Towards GAG glycomics: analysis of highly sulfated heparins by MALDI-TOF mass spectrometry

High-Throughput Glycomic Methods

Glycomics aims to identify the structure and function of the glycome, the complete set of oligosaccharides (glycans), produced in a given cell or organism, as well as to identify genes and other factors that govern glycosylation. This challenging endeavor requires highly robust, sensitive, and potentially automatable analytical technologies for the analysis of hundreds or thousands of glycomes in a timely manner (termed high-throughput glycomics). This review provides a historic overview as well as highlights recent developments and challenges of glycomic profiling by the most prominent high-throughput glycomic approaches, with N-glycosylation analysis as the focal point. It describes the current state-of-the-art regarding levels of characterization and most widely used technologies, selected applications of high-throughput glycomics in deciphering glycosylation process in healthy and disease states, as well as future perspectives.

Straightforward Analysis of Sulfated Glycosaminoglycans by MALDI-TOF Mass Spectrometry from Biological Samples

Glycosaminoglycans (GAGs) are considered to be the most difficult type of glycoconjugates to analyze as they are constituted of linear long polysaccharidic chains having molecular weights reaching up to several million daltons. Bottom-up analysis of glycosaminoglycans from biological samples is a long and work-extensive procedure due to the many preparation steps involved. In addition, so far, only few research articles have been dedicated to the analysis of GAGs by means of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) because their intact ionization can be problematic due to the presence of labile sulfate groups. In this work, we had the aim of exploring the sulfation pattern of monosulfated chondroitin/dermatan sulfate (CS/DS) disaccharides in human tissue samples because they represent the most abundant form of sulfation in disaccharides. We present here an optimized strategy to analyze on-target derivatized CS/DS disaccharides via MALDI-TOF-MS using a fast workflow that does not require any purification after enzymatic cleavage. For the first time, we show that MALDI-TOF/TOF experiments allow for discrimination between monosulfated CS disaccharide isomers via specific fragments corresponding to glycosidic linkages and to cross-ring cleavages. This proof of concept is illustrated via the analysis of CS/DS disaccharides of atherosclerotic lesions of different histological origins, in which we were able to identify their monosulfation patterns.

Developments in Mass Spectrometry for Glycosaminoglycan Analysis: A Review

This review covers recent developments in glycosaminoglycan (GAG) analysis via mass spectrometry (MS). GAGs participate in a variety of biological functions, including cellular communication, wound healing, and anticoagulation, and are important targets for structural characterization. GAGs exhibit a diverse range of structural features due to the variety of O- and N-sulfation modifications and uronic acid C-5 epimerization that can occur, making their analysis a challenging target. Mass spectrometry approaches to the structure assignment of GAGs have been widely investigated, and new methodologies remain the subject of development. Advances in sample preparation, tandem MS techniques (MS/MS), online separations, and automated analysis software have advanced the field of GAG analysis. These recent developments have led to remarkable improvements in the precision and time efficiency for the structural characterization of GAGs.

Advances in glycosaminoglycan detection

BACKGROUND

Glycosaminoglycans (GAGs) are negatively charged long linear (highly sulfated) polysaccharides consisting of repeating disaccharide units that are expressed on the surfaces of all nucleated cells. The expression of GAGs is required for embryogenesis, regulation of cell growth and proliferation, maintenance of tissue hydration, and interactions of the cells via receptors. Mucopolysaccharidoses (MPS) are caused by deficiency of specific lysosomal enzymes that result in the accumulation of GAGs in multiple tissues leading to organ dysfunction. Therefore, GAGs are important biomarkers for MPS. Without any treatment, patients with severe forms of MPS die within the first two decades of life.

SCOPE OF REVIEW

Accurate measurement of GAGs is important to understand the diagnosis and pathogenesis of MPS and to monitor therapeutic efficacy before, during, and after treatment of the disease. This review covers various qualitative and quantitative methods for measurement of GAGs, including dye specific, thin layer chromatography (TLC), capillary electrophoresis, high-performance liquid chromatography (HPLC), liquid chromatography-tandem mass spectrometry (LC-MS/MS), gas chromatography, ELISA, and automated high-throughput mass spectrometry. Major conclusion: There are several methods for GAG detection however, specific GAG detection in the various biological systems requires rapid, sensitive, specific, and cost-effective methods such as LC-MS/MS.

GENERAL SIGNIFICANCE

This review will describe different methods for GAG detection and analysis, including their advantages and limitation.

