Labelling saccharides with phenylhydrazine for electrospray and matrix-assisted laser desorption-ionization mass spectrometry

A low-cost efficient online derivatization system for the determination of saccharides by high-performance liquid chromatograph-ultraviolet detector

In this study, a low-cost efficient online derivatization system was developed which allows for the detection of various types of mono- and oligo-saccharides only utilizing high-performance liquid chromatography (HPLC)-ultraviolet detector (UV) system. In the proposed method, phenylhydrazine was used as the derivatization reagent and directly spiked in the mobile phase, allowing for the separation and detection of mono- and oligosaccharides in an accessible instrument system (HPLC-UV). And the online derivatization design of the proposed method has significantly reduced the potential harm of derivatization reagents to the analysts. Furthermore, critical chromatographic parameters were optimized via the Box-Behnken design strategy, culminating in the ideal response for saccharides. Finally, the methodology validation of the proposed method was conducted. The proposed method showed satisfactory linear ranges with acceptable correlation coefficients (R2  > 0.99), outstanding accuracy (Recovery: 95.3%-105.6%), high intra-day precision (relative standard deviation [RSD]: 1.4%-7.1%) and inter-day precision (RSD: 2.0%-7.4%). The robustness and ruggedness of the proposed method were proved as the recovery values in the range of 95.0%-104.6% and 95.1%-104.8% for robustness and ruggedness, respectively. These satisfactory validation results confirm the applicability and reliability of the proposed method for the analysis of saccharides in various complex real-world samples.

MS-based glycomics and glycoproteomics methods enabling isomeric characterization

Glycosylation is one of the most significant and abundant posttranslational modifications in mammalian cells. It mediates a wide range of biofunctions, including cell adhesion, cell communication, immune cell trafficking, and protein stability. Also, aberrant glycosylation has been associated with various diseases such as diabetes, Alzheimer's disease, inflammation, immune deficiencies, congenital disorders, and cancers. The alterations in the distributions of glycan and glycopeptide isomers are involved in the development and progression of several human diseases. However, the microheterogeneity of glycosylation brings a great challenge to glycomic and glycoproteomic analysis, including the characterization of isomers. Over several decades, different methods and approaches have been developed to facilitate the characterization of glycan and glycopeptide isomers. Mass spectrometry (MS) has been a powerful tool utilized for glycomic and glycoproteomic isomeric analysis due to its high sensitivity and rich structural information using different fragmentation techniques. However, a comprehensive characterization of glycan and glycopeptide isomers remains a challenge when utilizing MS alone. Therefore, various separation methods, including liquid chromatography, capillary electrophoresis, and ion mobility, were developed to resolve glycan and glycopeptide isomers before MS. These separation techniques were coupled to MS for a better identification and quantitation of glycan and glycopeptide isomers. Additionally, bioinformatic tools are essential for the automated processing of glycan and glycopeptide isomeric data to facilitate isomeric studies in biological cohorts. Here in this review, we discuss commonly employed MS-based techniques, separation hyphenated MS methods, and software, facilitating the separation, identification, and quantitation of glycan and glycopeptide isomers.

MS-based glycomics: An analytical tool to assess nervous system diseases

Neurological diseases affect millions of peopleochemistryorldwide and are continuously increasing due to the globe's aging population. Such diseases affect the nervous system and are characterized by a progressive decline in brain function and progressive cognitive impairment, decreasing the quality of life for those with the disease as well as for their families and loved ones. The increased burden of nervous system diseases demands a deeper insight into the biomolecular mechanisms at work during disease development in order to improve clinical diagnosis and drug design. Recently, evidence has related glycosylation to nervous system diseases. Glycosylation is a vital post-translational modification that mediates many biological functions, and aberrant glycosylation has been associated with a variety of diseases. Thus, the investigation of glycosylation in neurological diseases could provide novel biomarkers and information for disease pathology. During the last decades, many techniques have been developed for facilitation of reliable and efficient glycomic analysis. Among these, mass spectrometry (MS) is considered the most powerful tool for glycan analysis due to its high resolution, high sensitivity, and the ability to acquire adequate structural information for glycan identification. Along with MS, a variety of approaches and strategies are employed to enhance the MS-based identification and quantitation of glycans in neurological samples. Here, we review the advanced glycomic tools used in nervous system disease studies, including separation techniques prior to MS, fragmentation techniques in MS, and corresponding strategies. The glycan markers in common clinical nervous system diseases discovered by utilizing such MS-based glycomic tools are also summarized and discussed.

