remarkably effective for quantification of Neu5Ac and Neu5Gc at the femtomole level. Indeed, we were able to successfully determine the absolute quantitation of Neu5Gc from 30 healthy donors in the range of 3.336 ± 1.252 pg/μL (mean ± SD), 10,000 times lower than Neu5Ac. In particular, analysis of sialic acids in protein-free serum revealed that both Neu5Ac and Neu5G are mostly bound to proteins and/or lipids, but not in free form. In addition, the correlation between expression level of Neu5Gc and biological factors such as BMI, age, and sex was investigated. This method can be widely used in studies requiring sialic acid-related measurements such as disease diagnosis or prediction of immunogenicity in biopharmaceuticals as it is both fast and highly sensitive.

Protocols for isolating and characterizing polysaccharides from plant cell walls: a case study using rhamnogalacturonan-II

BACKGROUND

In plants, a large diversity of polysaccharides comprise the cell wall. Each major type of plant cell wall polysaccharide, including cellulose, hemicellulose, and pectin, has distinct structures and functions that contribute to wall mechanics and influence plant morphogenesis. In recent years, pectin valorization has attracted much attention due to its expanding roles in biomass deconstruction, food and material science, and environmental remediation. However, pectin utilization has been limited by our incomplete knowledge of its structure. Herein, we present a workflow of principles relevant for the characterization of polysaccharide primary structure using nature's most complex polysaccharide, rhamnogalacturonan-II (RG-II), as a model.

RESULTS

We outline how to isolate RG-II from celery and duckweed cell walls and from red wine using chemical or enzymatic treatments coupled with size-exclusion chromatography. From there, we applied mass spectrometry (MS)-based techniques to determine the glycosyl residue and linkage compositions of the intact RG-II and derived oligosaccharides including special considerations for labile monosaccharides. In doing so, we demonstrated that in the duckweed Wolffiella repanda the arabinopyranosyl (Arap) residue of side chain B is substituted at O-2 with rhamnose. We used electrospray-MS techniques to identify non-glycosyl modifications including methyl-ethers, methyl-esters, and acetyl-esters on RG-II-derived oligosaccharides. We then showed the utility of proton nuclear magnetic resonance spectroscopy (¹H-NMR) to investigate the structure of intact RG-II and to complement the RG-II dimerization studies performed using size-exclusion chromatography.

CONCLUSIONS

The complexity of pectic polysaccharide structures has hampered efforts aimed at their valorization. In this work, we used RG-II as a model to demonstrate the steps necessary to isolate and characterize polysaccharides using chromatographic, MS, and NMR techniques. The principles can be applied to the characterization of other saccharide structures and will help inform researchers on how saccharide structure relates to functional properties in the future.

Organically-bound silicon enhances resistance to enzymatic degradation and nanomechanical properties of rice plant cell walls

Plant cell walls exhibit excellent mechanical properties, which form the structural basis for sustainable bioresources and multifunctional nanocelluloses. The wall nanomechanical properties of living cells through covalent modifications of hybrid inorganic elements, such as silicon, may confer significant influence on local mechano-response and enzymatic degradation. Here, we present a combination of ex situ measurements of enzyme-released oligosaccharide fragments using MALDI-TOF MS and in situ atomic force microscopy (AFM) imaging through PeakForce quantitative nanomechanical mapping of tip-functionalized single-molecule enzyme-polysaccharide substrate recognition and the nanoscale dissolution kinetics of individual cellulose microfibrils of living rice (Oryza sativa) cells following silicate cross-linking of cell wall xyloglucan. We find that xyloglucan-bound silicon enhances the resistance to degradation by cellulase and improves the wall nanomechanical properties in the elastic modulus at the single-cell level. The findings establish a direct link between an inorganic element of silicon and the nanoscale architecture of plant cell wall materials for sustainable utilization.

