Applications of ion mobility mass spectrometry for high throughput, high resolution glycan analysis

Effects of Different Adduct Ions, Ionization Temperatures, and Solvents on the Ion Mobility of Glycans

The structural analysis of glycans remains a major challenge due to their high isomeric complexity and conformational flexibility arising from diverse glycosidic linkages and dynamic three-dimensional structures. Ion mobility-mass spectrometry (IM-MS) has been attracting attention as a way to develop the structural analysis of glycans. In this study, the effects of ionization conditions-including different types of adduct ions, ionization temperatures, and solvent environments-on the ion mobility behavior of glycans were systematically investigated. IM-MS measurements of ethylamine-tagged glycans showed broad arrival time distributions of monoprotonated ions indicating the presence of multiple conformers of glycans. Increased ionization temperatures and the use of methanol as a solvent further broadened the distribution, suggesting the enhanced conformational dynamics of the glycan ions. In contrast, sodium adduct ions yielded narrower distributions, implying that the interactions between sodium ions and glycans constrained structural flexibility. These results demonstrate that ionization parameters have a significant impact on glycan conformational behavior and mobility in the gas phase. This study provides insights into the analytical conditions for IM-MS measurements of glycans and highlights the utility of this method as a powerful tool for elucidating glycan structure and dynamics.

Characterization of Sugammadex-Related Isomeric Cyclodextrin Impurities Using Cyclic Ion Mobility High-Resolution Mass Spectrometry

Cyclic ion mobility-mass spectrometry (cIM-MS) is a powerful technique for separating and identifying isomeric mixtures of compounds. When coupled with chromatography, cIM-MS creates a multidimensional separation system, with high resolving power and peak capacity. In this study, we report the cyclic ion mobility separation and high-resolution mass spectrometry identification of four regioisomers of a Sugammadex-related impurity, abbreviated as Di-OH-SGM. Separation using multipass cyclic ion mobility was achieved by selecting the [M + 2Na]2+ ion, while other adducts, such as [M + Na]+, [M + 2H]2+, [M + H + Na]2+, and [M - 2H]2- did not yield isomer separation. Two methods were developed for ion mobility separation of the isomers: a conventional multipass method and a slicing method. Isomer assignment was based on the characteristic fragment ions. The collision cross section values (cTWCCSN2) of the resolved cyclodextrin isomers were also determined. Ion mobility separation of structurally different fragment ions was demonstrated. Additionally, by coupling cIM-MS with reversed-phase liquid chromatography (HPLC-cIM-MS), two-dimensional separation of the isomers was achieved. The isomers, separated using HPLC-cIM-MS, were identified with the same approach as with cIM-MS alone, and their elution order provided insights into their relative hydrophobicity.

Recent advances in N-glycan biomarker discovery among human diseases

N-glycans play important roles in a variety of biological processes. In recent years, analytical technologies with high resolution and sensitivity have advanced exponentially, enabling analysts to investigate N-glycomic changes in different states. Specific glycan and glycosylation signatures have been identified in multiple diseases, including cancer, autoimmune diseases, nervous system disorders, and metabolic and cardiovascular diseases. These glycans demonstrate comparable or superior indicating capability in disease diagnosis and prognosis over routine biomarkers. Moreover, synchronous glycan alterations concurrent with disease initiation and progression provide novel insights into pathogenetic mechanisms and potential treatment targets. This review elucidates the biological significance of N-glycans, compares the existing glycomic technologies, and delineates the clinical performance of N-glycans across a range of diseases.

Potential of ion mobility mass spectrometry in cellulose ether analysis: substitution pattern of hydroxyethyl celluloses

Ion mobility mass spectrometry (ESI-tims-ToF-MS, syringe pump infusion) has been applied to glucose and oligosaccharide ethers derived from hydroxyethyl-methyl celluloses (HEMC) and hydroxyethyl celluloses (HEC) after permethylation and partial depolymerization: by hydrolysis without or with subsequent reductive amination with m-amino benzoic acid (mABA) or by reductive cleavage. As model compounds without tandem substitution methoxyethylated methylcellulose was used. Regioisomeric glucose ethers were separated according to their ion mobility, and positions of substitution could be assigned. Glucose ethers including isomers with tandem substitution showed additional signals with a smaller collision cross-section (CCS) than core-substituted isomers. Positional isomers of cellobiose ethers were only partly resolved due to too high complexity but showed a characteristic fingerprint that might allow classifying samples. Relative intensities of signals of glucose ether isomers could only be quantified in case of ABA derivatives with its fixed charge, while sodium adducts of methoxyethyl ethers showed an influence of the MeOEt position on ion yield. Results were in very good agreement with reference analysis. [M + Na]+ adducts of α- and β-anomers of glucose derivatives were separated in IM, complicating position assignment. This could be overcome by reductive cleavage of the permethylated HE(M)C yielding 1,5-anhydroglucitol-terminated oligosaccharides, showing the best resolved fingerprints of the cellobiose ethers of a particular cellulose ether. With this first application of ion mobility MS to the analysis of complex cellulose ethers, the promising potential of this additional separation dimension in mass spectrometry is demonstrated and discussed.

Applications of propolis encapsulation in food products

Propolis has beneficial health properties attributed to of phenolic compounds. However, its application is limited. Thus, encapsulation protects the bioactive compounds of propolis from degradation, allowing their release under controlled and specific conditions and increasing their solubility. In addition to protecting flavonoids, encapsulation also minimises the undesirable characteristics of propolis, such as strong odour. We brought attention to the high antioxidant and antimicrobial activities of encapsulated propolis, and its maintained biological activity enables more uses in different areas. Encapsulated propolis can be applied in food products as an ingredient. This review describes recent advances in improving the bioactivity of propolis extracts by using encapsulation techniques, and biopolymer research strategies, focusing on applications in food products. Encapsulated propolis has a promising market perspective due to the industrial and scientific-technological advancement, the increase in the amount of research, the improvement of propolis extraction techniques, and the need of consumers for innovative products.