The potency of HPLC-DAD and LC-MS/MS combined with ion chromatography for detection/purification of levulinic acid and bio-compounds from acid hydrolysis of OPEFB

This work reports a new strategy for the detection and purification of levulinic acid (LA) and bio-compounds from the acid hydrolysis and enzymatic treatment of oil palm empty fruit bunch (OPEFB) through high-performance liquid chromatography (HPLC) techniques combined with ion/ligand chromatography. The detections of LA, biomass-saccharides, hydroxymethylfurfural (HMF), and furfural were successfully elucidated by optimizing the multiple reaction monitoring mode (MRM) and liquid chromatography conditions using a Pb²⁺ ligand exchange column in the liquid chromatography with tandem mass spectrometry (LC-MS/MS) approach. High-performance liquid chromatography with diode-array detection (HPLC-DAD) combined with an H⁺ ion exchange column also showed potency for detecting chromophoric compounds such as LA, HMF, furfural, and acid (by-products) but not biomass-saccharides. Both techniques showed acceptable validation in terms of linearity, limit of detection (LOD), limit of quantitation (LOQ), accuracy, precision, and stability in both quantitative and qualitative analysis. However, the LC-MS/MS approach showed higher sensitivity for detecting LA and HMF compared with HPLC-DAD. Samples comprised of cellobiose, glucose, HMF, and LA from the acid hydrolysis of cellulose to LA with a mineral acid, and the biocatalysis of cellulase and β-glucosidase catalyzed cellulose (from OPEFB) to glucose were successfully monitored through the LC-MS/MS approach. In addition, using the optimal HPLC conditions obtained from LC-MS/MS, the purification of LA from other substances obtained from the hydrolysis reaction of cellulose (5 g) was successfully demonstrated by HPLC-DAD equipped with a fraction collector combined with an H⁺ ion exchange column at gram-scale of 1 g LA with a purification rate of 0.63 g ml⁻¹ min⁻¹.

The analytical approach for detection and purification levulinic acid from and bio-compound in hydrolysis biomass.

Synthesis of naphthalimide-type chemsensor and its application in quality evaluation for polygonatum sibiricum Red

The premise and key of ensuring the safety and effectiveness of traditional Chinese medicine (TCM) is to construct appropriate quality evaluation system of TCM. This study aimed to establish a pre-column derivatization HPLC method for achieving the quality control of Polygonatum sibiricum by reacting synthesized 4-hydrazino-1,8-naphthalimide (HAN) with diverse monosaccharides from the hydrolytic product of P. sibiricum polysaccharides (PSPs), followed by HPLC separation. The HAN was synthesized based on a CuI-catalyzed cross-coupling reaction in water, and then employed as a novel chemosensor that reacts with reducing sugars. Good separation was achieved at a detection wavelength of 448 nm using an ZORBAX SB-C8 column under a gradient elution at a flow rate of 0.5 ml/min within 12 min. The monosaccharide compositions of PSP mainly include two hexoses [glucose (Glc), galactose (Gal)] and two hexuronic acids [glucuronic acid (GlcA) and galacturonic acid (GalA)], and the molar ratio of Glc, Gal, GlcA and GalA is 16.67:52.94:10.58:19.81. The verified HPLC method, possessing excellent precision and good accuracy, successfully achieved rapid qualitative and quantitative determination for PSP. Additionally, the HAN displayed fluorescence enhancement through “push–pull” mode, and fluorescence decreased through “pull–pull” mode after binding to monosaccharides, which is a potential for fluorescence determination of different monosaccharides.

Discovery and Development of Promiscuous O-Glycan Hydrolases for Removal of Intact Sialyl T-Antigen

Mucin-type O-glycosylation (O-glycosylation) is a common post-translational modification that confers distinct biophysical properties to proteins and plays crucial roles in intercellular signaling. Yet, despite the importance of O-glycans, relatively few tools exist for their analysis and modification. In particular, there is a need for enzymes that can cleave the wide range of O-glycan structures found on protein surfaces, to facilitate glycan profiling and editing. Through functional metagenomic screening of the human gut microbiome, we discovered endo-O-glycan hydrolases from CAZy family GH101 that are capable of slowly cleaving the intact sialyl T-antigen trisaccharide (a ubiquitous O-glycan structure in humans) in addition to their primary activity against the T-antigen disaccharide. We then further explored this sequence space through phylogenetic profiling and analysis of representative enzymes, revealing large differences in the levels of this promiscuous activity between enzymes within the family. Through structural and sequence analysis, we identified active site residues that modulate specificity. Through subsequent rational protein engineering, we improved the activity of an enzyme identified by phylogenetic profiling sufficiently that substantial removal of the intact sialyl T-antigen from proteins could be readily achieved. Our best sialyl T-antigen hydrolase mutant, SpGH101 Q868G, is further shown to function on a number of proteins, tissues, and cells. Access to this enzyme opens up improved methodologies for unraveling the glycan code.

