Competing fragmentation processes in tandem mass spectra of heparin-like glycosaminoglycans

A 3D-Printed Offline Nano-ESI Source for Bruker MS Instruments

Nanoelectrospray ionization (nano-ESI) is a highly efficient and a widely used technique for the ionization of minute amounts of analyte. Offline nano-ESI sources are convenient for the direct infusion of complex mixtures that suffer from high matrix content and are crucial for the native mass spectrometric analysis of proteins. For Bruker instruments, no such source is readily available. Here we close this gap and present a 3D-printable nano-ESI source for Bruker instruments, which can be assembled by anyone with access to 3D printers. The source can be fitted to any Bruker mass spectrometer with an ionBooster ESI source and only requires minor, reversible changes to the original Bruker hardware. The general utility was demonstrated by recording high-resolution MS spectra of small molecules, intact proteins, as well as complex biological samples in negative and positive ion mode on two different Bruker instruments.

Glycosaminoglycan-directed cobalt complexes

The biological activity of the 6+ Co containing Werner's Complex has been described and mechanistic considerations suggest that the highly anionic glycosaminoglycans (heparan sulfate, HS, GAGs) are implicated in this activity [Paiva et al. 2021]. To examine in detail the molecular basis of Werner's Complex biological properties we have examined a selection of simple mononuclear Co3+ compounds for their interactions with HS and Fondaparinux (FPX). FPX is a highly sulfated synthetic pentasaccharide used as a model HS substrate [Mangrum et al. 2014, Peterson et al. 2017]. The Co complexes were chosen to be formally substitution-inert and/or have the potential for covalent binding to the biomolecule. Using both indirect competitive inhibition assays and direct mass spectrometric assays, formally substitution-inert complexes bound to FPX with protection from multiple sulfate loss in the gas phase through metalloshielding. Covalent binding of Co-Cl complexes as in [CoCl(NH3)5]2+ and cis-[CoCl2(en)2]+ was confirmed by mass spectrometry. Interestingly, the former complex was shown to be an effective inhibitor of bacterial heparinase enzyme activity and to inhibit heparanase-dependent cellular invasion through the extracellular matrix (ECM). Pursuing the theme of metalloglycomics, we have observed the hitherto unappreciated biological activity of the simple [CoCl(NH3)5]2+ compound, a staple of most inorganic chemistry lab curricula.

State-of-the-art glycosaminoglycan characterization

Glycosaminoglycans (GAGs) are heterogeneous acidic polysaccharides involved in a range of biological functions. They have a significant influence on the regulation of cellular processes and the development of various diseases and infections. To fully understand the functional roles that GAGs play in mammalian systems, including disease processes, it is essential to understand their structural features. Despite having a linear structure and a repetitive disaccharide backbone, their structural analysis is challenging and requires elaborate preparative and analytical techniques. In particular, the extent to which GAGs are sulfated, as well as variation in sulfate position across the entire oligosaccharide or on individual monosaccharides, represents a major obstacle. Here, we summarize the current state-of-the-art methodologies used for GAG sample preparation and analysis, discussing in detail liquid chromatograpy and mass spectrometry-based approaches, including advanced ion activation methods, ion mobility separations and infrared action spectroscopy of mass-selected species.

Biological activated carbon process for biotransformation of azo dye Carmoisine by Klebsiella spp

The feasibility of employing the biological activated carbon (BAC) process to debilitate azo dye Carmoisine by Klebsiella spp. was investigated. Plate assay revealed the capability of Klebsiella spp. for removal of Carmoisine via degradation. Kinetic parameters were measured for Carmoisine debilitation by Klebsiella spp. using the suspended anaerobic process. Two types of granular and rod-shaped activated carbon were used to form the biological beds in order to study the Carmoisine debilitation in batch processes. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) were used to indicate the colonization and biofilm formation of bacteria grown on activated carbon particles (ACPs). Thin-layer chromatography (TLC), liquid chromatography-mass spectrometry (LC-MS), high-pressure liquid chromatography (HPLC) and biosorption studies demonstrated biotransformation of Carmoisine into its constituent aromatic amines during the Carmoisine debilitation in suspended anaerobic and BAC processes. The porosity of activated carbons, inoculation size and age of biological beds were the important factors affecting the viability of bacterial cells grown on ACPs and, consequently, the rate and efficiency of the Carmoisine debilitation process determined through spectrophotometry. The reusability of biological beds was demonstrated by conducting sequential batch experiments. In conclusion, the BAC process proved to be an efficient method for anaerobic dye degradation.

Mass Spectrometric Methods for the Analysis of Heparin and Heparan Sulfate

Glycosaminoglycans like heparin and heparan sulfate exhibit a high degree of structural microheterogeneity. This structural heterogeneity results from the biosynthetic process that produces these linear polysaccharides in cells and tissues. Heparin and heparan sulfate play critical roles in normal physiology and pathophysiology, hence it is important to understand how their structural features may influence overall activity. Therefore, high-resolution techniques like mass spectrometry represent a key part of the suite of methodologies available to probe the fine structural details of heparin and heparan sulfate. This chapter outlines the application of techniques like LC-MS and LC-MS/MS to study the composition of these polysaccharides, and techniques like GPC-MS that allow for an analysis of oligosaccharide fragments in these mixtures.

