Rapid and sensitive analysis of mucin-type glycans using an in-line flow glycan-releasing apparatus

Liquid Chromatography and Capillary Electrophoresis Analysis of 2AA-Labeled O-Glycans

To reveal O-glycan structures in mucins, it is necessary to release covalently bound O-glycans from the polypeptide backbone and derivatize to a form suitable for structural analysis. Various derivatization methods can now be applied in the analysis of O-glycans following the development of O-glycan release methods. Among the many derivatization methods available, we prefer to use fluorescent labeling with 2-aminobenzoic acid (anthranilic acid, 2AA). 2AA-labeled O-glycans can be detected with high sensitivity using liquid chromatography fluorescence detection (LC-FD) analysis because of the strong fluorescence. In addition, as 2AA has a carboxyl group that carries a negative charge, 2AA-labeled O-glycans can be analyzed with high sensitivity in negative ion mode mass spectrometry. Furthermore, because the negative charge of 2AA provides a driving force for electrophoresis, 2AA-labeled O-glycans can be analyzed using capillary electrophoresis (CE) and capillary affinity electrophoresis. High detection sensitivity and versatility are key advantages of the 2AA-labeling method. Here we present our preferred LC-FD and CE analytical methods for 2AA-labeled O-glycans.

Preparation of O-Glycans from Mucins Using Hydrazine Treatment

Mucin glycomic analysis is crucial owing to the participation of mucin O-glycans in several biological functions. Liquid chromatographic analysis of fluorescently labeled glycans is an effective tool for glycomic analysis. The first step of this analysis involves the release of O-glycans from mucins. As no enzyme is known to release all glycans, chemical methods are required for the process; therefore, hydrazine treatment is a commonly used chemical method. It enables the release of O-glycans from mucin while preserving the aldehyde group at the reducing end. This ensures that the reducing end can be modified using fluorescent reagents. However, it is also accompanied by the degradation of the glycans through a process called "peeling." Here, we describe a method for releasing glycans from mucins using hydrazine treatment with minimal "peeling."

Infant Gut Microbial Metagenome Mining of α-l-Fucosidases with Activity on Fucosylated Human Milk Oligosaccharides and Glycoconjugates

The gastrointestinal microbiota members produce α-l-fucosidases that play key roles in mucosal, human milk, and dietary oligosaccharide assimilation. Here, 36 open reading frames (ORFs) coding for putative α-l-fucosidases belonging to glycosyl hydrolase family 29 (GH29) were identified through metagenome analysis of breast-fed infant fecal microbiome. Twenty-two of those ORFs showed a complete coding sequence with deduced amino acid sequences displaying the highest degree of identity with α-l-fucosidases from Bacteroides thetaiotaomicron, Bacteroides caccae, Phocaeicola vulgatus, Phocaeicola dorei, Ruminococcus gnavus, and Streptococcus parasanguinis. Based on sequence homology, 10 α-l-fucosidase genes were selected for substrate specificity characterization. The α-l-fucosidases Fuc18, Fuc19A, Fuc35B, Fuc39, and Fuc1584 showed hydrolytic activity on α1,3/4-linked fucose present in Lewis blood antigens and the human milk oligosaccharide (HMO) 3-fucosyllactose. In addition, Fuc1584 also hydrolyzed fucosyl-α-1,6-N-acetylglucosamine (6FN), a component of the core fucosylation of N-glycans. Fuc35A and Fuc193 showed activity on α1,2/3/4/6 linkages from H type-2, Lewis blood antigens, HMOs and 6FN. Fuc30 displayed activity only on α1,6-linked l-fucose, and Fuc5372 showed a preference for α1,2 linkages. Fuc2358 exhibited a broad substrate specificity releasing l-fucose from all the tested free histo-blood group antigens, HMOs, and 6FN. This latest enzyme also displayed activity in glycoconjugates carrying lacto-N-fucopentaose II (Lea) and lacto-N-fucopentaose III (Lex) and in the glycoprotein mucin. Fuc18, Fuc19A, and Fuc39 also removed l-fucose from neoglycoproteins and human α-1 acid glycoprotein. These results give insight into the great diversity of α-l-fucosidases from the infant gut microbiota, thus supporting the hypothesis that fucosylated glycans are crucial for shaping the newborn microbiota composition. IMPORTANCE α-l-Fucosyl residues are frequently present in many relevant glycans, such as human milk oligosaccharides (HMOs), histo-blood group antigens (HBGAs), and epitopes on cell surface glycoconjugate receptors. These fucosylated glycans are involved in a number of mammalian physiological processes, including adhesion of pathogens and immune responses. The modulation of l-fucose content in such processes may provide new insights and knowledge regarding molecular interactions and may help to devise new therapeutic strategies. Microbial α-l-fucosidases are exoglycosidases that remove α-l-fucosyl residues from free oligosaccharides and glycoconjugates and can be also used in transglycosylation reactions to synthesize oligosaccharides. In this work, α-l-fucosidases from the GH29 family were identified and characterized from the metagenome of fecal samples of breastfed infants. These enzymes showed different substrate specificities toward HMOs, HBGAs, naturally occurring glycoproteins, and neoglycoproteins. These novel glycosidase enzymes from the breast-fed infant gut microbiota, which resulted in a good source of α-l-fucosidases, have great biotechnological potential.