Characterization of multi-cationic aminopyrene-based tag for oligosaccharide labeling by capillary electrophoresis with laser-induced fluorescence detection

In this work, we characterize a previously synthesized multi-cationic aminopyrene-based labeling tag for oligosaccharide analysis by capillary electrophoresis with laser-induced fluorescence detection (CE/LIF). The fluorescent tag, 4,4',4''-(8-aminopyrene-1,3,6-trisulfonyl)tris(1-methylpiperazine) (APTMP), was characterized by reaction with standard maltooligosaccharides and the labeling parameters such as fluorescent tag concentration, labeling temperature, and time as well as influence of a reducing agent and its solvent were investigated in terms of labeling efficiency. The nanomolar limit of detection of CE/LIF analysis of APTMP labeled maltopentaose was determined. However, significant amount of the oligosaccharides was reduced to alditols, which negatively affects the yield and rate of the labeling reaction. Under optimized conditions, a highly reproducible labeling by multi-cationic APTMP was obtained; however, the most commonly used labeling by multi-anionic 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt (APTS) is superior compared to APTMP labeling. Lower reactivity of APTMP compared to APTS can be explained by the loss of nucleophilicity induced by substitution of the sulfonate groups with more electron-withdrawing aminosulfonyl ones. On contrary, APTMP is still a promising tag for oligosaccharide labeling followed by CE-MS in a positive ion mode, which is considered to be more sensitive than MS detection of APTS in a negative ion mode.

A robust glycan labeling strategy using a new cationic hydrazide tag for MALDI-MS-based rapid and sensitive glycomics analysis

Chemical derivatization of glycans is a common strategy to increase the analytical performance of MALDI-MS-based glycan profiling techniques. Hydrazide, one of the most popular tags, offers important advantages including allowing purification-free procedures. Several hydrazides have thus been used for glycomics combined with an on-target strategy to further simplify the analytical procedures. Usually, gentle heating and mildly acidic conditions with somewhat long reaction times are needed for these hydrazide derivatizations to reach a high reaction efficiency, which makes the current hydrazide tags not yet perfectly conducive to high-throughput analysis. To further optimize these hydrazide tags for high-throughput analysis, based on the structure of a reported hydrazide and the theoretical calculations, a new cationic hydrazide tag, 4-(hydrazinecarbonyl)-N,N,N-trimethylbenzenaminium (HTMBA), was designed, synthesized and tested in this work. HTMBA could completely derivatize glycans at room temperature in several seconds under very mildly acidic conditions (<3% acetic acid). A 19-fold enhancement in the signal intensity was obtained without interference from alkali adduct ions in the MALDI-MS detection of HTMBA-labeled maltoheptaose. To broaden the applicability of HTMBA, an HTMBA on-target derivatization (HOD) strategy was developed and fully validated with maltoheptaose and RNase B, and the method showed a good repeatability and stability. Finally, the HOD strategy was successfully applied to serum samples, 44 glycans in human serum were detected, and the O-acetylation information of sialic acid in horse serum was preserved. These results showed that the HOD strategy was suitable for the MS-based rapid analysis of all glycoforms in complex biological samples.

A practical method for preparing fluorescent-labeled glycans with a 9-fluorenylmethyl derivative to simplify a fluorimetric HPLC-based analysis

Analysis of glycans in glycoproteins is often performed by liquid chromatography (LC) separation coupled with fluorescence detection and/or mass spectrometric detection. Enzymatically or chemically released glycans from glycoproteins are usually labeled by reductive amination with a fluorophore reagent. Although labeling techniques based on reductive amination have been well-established as sample preparation methods for fluorometric HPLC-based glycan analysis, they often include time-consuming and tedious purification steps. Here, we reported an alternative fluorescent labeling method based on the synthesis of hydrazone and its reduction using 9-fluorenylmethyl carbazate (Fmoc-hydrazine) as a fluorophore reagent. Using isomaltopentaose and N-glycans from human IgG, we optimized the Fmoc-labeling conditions and purification procedure of Fmoc-labeled N-glycans and applied the optimized method for the analysis of N-glycans released from four glycoproteins (bovine RNase B, human fibrinogen, human α1-acid glycoprotein, and bovine fetuin). The complete workflow for preparation of fluorescent-labeled N-glycans takes a total of 3.5 h and is simple to implement. The method presented here lowers the overall cost of a fluorescently labeled N-glycan and will be practically useful for the screening of disease-related glycans or routine analysis at an early stage of development of biopharmaceuticals.

