Two-dimensional chromatography in the analysis of complex glycans from transferrin

The Pre- and Post-Column Derivatization on Monosaccharide Composition Analysis, a Review

Polysaccharides, as common metabolic products in organisms, play a crucial role in the growth and development of living organisms. For humans, polysaccharides represent a class of compounds with diverse applications, particularly in the medical field. Therefore, the exploration of the monosaccharide composition and structural characteristics of polysaccharides holds significant importance in understanding their biological functions. This review provides a comprehensive overview of extraction methods and hydrolysis strategies for polysaccharides. It systematically analyzes strategies and technologies for determining polysaccharide composition and discusses common derivatization reagents employed in further polysaccharide studies. Derivatization is considered a fundamental strategy for determining monosaccharides, as it not only enhances the detectability of analytes but also increases detection sensitivity, especially in liquid chromatography (LC), capillary electrophoresis (CE), and gas chromatography (GC) techniques. The review meticulously examines pre-column and post-column derivatization techniques for monosaccharide analysis, categorizing them based on diverse detection methodologies. It delves into the principles and distinctive features of various derivatization reagents, offering a comparative analysis of their strengths and limitations. Ultimately, the aim is to provide guidance for selecting the most suitable derivatization approach, taking into account the structural nuances, biological functions, and reaction dynamics of polysaccharides.

Discrimination between sialic acid linkage modes using sialyllactose-imprinted polymers

Glycosylation plays an important role in various pathological processes such as cancer. One key alteration in the glycosylation pattern correlated with cancer progression is an increased level as well as changes in the type of sialylation. Developing molecularly-imprinted polymers (MIPs) with high affinity for sialic acid able to distinguish different glycoforms such as sialic acid linkages is an important task which can help in early cancer diagnosis. Sialyllactose with α2,6′ vs. α2,3′ sialic acid linkage served as a model trisaccharide template. Boronate chemistry was employed in combination with a library of imidazolium-based monomers targeting the carboxylate group of sialic acid. The influence of counterions of the cationic monomers and template on their interactions was investigated by means of ¹H NMR titration studies. The highest affinities were afforded using a combination of Br⁻ and Na⁺ counterions of the monomers and template, respectively. The boronate ester formation was confirmed by MS and ¹H/¹¹B NMR, indicating 1 : 2 stoichiometries between sialyllactoses and boronic acid monomer. Polymers were synthesized in the form of microparticles using boronate and imidazolium monomers. This combinatorial approach afforded MIPs selective for the sialic acid linkages and compatible with an aqueous environment. The molecular recognition properties with respect to saccharide templates and glycosylated targets were reported.

2,6′- and 2,3′-sialyllactose imprinted polymers (MIPs) capable of discriminating between two modes of sialic acid linkages in glycans are reported.

NEGATIVE ION MASS SPECTROMETRY FOR THE ANALYSIS OF N-LINKED GLYCANS

N-glycans from glycoproteins are complex, branched structures whose structural determination presents many analytical problems. Mass spectrometry, usually conducted in positive ion mode, often requires extensive sample manipulation, usually by derivatization such as permethylation, to provide the necessary structure-revealing fragment ions. The newer but, so far, lesser used negative ion techniques, on the contrary, provide a wealth of structural information not present in positive ion spectra that greatly simplify the analysis of these compounds and can usually be conducted without the need for derivatization. This review describes the use of negative ion mass spectrometry for the structural analysis of N-linked glycans and emphasises the many advantages that can be gained by this mode of operation. Biosynthesis and structures of the compounds are described followed by methods for release of the glycans from the protein. Methods for ionization are discussed with emphasis on matrix-assisted laser desorption/ionization (MALDI) and methods for producing negative ions from neutral compounds. Acidic glycans naturally give deprotonated species under most ionization conditions. Fragmentation of negative ions is discussed next with particular reference to those ions that are diagnostic for specific features such as the branching topology of the glycans and substitution positions of moieties such as fucose and sulfate, features that are often difficult to identify easily by conventional techniques such as positive ion fragmentation and exoglycosidase digestions. The advantages of negative over positive ions for this structural work are emphasised with an example of a series of glycans where all other methods failed to produce a structure. Fragmentation of derivatized glycans is discussed next, both with respect to derivatives at the reducing terminus of the molecules, and to methods for neutralization of the acidic groups on sialic acids to both stabilize them for MALDI analysis and to produce the diagnostic fragments seen with the neutral glycans. The use of ion mobility, combined with conventional mass spectrometry is described with emphasis on its use to extract clean glycan spectra both before and after fragmentation, to separate isomers and its use to extract additional information from separated fragment ions. A section on applications follows with examples of the identification of novel structures from lower organisms and tables listing the use of negative ions for structural identification of specific glycoproteins, glycans from viruses and uses in the biopharmaceutical industry and in medicine. The review concludes with a summary of the advantages and disadvantages of the technique. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Human Cancer Antigen Globo H Is a Cell-Surface Ligand for Human Ribonuclease 1