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.

Circulating natural antibodies against 3'-sialyllactose complement the diagnostic performance of CA19-9 for the early detection of pancreatic ductal adenocarcinoma

BACKGROUND

Pancreatic ductal adenocarcinoma is a devastating malignancy with an extremely poor prognosis. Although the most widely used biomarker for pancreatic cancer is carbohydrate antigen CA19-9, it is elevated mainly in the late stage of pancreatic cancer. Some serum natural antibodies against carbohydrates have been shown to be possible diagnostic markers for cancer.

OBJECTIVE

This study was conducted to determine whether the level of natural antibodies against carbohydrates fluctuates in pancreatic ductal adenocarcinoma.

METHODS

Serum from pancreatic cancer subjects (n= 55) and 43 subjects free of malignant disease were studied. The contents of natural antibodies against sialyl glycans and CA19-9 in serum were determined by enzyme-linked immunosorbent assay.

RESULTS

The level of serum anti-3'-sialyllactose antibodies in pancreatic cancer subjects was significantly lower than that in healthy controls. In contrast, the amounts of serum antibodies against other sialyl glycans were comparable between the two groups. Concentration of serum anti-3'-sialyllactose IgG provided excellent AUC of 0.86, with sensitivity 82%, specificity 81%, and accuracy 82%. The combination of serum anti-3'-sialyllactose IgG with CA19-9 improved the sensitivity of pancreatic cancer detection at an early stage.

CONCLUSIONS

Natural antibodies against 3'-sialyllactose constitute a promising biomarker for pancreatic cancer detection. The measurement of serum anti-3'-sialyllactose antibodies could play a supportive role in diagnostics and complement the performance of CA19-9 for the early detection of pancreatic ductal adenocarcinoma.

A practical method of liberating O-linked glycans from glycoproteins using hydroxylamine and an organic superbase

O-Linked glycan liberation from proteins through reductive beta-elimination and hydrazinolysis is widely used, but have yet to satisfy the recent needs for glycan analysis in glycan biomarker research and microheterogeneity evaluation of biopharmaceutical glycosylation. Here, we introduce an alternative method by using hydroxylamine and an organic superbase, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and optimize the reaction conditions. The developed method afforded comparable results to those of hydrazinolysis, but with less degraded products. In addition, we examined the compatibility of the optimized O-linked glycan liberation with denaturant and detergents. The optimized method also released glycans containing NeuGc without degradation or deacylation. To demonstrate the feasibility of the developed method, we analyzed O-linked glycans of porcine submaxillary mucins separated by supported molecular matrix electrophoresis (SMME) which is previously developed to characterize mucins. The method for O-linked glycan liberation and fluorescent labeling presented here was easy and rapid, and will be practically useful for O-linked glycan analyses.

Identification of internally sialylated carbohydrate tumor marker candidates, including Sda/CAD antigens, by focused glycomic analyses utilizing the substrate specificity of neuraminidase

In our previous study, 14 sulfated carbohydrate tumor marker candidates were identified by focused glycomic analyses. Here, glycomic analyses focused on internally sialylated glycans to identify novel marker candidates. Internally sialylated glycans were enriched by digestion of pyridylaminated glycans prepared from sera with α-neuraminidase from Salmonella typhimurium, which did not cleave sialic acids linked to internal residues, followed by anion-exchange chromatography. Next, internally sialylated O-glycan profiles were constructed using two types of high performance liquid chromatography, which were compared between 20 healthy controls and 11 patients with gastric cancer and 9 patients with pancreatic cancer. In all, 17 marker candidates were identified. The structures of glycan candidates were precisely analyzed using enzymatic digestion, glycan synthesis, 2D mapping and mass spectrometry. Among 17 candidates, one was STn, and the other 16 comprised 10 core1, 1 core2 and 5 core3 glycans. The various structures included a α2,6-sialylated reducing terminal GalNAc and α2,6-sialylated type1 N-acetyl-lactosamine. Eight candidates possessed the Sda/CAD antigen. The levels of these candidate glycans in sera from all 40 subjects were quantified using a selected reaction monitoring assay and found to be elevated in at least one or more patients. Although the serum levels of each candidate glycan varied between patients, those candidates having the same backbone or determinant, such as core3 backbone and core1 structures with extended type1 N-acetyl-lactosamine, displayed similar patterns of elevation. These results suggest that analysis of multiple markers may be an effective means of diagnosing various cancers.