Novel methods in glycomics: a 2019 update

Introduction: Glycomics, which aims to define the glycome of a biological system to better assess the biological attributes of the glycans, has attracted increasing interest. However, the complexity and diversity of glycans present challenging barriers to glycome definition. Technological advances are major drivers in glycomics.Areas covered: This review summarizes the main methods and emphasizes the most recent advances in mass spectrometry-based methods regarding glycomics following the general workflow in glycomic analysis.Expert opinion: Recent mass spectrometry-based technological advances have significantly lowered the barriers in glycomics. The field of glycomics is moving toward both generic and precise analysis.

Simultaneous Identification and Dynamic Analysis of Saccharides during Steam Processing of Rhizomes of Polygonatum cyrtonema by HPLC⁻QTOF⁻MS/MS

The sweet rhizomes of Polygonatum cyrtonema are widely used as a tonic and functional food. A sensitive and rapid analytical method was developed for simultaneous identification and dynamic analysis of saccharides during steam processing in P. cyrtonema using HPLC–QTOF–MS/MS. Fructose, sorbitol, glucose, galactose, sucrose, and 1-kestose were identified, as well as a large number of oligosaccharides constituted of fructose units through β-(2→1) or β-(2→6). Polysaccharides and oligosaccharides were decomposed to monosaccharides during a steaming process, since the contents of glucose, galactose, and fructose were increased, while those of sucrose, 1-kestose, and polysaccharides were decreased. The high content of fructose was revealed to be the main determinant for increasing the level of sweetness after steaming. The samples of different repeated steaming times were shown to be well grouped and gradually shift along the PC1 (72.4%) axis by principal component analysis. The small-molecule saccharides, especially fructose, could be considered as markers for the steaming process of rhizomes of P. cyrtonema.

Quantitative glycomics using liquid phase separations coupled to mass spectrometry

Post-translational modification of proteins by the attachment of glycans is governed by a variety of highly specific enzymes and is associated with fundamental impacts on the parent protein's physical, chemical and biological properties. The inherent connection between cellular physiology and specific glycosylation patterns has been shown to offer potential for diagnostic and prognostic monitoring of altered glycosylation in the disease state. Conversely, glycoprotein based biopharmaceuticals have emerged as dominant therapeutic strategies in the treatment of intricate diseases. Glycosylation present on these biopharmaceuticals represents a major critical quality attribute with impacts on both pharmacokinetics and pharmacodynamics. The structural variety of glycans, based upon their non-template driven assembly, poses a significant analytical challenge for both qualitative and quantitative analysis. Labile monosaccharide constituents, isomeric species and often low sample availability from biological sources necessitates meticulous sample handling, ultra-high-resolution analytical separation and sensitive detection techniques, respectively. In this article a critical review of analytical quantitation approaches using liquid phase separations coupled to mass spectrometry for released glycans of biopharmaceutical and biomedical significance is presented. Considerations associated with sample derivatisation strategies, ionisation, relative quantitation through isotopic as well as isobaric labelling, metabolic/enzymatic incorporation and targeted analysis are all thoroughly discussed.

Advances in mass spectrometry-based glycomics

The diversification of the chemical properties and biological functions of proteins is attained through posttranslational modifications, such as glycosylation. Glycans, which are covalently attached to proteins, play a vital role in cell activities. The microheterogeneity and complexity of glycan structures associated with proteins make comprehensive glycomic analysis challenging. However, recent advancements in mass spectrometry (MS), separation techniques, and sample preparation methods have primarily facilitated structural elucidation and quantitation of glycans. This review focuses on describing recent advances in MS-based techniques used for glycomic analysis (2012-2018), including ionization, tandem MS, and separation techniques coupled with MS. Progress in glycomics workflow involving glycan release, purification, derivatization, and separation will also be highlighted here. Additionally, the recent development of quantitative glycomics through comparative and multiplex approaches will also be described.

