Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein 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, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of 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. Most of the applications are 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 highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Synthetic fragments of plant polysaccharides as tools for cell wall biology

A sustainable bioeconomy that includes increased agricultural productivity and new technologies to convert renewable biomass to value-added products may help meet the demands of a growing world population for food, energy and materials. The potential use of plant biomass is determined by the properties of the cell walls, consisting of polysaccharides, proteins, and the polyphenolic polymer lignin. Comprehensive knowledge of cell wall glycan structure and biosynthesis is therefore essential for optimal utilization. However, several areas of plant cell wall research are hampered by a lack of available pure oligosaccharide samples that represent structural features of cell wall glycans. Here, we provide an update on recent chemical syntheses of plant cell wall oligosaccharides and their application in characterizing plant cell wall-directed antibodies and carbohydrate-active enzymes including glycosyltransferases and glycosyl hydrolases, with a particular focus on glycan array technology.

Enzymatic Synthesis of Xylan Microparticles with Tunable Morphologies

Xylans are a diverse family of hemicellulosic polysaccharides found in abundance within the cell walls of nearly all flowering plants. Unfortunately, naturally occurring xylans are highly heterogeneous, limiting studies of their synthesis and structure-function relationships. Here, we demonstrate that xylan synthase 1 from the charophyte alga Klebsormidium flaccidum is a powerful biocatalytic tool for the bottom-up synthesis of pure β-1,4 xylan polymers that self-assemble into microparticles in vitro. Using uridine diphosphate-xylose (UDP-xylose) and defined saccharide primers as substrates, we demonstrate that the shape, composition, and properties of the self-assembling xylan microparticles could be readily controlled via the fine structure of the xylan oligosaccharide primer used to initiate polymer elongation. Furthermore, we highlight two approaches for bottom-up and surface functionalization of xylan microparticles with chemical probes and explore the susceptibility of xylan microparticles to enzymatic hydrolysis. Together, these results provide a useful platform for structural and functional studies of xylans to investigate cell wall biosynthesis and polymer-polymer interactions and suggest possible routes to new biobased materials with favorable properties for biomedical and renewable applications.

Tailormade Wheat Arabinoxylan Reveals the Role of Substitution in Regulating Gelatinization and Retrogradation Behavior of Wheat Starch

To elucidate the role of substitution of arabinoxylan (AX) in the characteristics of wheat starch, this study prepared AX with a well-defined structure by targeted enzymatic hydrolysis and comparatively investigated the effects of AX with different degrees of substitution on gelatinization and retrogradation behavior of starch. Removal of major arabinofuranosyl (Araf) of mono- or disubstituted xylopyranosyl (Xylp) of both low-molecular-weight (Mw: 62.5 kDa, Araf/Xylp: 0.61) and high-molecular-weight AX (Mw: 401.2 kDa, Araf/Xylp: 0.61) reversed the decreased gelatinization viscosity and recrystallization of amylose induced by AX to a similar extent. Upon retrogradation for 30 days, the Araf of mono- and disubstituted Xylp contributed to the water distribution and the effect depended on the molecular chain length. The C3-linked Araf of disubstituted Xylp was more involved in prohibiting the retardation of recrystallization of amylopectin, while the presence of Araf of monosubstituted Xylp might hinder the interactions between AX and amylopectin.

Synthetic Plant Glycan Microarrays as Tools for Plant Biology

Chemically synthesized plant oligosaccharides have recently evolved as powerful molecular tools for plant cell wall biology. Synthetic plant glycan microarrays equipped with these oligosaccharides enable high-throughput analyses of glycan-binding proteins and carbohydrate-active enzymes. To produce these glycan microarrays, small amounts of glycan solution are printed on suitable surfaces for covalent or non-covalent immobilization. Synthetic plant glycan microarrays have been used for example to map the epitopes of plant cell wall-directed antibodies, to characterize glycosyl hydrolases and glycosyl transferases, and to analyze lectin binding. In this chapter, detailed experimental procedures for the production of synthetic glycan microarrays and their use for the characterization of cell wall glycan-directed antibodies are described.