Conformational Modulation of Iduronic Acid-Containing Sulfated Glycosaminoglycans by a Polynuclear Platinum Compound and Implications for Development of Antimetastatic Platinum Drugs

1 H NMR spectroscopic studies on the 1:1 adduct of the pentasaccharide Fondaparinux (FPX) and the substitution-inert polynuclear platinum complex TriplatinNC show significant modulation of geometry around the glycosidic linkages of the FPX constituent monosaccharides. FPX is a valid model for the highly sulfated cell signalling molecule heparan sulfate (HS). The conformational ratio of the 1 C4 :2 S0 forms of the FPX residue IdoA(2S) is altered from ca. 35:65 (free FPX) to ca. 75:25 in the adduct; the first demonstration of a small molecule affecting conformational changes on a HS oligosaccharide. Functional consequences of such binding are suggested to be inhibition of HS cleavage in MDA-MB-231 triple-negative breast cancer (TNBC) cells. We further describe inhibition of metastasis by TriplatinNC in the TNBC 4T1 syngeneic tumour model. Our work provides insight into a novel approach for design of platinum drugs (and coordination compounds in general) with intrinsic anti-metastatic potential.

Mammal Hyaluronidase Activity on Chondroitin Sulfate and Dermatan Sulfate: Mass Spectrometry Analysis of Oligosaccharide Products

Mammalian hyaluronidases are endo-N-acetyl-D-hexosaminidases involved in the catabolism of hyaluronic acid (HA) but their role in the catabolism of chondroitin sulfate (CS) is also examined. HA and CS are glycosaminoglycans (GAGs) implicated in several physiological and pathological processes, and understanding their metabolism is of significant importance. Data have been previously reported on the degradation of CS under the action of hyaluronidase, yet a detailed structural investigation of CS depolymerization products remains necessary to improve our knowledge of the CS depolymerizyng activity of hyaluronidase. For that purpose, the fine structural characterization of CS oligosaccharides formed upon the enzymatic depolymerization of various CS sub-types by hyaluronidase has been carried out by high resolution Orbitrap mass spectrometry and extreme UV (XUV) photodissociation tandem mass spectrometry. The exact mass measurements show the formation of wide size range of even oligosaccharides upon digestion of CS-A and CS-C comprising hexa- and octa-saccharides among the main digestion products, as well as formation of small quantities of odd-numbered oligosaccharides, while no hyaluronidase activity was detected on CS-B. In addition, slight differences have been observed in the distribution of oligosaccharides in the digestion mixture of CS-A and CS-C, the contribution of longer oligosaccharides being significantly higher for CS-C. The sequence of CS oligosaccharide products determined XUV photodissociation experiments verifies the selective β(1 → 4) glycosidic bond cleavage catalyzed by mammal hyaluronidase. The ability of the mammal hyaluronidase to produce hexa- and higher oligosaccharides supports its role in the catabolism of CS anchored to membrane proteoglycans and in extra-cellular matrix.

Identification of Protein Recognition Elements within Heparin Chains Using Enzymatic Foot-Printing in Solution and Online SEC/MS

Understanding molecular mechanisms governing interactions of glycosaminoglycans (such as heparin) with proteins remains challenging due to their enormous structural heterogeneity. Commonly accepted approaches seek to reduce the structural complexity by searching for "binding epitopes" within the limited subsets of short heparin oligomers produced either enzymatically or synthetically. A top-down approach presented in this work seeks to preserve the chemical diversity displayed by heparin by allowing the longer and structurally diverse chains to interact with the client protein. Enzymatic lysis of the protein-bound heparin chains followed by the product analysis using size exclusion chromatography with online mass spectrometry detection (SEC/MS) reveals the oligomers that are protected from lysis due to their tight association with the protein, and enables their characterization (both the oligomer length, and the number of incorporated sulfate and acetyl groups). When applied to a paradigmatic heparin/antithrombin system, the new method generates a series of oligomers with surprisingly distinct sulfation levels. The extent of sulfation of the minimal-length binder (hexamer) is relatively modest yet persistent, consistent with the notion of six sulfate groups being both essential and sufficient for antithrombin binding. However, the masses of longer surviving chains indicate complete sulfation of disaccharides beyond the hexasaccharide core. Molecular dynamics simulations confirm the existence of favorable electrostatic interactions between the high charge-density saccharide residues flanking the "canonical" antithrombin-binding hexasaccharide and the positive patch on the surface of the overall negatively charged protein. Furthermore, electrostatics may rescue the heparin/protein interaction in the absence of the canonical binding element.