High resolution MALDI-TOF-MS and MS/MS: Application for the structural characterization of sulfated oligosaccharides

Sulfated oligosaccharides are involved in important biological events that are often modulated by specific sequences and sulfation patterns, but their structural analysis remains challenging. Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) analysis of three different sulfated oligosaccharides (Fondaparinux, the octasulfated pentasaccharide, a disulfated heparin-derived tetrasaccharide 1, and an octasulfated maltoheptaose) 2 was performed using the 2-(4-hydroxyphenylazo)benzoic acid-tetramethylguanidinium (HABA-TMG₂) matrix. High resolution mass spectrometry of the main ions observed was successful, and this was complemented by tandem mass spectrometry (MS/MS) analysis for structural assessment. Despite sulfate losses, fully sulfated molecular ions were observed and these allowed the determination of oligosaccharide structures: UA-GlcNAc-UA(2S)-AnhMan(6S) for compound 1 and (Glc6S)₆-Glc (1S,6S) for compound 2.

Ionic Liquid-Assisted Laser Desorption/Ionization-Mass Spectrometry: Matrices, Microextraction, and Separation

Ionic liquids (ILs) have advanced a variety of applications, including matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). ILs can be used as matrices and solvents for analyte extraction and separation prior to analysis using laser desorption/ionization-mass spectrometry (LDI-MS). Most ILs show high stability with negligible sublimation under vacuum, provide high ionization efficiency, can be used for qualitative and quantitative analyses with and without internal standards, show high reproducibility, form homogenous spots during sampling, and offer high solvation efficiency for a wide range of analytes. Ionic liquids can be used as solvents and pseudo-stationary phases for extraction and separation of a wide range of analytes, including proteins, peptides, lipids, carbohydrates, pathogenic bacteria, and small molecules. This review article summarizes the recent advances of ILs applications using MALDI-MS. The applications of ILs as matrices, solvents, and pseudo-stationary phases, are also reviewed.

Mass spectrometry imaging with laser-induced postionization

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) can simultaneously record the lateral distribution of numerous biomolecules in tissue slices, but its sensitivity is restricted by limited ionization. We used a wavelength-tunable postionization laser to initiate secondary MALDI-like ionization processes in the gas phase. In this way, we could increase the ion yields for numerous lipid classes, liposoluble vitamins, and saccharides, imaged in animal and plant tissue with a 5-micrometer-wide laser spot, by up to two orders of magnitude. Critical parameters for initiation of the secondary ionization processes are pressure of the cooling gas in the ion source, laser wavelength, pulse energy, and delay between the two laser pulses. The technology could enable sensitive MALDI-MS imaging with a lateral resolution in the low micrometer range.

Applications of mass spectrometry to structural analysis of marine oligosaccharides

Marine oligosaccharides have attracted increasing attention recently in developing potential drugs and biomaterials for their particular physical and chemical properties. However, the composition and sequence analysis of marine oligosaccharides are very challenging for their structural complexity and heterogeneity. Mass spectrometry (MS) has become an important technique for carbohydrate analysis by providing more detailed structural information, including molecular mass, sugar constituent, sequence, inter-residue linkage position and substitution pattern. This paper provides an overview of the structural analysis based on MS approaches in marine oligosaccharides, which are derived from some biologically important marine polysaccharides, including agaran, carrageenan, alginate, sulfated fucan, chitosan, glycosaminoglycan (GAG) and GAG-like polysaccharides. Applications of electrospray ionization mass spectrometry (ESI-MS) are mainly presented and the general applications of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) are also outlined. Some technical challenges in the structural analysis of marine oligosaccharides by MS have also been pointed out.

Water ice is a soft matrix for the structural characterization of glycosaminoglycans by infrared matrix-assisted laser desorption/ionization

Glycosaminoglycans (GAGs) are a class of heterogeneous, often highly sulfated glycans that form linear chains consisting of up to 100 monosaccharide building blocks and more. GAGs are ubiquitous constituents of connective tissue, cartilage, and the extracellular matrix, where they have key functions in many important biological processes. For their characterization by mass spectrometry (MS) and tandem MS, the high molecular weight polymers are usually enzymatically digested to oligomers with a low degree of polymerization (dp), typically disaccharides. However, owing to their lability elimination of sulfate groups upon desorption/ionization is often encountered leading to a loss of information on the analyte. Here, we demonstrate that, in particular, water ice constitutes an extremely mild matrix for the analysis of highly sulfated GAG disaccharides by infrared matrix-assisted laser desorption/ionization (IR-MALDI) mass spectrometry. Depending on the degree of sulfation, next to the singly charged ionic species doubly- and even triply charged ions are formed. An unambiguous assignment of the sulfation sites becomes possible by subjecting sodium adducts of the GAGs to low-energy collision-induced dissociation tandem MS. These ionic species exhibit a remarkable stability of the sulfate substituents, allowing the formation of fragment ions retaining their sulfation that arise from either cross-ring cleavages or rupture of the glycosidic bonds, thereby allowing an unambiguous assignment of the sulfation sites.