Reprint of: Advanced glycosidases as ingenious biosynthetic instruments

Until recently, glycosidases, naturally hydrolyzing carbohydrate-active enzymes, have found few synthetic applications in industry, being primarily used for cleaving unwanted carbohydrates. With the establishment of glycosynthase and transglycosidase technology by genetic engineering, the view of glycosidases as industrial biotechnology tools has started to change. Their easy production, affordability, robustness, and substrate versatility, added to the possibility of controlling undesired side hydrolysis by enzyme engineering, have made glycosidases competitive synthetic tools. Current promising applications of engineered glycosidases include the production of well-defined chitooligomers, precious galactooligosaccharides or specialty chemicals such as glycosylated flavonoids. Other synthetic pathways leading to human milk oligosaccharides or remodeled antibodies are on the horizon. This work provides an overview of the synthetic achievements to date for glycosidases, emphasizing the latest trends and outlining possible developments in the field.

Progress and challenges in the synthesis of sequence controlled polysaccharides

The sequence, length and substitution of a polysaccharide influence its physical and biological properties. Thus, sequence controlled polysaccharides are important targets to establish structure-properties correlations. Polymerization techniques and enzymatic methods have been optimized to obtain samples with well-defined substitution patterns and narrow molecular weight distribution. Chemical synthesis has granted access to polysaccharides with full control over the length. Here, we review the progress towards the synthesis of well-defined polysaccharides. For each class of polysaccharides, we discuss the available synthetic approaches and their current limitations.

Advanced glycosidases as ingenious biosynthetic instruments

Until recently, glycosidases, naturally hydrolyzing carbohydrate-active enzymes, have found few synthetic applications in industry, being primarily used for cleaving unwanted carbohydrates. With the establishment of glycosynthase and transglycosidase technology by genetic engineering, the view of glycosidases as industrial biotechnology tools has started to change. Their easy production, affordability, robustness, and substrate versatility, added to the possibility of controlling undesired side hydrolysis by enzyme engineering, have made glycosidases competitive synthetic tools. Current promising applications of engineered glycosidases include the production of well-defined chitooligomers, precious galactooligosaccharides or specialty chemicals such as glycosylated flavonoids. Other synthetic pathways leading to human milk oligosaccharides or remodeled antibodies are on the horizon. This work provides an overview of the synthetic achievements to date for glycosidases, emphasizing the latest trends and outlining possible developments in the field.

Synthesis and Biopharmaceutical Applications of Sugar-Based Polymers: New Advances and Future Prospects

The rapid rise in research interest in carbohydrate-based polymers is undoubtedly due to the nontoxic nature of such materials in an in vivo environment and the versatile roles that the polymers can play in cellular functions. Such polymers have served as therapeutic tools for drug delivery, including antigens, proteins, and genes, as well as diagnostic devices. Our focus in the first half of this Review is on synthetic methods based on ring-opening polymerization and enzyme-catalyzed polymerization, along with controlled radical polymerization. In the second half of this Review, sugar-based polymers are discussed on the basis of their remarkable success in competitive receptor binding, as multifunctional nanocarriers of targeting inhibitors for cancer treatment, in genome-editing delivery, in immunotherapy based on endogenous antibody recruitment, and in treatment of respiratory diseases, including influenza A. Particular emphasis is put on the synthesis and biopharmaceutical applications of sugar-based polymers published in the most recent 5 years. A noticeable attribute of carbohydrate-based polymers is that the sugar-receptor interactions can be facilitated by the cooperative effect of multiple sugar units. Their diversified topology and structures will drive the development of new synthetic strategies and bring about important applications, including coronavirus-related drug therapy.

Enzyme promiscuity of carbohydrate active enzymes and their applications in biocatalysis

The application of biocatalysis for the synthesis of glycans and glycoconjugates is a well-established and successful strategy, both for small and large scale synthesis. Compared to chemical synthesis, is has the advantage of high selectivity, but biocatalysis had been largely limited to natural glycans both in terms of reactivity and substrates. This review describes recent advances in exploiting enzyme promiscuity to expand the range of substrates and reactions that carbohydrate active enzymes (CAZymes) can catalyse. The main focus is on formation and hydrolysis of glycosidic linkages, including sugar kinases, reactions that are central to glycobiotechnology. In addition, biocatalysts that generate sugar analogues and modify carbohydrates, such as oxidases, transaminases and acylases are reviewed. As carbohydrate active enzymes become more accessible and protein engineering strategies become faster, the application of biocatalysis in the generation of a wide range of glycoconjugates, beyond natural structures is expected to expand.