Exploiting ion-mobility mass spectrometry for unraveling proteome complexity

Ion mobility spectrometry-mass spectrometry (IMS-MS) is experiencing rapid growth in proteomic studies, driven by its enhancements in dynamic range and throughput, increasing the quantitation precision, and the depth of proteome coverage. The core principle of ion mobility spectrometry is to separate ions in an inert gas under the influence of an electric field based on differences in drift time. This minireview provides an introduction to IMS operation modes and a description of advantages and limitations is presented. Moreover, the principles of trapped IMS-MS (TIMS-MS), including parallel accumulation-serial fragmentation are discussed. Finally, emerging applications linked to TIMS focusing on sample throughput (in clinical proteomics) and sensitivity (single-cell proteomics) are reviewed, and the possibilities of intact protein analysis are discussed.

Ring-Size Memory of Galactose-Containing MS/MS Fragments: Application to the Detection of Galactofuranose in Oligosaccharides and Their Sequencing

Analysis of glycans remains a difficult task due to their isomeric complexity. Despite recent progress, determining monosaccharide ring size, a type of isomerism, is still challenging due to the high flexibility of the five-membered ring (also called furanose). Galactose is a monosaccharide that can be naturally found in furanose configuration in plant and bacterial polysaccharides. In this study, we used the coupling of tandem mass spectrometry and infrared ion spectroscopy (MS/MS-IR) to investigate compounds containing galactofuranose and galactopyranose. We report the IR fingerprints of monosaccharide fragments and demonstrate for the first time galactose ring-size memory upon collision-induced dissociation (CID) conditions. The linkage of the galactose unit is further obtained by analyzing disaccharide fragments. These findings enable two possible applications. First, labeled oligosaccharide patterns can be analyzed by MS/MS-IR, yielding full sequence information, including the ring size of the galactose unit; second, MS/MS-IR can be readily applied to unlabeled oligosaccharides to rapidly identify the presence of a galactofuranose unit, as a standalone analysis or prior to further sequencing.

Multistage Ion Mobility Spectrometry Combined with Infrared Spectroscopy for Glycan Analysis

The structural complexity of glycans makes their characterization challenging, not only because of the presence of various isomeric forms of the precursor molecule but also because the fragments can themselves be isomeric. We have recently developed an IMS-CID-IMS approach using structures for lossless ion manipulations (SLIM) combined with cryogenic infrared (IR) spectroscopy for glycan analysis. It allows mobility separation and collision-induced dissociation of a precursor glycan followed by mobility separation and IR spectroscopy of the fragments. While this approach holds great promise for glycan analysis, we often encounter fragments for which we have no standards to identify their spectroscopic fingerprint. In this work, we perform proof-of-principle experiments employing a multistage SLIM-based IMS-CID technique to generate second-generation fragments, followed by their mobility separation and spectroscopic interrogation. This approach provides detailed structural information about the first-generation fragments, including their anomeric form, which in turn can be used to identify the precursor glycan.

In-line sample trap columns with diatomite for large-volume injection in CZE-IM-MS

The analysis of low-abundant compounds with capillary zone electrophoresis-drift-tube ion mobility spectrometry-mass spectrometry (CZE-DTIMS-MS) is compromised due to the low injectable sample volumes in CZE and low duty cycle in DTIMS. Fritless packed in-line trap columns, using solid-phase extraction sorbent particles, have been used to increase injection volumes in CZE, but these columns are difficult to prepare and exhibit rapidly increasing back pressures. To provide smooth and complete filling of trap columns as well as to ensure higher and sustained flow rates though the columns, blends of cation and anion exchange particles with diatomite were used. The application of diatomite blends ensured the use of trap columns for at least 100 injections, with maximum injection volumes over 10 µl, which corresponds to an enrichment factor of more than 1000 over conventional injections in CZE-MS, enabling the detection of low nM concentrations of N-glycans with CZE-IMS-MS.

Differentiation of Isomeric, Nonseparable Carbohydrates Using Tandem-Trapped Ion Mobility Spectrometry-Mass Spectrometry

Carbohydrates play important roles in biological processes, but their identification remains a significant analytical problem. While mass spectrometry has increasingly enabled the elucidation of carbohydrates, current approaches are limited in their abilities to differentiate isomeric carbohydrates when these are not separated prior to tandem-mass spectrometry analysis. This analytical challenge takes on increased relevance because of the pervasive presence of isomeric carbohydrates in biological systems. Here, we demonstrate that TIMS2-MS2 workflows enabled by tandem-trapped ion mobility spectrometry-mass spectrometry (tTIMS/MS) provide a general approach to differentiate isomeric, nonseparated carbohydrates. Our analysis shows that (1) cross sections measured by TIMS are sufficiently precise and robust for ion identification; (2) fragment ion cross sections from TIMS2 analysis can be analytically exploited to identify carbohydrate precursors even if the precursor ions are not separated by TIMS; (3) low-abundant fragment ions can be exploited to identify carbohydrate precursors even if the precursor ions are not separated by IMS. (4) MS2 analysis of fragment ions produced by TIMS2 can be used to validate and/or further characterize carbohydrate structures. Taken together, our analysis underlines the opportunities that tandem-ion mobility spectrometry/MS methods offer for the characterization of mixtures of isomeric carbohydrates.

High-Throughput Glycomic Methods

Glycomics aims to identify the structure and function of the glycome, the complete set of oligosaccharides (glycans), produced in a given cell or organism, as well as to identify genes and other factors that govern glycosylation. This challenging endeavor requires highly robust, sensitive, and potentially automatable analytical technologies for the analysis of hundreds or thousands of glycomes in a timely manner (termed high-throughput glycomics). This review provides a historic overview as well as highlights recent developments and challenges of glycomic profiling by the most prominent high-throughput glycomic approaches, with N-glycosylation analysis as the focal point. It describes the current state-of-the-art regarding levels of characterization and most widely used technologies, selected applications of high-throughput glycomics in deciphering glycosylation process in healthy and disease states, as well as future perspectives.