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

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

Reductive oxyamination: a method for the qualitative and quantitative analysis of monosaccharides with a new aminooxy reagent using high-performance liquid chromatography with fluorescence detection

Derivatization of carbohydrates with aminooxy agents to form oximes can be used for qualitative and quantitative analysis of carbohydrates; however, the formation of isomeric products limits its application. A new reductive oxyamination procedure developed for the analysis of monosaccharides with a novel fluorescent O-substituted aminooxy reagent, 4-((aminooxy)methyl)-6-chloro-7-hydroxycoumarin (AOCC), is reported. In this procedure, monosaccharides undergo an oxime formation reaction with AOCC and are then readily reduced with 2-picoline-borane, followed by analysis with high-performance liquid chromatography with fluorescence detection. Good separation of five monosaccharide derivatives was achieved within 40 min with acetonitrile-water-tetrahydrofuran as the mobile phase. The detection limits were on the order of femtomoles. The linear range was 0.2-4000 nM, with a good correlation coefficient (R ≥ 0.9985). Furthermore, the method was applied for analysis of real samples, such as bovine milk powder, without complicated and tedious sample treatment. This reductive oxyamination method circumvents the problem caused by oxime isomers and can be used for the highly sensitive and selective analysis of monosaccharides with high accuracy, providing an effective and promising method for the analysis of carbonyls with aminooxy agents.

Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry: Mechanistic Studies and Methods for Improving the Structural Identification of Carbohydrates

Although matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is one of the most widely used soft ionization methods for biomolecules, the lack of detailed understanding of ionization mechanisms restricts its application in the analysis of carbohydrates. Structural identification of carbohydrates achieved by MALDI mass spectrometry helps us to gain insights into biological functions and pathogenesis of disease. In this review, we highlight mechanistic details of MALDI, including both ionization and desorption. Strategies to improve the ion yield of carbohydrates are also reviewed. Furthermore, commonly used fragmentation methods to identify the structure are discussed.

Characterization of isomeric glycan structures by LC-MS/MS

The characterization of glycosylation is critical for obtaining a comprehensive view of the regulation and functions of glycoproteins of interest. Due to the complex nature of oligosaccharides, stemming from variable compositions and linkages, and ion suppression effects, the chromatographic separation of glycans, including isomeric structures, is necessary for exhaustive characterization by MS. This review introduces the fundamental principles underlying the techniques in LC utilized by modern day glycomics researchers. Recent advances in porous graphitized carbon, reverse phase, ion exchange, and hydrophilic interaction LC utilized in conjunction with MS, for the characterization of protein glycosylation, are described with an emphasis on methods capable of resolving isomeric glycan structures.

Quantitative Glycomics: A Combined Analytical and Bioinformatics Approach

Glycosylation is one of the most common and essential protein modifications. Glycans conjugated to biomolecules modulate the function of such molecules through both direct recognition of glycan structures and indirect mechanisms that involve the control of protein turnover rates, stability, and conformation. The biological attributes of glycans in numerous biological processes and implications in a number of diseases highlight the necessity for comprehensive characterization of protein glycosylation. This chapter reviews cutting-edge methods and tools developed to facilitate quantitative glycomics. This chapter highlights the different methods employed for the release and purification of glycans from biological samples. The most effective labeling methods developed for sensitive quantitative glycomics are also described and discussed. The chromatographic approaches that have been used effectively in glycomics are also highlighted.

Reversed-phase separation methods for glycan analysis

Reversed-phase chromatography is a method that is often used for glycan separation. For this, glycans are often derivatized with a hydrophobic tag to achieve retention on hydrophobic stationary phases. The separation and elution order of glycans in reversed-phase chromatography is highly dependent on the hydrophobicity of the tag and the contribution of the glycan itself to the retention. The contribution of the different monosaccharides to the retention strongly depends on the position and linkage, and isomer separation may be achieved. The influence of sialic acids and fucoses on the retention of glycans is still incompletely understood and deserves further study. Analysis of complex samples may come with incomplete separation of glycan species, thereby complicating reversed-phase chromatography with fluorescence or UV detection, whereas coupling with mass spectrometry detection allows the resolution of complex mixtures. Depending on the column properties, eluents, and run time, separation of isomeric and isobaric structures can be accomplished with reversed-phase chromatography. Alternatively, porous graphitized carbon chromatography and hydrophilic interaction liquid chromatography are also able to separate isomeric and isobaric structures, generally without the necessity of glycan labeling. Hydrophilic interaction liquid chromatography, porous graphitized carbon chromatography, and reversed-phase chromatography all serve different research purposes and thus can be used for different research questions. A great advantage of reversed-phase chromatography is its broad distribution as it is used in virtually every bioanalytical research laboratory, making it an attracting platform for glycan analysis.

Graphical Abstract

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.