Comparison of Methods to Release Mucin-Type O-Glycans for Glycomic Analysis

Mucin-type O-glycans (O-glycans) are one of the most common glycans attached to proteins. To develop an optimized glycomic analysis protocol, O-glycans were released from glycoproteins using hydrazine, ammonia, or sodium hydroxide treatment, followed by hydrophilic interaction liquid chromatography to evaluate O-glycan release. We found that porcine gastric mucin or bovine fetuin treated at 60 °C for 6 h with hydrazine gas in the presence of malonic acid yielded O-glycans with only a small amount of degraded, so-called "peeled" products. Ammonia treatment also yielded intact O-glycans but with additional peeled products containing GlcNAc at the reducing end. In contrast, sodium hydroxide treatment yielded mainly peeled glycans, including those containing GlcNAc at the reducing end. Importantly, O-glycans obtained from rat gastric mucin treated with hydrazine and labeled with anthranilic acid had a nearly identical profile following hydrophilic interaction liquid chromatography as permethylated O-glycan alditols analyzed by mass spectroscopy. Taken together, the data suggest that glycan release using hydrazine treatment, followed by high-performance liquid chromatography after fluorescent labeling, is a suitable method for glycomic analysis of mucin-type O-glycans.

Current landscape of protein glycosylation analysis and recent progress toward a novel paradigm of glycoscience research

This review covers the basics and some applications of methodologies for the analysis of glycoprotein glycans. Analytical techniques used for glycoprotein glycans, including liquid chromatography (LC), capillary electrophoresis (CE), mass spectrometry (MS), and high-throughput analytical methods based on microfluidics, were described to supply the essentials about biopharmaceutical and biomarker glycoproteins. We will also describe the MS analysis of glycoproteins and glycopeptides as well as the chemical and enzymatic releasing methods of glycans from glycoproteins and the chemical reactions used for the derivatization of glycans. We hope the techniques have accommodated most of the requests from glycoproteomics researchers.

Merging carbohydrate chemistry with lectin histochemistry to study inhibition of lectin binding by glycoclusters in the natural tissue context

Recognition of glycans by lectins leads to cell adhesion and growth regulation. The specificity and selectivity of this process are determined by carbohydrate structure (sequence and shape) and topology of its presentation. The synthesis of (neo)glycoconjugates with bi- to oligo-valency (glycoclusters) affords tools to delineate structure-activity relationships by blocking lectin binding to an artificial matrix, often a glycoprotein, or cultured cell lines. The drawback of these assays is that glycan presentation is different from that in tissues. In order to approach the natural context, we here introduce lectin histochemistry on fixed tissue sections to determine the susceptibility of binding of two plant lectins, i.e., GSA-II and WGA, to a series of 10 glycoclusters. Besides valency, this panel covers changes in the anomeric position (α/β) and the atom at the glycosidic linkage (O/S). Flanked by cell and solid-phase assays with human tumor lines and two mucins, respectively, staining (intensity and profile) was analyzed in sections of murine jejunum, stomach and epididymis as a function of glycocluster presence. The marked and differential sensitivity of signal generation to structural aspects of the glycoclusters proves the applicability of this method. This enables comparisons between data sets obtained by using (neo)glycoconjugates, cells and the tissue context as platforms. The special advantage of processing tissue sections is the monitoring of interference with lectin association at sites that are relevant for functionality. Testing glycoclusters in lectin histochemistry will especially be attractive in cases of multi-target recognition (glycans, proteins and lipids) by a tissue lectin.

A rapid and highly sensitive microchip electrophoresis of mono- and mucin-type oligosaccharides labeled with 7-amino-4-methylcoumarin

A selective separation method using a poly(methylmethacrylate) microchip was developed for 7-amino-4-methylcoumarin-labeled saccharides in a crude reaction mixture. In an alkaline borate buffer, saccharide derivatives formed strong anionic borate complexes. These complexes moved from the cathode to the anode in an electric field and were detected near the anode. Excess labeling reagents and other foreign substances remained at the inlet reservoir. A confocal fluorimetric detection system enabled the determination of monosaccharide derivatives with good linearity between at least 5 and 100 nM, corresponding to 50 fmol to 1 pmol per injection. The lower limit of detection (signal-to-noise = 5) was 2 nM. The sensitivity and linear quantitation range were comparable to reported values using fluorometric detection, capillary electrophoresis, or liquid chromatography. Application of the method showed excellent resolution in the analysis of O-linked glycans chemically released from glycoproteins.