Appropriate aglycone modification significantly expands the glycan substrate acceptability of α1,6-fucosyltransferase (FUT8)

The α1,6-fucosyltransferase, FUT8, is the sole enzyme catalyzing the core-fucosylation of N-glycoproteins in mammalian systems. Previous studies using free N-glycans as acceptor substrates indicated that a terminal β1,2-GlcNAc moiety on the Man-α1,3-Man arm of N-glycan substrates is required for efficient FUT8-catalyzed core-fucosylation. In contrast, we recently demonstrated that, in a proper protein context, FUT8 could also fucosylate Man5GlcNAc2 without a GlcNAc at the non-reducing end. We describe here a further study of the substrate specificity of FUT8 using a range of N-glycans containing different aglycones. We found that FUT8 could fucosylate most of high-mannose and complex-type N-glycans, including highly branched N-glycans from chicken ovalbumin, when the aglycone moiety is modified with a 9-fluorenylmethyloxycarbonyl (Fmoc) moiety or in a suitable peptide/protein context, even if they lack the terminal GlcNAc moiety on the Man-α1,3-Man arm. FUT8 could also fucosylate paucimannose structures when they are on glycoprotein substrates. Such core-fucosylated paucimannosylation is a prominent feature of lysosomal proteins of human neutrophils and several types of cancers. We also found that sialylation of N-glycans significantly reduced their activity as a substrate of FUT8. Kinetic analysis demonstrated that Fmoc aglycone modification could either improve the turnover rate or decrease the KM value depending on the nature of the substrates, thus significantly enhancing the overall efficiency of FUT8 catalyzed fucosylation. Our results indicate that an appropriate aglycone context of N-glycans could significantly broaden the acceptor substrate specificity of FUT8 beyond what has previously been thought.

Magnetic porous carbon-dependent platform for the determination of N-glycans from urine exosomes

A magnetic porous carbon-dependent platform is established to separate and determine N-glycans from urine exosomes of healthy people and patients with gastric cancer. The results of the comparison reveal that 6 N-glycans shared by the two groups are downregulated, most of which present core fucose or bisecting N-acetylglucosamine (GlcNAc) type. In addition, five shared N-glycans including two of sialic acid type are upregulated. These obvious differences indicate the close relationship between glycans and gastric cancer thus permitting early diagnosis. A magnetic porous carbon material (FeMPC) from MIL-101(Fe) was employed to separate and analyze N-glycans from urine exosomes of healthy people and patients with gastric cancer.

N-Glycan Modifications with Negative Charge in a Natural Polymer Mucin from Bovine Submaxillary Glands, and Their Structural Role

Bovine submaxillary mucin (BSM) is a natural polymer used in biomaterial applications for its viscoelasticity, lubricity, biocompatibility, and biodegradability. N-glycans are important for mucin stability and function, but their structures have not been fully characterized, unlike that of O-glycans. In this study, BSM N-glycans were investigated using liquid chromatography-tandem mass spectrometry. The microheterogeneous structures of 32 N-glycans were identified, and the quantities (%) of each N-glycan relative to total N-glycans (100%) were obtained. The terminal N-acetylgalactosamines in 12 N-glycans (sum of relative quantities; 27.9%) were modified with mono- (10 glycans) and disulfations (2 glycans). Total concentration of all sulfated N-glycans was 6.1 pmol in BSM (20 µg), corresponding to 25.3% of all negatively charged glycans (sum of present N-glycans and reported O-glycans). No N-glycans with sialylated or phosphorylated forms were identified, and sulfate modification ions were the only negative charges in BSM N-glycans. Mucin structures, including sulfated N-glycans located in the hydrophobic terminal regions, were indicated. This is the first study to identify the structures and quantities of 12 sulfated N-glycans in natural mucins. These sulfations play important structural roles in hydration, viscoelasticity control, protection from bacterial sialidases, and polymer stabilization to support the functionality of BSM via electrostatic interactions.

Synergistic integration of FeNi magnetic nanoparticles with graphene-based porous carbon for efficient capture of N-linked glycans

Developing functional porous carbon is greatly desired for the capture of N-glycans from complex bio-samples. In this work, ferronickel graphene-based porous carbon composites (FeNi-G/PC-T, T = carbonization temperature) are facilely prepared and are characterized by the synergistic integration of magnetic separation, porosity and polar interaction. Studies of capture of N-linked glycans reveal that FeNi-G/PC-800 shows a remarkable performance to enrich N-linked glycans from standard bio-samples and real human serum, resulting in the successful profiling of 48 N-linked glycans in 5 μL human serum. Structure-property relationship studies further demonstrate that the synergistically integrated FeNi nanoparticles and graphene-based porous carbon in FeNi-G/PC-800 should play a key role in the capture performance.

