Investigations on β1,4-galactosyltransferase I using 6-sulfo-GlcNAc as an acceptor sugar substrate

Capillary Nanogel Electrophoresis for the Determination of the β1-4 Galactosyltransferase Michaelis-Menten Constant and Real-Time Addition of Galactose Residues to N-Glycans and Glycoprotein

A thermally reversible nanogel is used in capillary electrophoresis to create discrete regions for a galactosyltransferase reaction and separation. The β1-4 galactosyltransferase enzyme, donor, and co-factor were patterned in the capillary. The substrate was driven through these zones and converted to galactosylated products, which were separated and identified. Using this capillary electrophoresis method, the degree of glycosylation was discernible for a pentasaccharide and for biantennary N-glycans. With the ability to distinguish between reaction products for which either one or two galactose residues were transferred, the capillary nanogel electrophoresis system was used to determine the Michaelis-Menten value, KM. For the β1-4 galactosyltransferase, the KM value obtained for a pentasaccharide substrate was 1.23 ± 0.08 mM. Once KM was established, the enzyme/substrate ratio was evaluated to add a single galactose residue or to fully galactosylate a biantennary N-glycan. Additionally, capillary nanogel electrophoresis was adapted to transfer galactose residues to protein. The applicability of the method for real-time online modification of whole protein was demonstrated with the Herceptin glycoprotein. Complete retardation by Erythrina cristagalli lectin after enzymatic modification confirmed the addition of galactose residues to the Herceptin. This demonstrated the potential of the method to be used for online modification of other glycoproteins.

Advances in enzyme substrate analysis with capillary electrophoresis

Capillary electrophoresis provides a rapid, cost-effective platform for enzyme and substrate characterization. The high resolution achievable by capillary electrophoresis enables the analysis of substrates and products that are indistinguishable by spectroscopic techniques alone, while the small volume requirement enables analysis of enzymes or substrates in limited supply. Furthermore, the compatibility of capillary electrophoresis with various detectors makes it suitable for KM determinations ranging from nanomolar to millimolar concentrations. Capillary electrophoresis fundamentals are discussed with an emphasis on the separation mechanisms relevant to evaluate sets of substrate and product that are charged, neutral, and even chiral. The basic principles of Michaelis-Menten determinations are reviewed and the process of translating capillary electrophoresis electropherograms into a Michaelis-Menten curve is outlined. The conditions that must be optimized in order to couple off-line and on-line enzyme reactions with capillary electrophoresis separations, such as incubation time, buffer pH and ionic strength, and temperature, are examined to provide insight into how the techniques can be best utilized. The application of capillary electrophoresis to quantify enzyme inhibition, in the form of KI or IC50 is detailed. The concept and implementation of the immobilized enzyme reactor is described as a means to increase enzyme stability and reusability, as well as a powerful tool for screening enzyme substrates and inhibitors. Emerging techniques focused on applying capillary electrophoresis as a rapid assay to obtain structural identification or sequence information about a substrate and in-line digestions of peptides and proteins coupled to mass spectrometry analyses are highlighted.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth 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 2014. 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. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.