Pancreatic-type ribonucleases are secretory enzymes that catalyze the cleavage of RNA. Recent efforts have endowed the homologues from cow (RNase A) and human (RNase 1) with toxicity for cancer cells, leading to a clinical trial. The basis for the selective toxicity of ribonuclease variants for cancerous versus noncancerous cells has, however, been unclear. A screen for RNase A ligands in an array of mammalian cell-surface glycans revealed strong affinity for a hexasaccharide, Globo H, that is a tumor-associated antigen and the basis for a vaccine in clinical trials. The affinity of RNase A and RNase 1 for immobilized Globo H is in the low micromolar-high nanomolar range. Moreover, reducing the display of Globo H on the surface of human breast adenocarcinoma cells with a small-molecule inhibitor of biosynthesis or a monoclonal antibody antagonist decreases the toxicity of an RNase 1 variant. Finally, heteronuclear single quantum coherence (HSQC) NMR spectroscopy showed that RNase 1 interacts with Globo H by using residues that are distal from the enzymic active site. The discovery that a systemic human ribonuclease binds to a moiety displayed on human cancer cells links two clinical paradigms and suggests a mechanism for innate resistance to cancer.

Iron and bismuth bound human serum transferrin reveals a partially-opened conformation in the N-lobe

Human serum transferrin (hTF) binds Fe(III) tightly but reversibly, and delivers it to cells via a receptor-mediated endocytosis process. The metal-binding and release result in significant conformational changes of the protein. Here, we report the crystal structures of diferric-hTF (Fe_NFe_C-hTF) and bismuth-bound hTF (Bi_NFe_C-hTF) at 2.8 and 2.4 Å resolutions respectively. Notably, the N-lobes of both structures exhibit unique “partially-opened” conformations between those of the apo-hTF and holo-hTF. Fe(III) and Bi(III) in the N-lobe coordinate to, besides anions, only two (Tyr95 and Tyr188) and one (Tyr188) tyrosine residues, respectively, in contrast to four residues in the holo-hTF. The C-lobe of both structures are fully closed with iron coordinating to four residues and a carbonate. The structures of hTF observed here represent key conformers captured in the dynamic nature of the transferrin family proteins and provide a structural basis for understanding the mechanism of metal uptake and release in transferrin families.

Development of a single column method for the separation of lipid- and protein-derived oligosaccharides

Fluorescent labeling of oligosaccharides with anthranilic acid (2-aminobenzoic acid; 2AA), or 2-aminobenzamide (2AB) permits the rapid, sensitive analysis of structures present in cells and tissues. Normal-phase (NP)/hydrophilic interaction chromatography (HILIC) is commonly used to separate fluorophore-derivatized oligosaccharides. Column elution is expressed as glucose units (GU) following calculation of relative retention when compared to an external glucose oligomer standard. However, there is significant overlap between sialylated and neutral oligosaccharides. Normal-phase anion-exchange (NP-AE) HPLC can separate differing classes of oligosaccharides according to the number of charged residues, but relative retention times in GU cannot be calculated across the entire gradient. We have overcome this difficulty by use of a Dionex AS11 column that combines both hydrophilic interaction and anion-exchange chromatographies, termed HIAX, which enables the calculation of GU values for oligosaccharides that carry sialylated or other negatively charged groups. The same method may also be employed for 2AB and other fluorophore-labeled oligosaccharides. Additionally, the same HPLC eluants are used for the differing HPLC columns. Therefore, analysis of HILIC- or HIAX-separated fluorophore-labeled oligosaccharides can be performed using a single HPLC system with a single set of eluents following a simple column change.