Site-specific analysis of the O-glycosylation of bovine fetuin by electron-transfer dissociation mass spectrometry

Bovine fetuin often finds use as a test model for analytical methods, but the exact occupancy of its O-glycosylation sites has not yet been determined. An obstacle for a closer inspection of the five or six O-glycosylation sites is the close spacing of several sites on the same tryptic peptide. The advent of ion-trap instruments with electron-transfer dissociation (ETD) capability and - for the type of instrument - high resolution prompted us to probe this technology for the investigation of the intricate posttranslational modifications O-glycosylation and phosphorylation. Much information could be obtained by direct-infusion ETD analysis of the fully sialylated tryptic 61-residue peptide harboring 8 hydroxyl amino acids of which four were indeed found to be, if only partially, glycosylated. The middle-down approach allowed recognizing an order of action of O-GalNAc transferase(s). No such hierarchy could be observed for phosphorylation. ETD fragmentation on an ion trap thus allowed in-depth analysis of a large, multiply O-glycosylated peptide, however, only by data accumulation over several minutes by direct infusion of a prefractionated sample. O-glycosylation and phosphorylation sites re-defined and their occupancy including that of N-glycans were defined by this study.

BIOLOGICAL SIGNIFICANCE

O-glycosylation of natural or recombinant proteins poses a challenge because of the lack of unambiguous consensus sites, the agglomeration of several O-glycans in close proximity and the lack of efficient O-glycosidases. Even bovine fetuin, a frequently used test glycoprotein for glycosylation analysis, has hitherto not been fully characterized in terms of site occupancy. This gap shall hereby be closed by application of electron-transfer dissociation mass spectroscopy.

Bovine κ-casein inhibits human rotavirus (HRV) infection via direct binding of glycans to HRV

Human rotavirus (HRV) is a major etiologic agent of severe infantile gastroenteritis. κ-Casein (κ-CN) from both human and bovine mature milk has been reported to have anti-HRV activity; however, the mechanism of this activity is poorly understood. The present study examined the molecular basis for the protective effect of bovine κ-CN derived from late colostrum (6-7 d after parturition) and from mature milk. Among the components of casein, κ-CN is the only glycosylated protein that has been identified. Therefore, we investigated whether the glycan residues in κ-CN were involved in the anti-HRV activity. Desialylated CN obtained by neuraminidase treatment exhibited anti-HRV activity, whereas deglycosylated CN obtained by o-glycosidase treatment lacked antiviral activity, indicating that glycans were responsible for the antiviral activity of CN. Furthermore, an evanescent-field fluorescence-assisted assay showed that HRV particles directly bound to heated casein (at 95°C for 30 min) in a viral titer-dependent manner. Although the heated κ-CN retained inhibitory activity in a neutralization assay, the activity was weaker than that observed before heat treatment. Our findings indicate that the inhibitory mechanism of bovine κ-CN against HRV involves direct binding to viral particles via glycan residues. In addition, heat-labile structures in κ-CN may play an important role in maintenance of κ-CN binding to HRV.

Infection of swine ex vivo tissues with avian viruses including H7N9 and correlation with glycomic analysis

Objectives

Swine have been regarded as intermediate hosts in the spread of influenza from birds to humans but studies of the sialylated glycans that comprise their respiratory tract have not been extensively studied in the past. This study analyzed the sialylated N‐glycan and O‐glycan profile of swine trachea and lung and correlated this with ex‐vivo infection of swine explants with avian influenza viruses.

Sample

Lungs and tracheal samples were obtained from normal farm and laboratory raised swine and used for ex vivo infection as well as mass spectrometric analysis. Infection of the ex vivo tissues used high pathogenic and low pathogenic avian viruses including the novel H7N9 virus that emerged in China in early 2013.

Main outcome measures

Assessment of successful replication was determined by TCID50 as well as virus immunohistochemistry. The N‐glycan and O‐glycan profiles were measured by MALDI‐TOF and sialylated linkages were determined by sialidase treatment. Lectin binding histochemistry was also performed on formalin fixed tissue samples with positive binding detected by chromogen staining.

Results

The swine respiratory tract glycans differed from the human respiratory tact glycans in two main areas. There was a greater abundance of Gal‐α‐Gal linkages resulting in a relative decrease in sialylated glycans. The swine respiratory tract also had a greater proportion of glycans containing Neu5Gc and Siaα2‐6 glycans than the human respiratory tract. Infection with avian viruses was confined primarily to lung bronchioles rather than trachea and parenchyma.

Conclusions

In contrast to previous studies we found that there was not as much expression of Siaα2‐3 glycans on the surface of the trachea. Infection of Siaα2‐3 binding avian viruses was restricted to the lower respiratory tract bronchioles. This finding may diminish the ability of the swine to act as an intermediary in the transmission of avian viruses to humans.