Collision-induced dissociation of Na+-tagged ketohexoses: experimental and computational studies on fructose

Collision-induced dissociation tandem mass spectrometry (CID-MSⁿ) and computational investigation at the MP2/6-311+G(d,p) level of theory have been employed to study Na⁺-tagged fructose, an example of a ketohexose featuring four cyclic isomers: α-fructofuranose (αFruf), β-fructofuranose (βFruf), α-fructopyranose (αFrup), and β-fructopyranose (βFrup). The four isomers can be separated by high-performance liquid chromatography (HPLC) and they show different mass spectra, indicating that CID-MSⁿ can distinguish the different fructose forms. Based on a simulation using a micro-kinetic model, we have obtained an overview of the mechanisms for the different dissociation pathways. It has been demonstrated that the preference for the C-C cleavage over the competing isomerization of linear fructose is the main reason for the previously reported differences between the CID-MS spectra of aldohexoses and ketohexoses. In addition, the kinetic modeling helped to confirm the assignment of the different measured mass spectra to the different fructose isomers. The previously reported assignment based on the peak intensities in the HPLC chromatogram had left some open questions as the preference for the dehydration channels did not always follow trends previously observed for aldohexoses. Setting up the kinetic model further enabled us to directly compare the computational and experimental results, which indicated that the model can reproduce most trends in the differences between the dissociation pathways of the four cyclic fructose isomers.

Structural characterization of mushroom polysaccharides by cyclic ion mobility-mass spectrometry

Polysaccharides are biopolymers known to possess various bioactivities. Because of their molecular complexity, the structural characterization of polysaccharides remains challenging, and difficult to be completed with a single analytical method. In this study, a novel approach for the characterization of linkages and anomeric configuration of polysaccharides was proposed. Based on ion mobility-mass spectrometry (IM-MS), a database containing 5 glucotriose standards was set up. Information about the arrival time distribution and fragmentation patterns of these standards were included. The method was validated by three commercially available purified polysaccharides, namely laminarin, dextrin, and dextran, each having distinct connectivity and configuration of the glycosidic bonds. Lastly, the method was successfully applied to analyze polysaccharides prepared from three medicinal mushrooms, namely Xylaria nigripes, Grifola frondosa, and Laetiporus sulphureus. The results showed that water-soluble non-digestible polysaccharides of X. nigripes and G. frondosa were mainly composed of (1→3)-β-glucan, while that of L. sulphureus was composed of (1→3)-ɑ-glucan. The present method has the advantages of being simple in sample preparation and short analysis time.

Exploring Gas-Phase MS Methodologies for Structural Elucidation of Branched N-Glycan Isomers

Structural isomers of N-glycans that are identical in mass and atomic composition provide a great challenge to conventional mass spectrometry (MS). This study employs additional dimensions of structural elucidation including ion mobility (IM) spectroscopy coupled to hydrogen/deuterium exchange (HDX) and electron capture dissociation (ECD) to characterize three main A2 N-glycans and their conformers. A series of IM-MS experiments were able to separate the low abundance N-glycans and their linkage-based isomers (α1-3 and α1-6 for A2G1). HDX-IM-MS data indicated the presence of multiple gas-phase structures for each N-glycan including the isomers of A2G1. Identification of A2G1 isomers by their collision cross section was complicated due to the preferential collapse of sugars in the gas phase, but it was possible by further ECD fragmentation. The cyclic IM-ECD approach was capable of assigning and identifying each isomer to its IM peak. Two unique cross-ring fragments were identified for each isomer: m/z = 624.21 for α1-6 and m/z = 462.16 for α1-3. Based on these key fragments, the first IM peak, indicating a more compact conformation, was assigned to α1-3 and the second IM peak, a more extended conformer, was assigned to α1-6.

Developments and perspectives in high-throughput protein glycomics: enabling the analysis of thousands of samples

Glycans expand the structural complexity of proteins by several orders of magnitude, resulting in a tremendous analytical challenge when including them in biomedical research. Recent glycobiological research is painting a picture in which glycans represent a crucial structural and functional component of the majority of proteins, with alternative glycosylation of proteins and lipids being an important regulatory mechanism in many biological and pathological processes. Since interindividual differences in glycosylation are extensive, large studies are needed to map the structures and to understand the role of glycosylation in human (patho)physiology. Driven by these challenges, methods have emerged, which can tackle the complexity of glycosylation in thousands of samples, also known as high-throughput (HT) glycomics. For facile dissemination and implementation of HT glycomics technology, the sample preparation, analysis, as well as data mining, need to be stable over a long period of time (months/years), amenable to automation, and available to non-specialized laboratories. Current HT glycomics methods mainly focus on protein N-glycosylation and allow to extensively characterize this subset of the human glycome in large numbers of various biological samples. The ultimate goal in HT glycomics is to gain better knowledge and understanding of the complete human glycome using methods that are easy to adapt and implement in (basic) biomedical research. Aiming to promote wider use and development of HT glycomics, here, we present currently available, emerging, and prospective methods and some of their applications, revealing a largely unexplored molecular layer of the complexity of life.

Mass Spectrometry-Based Techniques to Elucidate the Sugar Code

Cells encode information in the sequence of biopolymers, such as nucleic acids, proteins, and glycans. Although glycans are essential to all living organisms, surprisingly little is known about the "sugar code" and the biological roles of these molecules. The reason glycobiology lags behind its counterparts dealing with nucleic acids and proteins lies in the complexity of carbohydrate structures, which renders their analysis extremely challenging. Building blocks that may differ only in the configuration of a single stereocenter, combined with the vast possibilities to connect monosaccharide units, lead to an immense variety of isomers, which poses a formidable challenge to conventional mass spectrometry. In recent years, however, a combination of innovative ion activation methods, commercialization of ion mobility-mass spectrometry, progress in gas-phase ion spectroscopy, and advances in computational chemistry have led to a revolution in mass spectrometry-based glycan analysis. The present review focuses on the above techniques that expanded the traditional glycomics toolkit and provided spectacular insight into the structure of these fascinating biomolecules. To emphasize the specific challenges associated with them, major classes of mammalian glycans are discussed in separate sections. By doing so, we aim to put the spotlight on the most important element of glycobiology: the glycans themselves.