Evaluation of top-down mass spectrometry and ion-mobility spectroscopy as a means of mapping protein-binding motifs within heparin chains

Identifying structural elements within heparin (as well as other glycosaminoglycan) chains that enable their interaction with a specific client protein remains a challenging task due to the high degree of both intra- and inter-chain heterogeneity exhibited by this polysaccharide. The new experimental approach explored in this work is based on the assumption that the heparin chain segments bound to the protein surface will be less prone to collision-induced dissociation (CID) in the gas phase compared to the chain regions that are not involved in binding. Facile removal of the unbound chain segments from the protein/heparin complex should allow the length and the number of sulfate groups within the protein-binding segment of the heparin chain to be determined by measuring the mass of the truncated heparin chain that remains bound to the protein. Conformational integrity of the heparin-binding interface on the protein surface in the course of CID is ensured by monitoring the evolution of collisional cross-section (CCS) of the protein/heparin complexes as a function of collisional energy. A dramatic increase in CCS signals the occurrence of large-scale conformational changes within the protein and identifies the energy threshold, beyond which relevant information on the protein-binding segments of heparin chains is unlikely to be obtained. Testing this approach using a 1 : 1 complex formed by a recombinant form of an acidic fibroblast growth factor (FGF-1) and a synthetic pentasaccharide GlcNS,6S-GlcA-GlcNS,3S,6S-IdoA2S-GlcNS,6S-Me as a model system indicated that a tri-saccharide fragment is the minimal-length FGF-binding segment. Extension of this approach to a decameric heparin chain (dp10) allowed meaningful binding data to be obtained for a 1 : 1 protein/dp10 complex, while the ions representing the higher stoichiometry complex (2 : 1) underwent dissociation via asymmetric charge partitioning without generating truncated heparin chains that remain bound to the protein.

Microbial degradation of azo dye carmoisine in aqueous medium using Saccharomyces cerevisiae ATCC 9763

Carmoisine is an azo dye widely used in many industries, and therefore frequently occurs in the effluent of many factories. To our knowledge, biological degradation of carmoisine has received little attention. The present study investigates the capability of Saccharomyces cerevisiae ATCC 9763 for degradation of carmoisine. Spectrophotometry data indicates that carmoisine (50 mg/l) was eliminated from the aqueous medium after approximately 7 h of incubation with Saccharomyces under anaerobic shaking conditions. Thin layer chromatography (TLC) revealed the removal of carmoisine as well as the appearance of aromatic amines in samples collected from the decolourized medium by S. cerevisiae and this was subsequently confirmed by Fourier transform infrared (FTIR) spectroscopy. Liquid chromatography mass spectrometry (LC/MS) was carried out on fractions from consecutive column chromatography and two-dimensional (2D) chromatography. LC/MS indicated degradation of carmoisine into its constituent aromatic amines. In addition, investigating the effect of environmental conditions on the decolourization process indicated that yeast extract could positively affect decolourization rates; shaking significantly accelerated decolourization and shortened the time required for complete biodecolourization from ≃ 8 days to ≃ 7 h; and Saccharomyces was able to consume sucrose as a carbon source and remove the carmoisine despite the presence of sunset yellow, which remained unaffected.

Structural Characterization of Glycosaminoglycan Carbohydrates Using Ultraviolet Photodissociation

Structural characterization of sulfated glycosaminoglycans (GAGs) by mass spectrometry has long been a formidable analytical challenge owing to their high structural variability and the propensity for sulfate decomposition upon activation with low-energy ion activation methods. While derivatization and complexation workflows have aimed to generate informative spectra using low-energy ion activation methods, alternative ion activation methods present the opportunity to obtain informative spectra from native GAG structures. Both electron- and photon-based activation methods, including electron detachment dissociation (EDD), negative electron transfer dissociation (NETD), and extreme ultraviolet photon activation, have been explored previously to overcome the limitations associated with low-energy activation methods for GAGs and other sulfated oligosaccharides. Further, implementation of such methods on high-resolution mass spectrometers has aided the interpretation of the complex spectra generated. Here, we explore ultraviolet photodissociation (UVPD) implemented on an Orbitrap mass spectrometer as another option for structural characterization of GAGs. UVPD spectra for both dermatan and heparan sulfate structures display extensive fragmentation including both glycosidic and cross-ring cleavages with the extent of sulfate retention comparable to that observed by EDD and NETD. In addition, the relatively short activation time of UVPD makes it promising for higher throughput analysis of GAGs in complex mixtures.

Glycosaminoglycan Analysis by Cryogenic Messenger-Tagging IR Spectroscopy Combined with IMS-MS

We combine ion mobility spectrometry with cryogenic, messenger-tagging, infrared spectroscopy and mass spectrometry to identify different isomeric disaccharides of chondroitin sulfate (CS) and heparan sulfate (HS), which are representatives of two major subclasses of glycosaminoglycans. Our analysis shows that while CS and HS disaccharide isomers have similar drift times, they can be uniquely distinguished by their vibrational spectrum between ∼3200 and 3700 cm-1 due to their different OH hydrogen-bonding patterns. We suggest that this combination of techniques is well suited to identify and characterize glycan isomers directly, which presents tremendous challenges for existing methods.