Free glycans derived from glycoproteins present in human sera

During the course of studies on the analysis of O-glycans in biological samples, we found that significant amount of free glycans are present in normal human serum samples. The most abundant free glycan was disialo-biantennary glycan typically observed in transferrin which is one of the abundant glycoproteins found in sera. Minor glycans were also considered to be mainly due to transferrin, but some glycans were derived from mucin-type O-glycans, although the amount was quite minute. However, high mannose-type glycans could not be detected at all. Although there have been many reports on the presence of intracellular "free" N-glycans (mainly derived from high mannose-type glycans) generated either from lipid-linked oligosaccharides or from misfolded glycoproteins through endoplasmic-reticulum associated protein degradation pathway, there is little information on the presence of free glycans in extracellular matrix and biological fluids such as serum. This report is the first one which demonstrates the presence of free glycans due to glycoproteins in sera.

Analysis of O-glycans as 9-fluorenylmethyl derivatives and its application to the studies on glycan array

A method is proposed for the analysis of O-glycans as 9-fluorenylmethyl (Fmoc) derivatives. After releasing the O-glycans from the protein backbone in the presence of ammonia-based media, the glycosylamines thus formed are conveniently labeled with Fmoc-Cl and analyzed by HPLC and MALDI-TOF MS after easy purification. Fmoc labeled O-glycans showed 3.5 times higher sensitivities than those labeled with 2-aminobenzoic acid in fluorescent detection. Various types of O-glycans having sialic acids, fucose, and/or sulfate residues were successfully labeled with Fmoc and analyzed by HPLC and MALDI-TOF MS. The method was applied to the comprehensive analysis of O-glycans expressed on MKN45 cells (human gastric adenocarcinoma). In addition, Fmoc-derivatized O-glycans were easily converted to free hemiacetal or glycosylamine-form glycans that are available for fabrication of glycan array and neoglycoproteins. To demonstrate the availability of our methods, we fabricate the glycan array with Fmoc labeled glycans derived from mucin samples and cancer cells. The model studies using the glycan array showed clear interactions between immobilized glycans and some lectins.

The sweet tooth of biopharmaceuticals: importance of recombinant protein glycosylation analysis

Biopharmaceuticals currently represent the fastest growing sector of the pharmaceutical industry, mainly driven by a rapid expansion in the manufacture of recombinant protein-based drugs. Glycosylation is the most prominent post-translational modification occurring on these protein drugs. It constitutes one of the critical quality attributes that requires thorough analysis for optimal efficacy and safety. This review examines the functional importance of glycosylation of recombinant protein drugs, illustrated using three examples of protein biopharmaceuticals: IgG antibodies, erythropoietin and glucocerebrosidase. Current analytical methods are reviewed as solutions for qualitative and quantitative measurements of glycosylation to monitor quality target product profiles of recombinant glycoprotein drugs. Finally, we propose a framework for designing the quality target product profile of recombinant glycoproteins and planning workflow for glycosylation analysis with the selection of available analytical methods and tools.

Cytotoxicity and glycan-binding properties of an 18 kDa lectin isolated from the marine sponge Halichondria okadai

A divalent cation-independent lectin-HOL-18, with cytotoxic activity against leukemia cells, was purified from a demosponge, Halichondria okadai. HOL-18 is a 72 kDa tetrameric lectin that consists of four non-covalently bonded 18 kDa subunits. Hemagglutination activity of the lectin was strongly inhibited by chitotriose (GlcNAcβ1-4GlcNAcβ1-4GlcNAc), fetuin and mucins from porcine stomach and bovine submaxillary gland. Lectin activity was stable at pH 4-12 and temperatures lower than 60 °C. Frontal affinity chromatography with 16 types of pyridylaminated oligosaccharides indicated that the lectin had an affinity for N-linked complex-type and sphingolipid-type oligosaccharides with N-acetylated hexosamines and neuramic acid at the non-reducing termini. The lectin killed Jurkat leukemia T cells and K562 erythroleukemia cells in a dose- and carbohydrate-dependent manner.

One-pot characterization of cancer cells by the analysis of mucin-type glycans and glycosaminoglycans

We developed an automated apparatus for rapid releasing of O-glycans from mucin-type glycoproteins [Anal. Biochem. 371 (2007) 52-61; Anal. Chem. 82 (2010) 7436-7443] and applied the device to analyze them in some cancer cell lines [J. Proteome Res. 8 (2009) 521-537]. We also found that the device is useful to release glycosaminoglycans from proteoglycans [Anal. Biochem. 362 (2007) 245-251]. Based on these studies, we developed a method for one-pot analysis of mucin-type glycans and glycosaminoglycans after releasing them from total protein pool obtained from some cancer cell lines. Mucin-type glycans were analyzed by a combination of high-performance liquid chromatography and mass spectrometry techniques, and glycosaminoglycans were analyzed by capillary electrophoresis as fluorescent-labeled unsaturated disaccharides after digestion with specific eliminases followed by fluorescent labeling. Ten cancer cell lines, including blood cancer cells as well as epithelial cancer cells, were used to assess the method. The results clearly revealed that both mucin-type glycans and glycosaminoglycans showed quite interesting profiles. Thus, the current technique will be a powerful tool for discovery of glycan markers of diseases.