New methods to study the composition and structure of the extracellular matrix in natural and bioengineered tissues

The extracellular matrix (ECM) comprises a gel of numerous biopolymers that occurs in a multitude of biological tissues. The ECM provides the basic support and mechanical strength of skeletal tissue and is responsible for shape retention. At the same time, the ECM is responsible for the viscoelastic properties and the elasticity of soft tissues. As expected, there are several important diseases that affect and degenerate the ECM with severe consequences for its properties. Bioengineering is a promising approach to support the regenerative capacity of the body. Unfortunately, the biomechanical properties of bioengineered ECM often only poorly meet the standards of their native counterparts. Many bioengineered tissues are characterized by an increased glycosaminoglycan (GAG) but decreased collagen content. This leads to an enhanced water content that strongly alters the viscoelastic and thus the biomechanical properties. Therefore, compositional analysis is important to estimate the tissue quality. We will show that nuclear magnetic resonance (NMR) spectroscopy and soft-ionization mass spectrometry (MS) represent useful techniques for ECM research both in natural and bioengineered tissues. Both methods are strongly complimentary: while MS techniques such as matrix-assisted laser desorption and ionization (MALDI) are excellent and very sensitive analytical tools to determine the collagen and the GAG contents of tissues, NMR spectroscopy provides insight into the molecular architecture of the ECM, its dynamics and other important parameters such as the water content of the tissue as well as the diffusion of molecules within the ECM.

New targets for glycosaminoglycans and glycosaminoglycans as novel targets

Biological functions of a variety of proteins are mediated via their interaction with glycosaminoglycans (GAGs). The structural diversity within the wide GAG landscape provides individual interaction sites for a multitude of proteins involved in several pathophysiological processes. This 'GAG angle' of such proteins as well as their specific GAG ligands give rise to novel therapeutic concepts for drug development. Current glycomic technologies to elucidate the glycan structure-function relationships, methods to investigate the selectivity and specificity of glycan-protein interactions and existing therapeutic approaches to interfere with GAG-protein interactions are discussed.

An approach for separation and complete structural sequencing of heparin/heparan sulfate-like oligosaccharides

As members of the glycosaminoglycan (GAG) family, heparin and heparan sulfate (HS) are responsible for mediation of a wide range of essential biological actions, most of which are mediated by specific patterns of modifications of regions of these polysaccharides. To fully understand the regulation of HS modification and the biological function of HS through its interactions with protein ligands, it is essential to know the specific HS sequences present. However, the sequencing of mixtures of HS oligosaccharides presents major challenges due to the lability of the sulfate modifications, as well as difficulties in separating isomeric HS chains. Here, we apply a sequential chemical derivatization strategy involving permethylation, desulfation, and trideuteroperacetylation to label original sulfation sites with stable and hydrophobic trideuteroacetyl groups. The derivatization chemistry differentiates between all possible heparin/HS sequences solely by glycosidic bond cleavages, without the need to generate cross-ring cleavages. This derivatization strategy combined with LC-MS/MS analysis has been used to separate and sequence five synthetic HS-like oligosaccharides of sizes up to dodecasaccharide, as well as a highly sulfated Arixtra-like heptamer. This strategy offers a unique capability for the sequencing of microgram quantities of HS oligosaccharide mixtures by LC-MS/MS.

Structurally informative tandem mass spectrometry of highly sulfated natural and chemoenzymatically synthesized heparin and heparan sulfate glycosaminoglycans

The highly sulfated glycosaminoglycan oligosaccharides derived from heparin and heparan sulfate have been a highly intractable class of molecules to analyze by tandem mass spectrometry. Under the many methods of ion activation, this class of molecules generally exhibits SO3 loss as the most significant fragmentation pathway, interfering with the assignment of the location of sulfo groups in glycosaminoglycan chains. We report here a method that stabilizes sulfo groups and facilitates the complete structural analysis of densely sulfated (two or more sulfo groups per disaccharide repeat unit) heparin and heparan sulfate oligomers. This is achieved by complete removal of all ionizable protons, either by charging during electrospray ionization or by Na(+)/H(+) exchange. The addition of millimolar levels of NaOH to the sample solution facilitates the production of precursor ions that meet this criterion. This approach is found to work for a variety of heparin sulfate oligosaccharides derived from natural sources or produced by chemoenzymatic synthesis, with up to 12 saccharide subunits and up to 11 sulfo groups.