Charge Transfer Dissociation of Complex Oligosaccharides: Comparison with Collision-Induced Dissociation and Extreme Ultraviolet Dissociative Photoionization

The structural characterization of oligosaccharides still challenges the field of analytical chemistry. Tandem mass spectrometry offers many advantages toward this aim, although the generic fragmentation method (low-energy collision-induced dissociation) shows clear limitations and is often insufficient to retrieve some essential structural information on these molecules. In this work, we present the first application of helium charge transfer dissociation (He-CTD) to characterize the structure of complex oligosaccharides. We compare this method with low-energy collision-induced dissociation and extreme-ultraviolet dissociative photoionization (XUV-DPI), which was shown previously to ensure the successful characterization of complex glycans. Similarly to what could be obtained by XUV-DPI, He-CTD provides a complete description of the investigated structures by producing many informative cross-ring fragments and no ambiguous fragmentation. Unlike XUV-DPI, which is performed at a synchrotron source, He-CTD has the undeniable advantage of being implementable in a conventional benchtop ion trap in a conventional laboratory setting. Graphical Abstract ᅟ.

Online coupling of high-resolution chromatography with extreme UV photon activation tandem mass spectrometry: Application to the structural investigation of complex glycans by dissociative photoionization

The activation of ions by extreme-energy photons (XUV) produced by a synchrotron radiation beamline is a powerful method for characterizing complex glycans using tandem mass spectrometry (MS). As previously described, this activation method leads to rich fragmentation spectra with many structurally valuable cross-ring cleavages while maintaining labile modifications on the glycan structures. However, until now, the tandem MS event was too long to be compatible with liquid chromatography elution times. In this work, the duty cycle of the activation and detection of fragments was shortened, and the background signal on the spectra was drastically reduced. Both improvements allowed, for the first time, the successful coupling of a UHPLC system to XUV-activated tandem MS. The approach was used to characterize a complex mixture of oligo-porphyrans, which are a class of highly sulfated oligosaccharides, in a fully automated way. Due to an enhanced dynamic range and an increased sensitivity, some hypothetical structures of low abundance have been unequivocally confirmed in this study and others have been revised. Some previously undescribed species of oligo-porphyrans that exhibit lateral branching have been fully resolved. This work contributes to the scarce knowledge of the structure of porphyrans in red algae and pushes the current capacities of XUV-activation tandem MS by demonstrating the possibility of a direct coupling with UHPLC. This study will considerably broaden the applicability and practicality of this method in many fields of analytical biology.

Effects of calcium complexation on heparin-like disaccharides. A combined theoretical, tandem mass spectrometry and ultraviolet experiment

RATIONALE

In order to shed light on the influence of the Ca(2+) metal cation on the structure of heparin-like (Hp) disaccharides, we have explored the gas-phase structures of both [Hp, -2H](2-) and [Ca(Hp), -3H](-) ions by coupling experimental and theoretical methods.

METHODS

The goal of this work was to (i) provide new evidence of the metal influence on the Hp structure, which can have important biological consequences, and (ii) to study the usefulness of metal complexation for the analytical distinction of Hp isomers. Collision-induced dissociation (CID) and ultraviolet photodissociation (UVPD) fragments, as well as optical spectra recorded in the gas phase for both [Hp, -2H](2-) and [Ca(Hp), -3H](-) complexes were compared for I-H, II-S and III-S isomers of Hp.

RESULTS

In the case of CID fragmentation, a change in the fragmentation pattern was observed upon calcium complexation, with respect to deprotonated Hp.

CONCLUSIONS

Remarkably, when optical spectra are compared in the UV range, the metal effect on the carboxylic group absorption can be detected by an unambiguous blue-shift (~20 nm).

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.

High-field asymmetric-waveform ion mobility spectrometry and electron detachment dissociation of isobaric mixtures of glycosaminoglycans

High-field asymmetric waveform ion mobility spectrometry (FAIMS) is shown to be capable of resolving isomeric and isobaric glycosaminoglycan negative ions and to have great utility for the analysis of this class of molecules when combined with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and tandem mass spectrometry. Electron detachment dissociation (EDD) and other ion activation methods for tandem mass spectrometry can be used to determine the sites of labile sulfate modifications and for assigning the stereochemistry of hexuronic acid residues of glycosaminoglycans (GAGs). However, mixtures with overlapping mass-to-charge values present a challenge, as their precursor species cannot be resolved by a mass analyzer prior to ion activation. FAIMS is shown to resolve two types of mass-to-charge overlaps. A mixture of chondroitin sulfate A (CSA) oligomers with 4-10 saccharides units produces ions of a single mass-to-charge by electrospray ionization, as the charge state increases in direct proportion to the degree of polymerization for these sulfated carbohydrates. FAIMS is shown to resolve the overlapping charge. A more challenging type of mass-to-charge overlap occurs for mixtures of diastereomers. FAIMS is shown to separate two sets of epimeric GAG tetramers. For the epimer pairs, the complexity of the separation is reduced when the reducing end is alkylated, suggesting that anomers are also resolved by FAIMS. The resolved components were activated by EDD and the fragment ions were analyzed by FTICR-MS. The resulting tandem mass spectra were able to distinguish the two epimers from each other.

