Capillary-based lectin affinity electrophoresis for interaction analysis between lectins and glycans

Recent advances in microscale separation techniques for glycome analysis

The glycomic analysis holds significant appeal due to the diverse roles that glycans and glycoconjugates play, acting as modulators and mediators in cellular interactions, cell/organism structure, drugs, energy sources, glyconanomaterials, and more. The glycomic analysis relies on liquid-phase separation technologies for molecular purification, separation, and identification. As a miniaturized form of liquid-phase separation technology, microscale separation technologies offer various advantages such as environmental friendliness, high resolution, sensitivity, fast speed, and integration capabilities. For glycan analysis, microscale separation technologies are continuously evolving to address the increasing challenges in their unique manners. This review discusses the fundamentals and applications of microscale separation technologies for glycomic analysis. It covers liquid-phase separation technologies operating at scales generally less than 100 µm, including capillary electrophoresis, nanoflow liquid chromatography, and microchip electrophoresis. We will provide a brief overview of glycomic analysis and describe new strategies in microscale separation and their applications in glycan analysis from 2014 to 2023.

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

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

Structure and function of non-digestible carbohydrates in the gut microbiome

Together with proteins and fats, carbohydrates are one of the macronutrients in the human diet. Digestible carbohydrates, such as starch, starch-based products, sucrose, lactose, glucose and some sugar alcohols and unusual (and fairly rare) α-linked glucans, directly provide us with energy while other carbohydrates including high molecular weight polysaccharides, mainly from plant cell walls, provide us with dietary fibre. Carbohydrates which are efficiently digested in the small intestine are not available in appreciable quantities to act as substrates for gut bacteria. Some oligo- and polysaccharides, many of which are also dietary fibres, are resistant to digestion in the small intestines and enter the colon where they provide substrates for the complex bacterial ecosystem that resides there. This review will focus on these non-digestible carbohydrates (NDC) and examine their impact on the gut microbiota and their physiological impact. Of particular focus will be the potential of non-digestible carbohydrates to act as prebiotics, but the review will also evaluate direct effects of NDC on human cells and systems.

Construction and application of carbohydrate microarrays to detect foodborne bacteria

The rapid detection of pathogenic bacteria is vital for the prevention of outbreaks of infectious diseases, including infections by the common foodborne bacteria E.coli and Salmonella Carbohydrate microarrays have been developed as a powerful method to investigate carbohydrate-protein interaction with only very small amounts of glycans, which show great potential for detect the carbohydrate mediated interaction with pathogens. Here, different mannose-coated microarrays were constructed and tested with E.coli (K-12 and BL-21) and Salmonella enterica strains (ATCC9184 and ATCC31685) exhibiting different mannose binding affinities. The optimized carbohydrate microarray was then applied to test the binding of 12 Salmonella enterica and 9 E.coli isolates from local patients for the first time and showed strong binding with certain serovars or subtypes. The results showed that microarray probed with the single mannose structure is not enough for the detection of bacteria with various serovars or subtypes, which contain a high degree of allelic variation in adhesin. We suggest that a complex carbohydrate microarray containing different glycan conformation may be needed for detection of different bacteria isolates.

Profiling the N-Glycan Composition of IgG with Lectins and Capillary Nanogel Electrophoresis

Glycosylated human IgG contains fucosylated biantennary N-glycans with different modifications including N-acetylglucosamine, which bisects the mannose core. Although only a limited number of IgG N-glycan structures are possible, human IgG N-glycans are predominantly biantennary and fucosylated and contain varying levels of α2–6-linked sialic acid, galactose, and bisected N-acetylglucosamine. Monitoring the relative abundance of bisecting N-acetylglucosamine is relevant to physiological processes. A rapid, inexpensive, and automated method is used to successfully profile N-linked IgG glycans and is suitable to distinguish differences in bisection, galactosylation, and sialylation in N-glycans derived from different sources of human IgG. The separation is facilitated with self-assembled nanogels that also contain a single stationary zone of lectin. When the lectin specificity matches the N-glycan, the peak disappears from the electropherogram, identifying the N-glycan structure. The nanogel electrophoresis generates separation efficiencies of 500 000 plates and resolves the positional isomers of monogalactosylated biantennary N-glycan and the monogalactosylated bisected N-glycan. Aleuria aurantia lectin, Erythrina cristagalli lectin (ECL), Sambucus nigra lectin, and Phaseolus vulgaris Erythroagglutinin (PHA-E) are used to identify fucose, galactose, α2–6-linked sialic acid, and bisected N-acetylglucosamine, respectively. Although PHA-E lectin has a strong binding affinity for bisected N-glycans that also contain a terminal galactose on the α1–6-linked mannose branch, this lectin has lower affinity for N-glycans containing terminal galactose and for agalactosylated bisected biantennary N-glycans. The lower affinity to these motifs is observed in the electropherograms as a change in peak width, which when used in conjunction with the results from the ECL lectin authenticates the composition of the agalactosylated bisected biantennary N-glycan. For runs performed at 17 °C, the precision in migration time and peak area was less than or equal to 0.08 and 4% relative standard deviation, respectively. The method is compatible with electrokinetic and hydrodynamic injections, with detection limits of 70 and 300 pM, respectively.

