Labeling of oligosaccharides and N-linked glycans by a rhodamine-based fluorescent tag for analysis by capillary electrophoresis with laser-induced fluorescence and mass spectrometry detection

In this work, we present the synthesis and application of fluorescent rhodamine B hydrazide for the derivatization of simple oligosaccharides and complex glycans using a hydrazone formation chemistry approach. The labeling conditions and the experimental setup of CE/LIF were optimized by analyzing oligosaccharide standards. The CE/LIF separations were performed in polybrene-coated capillaries eliminating the need for the purification step after derivatization. The addition of methanol to the background electrolyte significantly increased the LIF detection sensitivity reaching the limits of detection in the attomole range. The resolution of carbohydrate samples was improved by using long (98 cm) capillaries and polymer additives (polybrene). The developed method was applied for CE/LIF and CE-MS analysis of N-linked glycans released from bovine ribonuclease B and the therapeutic monoclonal antibody of trastuzumab.

Adapting the Laser-Induced Fluorescence Detection Setup of the Standard Capillary Electrophoresis Equipment to Achieve High-Sensitivity Detection of 2-Aminoacridone Labeled Oligosaccharides

The high-sensitivity capabilities of laser-induced fluorescence (LIF) detection continuously promote the development of various labels with different fluorescence properties. However, this strategy also requires the adaptation of existing detection systems to suit the excitation and emission characteristics of novel fluorescent tags. In this study, we adapted the LIF detector of the commercial capillary electrophoresis instrument to the specific fluorescence spectra of 2-aminoacridone labeled human milk oligosaccharides. An external solid-state laser with a wavelength of 405 nm was connected to the commercial capillary electrophoresis instrument via a simple 3D-printed laser-to-light-guide adapter, and different optical filter setups were compared based on the signal-to-noise ratio. The optimized setup provided detection limits as low as 0.27 to 0.34 nM, corresponding to injection of 3.4 to 4.6 attomoles of 2-aminoacridone labeled oligosaccharides. These findings show that the optimized laser and filter configuration can enhance the sensitivity of electrophoretic separation by several orders of magnitude. In addition, the presented setup can be utilized as a guide for coupling different lasers to the commercial instrument.

Recent advances and trends in sample preparation and chemical modification for glycan analysis

Growing significance of glycosylation in protein functions has accelerated the development of methodologies for detection, identification, and characterization of protein glycosylation. In the past decade, glycobiology research has been advanced by innovative techniques with further progression in the post-genome era. Although significant technical progress has been made in terms of analytical throughput, comprehensiveness, and sensitivity, most methods for glycosylation analysis still require laborious and time-consuming sample preparation tasks. Additionally, sample preparation methods that are focused on specific glycan(s) require an in-depth understanding of various issues in glycobiology. In this review, modern sample preparation and chemical modification methods for the structural and quantitative glycan analyses together with the challenges and advantages of recent sample preparation methods are summarized. The techniques presented herein can facilitate the exploration of biomarkers, understanding of unknown glycan functions, and development of biopharmaceuticals.

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.

Current landscape of protein glycosylation analysis and recent progress toward a novel paradigm of glycoscience research

This review covers the basics and some applications of methodologies for the analysis of glycoprotein glycans. Analytical techniques used for glycoprotein glycans, including liquid chromatography (LC), capillary electrophoresis (CE), mass spectrometry (MS), and high-throughput analytical methods based on microfluidics, were described to supply the essentials about biopharmaceutical and biomarker glycoproteins. We will also describe the MS analysis of glycoproteins and glycopeptides as well as the chemical and enzymatic releasing methods of glycans from glycoproteins and the chemical reactions used for the derivatization of glycans. We hope the techniques have accommodated most of the requests from glycoproteomics researchers.

A rapid and highly sensitive microchip electrophoresis of mono- and mucin-type oligosaccharides labeled with 7-amino-4-methylcoumarin

A selective separation method using a poly(methylmethacrylate) microchip was developed for 7-amino-4-methylcoumarin-labeled saccharides in a crude reaction mixture. In an alkaline borate buffer, saccharide derivatives formed strong anionic borate complexes. These complexes moved from the cathode to the anode in an electric field and were detected near the anode. Excess labeling reagents and other foreign substances remained at the inlet reservoir. A confocal fluorimetric detection system enabled the determination of monosaccharide derivatives with good linearity between at least 5 and 100 nM, corresponding to 50 fmol to 1 pmol per injection. The lower limit of detection (signal-to-noise = 5) was 2 nM. The sensitivity and linear quantitation range were comparable to reported values using fluorometric detection, capillary electrophoresis, or liquid chromatography. Application of the method showed excellent resolution in the analysis of O-linked glycans chemically released from glycoproteins.