One-pot nonreductive O-glycan release and labeling with 1-phenyl-3-methyl-5-pyrazolone followed by ESI-MS analysis

A novel one-pot procedure for the nonreductive release of O-linked glycans from glycoproteins and the simultaneous derivatization of released glycans with 1-phenyl-3-methyl-5-pyrazolone (PMP) is described. Unlike the traditional reductive β-elimination, which produces alditols, this new method employs PMP/ammonia aqueous solution as the reaction medium. The O-glycans are released from glycoproteins and derivatized with PMP nonreductively, specifically, and quantitatively. Samples can be easily purified from ammonia, excess PMP, and peptide residues by evaporation, chloroform extraction, and solid-phase extraction (SPE) column fractionation for HPLC, CE, or MS analysis. The procedure has been elaborated with two purified glycoproteins, porcine stomach mucin and bovine fetuin, and successfully applied to O-glycan profiling of a challenging biological specimen, healthy human plasma. This new procedure has shown methodological significance in O-glycan analysis.

Mass spectrometric O-glycan analysis after combined O-glycan release by beta-elimination and 1-phenyl-3-methyl-5-pyrazolone labeling

BACKGROUND

Analysis of protein glycosylation is an important first step towards establishing the functions of glycans in health and disease. In contrast to N-glycans which are generally enzymatically released for analysis, there is no corresponding enzyme for O-glycan liberation. Therefore, O-glycans are generally released by chemical methods involving tedious procedures.

METHODS

Here, a straightforward method for the combined release and labeling of O-linked glycans from glycoproteins is described. Dimethylamine serves as the releasing agent, and 1-phenyl-3-methyl-5-pyrazolone (PMP) is employed for a prompt reaction with the reducing end of the freshly released O-glycan structures via an aldol condensation followed by a Michael-type addition resulting in a 2:1 stoichiometry of PMP per glycan. Samples are analyzed by nanoLC coupled to mass spectrometry.

RESULTS

Mucin from bovine submaxillary gland was used as a model protein to evaluate and optimize the approach that was further applied to bile salt stimulated lipase (BSSL) isolated from human milk. Next to previously reported O-glycan structures two additional oligosaccharides could be detected for BSSL.

GENERAL SIGNIFICANCE

In conclusion, the facile protocol established is suitable for the analysis of complex O-linked oligosaccharides from various biological samples. This article is part of a Special Issue entitled Glycoproteomics.

Negative ion CID fragmentation of O-linked oligosaccharide aldoses--charge induced and charge remote fragmentation

Collision induced dissociation (CID) fragmentation was compared between reducing and reduced sulfated, sialylated, and neutral O-linked oligosaccharides. It was found that fragmentation of the [M - H](-) ions of aldoses with acidic residues gave unique Z-fragmentation of the reducing end GalNAc containing the acidic C-6 branch, where the entire C-3 branch was lost. This fragmentation pathway, which is not seen in the alditols, showed that the process involved charge remote fragmentation catalyzed by a reducing end acidic anomeric proton. With structures containing sialic acid on both the C-3 and C-6 branch, the [M - H](-) ions were dominated by the loss of sialic acid. This fragmentation pathway was also pronounced in the [M - 2H](2-) ions revealing both the C-6 Z-fragment plus its complementary C-3 C-fragment in addition to glycosidic and cross ring fragmentation. This generation of the Z/C-fragment pairs from GalNAc showed that the charges were not participating in their generation. Fragmentation of neutral aldoses showed pronounced Z-fragmentation believed to be generated by proton migration from the C-6 branch to the negatively charged GalNAc residue followed by charge remote fragmentation similar to the acidic oligosaccharides. In addition, A-type fragments generated by charge induced fragmentation of neutral oligosaccharides were observed when the charge migrated from C-1 of the GalNAc to the GlcNAc residue followed by rearrangement to accommodate the (0,2)A-fragmentation. LC-MS also showed that O-linked aldoses existed as interchangeable α/β pyranose anomers, in addition to a third isomer (25% of the total free aldose) believed to be the furanose form.