Hydrazino-s-triazine based labelling reagents for highly sensitive glycan analysis via liquid chromatography-electrospray mass spectrometry

Labelling strategy plays an important role in mass spectrometry (MS) based glycan analysis due to the high hydrophilicity and low ionization efficiency of glycans. Ten hydrazino-s-triazine based labelling reagents were synthesized under facile and controllable conditions for highly sensitive liquid chromatography-electrospray mass spectrometry glycan analysis in this work. Attached to N-glycans through non-reductive reactions, these new labelling reagents were evaluated in aspect of the differently enhanced glycan response to mass spectrometry. Three of the ten labelling reagents demonstrated to be reliable and remarkable for glycan analysis with satisfactory linearity and lowered limits of detection using maltoheptaose (DP7) as model. Furthermore, the most optimal labelling reagent was taken as an example for highly sensitive profiling of N-linked glycans both cleaved from chicken avidin and glycoproteins in human serum, indicating prospective availability for these labelling reagents in frontier of glycomics researches.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

Deuterated hydrazino-s-triazine as highly-efficient labelling reagent for glycan relative quantification analysis using electrospray ionization mass spectrometry

An innovative stable-isotope relative quantification strategy for N-glycans was achieved using self-designed non-reductive hydrazino-s-triazine deuterated derivative as labelling reagent combined with mass spectrometry.

Matrix-assisted laser desorption/ionization tandem mass spectrometry of N-glycans derivatized with isonicotinic hydrazide and its biotinylated form

RATIONALE

Successful structural characterization of glycans often requires derivatization prior to mass spectrometric analysis. Here we report on a new derivatization reagent for glycans, biotinylated isonicotinic hydrazide, allowing glycan analysis by both mass spectrometry (MS) and biochemically. Fragmentation behavior in MS and its use in structural elucidation were investigated and compared with other labels.

METHODS

Glycans, released from ribonuclease B and ovalbumin, were derivatized with hydrazine labels (isoniazid (INH), biotinylated isonicotinic hydrazide (BINH) and biotinamidocaproylhydrazide (BACH)). In addition, native counterparts and 2-aminobenzamide (2-AB) derivatives were prepared. Comparative matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI TOF/TOF) experiments were carried out to investigate the fragmentation pattern of the derivatives. Finally, the capability of BINH derivatives to bind lectins was explored.

RESULTS

Generally, derivatization provided beneficial enhancement in the mass spectrometric signal intensity as compared to native counterparts. The mass spectrometric fragmentation varied with the kind of label used. The most significant structure-revealing ions (cross-ring cleavages) were observed in the spectra of BINH derivatives, whereas mainly glycosidic cleavages were found with native form of glycans and 2-AB derivatives.

CONCLUSIONS

Hydrazine derivatization provided the means to obtain structurally informative fragment ions. Due to BINH derivatization, specific fragments of the isomers allowed the identification of diverse glycans. The derivatization reaction can be carried out without the need for purification. The biotin residue of BINH enabled for biochemical studies, i.e. protein-glycan interactions.

The usefulness of hydrazine derivatives for mass spectrometric analysis of carbohydrates

Over the last years, extensive studies have evaluated glycans from different biological samples and validated the importance of glycosylation as one of the most important post-translational modifications of proteins. Although a number of new methods for carbohydrate analysis have been published and there has been significant progress in their identification, the development of new approaches to study these biomolecules and understand their role in living systems are still vivid challenges that intrigue glycobiologists. In the last decade, the success in analyses of oligosaccharides has been driven mainly by the development of innovative, highly sensitive mass spectrometry techniques. For enhanced mass spectrometry detection, carbohydrate molecules are often derivatized. Besides, the type of labeling can influence the fragmentation pattern and make the structural analysis less complicated. In this regard, in 2003 we introduced the low scale, simple non-reductive tagging of glycans employing phenylhydrazine (PHN) as the derivatizing reagent. PHN-labeled glycans showed increased detection and as reported previously they can be analyzed by HPLC, ESI, or MALDI immediately after derivatization. Under tandem mass spectrometry conditions, PHN-derivatives produced useful data for the structural elucidation of oligosaccharides. This approach of analysis has helped to reveal new isomeric structures for glycans of known/unknown composition and has been successfully applied for the profiling of N-glycans obtained from serum samples and cancer cells. The efficacy of this labeling has also been evaluated for different substituted hydrazine reagents. This review summarizes all types of reducing-end labeling based on hydrazone-linkage that have been used for mass spectrometric analyses of oligosaccharides. This review is also aimed at correcting some past misconceptions or interpretations reported in the literature.