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.

Chitosan oligosaccharide induces resistance to Pst DC3000 in Arabidopsis via a non-canonical N-glycosylation regulation pattern

Roles of protein N-glycosylation in chitosan oligosaccharide (COS) induced resistance were investigated in the present study. Results demonstrated that N-glycosylation deficient Arabidopsis mutants (stt3a and ManI) were more susceptible against Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) than wild type (WT) plants. Surprisingly, in stt3a and ManI, COS-induced resistance to Pst DC3000 was mostly intact, and the up-regulation effect on SA- and JA-mediated signalling pathways also similar like WT. Nucleotide sugars accumulation and N-glycosylation related genes expression were differently regulated after COS treatment. Global glycomics analysis quantified 157 N-glycan isomers, and 56.7, 50.3 and 47.1 % of them were significantly changed in COS, mock + Pst, and COS + Pst treated plants, respectively. Moreover, COS pretreatment could reverse the effect of Pst DC3000 on many N-glycans, suggesting that COS regulates protein N-glycosylation via a non-canonical pattern compared with plant defense, which may contribute to its obvious disease control effect when N-glycosylation impairment occurs.

Synthesis of glycoconjugates utilizing the regioselectivity of a lytic polysaccharide monooxygenase

Polysaccharides from plant biomass are the most abundant renewable chemicals on Earth and can potentially be converted to a wide variety of useful glycoconjugates. Potential applications of glycoconjugates include therapeutics and drug delivery, vaccine development and as fine chemicals. While anomeric hydroxyl groups of carbohydrates are amenable to a variety of useful chemical modifications, selective cross-coupling to non-reducing ends has remained challenging. Several lytic polysaccharide monooxygenases (LPMOs), powerful enzymes known for their application in cellulose degradation, specifically oxidize non-reducing ends, introducing carbonyl groups that can be utilized for chemical coupling. This study provides a simple and highly specific approach to produce oxime-based glycoconjugates from LPMO-functionalized oligosaccharides. The products are evaluated by HPLC, mass spectrometry and NMR. Furthermore, we demonstrate potential biodegradability of these glycoconjugates using selective enzymes.

The glycomic sialylation profile of GNE Myopathy muscle cells does not point to consistent hyposialylation of individual glycoconjugates

GNE Myopathy is a recessive neuromuscular disorder characterized by adult-onset, slowly progressive distal and proximal muscle weakness, and a typical muscle pathology. Although GNE, which is the mutated gene in the disease, is well known as the key enzyme in the biosynthesis pathway of sialic acid, the pathophysiological pathway leading from GNE mutations to the muscle phenotype in GNE Myopathy is still unclear. The obvious hypothesis of impaired sialylation in patients' skeletal muscle as the cause of the disease is still controversial. In the present study we have investigated whether a distinctive altered pattern of sialylation in GNE Myopathy cultured muscle cells could be attributed to a specific glycoconjugate. Mass spectrometry based glycomic methodologies have been utilized to assess the sialylation level of protein N- and O-linked glycans and glycolipid derived glycans from patient and matched control samples. No consistent change in sialylation was detected in glycoconjugates. These results suggest potential additional roles for GNE that could account for the disease pathology.

Locating Methyl-Etherified and Methyl-Esterified Uronic Acids in the Plant Cell Wall Pectic Polysaccharide Rhamnogalacturonan II