Hyphenated technique for releasing and MALDI MS analysis of O-glycans in mucin-type glycoprotein samples

We developed an automatic apparatus for the release of O-glycans from mucin-type glycoproteins and proteoglycans (Matsuno, Y.-k.; Yamada, K.; Tanabe, A.; Kinoshita, M.; Maruyama, S.-z.; Osaka, Y.-s.; Masuko, T.; Kakehi, K. Anal. Biochem. 2007, 363, 245-257. Yamada, K.; Hyodo, S.; Matsuno, Y. K.; Kinoshita, M.; Maruyama, S. Z.; Osaka, Y. S.; Casal, E.; Lee, Y. C.; Kakehi, K. Anal. Biochem. 2007, 371, 52-61). The method allows rapid release of O-glycans as the reducing form within 10 min. In the present study, we connected the device to a MALDI-TOF MS spotter and achieved routine analysis of O-glycans in biological samples for clinical use after in situ derivatization of the released O-glycans with phenylhydrazine. We applied the method to the analysis of O-glycans expressed on MKN45 cells derived from human stomach cancer cells and found that MKN45 cells expressed characteristic trisialo-polylactosamine-type glycans as reported previously (Yamada, K.; Kinoshita, M.; Hayakawa, T.; Nakaya, S.; Kakehi, K. J. Proteome Res. 2009, 8, 521-537). We also applied the method to the analysis of O-glycans in serum samples. The present technique is the first attempt to use MS measurement for routine clinical diagnostic works.

Mass spectrometry and glycomics

Glycosylation defines the adhesive properties of animal cell surfaces and the surrounding extracellular environments. Because cells respond to stimuli by altering glycan expression, glycan structures vary according to spatial location in tissue and temporal factors. These dynamic structural expression patterns, combined with the essential roles glycans play in physiology, drive the need for analytical methods for glycoconjugates. In addition, recombinant glycoprotein drug products represent a multibillion dollar market. Effective analytical methods are needed to speed the identification of new targets and the development of industrial glycoprotein products, both new and biosimilar. Mass spectrometry is an enabling technology in glycomics. This review summarizes mass spectrometry of glycoconjugate glycans. The intent is to summarize appropriate methods for glycans given their chemical properties as distinct from those of proteins, lipids, and small molecule metabolites. Special attention is given to the uses of mass spectral profiling for glycomics with respect to the N-linked, O-linked, ganglioside, and glycosaminoglycan compound classes. Next, the uses of tandem mass spectrometry of glycans are summarized. The review finishes with an update on mass spectral glycoproteomics.

Glycome profiling using modern glycomics technology: technical aspects and applications

Glycomics research has become indispensable in many research fields such as immunity, signal transduction and development. Moreover, changes in the glycosylation of proteins and lipids have been reported in several diseases including cancer. The analysis of a complex post-translational modification such as glycosylation depends on the availability or development of appropriate analytical technologies. The research goal determines the sensitivity, resolution and throughput requirements and guides the choice of a particular technology. This review highlights the evolution of glycan profiling tools in the past 5 years. We focus on capillary electrophoresis, liquid chromatography, mass spectrometry and lectin microarrays.

Definitive evidence that a single N-glycan among three glycans on inducible costimulator is required for proper protein trafficking and ligand binding

Glycosylation is a widespread post-translational modification found in glycoproteins. Glycans play key roles in protein folding, quality control in the endoplasmic reticulum (ER) and protein trafficking within cells. However, it remains unclear whether all positions of protein glycosylation are involved in glycan functions, or if specific positions have individual roles. Here we demonstrate the integral involvement of a specific N-glycan from amongst the three glycans present on inducible costimulator (ICOS), a T-cell costimulatory molecule, in proper protein folding and intracellular trafficking to the cell surface membrane. We found that glycosylation-defective mutant proteins lacking N-glycan at amino-acid position 89 (N89), but not proteins lacking either N23 or N110, were retained within the cell and were not detected on the cell surface membrane. Additional evidence suggested that N89 glycosylation was indirectly involved in ICOS ligand binding. These data suggest that amongst the three putative ICOS glycosylation sites, N89 is required for proper ICOS protein folding in the ER, intracellular trafficking and ligand binding activity. This study represents a substantial contribution to the current mechanistic understanding of the necessity and potential functions of a specific N-glycan among the multiple glycans of glycoproteins.

Determination of Tn antigen released from cultured cancer cells by capillary electrophoresis

An incomplete elongation of O-glycans in mucins has been found in epithelial cancers, leading to the expression of shorter carbohydrate structures such as Tn antigen (GalNAc-O-Ser/Thr), which has been reported to be one of the most specific human cancer-associated structures. However, there have been no appropriate physicochemical methods for the determination of Tn antigen in biological samples. In the present paper, we developed a capillary electrophoresis method for the determination of Tn antigen, and applied the method to the analysis of the expressed Tn antigen on some leukemia and epithelial cancer cells.