Glycosaminoglycan glycomics using mass spectrometry

The fact that sulfated glycosaminoglycans (GAGs) are necessary for the functioning of all animal physiological systems drives the need to understand their biology. This understanding is limited, however, by the heterogeneous nature of GAG chains and their dynamic spatial and temporal expression patterns. GAGs have a regulated structure overlaid by heterogeneity but lack the detail necessary to build structure/function relationships. In order to provide this information, we need glycomics platforms that are sensitive, robust, high throughput, and information rich. This review summarizes progress on mass-spectrometry-based GAG glycomics methods. The areas covered include disaccharide analysis, oligosaccharide profiling, and tandem mass spectrometric sequencing.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.

Performance evaluation on a wide set of matrix-assisted laser desorption ionization matrices for the detection of oligosaccharides in a high-throughput mass spectrometric screening of carbohydrate depolymerizing enzymes

Compared to other analytical methods, matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) presents several unique advantages for the structural characterization of degradation products of carbohydrates. Our final goal is to implement this technique as a high-throughput platform, with the aim of exploring natural bio-diversity to discover new carbohydrate depolymerizing enzymes. In this approach, a variety of carbohydrates will be used as enzymes substrates and MALDI-MS will be employed to monitor the oligosaccharides produced. One drawback of MALDI, however, is that the choice of the matrix is largely dependent on the chemical properties of the analyte. In this context, our objective in the present work was to find the smallest set of MALDI matrices able to detect chemically heterogeneous oligosaccharides. This was done through the performance evaluation of more than 40 MALDI matrices preparations. Homogeneity of analyte-matrix deposits was considered as a critical feature, especially since the final objective is to fully automate the analyses. Evaluation of the matrices was done by means of a rigorous statistical approach. Amongst all tested compounds, our work proposes the use of the DHB/DMA ionic matrix as the most generic matrix, for rapid detection of a variety of polysaccharides including neutral, anionic, methylated, sulfated, and acetylated compounds. The selected matrices were then used to screen crude bacterial incubation media for the detection of enzymatic degradation products.

Heparan sulfate glycomics: towards systems biology strategies

HSs (heparan sulfates) are a complex family of cell-surface and matrix polysaccharides that have diverse biological functions, underpinned by structurally diverse patterns of backbone chain modification, especially by sulfate groups. These variant structures represent a molecular code, the 'heparanome', that confers the ability to interact selectively with a wide interactome of proteins, the 'heparactome', and thereby influence a network of cellular events. It is becoming increasingly apparent that understanding the structure-activity relationships of these enigmatic molecules requires the development of a holistic systems biology view of their structure and interactions. In the present paper, I describe some of the new tools available to realize this strategy, and discuss the future potential for the combined application of glycomics and other '-omics' approaches to define the molecular code of the heparanome.

An expression system for screening of proteins for glycan and protein interactions

Here we describe a versatile high-throughput expression system that permits genome-wide screening of type 1 membrane and secreted proteins for interactions with glycans and proteins using both cell-expressed and soluble forms of the expressed proteins. Based on Gateway cloning methodology, we have engineered a destination vector that directs expression of enhanced green fluorescent protein (EGFP)-tagged proteins at the cell surface via a glycosylphosphatidylinositol tail. The EGFP fusion proteins can then be cleaved with PreScission protease to release soluble forms of proteins that can be optionally biotinylated. We demonstrate the utility of this cloning and expression system for selected low-affinity membrane lectins from the siglec family of sialic acid-binding immunoglobulin-like lectins, for the glycosaminoglycan-binding proteins FGF-1 and BACE, and for the heterotypic adhesion molecules JAM-B and JAM-C. Cell-expressed proteins can be evaluated for glycan interactions using polyvalent soluble glycan probes and for protein interactions using either cells or soluble proteins. Following cleavage from the cell surface, proteins were complexed in solution and sufficient avidity was achieved to measure weak protein–glycan and weak protein–protein interactions using glycan arrays and surface plasmon resonance, respectively.

Heparin characterization: challenges and solutions

Although heparin is an important and widely prescribed pharmaceutical anticoagulant, its high degree of sequence microheterogeneity and size polydispersity make molecular-level characterization challenging. Unlike nucleic acids and proteins that are biosynthesized through template-driven assembly processes, heparin and the related glycosaminoglycan heparan sulfate are actively remodeled during biosynthesis through a series of enzymatic reactions that lead to variable levels of O- and N-sulfonation and uronic acid epimers. As summarized in this review, heparin sequence information is determined through a bottom-up approach that relies on depolymerization reactions, size- and charge-based separations, and sensitive mass spectrometric and nuclear magnetic resonance experiments to determine the structural identity of component oligosaccharides. The structure-elucidation process, along with its challenges and opportunities for future analytical improvements, is reviewed and illustrated for a heparin-derived hexasaccharide.