Measuring change in glycoprotein structure

Biosynthetic enzymes in the secretory pathway create distributions of glycans at each glycosite that elaborate the biophysical properties and biological functions of glycoproteins. Because the biosynthetic glycosylation reactions do not go to completion, each protein glycosite is heterogeneous with respect to glycosylation. This heterogeneity means that it is not sufficient to measure protein abundance in omics experiments. Rather, it is necessary to sample the distribution of glycosylation at each glycosite to quantify the changes that occur during biological processes. On the one hand, the use of data-dependent acquisition methods to sample glycopeptides is limited by the instrument duty cycle and the missing value problem. On the other, stepped window data-independent acquisition samples all precursors, but ion abundances are limited by duty cycle. Therefore, the ability to quantify accurately the flux in glycoprotein glycosylation that occurs during biological processes requires the exploitation of emerging mass spectrometry technologies capable of deep, comprehensive sampling and selective high confidence assignment of the complex glycopeptide mixtures. This review summarizes recent technical advances and mass spectral glycoproteomics analysis strategies and how these developments impact our ability to quantify the changes in glycosylation that occur during biological processes. We highlight specific improvements to glycopeptide characterization through activated electron dissociation, ion mobility trends and instrumentation, and efficient algorithmic approaches for glycopeptide assignment. We also discuss the emerging need for unified standards to enable interlaboratory collaborations and effective monitoring of structural changes in glycoproteins.

Identification of N-glycan positional isomers by combining IMS and vibrational fingerprinting of structurally determinant CID fragments

While glycans are present on the surface of cells in all living organisms and play key roles in most biological processes, their isomeric complexity makes their structural characterization challenging. Of particular importance are positional isomers, for which analytical standards are difficult to obtain. We combine ultrahigh-resolution ion-mobility spectrometry with collision-induced dissociation and cryogenic infrared spectroscopy to determine the structure of N-glycan positional isomers. This approach is based on first separating the parent molecules by SLIM-based IMS, producing diagnostic fragments specific to each positional isomer, separating the fragments by IMS, and identifying them by comparing their IR fingerprints to a previously recorded spectral database. We demonstrate this strategy using a bottom-up scheme to identify the positional isomers of the N-linked glycan G0-N, in which a terminal N-acetylglucosamine (GlcNAc) is attached to either the α-3 or α-6 branch of the common N-glycan pentasaccharide core. We then use IR fingerprints of these newly identified isomers to identify the positional isomers of G1 and G1F, which are biantennary complex-type N-glycans with a terminal galactose attached to either the α-3 or α-6 branch, and in the case of G1F a fucose attached to the reducing-end GlcNAc. Starting with just a few analytical standards, this fragment-based spectroscopy method allows us to develop a database which we can use to identify positional isomers. The generalization of this approach would greatly facilitate glycan analysis.

We combine high-resolution IMS-IMS with cryogenic vibrational spectroscopy for the indentification of N-glycan positional isomers.

Prediction of Collision Cross Section Values: Application to Non-Intentionally Added Substance Identification in Food Contact Materials

The synthetic chemicals in food contact materials can migrate into food and endanger human health. In this study, the traveling wave collision cross section in nitrogen values of more than 400 chemicals in food contact materials were experimentally derived by traveling wave ion mobility spectrometry. A support vector machine-based collision cross section (CCS) prediction model was developed based on CCS values of food contact chemicals and a series of molecular descriptors. More than 92% of protonated and 81% of sodiated adducts showed a relative deviation below 5%. Median relative errors for protonated and sodiated molecules were 1.50 and 1.82%, respectively. The model was then applied to the structural annotation of oligomers migrating from polyamide adhesives. The identification confidence of 11 oligomers was improved by the direct comparison of the experimental data with the predicted CCS values. Finally, the challenges and opportunities of current machine-learning models on CCS prediction were also discussed.

Structural Determination of Polysaccharides Lichenin Using Logically Derived Sequence Tandem Mass Spectrometry

A new mass spectrometry method, logically derived sequence (LODES) tandem mass spectrometry (MSⁿ), was applied to determine the primary structure of polysaccharide lichenin. Conventional polysaccharide structural analysis requires complex processes, including derivation, permethylation, gas chromatography-mass spectrometry, and nuclear magnetic resonance spectrometry. Many of these processes can be replaced by LODES/MSⁿ. In this new method, polysaccharides are hydrolyzed into monosaccharides, disaccharides, and oligosaccharides, and structures of these molecules are determined using LODES/MSⁿ. The application of LODES/MSⁿ for determination of primary structure of polysaccharide lichenin was demonstrated. The repeating unit of lichenin was determined to be An-Bn, where A represents β-Glc-(1 → 4)-β-Glc-(1 → 4)-β-Glc-(1 → 3)-Glc, B represents β-Glc-(1 → 4)-β-Glc-(1 → 4)-β-Glc-(1 → 4)-β-Glc-(1 → 3)-Glc, n is an integral, and n ≥ 2 exists but n = 1 cannot be excluded. LODES/MSⁿ, which substantially reduces the time, effort, and sample quantity necessary for structural determination of oligosaccharides, is a powerful tool for polysaccharide primary structural determination.

Experimental Measurements of Relative Mobility Shifts Resulting from Isotopic Substitutions with High-Resolution Cyclic Ion Mobility Separations

Herein, we report on the experimental measurements for estimated relative mobility shifts caused by changes in mass distribution from isotopic substitutions in isotopologues and isotopomers with high-resolution cyclic ion mobility separations. By utilizing unlabeled and fully labeled isotopologues with the same isotopic substitutions (i.e., ²H or ¹³C), we created a highly precise mobility scale for each set analyzed to determine the magnitude of such mass distribution shifts and thus calculate estimated deviations from expected, theoretical reduced mass contributions. We observed relative mobility shifts in various isotopologues (e.g., hexadecyltrimethylammonium, sucrose, and palmitic acid species) that deviated from reduced mass theory, according to the Mason-Schamp relationship, ranging in estimated magnitude from ∼0.007% up to ∼0.1% in relative mobility. More interestingly, it was found that two deuterated palmitic acid isotopomers also differed by ∼0.03% from one another in their respective relative mobility shifts. Our results are the first report of isotopologue and isotopomer separations on a commercially available cyclic ion mobility spectrometry-mass spectrometry platform. We envision that our presented mobility scale methodology will have broad applicability in studying the effect of mass distribution changes from isotopic substitutions in other biomolecules and help pave the way for the improvement of ion mobility theory and collision cross section calculators.

