General Label-Free Mass Spectrometry-Based Assay To Identify Glycosidase Substrate Competence

Rapid cyclic ion mobility separations of monosaccharide building blocks as a first step toward a high-throughput reaction screening platform for carbohydrate syntheses

Herein we present a new high-throughput screening method for carbohydrate syntheses based on cyclic ion mobility spectrometry-mass spectrometry (cIMS-MS)-based separations. We rapidly resolved the α/β anomers for carbohydrates with varying protecting groups after only 5 m of cIMS-MS separation and also detected their respective unwanted anomeric impurities at levels lower than 2%. All experiments were performed in 1 minute of total acquisition time demonstrating our method's high-throughput nature. Our methodology was also extended to the separation of an isomeric mixtures of two protected disaccharides illustrating its utility beyond only monosaccharides. We envision our presented workflow as a first step toward the development of a high-throughput screening platform for the rapid and sensitive detection of α/β anomeric selectivities and for trace isomeric/isobaric impurities.

Quantifying Carbohydrate-Active Enzyme Activity with Glycoprotein Substrates Using Electrospray Ionization Mass Spectrometry and Center-of-Mass Monitoring

Carbohydrate-active enzymes (CAZymes) play critical roles in diverse physiological and pathophysiological processes and are important for a wide range of biotechnology applications. Kinetic measurements offer insight into the activity and substrate specificity of CAZymes, information that is of fundamental interest and supports diverse applications. However, robust and versatile kinetic assays for monitoring the kinetics of intact glycoprotein and glycolipid substrates are lacking. Here, we introduce a simple but quantitative electrospray ionization mass spectrometry (ESI-MS) method for measuring the kinetics of CAZyme reactions involving glycoprotein substrates. The assay, referred to as center-of-mass (CoM) monitoring (CoMMon), relies on continuous (real-time) monitoring of the CoM of an ensemble of glycoprotein substrates and their corresponding CAZyme products. Notably, there is no requirement for calibration curves, internal standards, labeling, or mass spectrum deconvolution. To demonstrate the reliability of CoMMon, we applied the method to the neuraminidase-catalyzed cleavage of N-acetylneuraminic acid (Neu5Ac) residues from a series of glycoproteins of varying molecular weights and degrees of glycosylation. Reaction progress curves and initial rates determined with CoMMon are in good agreement (initial rates within ≤5%) with results obtained, simultaneously, using an isotopically labeled Neu5Ac internal standard, which enabled the time-dependent concentration of released Neu5Ac to be precisely measured. To illustrate the applicability of CoMMon to glycosyltransferase reactions, the assay was used to measure the kinetics of sialylation of a series of asialo-glycoproteins by a human sialyltransferase. Finally, we show how combining CoMMon and the competitive universal proxy receptor assay enables the relative reactivity of glycoprotein substrates to be quantitatively established.

High-Throughput Approaches in Carbohydrate-Active Enzymology: Glycosidase and Glycosyl Transferase Inhibitors, Evolution, and Discovery

Carbohydrates are attached and removed in living systems through the action of carbohydrate-active enzymes such as glycosyl transferases and glycoside hydrolases. The molecules resulting from these enzymes have many important roles in organisms, such as cellular communication, structural support, and energy metabolism. In general, each carbohydrate transformation requires a separate catalyst, and so these enzyme families are extremely diverse. To make this diversity manageable, high-throughput approaches look at many enzymes at once. Similarly, high-throughput approaches can be a powerful way of finding inhibitors that can be used to tune the reactivity of these enzymes, either in an industrial, a laboratory, or a medicinal setting. In this review, we provide an overview of how these enzymes and inhibitors can be sought using techniques such as high-throughput natural product and combinatorial library screening, phage and mRNA display of (glyco)peptides, fluorescence-activated cell sorting, and metagenomics.

Development of a Post-Column Liquid Chromatographic Chiral Addition Method for the Separation and Resolution of Common Mammalian Monosaccharides

The first solely MS-based methodology for the identification and resolution of the ten common mammalian monosaccharides is presented. Based on Cooks' fixed ligand kinetic method, this technique is effective on multiple classes of monosaccharides and includes the first example of two fixed ligand combinations used in a single multiplexed experiment. Subsequently, a post-HPLC chiral addition method is used in conjunction with this newly developed MS methodology for the separation and identification of mixtures of common neutral mammalian monosaccharides. This proposed technique is able to overcome a limitation of present carbohydrate analysis methods, namely the simultaneous isomeric resolution of multiple monosaccharides in a mixture. Graphical Abstract.