Comparative studies on the structural features of O-glycans between leukemia and epithelial cell lines

Recently, we developed an automated apparatus for rapid releasing of O-glycans from mucin-type glycoproteins and proteoglycans ( Anal. Biochem. 2007 , 362 , 245 - 251 ; 2007 , 371 , 52 - 61 ). In the present paper, we released O-glycans from some leukemia and epithelial cells using the apparatus, and compared the profiles of O-glycans among these cells after fluorescent labeling of the released glycans with 2-aminobenzoic acid. The fluorescent labeled glycans were analyzed using a combination of HPLC and off-line MALDI-(QIT)TOF mass spectrometry We found that leukemia cells generally showed simple glycan profiles and commonly contained sialyl-T (NeuAcalpha2-3Galbeta1-3GalNAc) and disialyl-T (NeuAcalpha2-3Galbeta1-3(NeuAcalpha2-6)GalNAc) antigens as major O-glycans. In contrast, epithelial cancer cell lines usually showed extremely complex profiles. We found that polylactosamine-type O-glycans were abundantly present in MKN45 cells. Especially, we found characteristic glycans, of which Galbeta1-3 residue of core1 structure is modified with biantennary polylactosamine units. In contrast, this cell line did not contain polylactosamine-type N-glycans ( J. Proteome Res. 2006 , 5 , 88 - 97 ). These results suggest that the different biosynthetic pathways for N- and O-glycans are proposed. The method presented here will accelerate the speed for comprehensive analysis of O-glycans in biological samples and will be a powerful tool for clinical/biochemical analysis in cancer biology.

Analytical performance of immobilized pronase for glycopeptide footprinting and implications for surpassing reductionist glycoproteomics

A fully developed understanding of protein glycosylation requires characterization of the modifying oligosaccharides, elucidation of their covalent attachment sites, and determination of the glycan heterogeneity at specific sites. Considering the complexity inherent to protein glycosylation, establishing these features for even a single protein can present an imposing challenge. To meet the demands of glycoproteomics, the capability to screen far more complex systems of glycosylated proteins must be developed. Although the proteome wide examination of carbohydrate modification has become an area of keen interest, the intricacy of protein glycosylation has frustrated the progress of large-scale, systems oriented research on site-specific protein-glycan relationships. Indeed, the analytical obstacles in this area have been more instrumental in shaping the current glycoproteomic paradigm than have the diverse functional roles and ubiquitous nature of glycans. This report describes the ongoing development and analytically salient features of bead immobilized pronase for glycosylation site footprinting. The present work bears on the ultimate goal of providing analytical tools capable of addressing the diversity of protein glycosylation in a more comprehensive and efficient manner. In particular, this approach has been assessed with respect to reproducibility, sensitivity, and tolerance to sample complexity. The efficiency of pronase immobilization, attainable pronase loading density, and the corresponding effects on glycoprotein digestion rate were also evaluated. In addition to being highly reproducible, the immobilized enzymes retained a high degree of proteolytic activity after repeat usage for up to 6 weeks. This method also afforded a low level of chemical background and provided favorable levels of sensitivity with respect to traditional glycoproteomic strategies. Thus, the application of immobilized pronase shows potential to contribute to the advancement of more comprehensive glycoproteomic research methods that are capable of providing site-specific glycosylation and microheterogeneity information across many proteins.

Identification of a pneumococcal glycosidase that modifies O-linked glycans

Colonization of the airway by Streptococcus pneumoniae is typically asymptomatic; however, progression of bacteria beyond the oronasopharynx can cause diseases including otitis media and pneumonia. The mechanisms by which S. pneumoniae establishes and maintains colonization remain poorly understood. Both N-linked and O-linked glycans are abundant in the airway. Our previous research demonstrated that S. pneumoniae can sequentially deglycosylate N-linked glycans and suggested that this modification of sugar structures may aid in colonization. There is published evidence that S. pneumoniae expresses a secreted O-glycosidase that cleaves galactose beta1-3 N-acetylgalactosamine (Galbeta1-3GalNAc) from core-1 O-linked glycans; however, the biological function of this enzyme has not previously been determined. We established that the activity is not secreted but is instead surface associated in a sortase-dependent manner. Genome analysis revealed an open reading frame predicted to encode a sortase-dependent surface protein with sequence similarity to the O-glycosidase of Bifidobacterium longum. Deletion of this pneumococcal open reading frame confirmed that this gene encodes an O-glycosidase. Experiments using a model glycoconjugate demonstrated that this O-glycosidase, together with the neuraminidase NanA, is required for S. pneumoniae to cleave sialylated core-1 O-linked glycans. The ability of the O-glycosidase mutant to cleave this glycan structure was restored by both genetic complementation and the addition of O-glycosidase. The mutant showed a reduction in adherence to human airway epithelial cells and a significantly decreased ability to colonize the upper respiratory tract, suggesting that cleavage of core-1 O-linked glycans enhances the ability of S. pneumoniae to colonize the human airway.