Characterization and Analysis of Food-Sourced Carbohydrates

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

A Rapid and Sensitive Method for the Simultaneous Determination of Multipolar Compounds in Plant Tea by Supercritical Fluid Chromatography Coupled to Ion Mobility Quadrupole Time-of-Flight Mass Spectrometry

In this study, matrix solid phase dispersion (MSPD) microextraction combined with supercritical fluid chromatography-ion mobility quadrupole time-of-flight mass spectrometry (SFC/IM-QTOF-MS) was used to analyze the multipolar compounds in plant tea. The parameters of stationary phase, mobile phase, make-up solution, temperature, and back pressure were optimized. The target analytes were gradient eluted in 8 min by supercritical CO₂ on a Zorbax RX-SIL column. Collisional Cross Section (CCS) values for single and multiple fields were measured. A series of validation studies were carried out under the optimal conditions, and the linear relationship and reproducibility were good. The limits of detection were 1.4 (Scoparone (1))~70 (Naringenin (4)) ng/mL, and the limits of quantification were 4.7 (Scoparone (1))~241 (Naringenin (4)) ng/mL. The recoveries of most compounds ranged from 60.7% to 127%. As a consequence, the proposed method was used for the separation and quantitative analysis of active ingredients in caulis dendrobii.

Capillary Zone Electrophoresis-Electrospray Ionization Tandem Mass Spectrometry for Total Analysis of Chondroitin/Dermatan Sulfate Oligosaccharides

Proteoglycans are heavily glycosylated proteins, covalently linked to one or more glycosaminoglycan (GAG) chains, abundantly expressed in the extracellular matrix (ECM). Among GAGs, chondroitin sulfate (CS) and dermatan sulfate (DS) play an essential role at the ECM level; however, the composition of the hybrid CS/DS as well as the distribution of the sulfate groups along the chain were also shown to influence biological activities in brain. The elevated structural diversity of CS/DS motifs, in which sulfation may occur at GalNAc and/or IdoA/GlcA in various combinations, requires the development of specific high performance analytical methods for reliable elucidation. Due to its sensitivity, reproducibility, and efficiency, capillary zone electrophoresis (CZE) for separation of CS/DS oligosaccharides coupled to electrospray ionization mass spectrometry (ESI-MS) for their structure determination contributed an essential progress to this field.In the present chapter, two powerful methods based on CZE for separation and ESI-MS for identification and structural analysis of CS/DS are presented. The first part is devoted to offline CZE-ESI-MS based on fraction collection, screening by negative ion mode nanoESI, and fragmentation analysis in tandem MS using collision-induced dissociation (CID) at low ion acceleration energies. In the second part of the chapter, a strategy for online CZE-ESI-MS in normal polarity and negative mode ESI followed by tandem MS in real-time data-dependent acquisition mode for CS/DS separation, screening, and fragmentation is described in detail. The latter method entails the in-laboratory manufacturing of a simple yet sturdy interface for the online CZE coupling to ESI-MS and the optimization of the coupled system for total analysis of regularly sulfated and irregularly, i.e., under- and oversulfated CS/DS domains.

Utilizing liquid chromatography, ion mobility spectrometry, and mass spectrometry to assess INLIGHT™ derivatized N-linked glycans in biological samples

Glycosylation is a ubiquitous co- and post-translational modification involved in the sorting, folding, and trafficking of proteins in biological systems; in humans, >50% of gene products are glycosylated with the cellular machinery of glycosylation compromising ~2% of the genome. Perturbations in glycosylation have been implicated in a variety of diseases including neurodegenerative diseases and certain types of cancer. However, understanding the relationship between a glycan and its biological role is often difficult due to the numerous glycan isomers that exist. To address this challenge, nanoflow liquid chromatography, ion mobility spectrometry, and mass spectrometry (nLC-IMS-MS) were combined with the Individuality Normalization when Labeling with the Isotopic Glycan Hydrazide Tags (INLIGHT™) strategy to study a series of glycan standards and those enzymatically released from the glycoproteins horseradish peroxidase, fetuin, and pooled human plasma. The combination of IMS and the natural (NAT) and stable-isotope label (SIL) in the INLIGHT™ strategy provided additional confidence for each glycan identification due to the mobility aligned NAT- and SIL-labeled glycans and further capabilities for isomer examinations. Additionally, molecular trend lines based on the IMS and MS dimensions were investigated for the INLIGHT™ derivatized glycans, facilitating rapid identification of putative glycans in complex biological samples.

Lipid analysis by ion mobility spectrometry combined with mass spectrometry: A brief update with a perspective on applications in the clinical laboratory

Ion mobility spectrometry (IMS) is an analytical technique where ions are separated in the gas phase based on their mobility through a buffer gas in the presence of an electric field. An ion passing through an IMS device has a characteristic collisional cross section (CCS) value that depends on the buffer gas used. IMS can be coupled with mass spectrometry (MS), which characterizes an ion based on a mass-to-charge ratio (m/z), to increase analytical specificity and provide further physicochemical information. In particular, IMS-MS is of ever-increasing interest for the analysis of lipids, which can be problematic to accurately identify and quantify in bodily fluids by liquid chromatography (LC) with MS alone due to the presence of isomers, isobars, and structurally similar analogs. IMS provides an additional layer of separation when combined with front-end LC approaches, thereby, enhancing peak capacity and analytical specificity. CCS (and also ion mobility drift time) can be plotted against m/z ion intensity and/or LC retention time in order to generate in-depth molecular profiles of a sample. Utilization of IMS-MS for routine clinical laboratory testing remains relatively unexplored, but areas do exist for potential implementation. A brief update is provided here on lipid analysis using IMS-MS with a perspective on some applications in the clinical laboratory.

Toward High-Throughput Cryogenic IR Fingerprinting of Mobility-Separated Glycan Isomers

Infrared (IR) spectroscopy is a powerful tool used to infer detailed structural information on molecules, often in conjunction with quantum-chemical calculations. When applied to cryogenically cooled ions, IR spectra provide unique fingerprints that can be used for biomolecular identification. This is particularly important in the analysis of isomeric biopolymers, which are difficult to distinguish using mass spectrometry. However, IR spectroscopy typically requires laser systems that need substantial user attention and measurement times of tens of minutes, which limits its analytical utility. We report here the development of a new high-throughput instrument that combines ultrahigh-resolution ion-mobility spectrometry with cryogenic IR spectroscopy and mass spectrometry, and we apply it to the analysis of isomeric glycans. The ion mobility step, which is based on structures for lossless ion manipulations (SLIM), separates glycan isomers, and an IR fingerprint spectrum identifies them. An innovative cryogenic ion trap allows multiplexing the acquisition of analyte IR fingerprints following mobility separation, and using a turn-key IR laser, we can obtain spectra and identify isomeric species in less than a minute. This work demonstrates the potential of IR fingerprinting methods to impact the analysis of isomeric biomolecules and more specifically glycans.