Rhamnogalacturonan II (RG-II) is a structurally complex pectic polysaccharide that exists as a borate ester cross-linked dimer in the cell walls of all vascular plants. The glycosyl sequence of RG-II is largely conserved, but there is evidence that galacturonic acid (GalA) methyl etherification and glucuronic acid (GlcA) methyl esterification vary in the A sidechain across plant species. Methyl esterification of the galacturonan backbone has also been reported but not confirmed. Here we describe a new procedure, utilizing aq. sodium borodeuteride (NaBD₄)-reduced RG-II, to identify the methyl esterification status of backbone GalAs. Our data suggest that up to two different GalAs are esterified in the RG-II backbone. We also adapted a procedure based on methanolysis and NaBD₄ reduction to identify 3-, 4-, and 3,4-O-methyl GalA in RG-II. These data, together with matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF) MS analysis of sidechain A generated from selected RG-IIs and their NaBD₄-reduced counterparts, suggest that methyl etherification of the β-linked GalA and methyl esterification of the GlcA are widespread. Nevertheless, the extent of these modifications varies between plant species. Our analysis of the sidechain B glycoforms in RG-II from different dicots and nonpoalean monocots suggests that this sidechain has a minimum structure of an O-acetylated hexasaccharide (Ara-[MeFuc]-Gal-AceA-Rha-Api-). To complement these studies, we provide further evidence showing that dimer formation and stability in vitro is cation and borate dependent. Taken together, our data further refine the primary sequence and sequence variation of RG-II and provide additional insight into dimer stability and factors controlling dimer self-assembly.

Off-target glycans encountered along the synthetic biology route toward humanized N-glycans in Pichia pastoris

The glycosylation pathways of several eukaryotic protein expression hosts are being engineered to enable the production of therapeutic glycoproteins with humanized application-customized glycan structures. In several expression hosts, this has been quite successful, but one caveat is that the new N-glycan structures inadvertently might be substrates for one or more of the multitude of endogenous glycosyltransferases in such heterologous background. This then results in the formation of novel, undesired glycan structures, which often remain insufficiently characterized. When expressing mouse interleukin-22 in a Pichia pastoris (syn. Komagataella phaffii) GlycoSwitchM5 strain, which had been optimized to produce Man₅ GlcNAc₂ N-glycans, glycan profiling revealed two major species: Man₅ GlcNAc₂ and an unexpected, partially α-mannosidase-resistant structure. A detailed structural analysis using exoglycosidase sequencing, mass spectrometry, linkage analysis, and nuclear magnetic resonance revealed that this novel glycan was Man₅ GlcNAc₂ modified with a Glcα-1,2-Manβ-1,2-Manβ-1,3-Glcα-1,3-R tetrasaccharide. Expression of a Golgi-targeted GlcNAc transferase-I strongly inhibited the formation of this novel modification, resulting in more homogeneous modification with the targeted GlcNAcMan₅ GlcNAc₂ structure. Our findings reinforce accumulating evidence that robustly customizing the N-glycosylation pathway in P. pastoris to produce particular human-type structures is still an incompletely solved synthetic biology challenge, which will require further innovation to enable safe glycoprotein pharmaceutical production.

Structural and Quantitative Characterization of Mucin-Type O-Glycans and the Identification of O-Glycosylation Sites in Bovine Submaxillary Mucin

Bovine submaxillary mucin (BSM) is a gel-forming glycoprotein polymer, and Ser/Thr-linked glycans (O-glycans) are important in regulating BSM's viscoelasticity and polymerization. However, details of O-glycosylation have not been reported. This study investigates the structural and quantitative characteristics of O-glycans and identifies O-glycosylation sites in BSM using liquid chromatography-tandem mass spectrometry. The O-glycans (consisting of di- to octa-saccharides) and their quantities (%) relative to total O-glycans (100%; 1.1 pmol per 1 μg of BSM) were identified with 14 major (>1.0%), 12 minor (0.1%-1.0%), and eight trace (<0.1%) O-glycans, which were characterized based on their constituents (sialylation (14 O-glycans; 81.9%, sum of relative quantities of each glycan), non-sialylation (20; 18.1%), fucosylation (20; 17.5%), and terminal-galactosylation (6; 3.6%)) and six core structure types [Gal-GalNAc, Gal-(GlcNAc)GalNAc, GlcNAc-GalNAc, GlcNAc-(GlcNAc)GalNAc, and GalNAc-GalNAc]. O-glycosylation sites were identified using O-glycopeptides (bold underlined; ₅₆SGETRTSVI, ₂₅₉SHSSSGRSRTI, ₂₇₂GSPSSVSSAEQI, ₃₀₇RPSYGAL, ₆₂₅QTLGPL, ₇₂₈TMTTRTSVVV, and ₁₀₈₀RPEDNTAVA) obtained from proteolytic BSM; these sites are in the four domains of BSM. The gel-forming mucins share common domain structures and glycosylation patterns; these results could provide useful information on mucin-type O-glycans. This is the first study to characterize O-glycans and identify O-glycosylation sites in BSM.