Hyphenated techniques for the analysis of heparin and heparan sulfate

The elucidation of the structure of glycosaminoglycan has proven to be challenging for analytical chemists. Molecules of glycosaminoglycan have a high negative charge and are polydisperse and microheterogeneous, thus requiring the application of multiple analytical techniques and methods. Heparin and heparan sulfate are the most structurally complex of the glycosaminoglycans and are widely distributed in nature. They play critical roles in physiological and pathophysiological processes through their interaction with heparin-binding proteins. Moreover, heparin and low-molecular weight heparin are currently used as pharmaceutical drugs to control blood coagulation. In 2008, the health crisis resulting from the contamination of pharmaceutical heparin led to considerable attention regarding their analysis and structural characterization. Modern analytical techniques, including high-performance liquid chromatography, capillary electrophoresis, mass spectrometry, and nuclear magnetic resonance spectroscopy, played critical roles in this effort. A successful combination of separation and spectral techniques will clearly provide a critical advantage in the future analysis of heparin and heparan sulfate. This review focuses on recent efforts to develop hyphenated techniques for the analysis of heparin and heparan sulfate.

Analysis of Glycosaminoglycans Using Mass Spectrometry

The glycosaminoglycans (GAGs) are linear polysaccharides expressed on animal cell surfaces and in extracellular matrices. Their biosynthesis is under complex control and confers a domain structure that is essential to their ability to bind to protein partners. Key to understanding the functions of GAGs are methods to determine accurately and rapidly patterns of sulfation, acetylation and uronic acid epimerization that correlate with protein binding or other biological activities. Mass spectrometry (MS) is particularly suitable for the analysis of GAGs for biomedical purposes. Using modern ionization techniques it is possible to accurately determine molecular weights of GAG oligosaccharides and their distributions within a mixture. Methods for direct interfacing with liquid chromatography have been developed to permit online mass spectrometric analysis of GAGs. New tandem mass spectrometric methods for fine structure determination of GAGs are emerging. This review summarizes MS-based approaches for analysis of GAGs, including tissue extraction and chromatographic methods compatible with LC/MS and tandem MS.

Applications of isotopes in advancing structural and functional heparanomics

Heparanomics is the study of all the biologically active oligosaccharide domain structures in the entire heparanome and the nature of the interactions among these domains and their protein ligands. Structural elucidation of heparan sulfate and heparin oligosaccharides is a major obstacle in advancing structure-function relationships and heparanomics. There are several factors that exacerbate the challenges involved in the structural elucidation of heparin and heparan sulfate; therefore, there is great interest in developing novel strategies and analytical tools to overcome the barriers in decoding the enigmatic heparanome. This review focuses on the applications of isotopes, both radioisotopes and stable isotopes, in the structural elucidation of the complex heparanome at the disaccharide or oligosaccharide level using liquid chromatography, nuclear magnetic resonance spectroscopy, and mass spectrometry. This review also outlines the utility of isotopes in determining the substrate specificity of biosynthetic enzymes that eventually dictate the emergence of biologically active oligosaccharides.

Lysine and arginine side chains in glycosaminoglycan-protein complexes investigated by NMR, cross-linking, and mass spectrometry: a case study of the factor H-heparin interaction

We have used the interaction between module 7 of complement factor H (CFH approximately 7) and a fully sulfated heparin tetrasaccharide to exemplify a new approach for studying contributions of basic side chains to the formation of glycosaminoglycan (GAG)-protein complexes. We first employed HISQC and H(2)CN NMR experiments to monitor the side-chain resonances of lysines and arginines in (15)N, (13)C-labeled protein during titrations with a fully sulfated heparin tetrasaccharide under physiological conditions. Under identical conditions and using (15)N-labeled protein, we then cross-linked tetrasaccharide to CFH approximately 7 and confirmed the 1:1 stoichiometry by FT-ICR-MS. We subsequently characterized this covalent protein-GAG conjugate by NMR and further MS techniques. MALDI-TOF MS identified protein fragments obtained via trypsin digestion or chemical fragmentation, yielding information concerning the site of GAG attachment. Combining MS and NMR data allowed us to identify the side chain of K405 as the point of attachment of the cross-linked heparin oligosaccharide to CFH approximately 7. On the basis of the analysis of NMR and MS data of the noncovalent and cross-linked CFH approximately 7-tetrasaccharide complexes, we conclude that the K446 side chain is not essential for binding the tetrasaccharide, despite the large chemical shift perturbations of its backbone amide (15)N and (1)H resonances during titrations. We show that R444 provides the most important charge-charge interaction within a C-terminal heparin-binding subsite of CFH approximately 7 whereas side chains of R404, K405, and K388 are the predominant contributors to an N-terminal binding subsite located in the immediate vicinity of residue 402, which is implicated in age-related macular degeneration (AMD).