Electron capture dissociation of divalent metal-adducted sulfated N-glycans released from bovine thyroid stimulating hormone

Sulfated N-glycans released from bovine thyroid stimulating hormone (bTSH) were ionized with the divalent metal cations Ca(2+), Mg(2+), and Co by electrospray ionization (ESI). These metal-adducted species were subjected to infrared multiphoton dissociation (IRMPD) and electron capture dissociation (ECD) and the corresponding fragmentation patterns were compared. IRMPD generated extensive glycosidic and cross-ring cleavages, but most product ions suffered from sulfonate loss. Internal fragments were also observed, which complicated the spectra. ECD provided complementary structural information compared with IRMPD, and all observed product ions retained the sulfonate group, allowing sulfonate localization. To our knowledge, this work represents the first application of ECD towards metal-adducted sulfated N-glycans released from a glycoprotein. Due to the ability of IRMPD and ECD to provide complementary structural information, the combination of the two strategies is a promising and valuable tool for glycan structural characterization. The influence of different metal ions was also examined. Calcium adducts appeared to be the most promising species because of high sensitivity and ability to provide extensive structural information.

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.

Tandem mass spectrometry of heparan sulfate negative ions: sulfate loss patterns and chemical modification methods for improvement of product ion profiles

Heparan sulfate (HS) is a polysaccharide modified with sulfation, acetylation, and epimerization that enable its binding with protein ligands and regulation of important biological processes. Tandem mass spectrometry has been employed to sequence linear biomolecules e.g., proteins and peptides. However, its application in structural characterization of HS is limited due to the neutral loss of sulfate (SO(3)) during collisional induced dissociation (CID). In this report, we studied the dissociation patterns of HS disaccharides and demonstrate that the N-sulfate (N-S) bond is especially facile during CID. We identified factors that influence the propensities of such losses from precursor ions and proposed a Free Proton Index (FPI) to help select ions that are able to produce meaningful backbone dissociations. We then investigated the thermodynamics and kinetics of SO(3) loss from sulfates that are protonated, deprotonated, and metal-adducted using density functional theory computations. The calculations showed that sulfate loss from a protonated site was much more facile than that from a deprotonated or metal-adducted site. Further, the loss of SO(3) from N-sulfate was energetically favored by 3-8 kcal/mol in transition states relative to O-sulfates, making it more prone to this process by a substantial factor. In order to reduce the FPI, representing the number of labile sulfates in HS native chains and oligosaccharides, we developed a series of chemical modifications to selectively replace the N-sulfates of the glucosamine with deuterated acetyl group. These modifications effectively reduced the sulfate density on the HS oligosaccharides and generated considerably more backbone dissociation using on-line LC/tandem MS.

Complete mass spectral characterization of a synthetic ultralow-molecular-weight heparin using collision-induced dissociation

Glycosaminoglycans (GAGs) are a class of biologically important molecules, and their structural analysis is the target of considerable research effort. Advances in tandem mass spectrometry (MS/MS) have recently enabled the structural characterization of several classes of GAGs; however, the highly sulfated GAGs, such as heparins, have remained a relatively intractable class due their tendency to lose SO(3) during MS/MS, producing few sequence-informative fragment ions. The present work demonstrates for the first time the complete structural characterization of the highly sulfated heparin-based drug Arixtra. This was achieved by Na(+)/H(+) exchange to create a more ionized species that was stable against SO(3) loss, and that produced complete sets of both glycosidic and cross-ring fragment ions. MS/MS enables the complete structural determination of Arixtra, including the stereochemistry of its uronic acid residues, and suggests an approach for solving the structure of more complex, highly sulfated heparin-based drugs.

Effective use of mass spectrometry for glycan and glycopeptide structural analysis

Most proteins are glycosylated. Mass spectrometry methods are used for mapping glycoprotein glycosylation and detailed glycan structural determination. This technology enables precise characterization of recombinant glycoproteins in the pharmaceutical industry and academic biomedicine.

Differential Characterization and Classification of Tissue Specific Glycosaminoglycans by Tandem Mass Spectrometry and Statistical Methods

The biological functions of glycoconjugate glycans arise in the context of structural heterogeneity resulting from non-template driven biosynthetic reactions. Such heterogeneity is particularly apparent for the glycosaminoglycan (GAG) classes, of which heparan sulfate (HS) is of particular interest for its properties in binding to many classes of growth factors and growth factor receptors. The structures of HS chains vary according to spatial and temporal factors in biological systems as a mechanism where by the functions of the relatively limited number of associated proteoglycan core proteins is elaborated. Thus, there is a strong driver for the development of methods to discover functionally relevant structures in HS preparations for different sources. In the present work, a set of targeted tandem mass spectra were acquired in automated mode on HS oligosaccharides deriving from two different tissue sources. Statistical methods were used to determine the precursor and product ions, the abundances of which differentiate between the tissue sources. The results demonstrate considerable potential for using this approach to constrain the number of positional glycoform isomers present in different biological preparations toward the end of discovery of functionally relevant structures.