Formation and fragmentation of doubly and triply charged ions in the negative ion spectra of neutral N-glycans from viral and other glycoproteins

Structural determination of N-glycans by mass spectrometry is ideally performed by negative ion collision-induced dissociation because the spectra are dominated by cross-ring fragments leading to ions that reveal structural details not available by many other methods. Most glycans form [M - H]- or [M + adduct]- ions but larger ones (above approx. m/z 2000) typically form doubly charged ions. Differences have been reported between the fragmentation of singly and doubly charged ions but a detailed comparison does not appear to have been reported. In addition to [M + adduct]- ions (this paper uses phosphate as the adduct) other doubly, triply, and quadruply charged ions of composition [Mn + (H2PO4)n]n- have been observed in mixtures of N-glycans released from viral and other glycoproteins. This paper explores the formation and fragmentation of these different types of multiply charged ions with particular reference to the presence of diagnostic fragments in the CID spectra and comments on how these ions can be used to characterize these glycans.

Identifying Mixtures of Isomeric Human Milk Oligosaccharides by the Decomposition of IR Spectral Fingerprints

The analysis of glycans presents a significant challenge that arises from their isomeric heterogeneity. While high-resolution ion mobility spectrometry (IMS) has shown the ability to resolve subtly different glycan isomers, their unambiguous assignment remains difficult. Here, we demonstrate an infrared (IR) spectroscopic approach for identifying isomers in a glycan mixture. To display the feasibility of this approach, we have constructed a small database of cryogenic spectra of five lacto-N-fucopentaose (LNFP) and six disaccharide isomers and demonstrated that in the cases where they cannot be separated by IMS, we can use a cryogenic IR spectrum to identify the isomeric components of a mixture.

A Multidimensional Mass Spectrometry-Based Workflow for De Novo Structural Elucidation of Oligosaccharides from Polysaccharides

Carbohydrates play essential roles in a variety of biological processes that are dictated by their structures. However, characterization of carbohydrate structures remains extremely difficult and generally unsolved. In this work, a de novo mass spectrometry-based workflow was developed to isolate and structurally elucidate oligosaccharides to provide sequence, monosaccharide compositions, and glycosidic linkage positions. The approach employs liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based methods in a 3-dimensional concept: one high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-QTOF MS) analysis for oligosaccharide sequencing and two ultra high performance liquid chromatography-triple quadrupole mass spectrometry (UHPLC-QqQ MS) analyses on fractionated oligosaccharides to determine their monosaccharides and linkages compositions. The workflow was validated by applying the procedure to maltooligosaccharide standards. The approach was then used to determine the structures of oligosaccharides derived from polysaccharide standards and whole food products. The integrated LC-MS workflow will reveal the in-depth structures of oligosaccharides.

Distinguishing Galactoside Isomers with Mass Spectrometry and Gas-Phase Infrared Spectroscopy

Sequencing glycans is demanding due to their structural diversity. Compared to mammalian glycans, bacterial glycans pose a steeper challenge because they are constructed from a larger pool of monosaccharide building blocks, including pyranose and furanose isomers. Though mammalian glycans incorporate only the pyranose form of galactose (Galp), many pathogens, including Mycobacterium tuberculosis and Klebsiella pneumoniae, contain galactofuranose (Galf) residues in their cell envelope. Thus, glycan sequencing would benefit from methods to distinguish between pyranose and furanose isomers of different anomeric configurations. We used infrared multiple photon dissociation (IRMPD) spectroscopy with mass spectrometry (MS-IR) to differentiate between pyranose- and furanose-linked galactose residues. These targets pose a challenge for MS-IR because the saccharides lack basic groups, and galactofuranose residues are highly flexible. We postulated cationic groups that could complex through hydrogen bonding would offer a solution. Here, we present the first MS-IR analysis of hexose ammonium adducts. We compared their IR fingerprints with those of lithium adducts. We determined the diagnostic MS-IR signatures of the α- and β-anomers of galactose in furanose and pyranose forms. We also showed these signatures could be applied to disaccharides to assign galactose ring size. Our findings highlight the utility of MS-IR for analyzing the unique substructures that occur in bacterial glycans.

Current status and future prospects for ion-mobility mass spectrometry in the biopharmaceutical industry

Detailed characterization of protein reagents and biopharmaceuticals is key in defining successful drug discovery campaigns, aimed at bringing molecules through different discovery stages up to development and commercialization. There are many challenges in this process, with complex and detailed analyses playing paramount roles in modern industry. Mass spectrometry (MS) has become an essential tool for characterization of proteins ever since the onset of soft ionization techniques and has taken the lead in quality assessment of biopharmaceutical molecules, and protein reagents, used in the drug discovery pipeline. MS use spans from identification of correct sequences, to intact molecule analyses, protein complexes and more recently epitope and paratope identification. MS toolkits could be incredibly diverse and with ever evolving instrumentation, increasingly novel MS-based techniques are becoming indispensable tools in the biopharmaceutical industry. Here we discuss application of Ion Mobility MS (IMMS) in an industrial setting, and what the current applications and outlook are for making IMMS more mainstream.

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

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Glycosaminoglycan-Protein Interactions and Their Roles in Human Disease

Glycosaminoglycans (GAGs) are a family of linear and negatively charged polysaccharides that exist ubiquitously on the human cell surface as well as in the extracellular matrix. GAGs interact with a wide range of proteins, including proteases, growth factors, cytokines, chemokines and adhesion molecules, enabling them to mediate many physiological processes, such as protein function, cellular adhesion and signaling. GAG-protein interactions participate in and intervene in a variety of human diseases, including cardiovascular disease, infectious disease, neurodegenerative diseases and tumors. The breakthrough in analytical tools and approaches during the last two decades has facilitated a greater understanding of the importance of GAG-protein interactions and their roles in human diseases. This review focuses on aspects of the molecular basis and mechanisms of GAG-protein interactions involved in human disease. The most recent advances in analytical tools, especially mass spectrometry-based GAG sequencing and binding motif characterization methods, are introduced. An update of selected families of GAG binding proteins is presented. Perspectives on development of novel therapeutics targeting specific GAG-protein interactions are also covered in this review.