Capillary Electrophoresis Separations of Glycans

Capillary electrophoresis has emerged as a powerful approach for carbohydrate analyses since 2014. The method provides high resolution capable of separating carbohydrates by charge-to-size ratio. Principle applications are heavily focused on N-glycans, which are highly relevant to biological therapeutics and biomarker research. Advances in techniques used for N-glycan structural identification include migration time indexing and exoglycosidase and lectin profiling, as well as mass spectrometry. Capillary electrophoresis methods have been developed that are capable of separating glycans with the same monosaccharide sequence but different positional isomers, as well as determining whether monosaccharides composing a glycan are alpha or beta linked. Significant applications of capillary electrophoresis to the analyses of N-glycans in biomarker discovery and biological therapeutics are emphasized with a brief discussion included on carbohydrate analyses of glycosaminoglycans and mono-, di-, and oligosaccharides relevant to food and plant products. Innovative, emerging techniques in the field are highlighted and the future direction of the technology is projected based on the significant contributions of capillary electrophoresis to glycoscience from 2014 to the present as discussed in this review.

Plug-plug kinetic capillary electrophoresis for in-capillary exoglycosidase digestion as a profiling tool for the analysis of glycoprotein glycans

An online exoglycosidase digestion was combined with a plug-plug kinetic mode of capillary electrophoresis (CE) for the analysis of glycoprotein-derived oligosaccharides. An exoglycosidase solution and a solution of glycoprotein glycans derivatized with 8-aminopyrene-1,3,6-trisulfonic acid (APTS) were introduced to a neutrally coated capillary previously filled with electrophoresis buffer solution containing 0.5w/v% hydroxypropylcellulose. After immersion of both ends of the capillary in the buffer solutions, a negative voltage was applied for analysis. An APTS group of an oligosaccharide derivative has triply negative charges, which forced saccharide derivatives to anode with fast mobility and pass through the enzyme plug, which are detected at the anodic end. If the terminal monosaccharides of APTS-labeled oligosaccharides are released by the action of an exoglycosidase, the migration times of the oligosaccharides shift to those of digested oligosaccharides. We examined β-galactosidase, α-mannosidase, β-N-acetylhexosaminidase, α-neuraminidase, and α-fucosidase, and found only β-galactosidase and α-neuraminidase showed good reactivity toward APTS-labeled oligosaccharides; the reaction was completed by injecting a 3.6cm long plug of 200 and 50mU/mL concentration of exoglycosidases. In contrast, other exoglycosidases could not react with APTS labeled oligosaccharides at a concentration up to 5U/mL. The β-N-acetylhexosaminidase reaction was successively followed by the electrophoretic mobility of APTS oligosaccharides and stopped for 10min when saccharide derivatives were achieved in the enzyme plug. The reaction of α-fucosidase and α-mannosidase was completed by decreasing the electrophoretic voltage to -2kV when the APTS oligosaccharides were passing through an exoglycosidase plug. We established the CE conditions for all of the glycosidic linkage analysis of glycoprotein glycans.

Recent advances on separation and characterization of human milk oligosaccharides

Free human milk oligosaccharides (HMOs) are unique due to their highly complex nature and important emerging biological and protective functions during early life such as prebiotic activity, pathogen deflection, and epithelial and immune cell modulation. Moreover, four genetically determined heterogeneous HMO secretory groups are known to be based on their structure and composition. Over the years, several analytical techniques have been applied to characterize and quantitate HMOs, including nuclear magnetic resonance spectroscopy, high-performance liquid chromatography (HPLC), high pH anion-exchange chromatography, off-line and on-line mass spectrometry (MS), and capillary electrophoresis (CE). Even if these techniques have proven to be efficient and simple, most glycans have no significant UV absorption and derivatization with fluorophore groups prior to separation usually results in higher sensitivity and an improved chromatographic/electrophoretic profile. Consequently, the analysis by HPLC/CE of derivatized milk oligosaccharides with different chromophoric active tags has been developed. However, UV or fluorescence detection does not provide specific structural information and this is a key point in particular related to the highly complex nature of the milk glycan mixtures. As a consequence, for a specific determination of complex mixtures of oligomers, analytical separation is usually required with evaluation by means of MS, which has been successfully applied to HMOs, resulting in efficient compositional analysis and profiling in various milk samples. This review aims to give an overview of the current state-of-the-art techniques used in HMO analysis.

The Lectin Frontier Database (LfDB), and data generation based on frontal affinity chromatography

Lectins are a large group of carbohydrate-binding proteins, having been shown to comprise at least 48 protein scaffolds or protein family entries. They occur ubiquitously in living organisms—from humans to microorganisms, including viruses—and while their functions are yet to be fully elucidated, their main underlying actions are thought to mediate cell-cell and cell-glycoconjugate interactions, which play important roles in an extensive range of biological processes. The basic feature of each lectin’s function resides in its specific sugar-binding properties. In this regard, it is beneficial for researchers to have access to fundamental information about the detailed oligosaccharide specificities of diverse lectins. In this review, the authors describe a publicly available lectin database named “Lectin frontier DataBase (LfDB)”, which undertakes the continuous publication and updating of comprehensive data for lectin-standard oligosaccharide interactions in terms of dissociation constants (K_d’s). For K_d determination, an advanced system of frontal affinity chromatography (FAC) is used, with which quantitative datasets of interactions between immobilized lectins and >100 fluorescently labeled standard glycans have been generated. The FAC system is unique in its clear principle, simple procedure and high sensitivity, with an increasing number (>67) of associated publications that attest to its reliability. Thus, LfDB, is expected to play an essential role in lectin research, not only in basic but also in applied fields of glycoscience.