Improved liquid chromatography-MS/MS of heparan sulfate oligosaccharides via chip-based pulsed makeup flow

Microfluidic chip-based hydrophilic interaction chromatography (HILIC) is a useful separation system for liquid chromatography-mass spectrometry (LC-MS) in compositional profiling of heparan sulfate (HS) oligosaccharides; however, ions observed using HILIC LC-MS are low in charge. Tandem MS of HS oligosaccharide ions with low charge results in undesirable losses of SO(3) from precursor ions during collision induced dissociation. One solution is to add metal cations to stabilize sulfate groups. Another is to add a nonvolatile, polar compound such as sulfolane, a molecule known to supercharge proteins, to produce a similar effect for oligosaccharides. We demonstrate use of a novel pulsed makeup flow (MUF) HPLC-chip. The chip enables controlled application of additives during specified chromatographic time windows and thus minimizes the extent to which nonvolatile additives build up in the ion source. The pulsed MUF system was applied to LC-MS/MS of HS oligosaccharides. Metal cations and sulfolane were tested as additives. The most promising results were obtained for sulfolane, for which supercharging of the oligosaccharide ions increased their signal strengths relative to controls. Tandem MS of these supercharged precursor ions showed decreased abundances of product ions from sulfate losses yet more abundant product ions from backbone cleavages.

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.

Photoinduced dissociation of heparin-derived oligosaccharides controlled by charge location

The development of strategies based on mass spectrometry to help for deep structural analysis of acidic oligosaccharides remains topical. We thus examined the dissociation behavior of deprotonated ions of heparin-derived di- to tetra-saccharides under UV irradiation at 220 nm. Depending on the ionization state of the carboxylic groups, an oxidized species issued from electron photodetachment was observed in complement to photoinduced fragmentation of precursor ions. The influence of the charge location in the oligosaccharide dianions on the balance between photodissociation and electron photodetachment is examined and a way to direct the relaxation pathways, (i.e., dissociation versus electron detachment), is proposed using sodium adducts. The oxidized species was subjected to activated-electron photodetachment (activated-EPD) leading to complementary informative fragment ions to those issued from photodissociation. Directed photoinduced dissociation at 220 nm and activated-EPD should complement the more conventional CAD and IRMPD activation modes for deeper structural analysis of acidic oligosaccharides-derived anions.

Wavelength-tunable ultraviolet photodissociation (UVPD) of heparin-derived disaccharides in a linear ion trap

A set of three heparin-derived disaccharide deprotonated ions was isolated in a linear ion trap and subjected to UV laser irradiation in the 220-290 nm wavelength range. The dissociation yields of the deprotonated molecular ions were recorded as a function of laser wavelength. They revealed maximum absorption at 220 nm for the nonsulfated disaccharide, but centered at 240 nm for the sulfated species. The comparison of the fragmentation patterns between ultraviolet photodissociation (UVPD) at 240 nm and CID modes showed roughly the same distribution of fragment ions resulting from glycosidic bond cleavages. Interestingly, UVPD favored additional cross ring cleavages of A and X type ion series enabling easier sulfate group location. It also reduced small neutral losses (H(2)O).

On-line separations combined with MS for analysis of glycosaminoglycans

The glycosaminoglycan (GAG) family of polysaccharides includes the unsulfated hyaluronan and the sulfated heparin, heparan sulfate, keratan sulfate, and chondroitin/dermatan sulfate. GAGs are biosynthesized by a series of enzymes, the activities of which are controlled by complex factors. Animal cells alter their responses to different growth conditions by changing the structures of GAGs expressed on their cell surfaces and in extracellular matrices. Because this variation is a means whereby the functions of the limited number of protein gene products in animal genomes is elaborated, the phenotypic and functional assessment of GAG structures expressed spatially and temporally is an important goal in glycomics. On-line mass spectrometric separations are essential for successful determination of expression patterns for the GAG compound classes due to their inherent complexity and heterogeneity. Options include size exclusion, anion exchange, reversed phase, reversed phase ion pairing, hydrophilic interaction, and graphitized carbon chromatographic modes and capillary electrophoresis. This review summarizes the application of these approaches to on-line MS analysis of the GAG classes.

Electron capture dissociation, electron detachment dissociation and infrared multiphoton dissociation of sucrose octasulfate

The structural analysis of sulfated carbohydrates such as glycosaminoglycans (GAGs) has been a long- standing challenge for the field of mass spectrometry. The dissociation of sulfated carbohydrates by collisionally- activated dissociation (CAD) or infrared multiphoton dissociation (IRMPD), which activate ions via vibrational excitation, typically result in few cleavages and abundant SO(3) loss for highly sulfated GAGs such as heparin and heparan sulfate, hampering efforts to determine sites of modification. The recent application of electron activation techniques, specifically electron capture dissociation (ECD) and electron detachment dissociation (EDD), provides a marked improvement for the mass spectrometry characterization of GAGs. In this work, we compare ECD, EDD and IRMPD for the dissociation of the highly sulfated carbohydrate sucrose octasulfate (SOS). Both positive and negative multiply-charged ions are investigated. ECD, EDD and IRMPD of SOS produce abundant and reproducible fragmentation. The product ions produced by ECD are quite different than those produced by IRMPD of SOS positive ions, suggesting different dissociation mechanisms as a result of electronic versus vibrational excitation. The product ions produced by EDD and IRMPD of SOS negative ions also differ from each other. Evidence for SO(3) rearrangement exists in the negative ion IRMPD data, complicating the assignment of product ions.