Neutral Human Milk Oligosaccharides Are Associated with Multiple Fixed and Modifiable Maternal and Infant Characteristics

We aimed to identify if maternal and infant factors were associated with neutral human milk oligosaccharides (HMOs) variability and examined the associations between HMOs concentration and infant growth and disease status in healthy Chinese mothers over a 6-month lactation period. We recruited mothers and their full-term infants as our subjects. At 1–5 days, 8–14 days, 4 weeks, and 6 months postpartum, all participants were interviewed to collect breast milk samples, obtain follow-up data and measure infant length and weight at their local hospital. A total of 23 neutral HMOs were analyzed by high performance liquid chromatography (HPLC)- mass spectrometer (MS). Secretor and Lewis phenotype were determined by the concentration of 2′-fucosyllactose (2′-FL) and Lacto-N-fucopentaose (LNFP)-II. The associations between maternal and infant factors with HMOs concentrations were investigated. A total of 464 human breast milk samples were collected from 116 mothers at four different time points. In total, 76.7% mothers were found to be Secretor and Lewis positive phenotype (Se+Le+), 17.2% were Se-Le+, 4.3% were Se+Le-, and 1.7% were Se-Le-. Several individual HMOs, including 2′-FL, Lactodifucotetraose (LDFT), LNFP-I were determined by Secretor phenotype. Most individual HMOs decreased at the later stage of lactation, except 3′-FL. We suggest that Secretor phenotype and lactation stage could influence most of the neutral HMOs. Concentrations of specific HMOs may be associated with maternal age, allergic history, pre-pregnancy body mass index (BMI), parity, delivery mode, infant gestational age and gender.

Purification of N- and O-glycans and their derivatives from biological samples by the absorbent cotton hydrophilic chromatographic column

Mass spectrum (MS) is one of the most commonly used tools for qualitative and quantitative analysis of glycans. However, due to the complexity of biological samples and the low ionization efficiency of glycans, these need to be purified and derivatized prior to MS analysis. Existing purification strategies require a combination of multiple methods and are cumbersome to operate. Here, we propose a new method for the purification of glycoprotein N/O-glycans and their derivatives using a hand-packed absorbent cotton hydrophilic interaction chromatography column (HILIC). The method's reliability and applicability were verified by purifying N/O-glycans and the derivatives of standard glycoproteins, such as chicken albumin and porcine stomach mucin. Stable isotope labelling was used to compare the glycans' recovery following different purification methods. Absorbent cotton HILIC was also successfully applied for the analysis of human serum and fetal bovine serum glycoprotein N-glycans. Finally, testing revealed high binding capacity (9 mg/g^-1 maltohexaose/absorbent cotton) and good recovery (average recovery was 91.7%) of glycans. Compared with traditional procedures, the proposed purification method offers considerable advantages, such as simplicity, high efficiency, economy, universality, and broad applicability for the pretreatment of glycans and their derivatives in biological samples prior to MS analysis.

Profiles of plant core-fucosylated N-glycans of acid alpha-glucosidases produced in transgenic rice cell suspension cultures treated with eight different conditions