Analyzing the Substrate Specificity of a Class of Long-Horned-Beetle-Derived Xylanases by Using Synthetic Arabinoxylan Oligo- and Polysaccharides

Xylophagous long-horned beetles thrive in challenging environments. To access nutrients, they secrete plant-cell-wall-degrading enzymes in their gut fluid; among them are cellulases of the subfamily 2 of glycoside hydrolase family 5 (GH5_2). Recently, we discovered that several beetle-derived GH5_2s use xylan as a substrate instead of cellulose, which is unusual for this family of enzymes. Here, we analyze the substrate specificity of a GH5_2 xylanase from the beetle Apriona japonica (AJAGH5_2-1) using commercially available substrates and synthetic arabinoxylan oligo- and polysaccharides. We demonstrate that AJAGH5_2-1 processes arabinoxylan polysaccharides in a manner distinct from classical xylanase families such as GH10 and GH11. AJAGH5_2-1 is active on long oligosaccharides and cleaves at the non-reducing end of a substituted xylose residue (position +1) only if: 1) three xylose residues are present upstream and downstream of the cleavage site, and 2) xylose residues at positions -1, -2, +2 and +3 are not substituted.

Exploitation of carbohydrate processing enzymes in biocatalysis

Exploitation of enzymes in biocatalytic processes provides scope both in the synthesis and degradation of molecules. Enzymes have power not only in their catalytic efficiency, but their chemoselectivity, regioselectivity, and stereoselectivity means the reactions they catalyze are precise and reproducible. Focusing on carbohydrate processing enzymes, this review covers advances in biocatalysis involving carbohydrates over the last 2-3 years. Given the notorious difficulties in the chemical synthesis of carbohydrates, the use of enzymes for synthesis has potential for significant impact in the future. The use of catabolic enzymes in the degradation of biomass, which can be exploited in the production of biofuels to provide a sustainable and greener source of energy, and the synthesis of molecules that have a range of applications including in the pharmaceutical and food industries will be explored.

Arabinoxylan/Cellulose Nanocrystal Hydrogels with Tunable Mechanical Properties

Hydrogels are three-dimensional networks of hydro-soluble polymers containing a large amount of water that have found a wide panel of applications in many sectors. The need for eco-friendly and nontoxic materials for the elaboration of sustainable hydrogels is obvious, and materials derived from biomass can easily meet these requirements. Cellulose nanocrystals (CNC) and arabinoxylans (AX) are abundant, biobased, hydrophilic, and renewable nanoparticles and polymers that interact together. In this study, we have built fully biobased hydrogels using CNC and AX. First, as revealed by Quartz Crystal Microbalance with Dissipation (QCM-D) experiments, AX adsorbs almost instantly on cellulosic surfaces in an irreversible manner. Nevertheless, gelation kinetics is not instantaneous and shows temperature dependence. The determination of phase diagrams using the inverted tube method leads to the conclusion that high AX/CNC ratios are needed for gel formation. The mechanical properties of CNC-AX hydrogels were investigated by measuring storage and loss moduli (G', G'') as a function of concentrations and hydrogel reformation after submission to high shear rates. Hydrogel properties were also tuned by increasing the ionic strength and the enzymatic removal of arabinose moieties from AX. In light of the obtained results, we hypothesize that gel formation occurs in two steps, i.e., AX adsorption followed by gelation of the complexes, and is due to the formation of reversible and tunable interactions between CNC/AX complexes interacting with each other, offering a wide panel of physicochemical tools to tune and trigger the final properties of hydrogels.

One-pot preparation of double network hydrogels via enzyme-mediated polymerization and post-self-assembly for wound healing

An enzymatic one-pot preparation method is used to prepare double network hydrogels for wound healing.