Glycome profiling using modern glycomics technology: technical aspects and applications

Glycomics research has become indispensable in many research fields such as immunity, signal transduction and development. Moreover, changes in the glycosylation of proteins and lipids have been reported in several diseases including cancer. The analysis of a complex post-translational modification such as glycosylation depends on the availability or development of appropriate analytical technologies. The research goal determines the sensitivity, resolution and throughput requirements and guides the choice of a particular technology. This review highlights the evolution of glycan profiling tools in the past 5 years. We focus on capillary electrophoresis, liquid chromatography, mass spectrometry and lectin microarrays.

Electrospray ionization mass spectrometric analysis of newly synthesized alpha,beta-unsaturated gamma-lactones fused to sugars

Knowledge of the fragmentation mechanisms of lactones and their behaviour under electrospray ionization (ESI) conditions can be extended to larger and more complex natural products that contain an alpha,beta-unsaturated gamma-lactone moiety in their structure. Moreover, little is known about the gas-phase behaviour of alpha,beta-unsaturated gamma-lactones linked or fused to sugars. Therefore, five alpha,beta-unsaturated gamma-lactones (butenolides) fused to a pyranose ring, recently synthesized compounds with potential relevance regarding their biological properties, were investigated using ESI-MS and ESI-MS/MS in both positive and negative ion modes. Their fragmentation mechanisms and product ion structures were compared. It was observed that two isomers could be unambiguously distinguished in the negative ion mode by the fragmentation pathways of their deprotonated molecules as well as in the positive ion mode by the fragmentation pathways of either the protonated or the sodiated molecule. Fragmentation mechanisms are proposed taking into account the MS/MS data and semi-empirical calculations using the PM6 Hamiltonean. The semi-empirical calculations were also very useful in determining the most probable protonation and cationization sites.

Glycomics profiling of heparan sulfate structure and activity

The heparan sulfate (HS) family of glycosaminoglycans are highly complex and structurally diverse polysaccharides with information encoded within the chains that imparts the ability to bind selectively to a wide range of proteins-the "HS interactome"-and to regulate their biological activities. However, there are two key questions which need to be addressed; first, the extent of structural variation of expressed HS structures-the "heparanome"-in specific biological contexts and second, the degree of functional selectivity exerted by these structures in regulating biological processes. There is a clear need to develop more systematic and high throughput approaches in order to address these questions. Here, we describe a cohort of protocols for profiling different aspects of HS structure and activity, focusing particularly on disaccharide building blocks and larger oligosaccharide domains, the latter representing the functional units of HS chains. A range of other complementary methods in the literature are also discussed. Together these provide a new and more comprehensive toolkit to investigate HS structure and activity in a higher throughput manner in selected biological systems. The implementation of such a glycomics strategy will enable development of a systems biology view of HS structure-function relationships and help to resolve the significant puzzle of the extensive interactome of HS, which remains a key question in the glycobiology field. We anticipate that the next decade will see major advances in our understanding of the complex biology of HS.

UV-MALDI-TOF mass spectrometry analysis of heparin oligosaccharides obtained by nitrous acid controlled degradation and high performance anion exchange chromatography

Nitrous acid degradation of heparin followed by high-performance anion-exchange chromatography (HPAEC) separation and ultraviolet matrix assisted laser desorption/ionization time-of-flight (UV-MALDI-TOF) analysis led to the structural determination of six sulfated oligosaccharides. Three different matrices (alpha-cyano-4-hydroxycinnamic acid (CHCA), nor-harmane, and dihydroxybenzoic acid (DHB)) have been used, and the complementary results obtained allowed in most cases to assign the position of sulfate groups. Based on the different cleavages produced on the purified oligosaccharides in source during the MS analysis by the use of the different matrices, this approach provides a new tool for structural analysis.

Mass spectrometry in the analysis of N-linked and O-linked glycans

Mass spectrometry (MS) continues to play a vital role in defining the structures of N-glycans and O-glycans in glycoproteins via glycomic and glycoproteomic methodologies. The former seeks to define the total N-glycan and/or O-glycan repertoire in a biological sample whilst the latter is concerned with the analysis of glycopeptides. Recent technical developments have included improvements in tandem mass spectrometry (MS/MS and MS(n)) sequencing methodologies, more sensitive methods for analysing sulfated and polysialylated glycans and better procedures for defining the sites of O-glycosylation. New tools have been introduced to assist data handling and publicly accessible databases are being populated with glycomics data. Progress is exemplified by recent research in the fields of glycoimmunology, reproductive glycobiology, stem cells, bacterial glycosylation and non-mucin O-glycosylation.