Electron-induced dissociation of glycosaminoglycan tetrasaccharides

Electron detachment dissociation (EDD) Fourier transform mass spectrometry has recently been shown to be a powerful tool for examining the structural features of sulfated glycosaminoglycans (GAGs). The characteristics of GAG fragmentation by EDD include abundant cross-ring fragmentation primarily on hexuronic acid residues, cleavage of all glycosidic bonds, and the formation of even- and odd-electron product ions. GAG dissociation by EDD has been proposed to occur through the formation of an excited species that can undergo direct decomposition or ejects an electron and then undergoes dissociation. In this work, we perform electron-induced dissociation (EID) on singly charged GAGs to identify products that form via direct decomposition by eliminating the pathway of electron detachment. EID of GAG tetrasaccharides produces cleavage of all glycosidic bonds and abundant cross-ring fragmentation primarily on hexuronic acid residues, producing fragmentation similar to EDD of the same molecules, but distinctly different from the products of infrared multiphoton dissociation or collisionally activated decomposition. These results suggest that observed abundant fragmentation of hexuronic acid residues occurs as a result of their increased lability when they undergo electronic excitation. EID fragmentation of GAG tetrasaccharides results in both even- and odd-electron products. EID of heparan sulfate tetrasaccharide epimers produces identical fragmentation, in contrast to EDD, in which the epimers can be distinguished by their fragment ions. These data suggest that for EDD, electron detachment plays a significant role in distinguishing glucuronic acid from iduronic acid.

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

Glycomics is a developing field that provides structural information on complex populations of glycans isolated from tissues, cells and organs. Strategies employing matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) are central to glycomic analysis. Current MALDI-based glycomic strategies are capable of efficiently analyzing glycoprotein and glycosphingolipid glycomes but little attention has been paid to devising glycomic methodologies suited to the analysis of glycosaminoglycan (GAG) polysaccharides which pose special problems for MALDI analysis because of their high level of sulfation and large size. In this paper, we describe MALDI strategies that have been optimized for the analysis of highly sulfated GAG-derived oligosaccharides. A crystalline matrix norharmane, as well as an ionic liquid 1-methylimidazolium alpha-cyano-4-hydroxycinnamate (ImCHCA), have been used for the analysis of heparin di-, tetra-, hexa- and decasaccharides carrying from 2 to 13 sulfate groups. Information about the maximum number of sulfate groups is obtained using the ionic liquid whereas MALDI-TOF/TOF MS/MS experiments using norharmane allowed the determination of the nature of the glycosidic backbone, and more precise information about the presence and the position in the sequence of N-acetylated residues.

Characterization of sulfated oligosaccharides in mucopolysaccharidosis type IIIA by electrospray ionization mass spectrometry

Heparan sulfate is a linear glycosaminoglycan with considerable structural diversity that binds a myriad of growth factors and proteins that play pivotal roles in a variety of biological processes. We have investigated the structural complexity of partially degraded fragments of heparan sulfate in mucopolysaccharidosis type IIIA in which there is a defect in heparan sulfate catabolism. Mono- to hexadecasaccharides were isolated from the urine of a mucopolysaccharidosis IIIA patient and shown to have non-reducing end glucosamine N-sulfate residues, reflecting the catabolic deficiency in heparan N-sulfatase (sulfamidase) activity. The use of nitrous acid digestion (pH 1.5) combined with separation by reverse-phase high-performance liquid chromatography and analysis by electrospray ionization-mass spectrometry identified multiple forms of these oligosaccharides with some N-acetylated glucosamine residues and one to three sulfates per disaccharide. Furthermore, we demonstrated that each oligosaccharide existed in multiple sulfated forms. Many structural isomers were present, suggesting a complex mixture of oligosaccharides present in the urine as a consequence of a defect in heparan sulfate degradation.

Distinguishing glucuronic from iduronic acid in glycosaminoglycan tetrasaccharides by using electron detachment dissociation

Distinguishing the epimers iduronic acid (IdoA) and glucuronic acid (GlcA) has been a long-standing challenge for the mass spectrometry analysis of glycosaminoglycan (GAG) oligosaccharides. In this work, electron detachment dissociation (EDD) and Fourier transform ion cyclotron resonance mass spectrometry is shown to provide mass spectral features that can distinguish GlcA from IdoA in heparan sulfate (HS) tetrasaccharides. EDD of HS tetrasaccharide dianions produces a radical species that fragments to produce information-rich glycosidic and cross-ring product ions which can be used to determine the sites of acetylation/sulfation. More significantly, EDD of HS tetrasaccharide epimers produces diagnostic product ions that can be used to distinguish IdoA from GlcA. These diagnostic product ions are not observed in the tandem mass spectra obtained by collisionally activated dissociation or infrared multiphoton dissociation of the tetrasaccharides, suggesting a radical-initiated mechanism for their formation. Differences in the observed product ions obtained by EDD of the tetrasaccharide epimers can be rationalized by simple alpha-cleavage of an oxy radical located at C2 or C3 or a radical at C3 or C4. These radicals are proposed to arise from a hydrogen rearrangement in which a hydrogen atom is transferred from the C2 or C3 hydroxyl group or C3 or C4 to a carboxy radical at C5. This hydrogen transfer depends on the proximity of the carboxy radical to the hydroxyl group on C2 or C3 or the hydrogen on C3 or C4 and is thus influenced by C5 stereochemistry. These epimer-sensitive fragmentations should allow this approach to be applied to the structural analysis of a wide variety of GAG oligosaccharides.