Structural glycomic analyses at high sensitivity: a decade of progress

The field of glycomics has recently advanced in response to the urgent need for structural characterization and quantification of complex carbohydrates in biologically and medically important applications. The recent success of analytical glycobiology at high sensitivity reflects numerous advances in biomolecular mass spectrometry and its instrumentation, capillary and microchip separation techniques, and microchemical manipulations of carbohydrate reactivity. The multimethodological approach appears to be necessary to gain an in-depth understanding of very complex glycomes in different biological systems.

Systematic comparison of reverse phase and hydrophilic interaction liquid chromatography platforms for the analysis of N-linked glycans

Due to the hydrophilic nature of glycans, reverse phase chromatography has not been widely used as a glycomic separation technique coupled to mass spectrometry. Other approaches such as hydrophilic interaction chromatography and porous graphitized carbon chromatography are often employed, though these strategies frequently suffer from decreased chromatographic resolution, long equilibration times, indefinite retention, and column bleed. Herein, it is shown that, through an efficient hydrazone formation derivatization of N-linked glycans (~4 h of additional sample preparation time which is carried out in parallel), numerous experimental and practical advantages are gained when analyzing the glycans by online reverse phase chromatography. These benefits include an increased number of glycans detected, increased peak capacity of the separation, and the ability to analyze glycans on the identical liquid chromatography-mass spectrometry platform commonly used for proteomic analyses. The data presented show that separation of derivatized N-linked glycans by reverse phase chromatography significantly out-performs traditional separation of native or derivatized glycans by hydrophilic interaction chromatography. Furthermore, the movement to a more ubiquitous separation technique will afford numerous research groups the opportunity to analyze both proteomic and glycomic samples on the same platform with minimal time and physical change between experiments, increasing the efficiency of "multiomic" biological approaches.

[Glycomics in quality control of tissue-engineered medical products]

Glycosylation of cells is known to alter with several biological events such as cell differentiations and proliferations as well as some diseases. "Glycomic approaches", comprehensive qualitative and quantitative glycan analyses of the cells, have become increasingly important as a means of discovering biomarkers that have the potential of being used as disease diagnostic markers and molecular markers for cell characterizations. In this paper, we introduce a method of quantitative glycan profiling by liquid chromatography/mass spectrometry with a combination of an isotope tagging method. In addition, we demonstrate the potential of glycan profiling as a tool for the identification of differentiated human bone marrow mesenchymal stem cell (hMSC) and non-differentiated hMSC.

High-throughput quantitative analysis of total N-glycans by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Accurate and reproducible quantification of glycans from protein drugs has become an important issue for quality control of therapeutic proteins in biopharmaceutical and biotechnology industries. Mass spectrometry is a promising tool for both qualitative and quantitative analysis of glycans owing to mass accuracy, efficiency, and reproducibility, but it has been of limited success in quantitative analysis for sialylated glycans in a high-throughput manner. Here, we present a solid-phase permethylation-based total N-glycan quantitative method that includes N-glycan releasing, purification, and derivatization on a 96-well plate platform. The solid-phase neutralization enabled us to perform reliable absolute quantification of the acidic N-glycans as well as neutral N-glycans from model glycoproteins (i.e., chicken ovalbumin and porcine thyroglobulin) by only using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Furthermore, low-abundance sialylated N-glycans from human serum prostate specific antigen (PSA), an extremely valuable prostate cancer marker, were initially quantified, and their chemical compositions were proposed. Taken together, these results demonstrate that our all-inclusive glycan preparation method based on a 96-well plate platform may contribute to the precise and reliable qualitative and quantitative analysis of glycans.

Stable-isotope labeled hydrophobic hydrazide reagents for the relative quantification of N-linked glycans by electrospray ionization mass spectrometry

This study presents the development of stable-isotope labeled hydrophobic, hydrazide reagents for the relative quantification of N-linked glycans. The P2GPN "light" ((12)C) and "heavy" ((13)C(6)) pair are used to differentially label two N-linked glycan samples. The samples are combined 1:1, separated using HILIC, and then mass differentiated and quantified using mass spectrometry. These reagents have several benefits: (1) impart hydrophobic character to the glycans affording an increase in electrospray ionization efficiency and MS detection; (2) indistinguishable chromatographic, MS, and MS/MS performance of the "light" and "heavy" reagents affording relative quantification; and (3) analytical variability is significantly reduced due to the two samples being mixed together after sample preparation. Obtaining these analytical benefits only requires ~4 h of sample preparation time. It is shown that these reagents are capable of quantifying changes in glycosylation in simple mixtures, and the analytical variability of the reagents in pooled plasma samples is shown to be less than ±30%. Additionally, the incorporation of an internal standard allows one to account for the difference in systematic error between the two samples due to the samples being processed in parallel and not mixed until after derivatization.