Identification of Isomeric N-Glycans by Conformer Distribution Fingerprinting using Ion Mobility Mass Spectrometry

Glycans possess unparalleled structural complexity arising from chemically similar monosaccharide building blocks, configurations of anomeric linkages and different branching patterns, potentially giving rise to many isomers. This level of complexity is one of the main reasons that identification of exact glycan structures in biological samples still lags behind that of other biomolecules. Here, we introduce a methodology to identify isomeric N-glycans by determining gas phase conformer distributions (CDs) by measuring arrival time distributions (ATDs) using drift-tube ion mobility spectrometry-mass spectrometry. Key to the approach is the use of a range of well-defined synthetic glycans that made it possible to investigate conformer distributions in the gas phase of isomeric glycans in a systematic manner. In addition, we have computed CD fingerprints by molecular dynamics (MD) simulation, which compared well with experimentally determined CDs. It supports that ATDs resemble conformational populations in the gas phase and offer the prospect that such an approach can contribute to generating a library of CCS distributions (CCSDs) for structure identification.

State-of-the-Art Glycomics Technologies in Glycobiotechnology

Glycosylation affects the properties of biologics; thus regulatory bodies classified it as critical quality attribute and force biopharma industry to capture and control it throughout all phases, from R&D till end of product lifetime. The shift from originators to biosimilars further increases importance and extent of glycoanalysis, which thus increases the need for technology platforms enabling reliable high-throughput and in-depth glycan analysis. In this chapter, we will first summarize on established glycoanalytical methods based on liquid chromatography focusing on hydrophilic interaction chromatography, capillary electrophoresis focusing on multiplexed capillary gel electrophoresis, and mass spectrometry focusing on matrix-assisted laser desorption; we will then highlight two emerging technologies based on porous graphitized carbon liquid chromatography and on ion-mobility mass spectrometry as both are highly promising tools to deliver an additional level of information for in-depth glycan analysis; additionally we elaborate on the advantages and challenges of different glycoanalytical technologies and their complementarity; finally, we briefly review applications thereof to biopharmaceutical products. This chapter provides an overview of current state-of-the-art analytical approaches for glycan characterization of biopharmaceuticals that can be employed to capture glycoprotein heterogeneity in a biopharmaceutical context.

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

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

Protein Glycosylation Investigated by Mass Spectrometry: An Overview

The protein glycosylation is a post-translational modification of crucial importance for its involvement in molecular recognition, protein trafficking, regulation, and inflammation. Indeed, abnormalities in protein glycosylation are correlated with several disease states such as cancer, inflammatory diseases, and congenial disorders. The understanding of cellular mechanisms through the elucidation of glycan composition encourages researchers to find analytical solutions for their detection. Actually, the multiplicity and diversity of glycan structures bond to the proteins, the variations in polarity of the individual saccharide residues, and the poor ionization efficiencies make their detection much trickier than other kinds of biopolymers. An overview of the most prominent techniques based on mass spectrometry (MS) for protein glycosylation (glycoproteomics) studies is here presented. The tricks and pre-treatments of samples are discussed as a crucial step prodromal to the MS analysis to improve the glycan ionization efficiency. Therefore, the different instrumental MS mode is also explored for the qualitative and quantitative analysis of glycopeptides and the glycans structural composition, thus contributing to the elucidation of biological mechanisms.

Combining online size exclusion chromatography and electrospray ionization mass spectrometry to characterize plant polysaccharides

Characterizing polysaccharides with large molecular weights and isomeric heterogeneity with mass spectrometry (MS) is generally difficult. In this work, we demonstrate how coupling size exclusion chromatography (SEC) and high-resolution MS with source-induced dissociation (SID) can be used for the separation and direct structural evaluation of intact polysaccharides. The analytical method was successfully developed using dextran standards up to 3755 kDa. This method was used to separate naturally occurring plant polysaccharides based on size, after which numerous polysaccharide fragments were identified from the resulting MS spectra. The results provided strong evidence for structural diversity, complexity, and heterogeneity among polysaccharides. MS showed superior sensitivity and reliability for the polysaccharides in eluted fractions when compared to a refractive index detector. Putative compositions for the fragments were proposed based on exact mass values. The work demonstrated that SEC-SID-MS is a feasible alternative for obtaining valuable structural information from the analysis of intact polysaccharides.

Mass spectrometry for the identification and analysis of highly complex glycosylation of therapeutic or pathogenic proteins

INTRODUCTION

Protein glycosylation influences characteristics such as folding, stability, protein interactions, and solubility. Therefore, glycan moieties of therapeutic proteins and proteins that are likely associated with disease pathogenesis should be analyzed in-depth, including glycan heterogeneity and modification sites. Recent advances in analytical methods and instrumentation have enabled comprehensive characterization of highly complex glycosylated proteins.

AREA COVERED

The following aspects should be considered when analyzing glycosylated proteins: sample preparation, chromatographic separation, mass spectrometry (MS) and fragmentation methods, and bioinformatics, such as software solutions for data analyses. Notably, analysis of glycoproteins with heavily sialylated glycans or multiple glycosylation sites requires special considerations. Here, we discuss recent methodological advances in MS that provide detailed characterization of heterogeneous glycoproteins.

EXPERT OPINION

As characterization of complex glycosylated proteins is still analytically challenging, the function or pathophysiological significance of these proteins is not fully understood. To reproducibly produce desired forms of therapeutic glycoproteins or to fully elucidate disease-specific patterns of protein glycosylation, a highly reproducible and robust analytical platform(s) should be established. In addition to advances in MS instrumentation, optimization of analytical and bioinformatics methods and utilization of glycoprotein/glycopeptide standards is desirable. Ultimately, we envision that an automated high-throughput MS analysis will provide additional power to clinical studies and precision medicine.