Mass spectrometric study of N-glycans from serum of woodchucks with liver cancer

Woodchucks have been a preferred lab animal model of chronic hepatitis B viral infection. The model recapitulates the disease progression of HBV infection to hepatocellular carcinoma (HCC) and has documented similarities in protein glycosylation with human HCC. This study examined N-glycans in serum of animals with(out) HCC. Oligosaccharides were released enzymatically using PNGaseF from total serum or from serum partially fractionated by extraction. Two different extraction procedures - reversed-phase high-performance liquid chromatography (RP-HPLC) and solid-phase extraction (SPE) on a cation-exchange/reversed-phase STRATA-XC cartridge - were used with the purpose of confirming glycosylation profiles. Oligosaccharides were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) after derivatization with phenylhydrazine and/or permethylation. Characteristic fragment ions produced under MS/MS conditions allowed discrimination between isomeric structures of oligosaccharides, including those sialylated with two types of acidic residues. The complementary methods allowed structural characterization of oligosaccharides from various N-glycan classes. Furthermore, to validate results, glycosylation profiles of woodchuck sera were compared to glycans obtained from mouse serum on the same conditions. In summary, we have identified 40 N-glycan structures in the serum of woodchucks and some types of oligosaccharide structures appeared to increase in HCC samples following protease digest. The study provides improved tools for the characterization of N-glycans from total serum in the progression of liver disease.

Analysis of oligosaccharides derived from heparin by ion-pair reversed-phase chromatography/mass spectrometry

Current chromatographic and mass spectrometric techniques have limitations for analyzing heparin and heparin oligomers due to their high polarity, structural diversity, and sulfate lability. A rapid method for the analysis of heparin oligosaccharides was developed using ion-pair reversed-phase ultraperformance liquid chromatography coupled with electrospray quadruple time-of-flight mass spectrometry (IPRP-UPLC ESI Q-TOF MS). The method utilizes an optimized buffer system containing a linear pentylamine and a unique additive, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), to achieve highly efficient separation together with enhanced mass response of heparin oligosaccharides. Analyses of a heparin oligosaccharide test mixture, dp6 through dp22, reveal that the chromatographic conditions enable baseline resolution of isomeric heparin oligosaccharides (dp6) and produce intact molecular ions with no sulfate losses during mass spectrometric analysis. In addition, the described conditions are amenable to the detection of heparin oligosaccharides in positive ion mode, yield stronger positive ion signals for corresponding oligosaccharides compared to the negative ion mode, and allow identification of structural isomers by an MS/MS approach. Because sensitive detection of oligosaccharides is also achieved with ultraviolet (UV) detection, the method utilizes a dual detection scheme (UV and MS in series) along with IPRP UPLC to simultaneously obtain quantification (UV) and characterization (MS) data for heparin oligosaccharides. The broad potential of this new method is further demonstrated for the analysis of a low-molecular-weight heparin (LMWH) preparation from porcine heparin. This approach will be of particular utility for profiling the molecular entities of heparin materials, as well as for structural variability comparison for samples from various sources.

Ionic liquids in analytical chemistry

The role of ionic liquids (ILs) in analytical chemistry is increasing substantially every year. A decade ago there were but a handful of papers in this area of research that were considered curiosities at best. Today, those publications are recognized as seminal articles that gave rise to one of the most rapidly expanding areas of research in chemical analysis. In this review, we briefly highlight early work involving ILs and discuss the most recent advances in separations, mass spectrometry, spectroscopy, and electroanalytical chemistry. Many of the most important advances in these fields depend on the development of new, often unique ILs and multifunctional ILs. A better understanding of the chemical and physical properties of ILs is also essential.

Matrix-assisted laser desorption/ionization mass spectrometric analysis of polysulfated-derived oligosaccharides using pyrenemethylguanidine

A better understanding of the biological roles of carbohydrates requires the use of tools able to provide efficient and rapid structural information. Unfortunately, highly acidic oligomers-such as polysulfated oligosaccharides-are very challenging to characterize because of their high polarity, structural diversity, and sulfate lability. These features pose special problems for matrix-assisted laser desorption/ionization mass spectrometric (MALDI-MS) analysis because polysulfated carbohydrates exhibit poor ionization efficiency and usually do not produce any signal. The present report demonstrates how MALDI-MS can be used to derive structural and compositional information from pure and mixed fractions of polysulfated oligosaccharides. Indeed, pyrenemethylguanidine (pmg, a derivatizing agent and ionization efficiency enhancer) was used for the analysis of di- to decasaccharides, carrying from two to nine sulfate groups. The method is applied to various highly sulfated chondroitin and carrageenan oligosaccharides as well as to the analysis of mixtures of compounds. In the mass spectra, the observation of a unique pmg-complexed ladder of peaks in both ionization modes allows an easy and rapid determination of both the number of sulfate groups carried by the analyte and its molecular weight. Moreover, we have developed a software tool for the rapid and automatic structural elucidation of carrageenans based on the mass spectra obtained.