Scope and limitations of carbohydrate hydrolysis for de novo glycan sequencing using a hydrogen peroxide/metallopeptide-based glycosidase mimetic

Acidic hydrolysis is commonly used as a first step to break down oligo- and polysaccharides into monosaccharide units for structural analysis. While easy to set up and amenable to mass spectrometry detection, acid hydrolysis is not without its drawbacks. For example, ring-destruction side reactions and degradation products, along with difficulties in optimizing conditions from analyte to analyte, greatly limits its broad utility. Herein we report studies on a hydrogen peroxide/CuGGH metallopeptide-based glycosidase mimetic design for a more efficient and controllable carbohydrate hydrolysis. A library of methyl glycosides consisting of ten common monosaccharide substrates, along with oligosaccharide substrates, was screened with the artificial glycosidase for hydrolytic activity in a high-throughput format with a robotic liquid handling system. The artificial glycosidase was found to be active towards most screened linkages, including alpha- and beta-anomers, thus serving as a potential alternative method for traditional acidic hydrolysis approaches of oligosaccharides.

A High-Throughput Mass-Spectrometry-Based Assay for Identifying the Biochemical Functions of Putative Glycosidases

The most commonly employed glycosidase assays rely on bulky ultraviolet or fluorescent tags at the anomeric position in potential carbohydrate substrates, thereby limiting the utility of these assays for broad substrate characterization. Here we report a qualitative mass spectrometry-based glycosidase assay amenable to high-throughput screening for the identification of the biochemical functions of putative glycosidases. The assay utilizes a library of methyl glycosides and is demonstrated on a high-throughput robotic liquid handling system for enzyme substrate screening. Identification of glycosidase biochemical function is achieved through the observation of an appropriate decrease in mass between a potential sugar substrate and its corresponding product by electrospray ionization mass spectrometry (ESI-MS). In addition to screening known glycosidases, the assay was demonstrated to characterize the biochemical function and enzyme substrate competency of the recombinantly expressed product of a putative glycosidase gene from the thermophilic bacterium Thermus thermophilus.

Recent Liquid Chromatographic Approaches and Developments for the Separation and Purification of Carbohydrates

Carbohydate purification remains a bottleneck in securing analytical standards from natural sources or by chemical or enzymatic synthesis. This review highlights the scope and remaining limitations of recent approaches and methods development in liquid chromatography for robust and higher-throughput carbohydrate separation and isolation.

Enantiomeric Excess Determination for Monosaccharides Using Chiral Transmission to Cold Gas-Phase Tryptophan in Ultraviolet Photodissociation

Chiral transmission between monosaccharides and amino acids via photodissociation in the gas phase was examined using a tandem mass spectrometer fitted with an electrospray ionization source and a cold ion trap in order to investigate the origin of the homochirality of biomolecules in molecular clouds. Ultraviolet photodissociation mass spectra of cold gas-phase noncovalent complexes of the monosaccharide enantiomers glucose (Glc) and galactose (Gal) with protonated L-tryptophan H⁺(L-Trp) were obtained by photoexcitation of the indole ring of L-Trp. L-Trp dissociated via C_α-C_β bond cleavage when noncovalently complexed with D-Glc; however, no dissociation of L-Trp occurred in the homochiral H⁺(L-Trp)(L-Glc) noncovalent complex, where the energy absorbed by L-Trp was released through the evaporation of L-Glc. This enantioselective photodissociation of Trp was due to the transmission of chirality from Glc to Trp via photodissociation in the gas-phase noncovalent complexes, and was applied to the quantitative chiral analysis of monosaccharides. The enantiomeric excess of monosaccharides in solution could be determined by measuring the relative abundance of the two product ions in a single photodissociation mass spectrum of the cold gas-phase noncovalent complex with H⁺(L-Trp), and by referring to the linear relationships derived in this work. Graphical Abstract ᅟ.