Shotgun ion mobility mass spectrometry sequencing of heparan sulfate saccharides

Despite evident regulatory roles of heparan sulfate (HS) saccharides in numerous biological processes, definitive information on the bioactive sequences of these polymers is lacking, with only a handful of natural structures sequenced to date. Here, we develop a “Shotgun” Ion Mobility Mass Spectrometry Sequencing (SIMMS²) method in which intact HS saccharides are dissociated in an ion mobility mass spectrometer and collision cross section values of fragments measured. Matching of data for intact and fragment ions against known values for 36 fully defined HS saccharide structures (from di- to decasaccharides) permits unambiguous sequence determination of validated standards and unknown natural saccharides, notably including variants with 3O-sulfate groups. SIMMS² analysis of two fibroblast growth factor-inhibiting hexasaccharides identified from a HS oligosaccharide library screen demonstrates that the approach allows elucidation of structure-activity relationships. SIMMS² thus overcomes the bottleneck for decoding the informational content of functional HS motifs which is crucial for their future biomedical exploitation.

Heparan sulfates (HS) contain functionally relevant structural motifs, but determining their monosaccharide sequence remains challenging. Here, the authors develop an ion mobility mass spectrometry-based method that allows unambiguous characterization of HS sequences and structure-activity relationships.

Glycomics studies using sialic acid derivatization and mass spectrometry

Proteins can undergo glycosylation during and/or after translation to afford glycoconjugates, which are often secreted by a cell or populate cell surfaces. Changes in the glycan portion can have a strong influence on a glycoconjugate and are associated with a multitude of human pathologies. Of particular interest are sialylated glycoconjugates, which exist as constitutional isomers that differ in their linkages (α2,3, α2,6, α2,8 or α2,9) between sialic acids and their neighbouring monosaccharides. In general, mass spectrometry enables the rapid and sensitive characterization of glycosylation, but there are challenges specific to identifying and (relatively) quantifying sialic acid isomers. These challenges can be addressed using linkage-specific methodologies for sialic acid derivatization, after which mass spectrometry can enable product identification. This Review is concerned with the new and important derivatization approaches reported in the past decade, which have been implemented in various mass-spectrometry-glycomics workflows and have found clinical glycomics applications. The convenience and wide applicability of the approaches make them attractive for studies of sialylation in different types of glycoconjugate.

Mass spectrometry hybridized with gas-phase InfraRed spectroscopy for glycan sequencing

Precise structural differentiation of often isomeric glycans is important given their roles in numerous biological processes. Mass spectrometry (MS) (and tandem MS) is one of the analytical techniques at the forefront of glycan analysis given its speed, sensitivity in producing structural information as well as the fact it can be coupled to other orthogonal analytical techniques such as liquid chromatography (LC) and ion mobility spectrometry (IMS). This review describes another family of techniques that are more commonly being hybridized to MS(/MS) namely gas-phase infrared (IR) spectroscopy, whose rise is in part due to the development and improved accessibility of tunable IR lasers. Gas-phase IR can often differentiate fine isomeric differences ubiquitous within carbohydrates that MS may be 'blind' to. There are also examples of cryogenic gas-phase IR spectroscopy with much greater spectral resolution as well as hybridizing with separative methods (LC, IMS). Furthermore, collision-induced dissociation (CID) product ions can also be probed by IR, which may be beneficial to deconvolute spectra, aid analysis and build spectral libraries, thus generating novel opportunities for fragment-based approaches to analyze glycans.

Composition and charge state influence on the ion-neutral collision cross sections of protonated N-linked glycopeptides: an experimental and theoretical deconstruction of coulombic repulsion vs. charge solvation effects

Ion mobility spectrometry (IMS) is of significant interest as a platform for glycoanalysis. While much attention has been focused on the resolution of isomeric carbohydrates and glycoconjugates, another appealing aspect of IMS is the ability to sort different classes of biomolecules into distinct regions of mass vs. mobility space. This capability has potential to greatly simplify glycoproteomic analyses, as glycosylated and non-glycosylated peptides can be rapidly partitioned in the gas phase. Nevertheless, the physical and chemical characteristics of glycopeptides that dictate their mass vs. mobility loci have yet to be systematically investigated. This report presents an IMS study of model protonated glycopeptide ions with systematically varied oligosaccharide topologies, polypeptide sequences, and charge states. In all, over 110 ion-neutral collision cross sections (CCSs) were measured and analyzed in the context of the physicochemical characteristics of the analytes. Glycan size and composition emerged as a decisive factor in dictating the CCS space occupied by the glycopeptides and exerted this influence in a charge state dependent fashion. Furthermore, elongation of the glycan group was found to either increase or decrease glycopeptide CCSs depending on the ion charge state and the size of the glycan. Molecular dynamics (MD) simulations of the gas phase structures and CCSs of selected glycopeptides revealed that the experimental observations were consistent with a glycan size and charge state dependent interplay between destabilizing coulombic repulsion effects (tending to result in more extended structures) and stabilizing charge solvation effects in which the glycan plays a major role (tending to result in more compact structures). Taken together, these IMS and MD findings suggest the possibility of predicting and delineating glycopeptide-enriched regions of mass vs. mobility space for applications in glycoproteomics.

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.

Combining Cryogenic Infrared Spectroscopy with Selective Enzymatic Cleavage for Determining Glycan Primary Structure

Given the biological relevance and intrinsic structural complexity of glycans, increasing efforts are being directed toward developing a general glycan database that includes information from different analytical methods. As recently demonstrated, cryogenic infrared (IR) spectroscopy is a promising technique for glycan analysis, as it provides unique vibrational fingerprints of specific glycan isomer ions. One of the main goals of a glycan database is the identification and detailed characterization of unknown species. In this work, we combine enzymatic digestion with cryogenic IR-spectroscopy and demonstrate how it can be used for glycan identification. We measured the IR-spectra of a series of cationic glycan standards of increasing complexity and compared them with spectra of the same species after enzymatic cleavage of larger glycans. We show that the cryogenic IR spectra of the cleaved glycans are highly structured and virtually identical to those of standards after both single and multiple cleavages. Our results suggest that the combination of these methods represents a potentially powerful and specific approach for the characterization of unknown glycans.