Advances in the separation, sensitive detection, and characterization of heparin and heparan sulfate

Elucidation of the relationship between the structure and biological function of the glycosaminoglycans (GAGs) heparin and heparan sulfate (HS) presents an important analytical challenge mainly due to the difficulty in determining their fine structure. Heparin and HS are responsible for mediation of a wide range of biological actions through specific binding to a variety of proteins including those involved in blood coagulation, cell proliferation, differentiation and adhesion, and host-pathogen interactions. Therefore, there is a growing interest in characterizing the microstructure of heparin and HS and in elucidating the molecular level details of their interaction with peptides and proteins. This review discusses recent developments in the analytical methods used for sensitive separation, detection, and structural characterization of heparin and HS. A brief discussion of the analysis of contaminants in pharmaceutical heparin is also presented.

Solid-phase synthesis of alpha-glucosamine sulfoforms with fragmentation analysis by tandem mass spectrometry

Sulfated epitopes of alpha-glucosamine (GlcN sulfoforms) were prepared by solid-phase synthesis as models of internal glucosamines within heparan sulfate. An orthogonally protected 2'-hydroxyethyl GlcN derivative was immobilized on a trityl resin support and subjected to regioselective deprotection and sulfonation conditions, which were optimized with the aid of on-resin infrared or Raman analysis. The sulfoforms were cleaved from the resin under mild Lewis acid conditions without affecting the O- or N-sulfate groups and purified by reversed-phase high-performance liquid chromatography (HPLC). The alpha-GlcN sulfoforms and their 4- O-benzyl ethers were examined by electrospray ionization tandem mass spectrometry (ESI-MS/MS), with product ion spectra produced by collision-induced dissociation (CID). ESI-MS/MS revealed significant differences in parent ion stabilities and fragmentation rates as a function of sulfate position. Ion fragmentation by CID resulted in characteristic mass losses with strong correlation to the positions of both free hydroxyl groups and sulfate ions. Most of these fragmentation patterns are consonant with elimination pathways, and suggest possible strategies for elucidating the structures of glucosamine-derived sulfoforms with identical m/ z ratios. In particular, fragmentation analysis can easily distinguish GlcN sulfoforms bearing the relatively rare 3- O-sulfate from isomers with the more common 6- O-sulfate.

Generation and characterization of a series of monoclonal antibodies that specifically recognize [HexA(+/-2S)-GlcNAc]n epitopes in heparan sulfate

Five monoclonal antibodies AS17, 22, 25, 38 and 48, a single monoclonal antibody ACH55, and three monoclonal antibodies NAH33, 43, 46, that recognize acharan sulfate (IdoA2S-GlcNAc)n, acharan (IdoA-GlcNAc)n and N-acetyl-heparosan (GlcA-GlcNAc)n, respectively, were generated by immunization of mice with keyhole limpet hemocyanin-conjugated polysaccharides. Specificity tests were performed using a panel of biotinylated GAGs that included chemically modified heparins. Each antibody bound avidly to the immunized polysaccharide, but did not bind to chondroitin sulfates, keratan sulfate, chondroitin nor hyaluronic acid. AS antibodies did not bind to heparan sulfate or heparin, but bound to 6-O-desulfated, N-desulfated and re-N-acetylated heparin to varying degrees. ACH55 bound to tri-desulfated and re-N-acetylated heparin but hardly bound to other modified heparins. NAH antibodies did not bind to heparin and modified heparins but bound to heparan sulfate to varying degrees. NAH43 and NAH46 also bound to partially N-de-acetylated N-acetyl-heparosan. Immunohistochemical analysis in rat cerebella was performed with the antibodies. While NAH46 stained endothelia, where heparan sulfate is typically present, neither ACH55 nor AS25 stained endothelia. On the contrary ACH55 and AS25 stained the molecular layer of the rat cerebella. Furthermore, ACH55 specifically stained Purkinje cells. These results suggest that there is unordinary expression of IdoA2S-GlcNAc and IdoA-GlcNAc in specific parts of the nervous system.