Direct On-Membrane Glycoproteomic Approach Using MALDI-TOF Mass Spectrometry Coupled with Microdispensing of Multiple Enzymes

We report a novel approach for direct on-membrane glycoproteomics by digestion of membrane-blotted glycoproteins with multiple enzymes using piezoelectric chemical inkjet printing technology and on-membrane direct MALDI-TOF mass spectrometry. With this approach, both N-linked glycan analyses and peptide mass fingerprinting of several standard glycoproteins were successfully performed using PNGase F and trypsin microscale digestions of the blotted spots on membrane from an SDS-PAGE gel. In addition, we performed a similar analysis for 2-DE separated serum glycoproteins as a demonstration of how the system could be used in human plasma glycoproteomics.

Using a nanoelectrospray-differential mobility spectrometer-mass spectrometer system for the analysis of oligosaccharides with solvent selected control over ESI aggregate ion formation

Differential mobility spectrometry (DMS), also commonly referred to as high field asymmetric waveform ion mobility spectrometry (FAIMS) is a rapidly advancing technology for gas-phase ion separation. The interfacing of DMS with mass spectrometry (MS) offers potential advantages over the use of mass spectrometry alone. Such advantages include improvements to mass spectral signal/noise, orthogonal/complementary ion separation to mass spectrometry, enhanced ion and complexation structural analysis, and the potential for rapid analyte quantitation. In this report, we demonstrate the successful use of our nanoESI-DMS-MS system, with a methanol drift gas modifier, for the separation of oligosaccharides. The tendency for ESI to form oligosaccharide aggregate ions and the negative impact this has on nanoESI-DMS-MS oligosaccharide analysis is described. In addition, we demonstrate the importance of sample solvent selection for controlling nanoESI oligosaccharide aggregate ion formation and its effect on glycan ionization and DMS separation. The successful use of a tetrachloroethane/methanol solvent solution to reduce ESI oligosaccharide aggregate ion formation while efficiently forming a dominant MH(+) molecular ion is presented. By reducing aggregate ion formation in favor of a dominant MH(+) ion, DMS selectivity and specificity is improved. In addition to DMS, we would expect the reduction in aggregate ion complexity to be beneficial to the analysis of oligosaccharides for other post-ESI separation techniques such as mass spectrometry and ion mobility. The solvent selected control over MH(+) molecular ion formation, offered by the use of the tetrachloroethane/methanol solvent, also holds promise for enhancing MS/MS structural characterization analysis of glycans.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update covering the period 1999-2000

This review describes the use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates and continues coverage of the field from the previous review published in 1999 (D. J. Harvey, Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates, 1999, Mass Spectrom Rev, 18:349-451) for the period 1999-2000. As MALDI mass spectrometry is acquiring the status of a mature technique in this field, there has been a greater emphasis on applications rather than to method development as opposed to the previous review. The present review covers applications to plant-derived carbohydrates, N- and O-linked glycans from glycoproteins, glycated proteins, mucins, glycosaminoglycans, bacterial glycolipids, glycosphingolipids, glycoglycerolipids and related compounds, and glycosides. Applications of MALDI mass spectrometry to the study of enzymes acting on carbohydrates (glycosyltransferases and glycosidases) and to the synthesis of carbohydrates, are also covered.

Early indication of effects of puromycin aminonucleoside using a fluorimetric assay of 2-aminoacridone-derivatized carbohydrates in urine

This paper describes a novel noninvasive method to study the changes in free carbohydrates excreted in urine as a result of toxicity in the rat induced by the administration of puromycin aminonucleoside (PAN). Urine samples were collected for 24 h prior to dosing and at 8, 24, and 32 h postdosing. For each sample, free carbohydrates were extracted from the urine using a graphitized carbon column and then labeled with 2-aminoacridone (2-AMAC) prior to analysis by hydrophilic interaction liquid chromatography (HILC). Dramatic changes were seen in the profile of the carbohydrates at the 8- and 24-h time points. These changes in carbohydrate profiles may be useful as early indicators of toxicity.