Recombinant human acid alpha-glucosidase (rhGAA) from Chinese hamster ovary cells is the only approved treatment for patients with Pompe disease. In this study, rhGAAs were produced in transgenic rice cell suspension cultures under eight different conditions; untreated, 5 μM of 2-fluoro-l-fucose (2-FF), 50 μM of 2-FF, 100 μM of 2-FF, 100 μM of 2-FF + 0.5% Pluronic F-68 (PF-68), 100 μM of 2-FF + 0.05% Tween 20 (Tw 20), 0.5% PF-68, and 0.05% Tw 20. The N-glycans of eight rhGAAs were analyzed using ultra-performance liquid chromatography (UPLC) and tandem mass spectrometry. The relative quantity (%) of each glycan was obtained from the corresponding UPLC peak area per the sum (100%) of individual UPLC peak area. Fifteen N-glycans, comprising seven core-fucosylated glycans (71.5%, sum of each relative quantities) that have immunogenicity-inducing potential, three de-core-fucosylated glycans (15.4%), and five non-core-fucosylated glycans (13.1%), were characterized with high mass accuracy and glycan-generated fragment ions. The increases or decreases of relative quantities of each glycan from seven rhGAAs were compared with those of untreated control. The percentages of the sum of the relative quantities of core-fucosylated glycans divided by the sums of those of de-core- (core-fucose removed) and non-core-fucosylated glycans were calculated, and the lowest percentage was obtained in 100 μM of 2-FF combined with 0.5% PF-68. These results indicate that the relative quantity of each glycan of rhGAA produced in rice cell suspension cultures is significantly affected by their culture condition. This study performed the comparison of the N-glycan profiles of rice cell-derived rhGAA to identify the core-fucosylated glycans using UPLC and tandem mass spectrometry.

Analysis of Active Site Architecture and Reaction Product Linkage Chemistry Reveals a Conserved Cleavage Substrate for an Endo-alpha-mannanase within Diverse Yeast Mannans

Yeast α-mannan (YM) is a densely branched N-linked glycan that decorates the surface of yeast cell walls. Owing to the high degree of branching, cleavage of the backbone of YM appears to rely on the coupled action of side-chain-cleaving enzymes. Upon examining the genome sequences of bovine-adapted Bacteroides thetaiotaomicron strains, isolated for their ability to degrade YM, we have identified a tandem pair of genes inserted into an orphan pathway predicted to be involved in YM metabolism. Here, we investigated the activity of one of these enzymes, a predicted endo-mannanase from glycoside hydrolase (GH) family 76 (BtGH76-MD40). Purified recombinant BtGH76-MD40 displayed activity on structurally distinct YMs from Saccharomyces cerevisiae and Schizosaccharomyces pombe. Linkage analysis of released oligosaccharide products from S. cerevisiae and S. pombe mannan determined BtGH76-MD40 targets a specific linkage that is conserved in structurally diverse YM substrates. In addition, using two differential derivatization methods, we have shown that there is an absolute requirement for undecorated d-mannopyranose in the -1 subsite. Determination of the BtGH76-MD40 X-ray crystal structure and structural superimposition and molecular docking of a branched alpha-mannopentatose substrate supported these findings. In contrast, BtGH76-MD40 can accommodate extended side chains in the +1 and -2 subsites, highlighting that a single alpha-1,6-mannosyl residue is a prerequisite for activity, and cleavage occurs at the reducing end of the undecorated monosaccharide. Collectively these results demonstrate how acquisition of new enzymes within extant pathways contributes to the functional abilities of saccharolytic bacteria persisting in complex digestive ecosystems.

Bovine serum albumin affects N-glycoforms of murine IgG monoclonal antibody purified from hybridoma supernatants

Immunoglobulin G (IgG) is a class of monoclonal antibodies (mAbs) commonly produced in mammalian cell lines. These cell lines are grown in finely adjusted culture media, which contain components that may impact glycoforms. As variation of N-glycoforms can impact the biological properties of IgGs, medium composition should be controlled. Here, we studied the effects on IgG N-glycoforms of different components in hybridoma culture media, specifically compared bovine serum albumin (BSA) with other small molecules, using a matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight multistage mass spectrometry (MALDI-QIT-TOF MSⁿ)-based approach. We show that small molecular additives caused little change in glycan species, though a number of these reagents, especially glutamine, affected levels of glycosylation. In comparison, the addition of macromolecular protein BSA significantly changed IgG N-glycan patterns, not only in species but also in glycosylation levels. Together, our finding suggests that BSA increases the complexity of IgG N-glycoforms, thus raising the difficulty in maintaining glycoforms consistency during antibody production. Therefore, the effect of BSA on IgG N-glycans should be considered when designing optimal medium formulations for IgG production. KEY POINTS: • Small molecular medium additives only affect glycosylation levels of IgG N-glycans. • BSA significantly changes IgG N-glycoforms as a medium additive. • BSA's skewing of IgG N-glycoforms should be considered in IgG production.