Chemical profiling of the deacetylase activity of acetyl xylan esterase A (AxeA) variants on chitooligosaccharides using hydrophilic interaction chromatography-mass spectrometry

Chitosan oligosaccharides (oligomers of (GlcNAc)(x)(GlcN)(y)) are used in the pharmaceutical, cosmetic and food industries and are reported to have therapeutic benefits. However, it is unknown whether their biological activity depends on the degree of deacetylation or the sequence of residues within the oligomer. We report here the development of a random mutagenesis method for directed evolution of Streptomyces lividans acetyl xylan esterase (AxeA), which we previously showed is able to deacetylate chitinous substrate, in order to obtain chitooligosaccharides with well-defined structural properties. A colorimetric assay was used to pre-screen libraries for p-nitrophenol acetate hydrolysis activity and an HPLC-UV absorbance assay was optimized to subsequently screen for deacetylase activity toward hexa-N-acetyl-glucosamine substrate (GlcNAc)(6). Native AxeA and two variants displaying>50% deacetylation of the oligohexamer substrate after reaction at 50°C for 24h in diluted culture supernatant were then selected for detailed analysis of the enzymatic products. A HILIC (hydrophilic interaction chromatography)-mode LC method was developed for profiling the deacetylated chitooligosaccharide products and HILIC-MS/MS sequencing revealed that ca. 30 different deacetylation products ranging from (GlcNAc)(5)(GlcN)(1) to (GlcNAc)(1)(GlcN)(5) and isomers thereof were produced. The AxeA variants produced, on average, 26% more unique products than the native enzyme; however, none were able to fully deacetylate the substrate to make (GlcN)(6). The long term goal of this multidisciplinary approach is to improve the activity of chitosan oligosaccharides to an industrially applicable level.

Glycan labeling strategies and their use in identification and quantification

Most methods for the analysis of oligosaccharides from biological sources require a glycan derivatization step: glycans may be derivatized to introduce a chromophore or fluorophore, facilitating detection after chromatographic or electrophoretic separation. Derivatization can also be applied to link charged or hydrophobic groups at the reducing end to enhance glycan separation and mass-spectrometric detection. Moreover, derivatization steps such as permethylation aim at stabilizing sialic acid residues, enhancing mass-spectrometric sensitivity, and supporting detailed structural characterization by (tandem) mass spectrometry. Finally, many glycan labels serve as a linker for oligosaccharide attachment to surfaces or carrier proteins, thereby allowing interaction studies with carbohydrate-binding proteins. In this review, various aspects of glycan labeling, separation, and detection strategies are discussed.

Mass spectrometric analysis of carbohydrates labeled with a biotinylated tag

A derivatization method for mass spectrometric analysis of oligosaccharides is presented. Small saccharides, complex, high-mannose-type oligosaccharides and oligosaccharides released from hen ovalbumin were converted into their biotin derivatives by incubating them with biotinamidocaproyl hydrazide (BACH). Improved sensitivity of mass spectrometric analysis of labeled glycans in comparison with their natural counterparts was achieved after derivatization. The labeling reagent contains a biotin handle at one end and a hydrazide group at the other. Hence, the key feature of biotinylated sugars is that in addition to their usefulness in functional studies (e.g. analysis of the interaction between lectins and biotin-derivatized oligosaccharides) they might be utilized also for structural analysis of oligosaccharides. Mass spectrometric studies were performed by matrix-assisted laser desorption/ionization time-of-flight and electrospray ionization mass spectrometry.

Method for investigation of oligosaccharides using phenylhydrazine derivatization

The reaction of carbohydrates with phenylhydrazine provides corresponding phenylhydrazone derivatives, yielding increased sensitivity for mass spectrometry (MS) and ultraviolet (UV) detection during high-performance liquid chromatography (HPLC) separation. After a simple derivatization procedure, 1 h of incubation at 37-70 degrees C, the samples can be analyzed by mass spectrometry techniques or with a combination of MS with HPLC using electrospray (ESI). Another useful aspect of this tagging is shown in the direct determination of glycosylation sites in proteins. Reaction conditions have enabled visualization of glycans next to their "mother peptides", that are otherwise usually not detectable because of suppression by abundant molecular ions of deglycosylated peptides.We have shown that oligosaccharides as phenylhydrazone derivatives under MALDI-tandem mass spectrometry (MS/MS) and post-source decay (PSD) conditions provide very useful data for the structural elucidation of saccharides, including assignment of dominant isomers. Sialylated oligosaccharides also produce B, C fragment ions and cross-ring cleavage fragments comprising sialic acid.