Electron detachment dissociation of glycosaminoglycan tetrasaccharides

The first application of electron detachment dissociation (EDD) to carbohydrates is presented. The structural characterization of glycosaminoglycan (GAG) oligosaccharides by mass spectrometry is a longstanding problem because of the lability of these acidic, polysulfated carbohydrates. Doubly-charged negative ions of four GAG tetrasaccharides are examined by EDD, collisionally activated dissociation (CAD), and infrared multiphoton dissociation (IRMPD). EDD is found to produce information-rich mass spectra with both cross ring and glycosidic cleavage product ions. In contrast, most of the product ions produced by CAD and IRMPD result from glycosidic cleavage. EDD shows great potential as a tool for locating the sites of sulfation and other modifications in glycosaminoglycan oligosaccharides.

GLYCOMICS APPROACH TO STRUCTURE-FUNCTION RELATIONSHIPS OF GLYCOSAMINOGLYCANS

Extracellular modulation of phenotype is an emerging paradigm in this current postgenomics age of molecular and cell biology. Glycosaminoglycans (GAGs) are primary components of the cell surface and the cell-extracellular matrix (ECM) interface. Advances in the technology to analyze GAGs and in whole-organism genetics have led to a dramatic increase in the known important biological role of these complex polysaccharides. Owing to their ubiquitous distribution at the cell-ECM interface, GAGs interact with numerous proteins and modulate their activity, thus impinging on fundamental biological processes such as cell growth and development. Many recent reviews have captured important aspects of GAG structure and biosynthesis, GAG-protein interactions, and GAG biology. GAG research is currently at a stage where there is a need for an integrated systems or glycomics approach, which involves an integration of all of the above concepts to define their structure-function relationships. Focusing on heparin/heparan (HSGAGs) and chondroitin/dermatan sulfate (CSGAGs), this review highlights the important aspects of GAGs and summarizes these aspects in the context of taking a glycomics approach that integrates the different technologies to define structure-function relationships of GAGs.

Ion-pairing reversed-phased chromatography/mass spectrometry of heparin

Heparin and heparin-derived components are widely applied anticoagulant drugs used for amongst other applications medical treatment of deep vein thrombosis and pulmonary embolism. Depolymerisation of native heparin results in complex mixtures of sulfated linear oligosaccharides that are usually not well characterised. In order to further characterise such mixtures, two on-line ion-pairing reverse-phased chromatography electrospray ionisation (ESI) mass spectrometry methods have been developed. One of the systems allows the determination of more than 200 components in a medium molecular weight heparin preparation, whereas the other system can be used to separate isomeric heparin oligosaccharides after previous separation according to size. This latter system allows semi-preparative isolation of isomeric heparin oligosaccharides. The experimental setup includes on-line cation exchange in order to prevent the ion-pairing reagent from entering the mass spectrometer.

Probing the intrinsic features and environmental stabilization of multiply charged anions

Multiply charged anions (MCAs) represent exotic, highly energetic species in the gas-phase due to their propensity to undergo unimolecular decay via electron loss or ionic fragmentation. There is considerable fundamental interest in these systems since they display novel potential energy surfaces that are characterized by Coulomb barriers. Over recent years, considerable progress has been made in understanding the factors that affect the stability, decay pathways and reactivity of gas-phase MCAs, mainly as a result of the application of electrospray ionization as a generic technique for transferring solution-phase MCAs into the gas-phase for detailed characterization. We review contemporary work in this field, focusing on the factors that control the intrinsic stability of MCAs, both as isolated gas-phase ions, and on their complexation with solvent molecules and counter-ions. While studies of MCAs are primarily of fundamental interest, several classes of important biological ions are commonly observed as MCAs in the gas-phase (e.g. oligonucleotides, sugars). Recent results for biologically relevant ions are emphasised, since a fundamental understanding of the properties of gas-phase MCAs will be highly valuable for developing further analytical methods to study these important systems.

Tandem mass spectrometry for the characterisation of sulphated-phosphorylated analogues of the carbohydrate-protein linkage region of proteoglycans

Carbohydrate-protein linkage region of proteoglycans is a key oligosaccharide structure because their sulphated and/or phosphorylated analogues control the biosynthesis of glucosaminoglycans or galactosaminoglycans. Therefore, synthesised sulphated and/or phosphorylated analogues were characterised by tandem mass spectrometry in the negative-ion mode. Results demonstrated that the product ion profile was characterised by glycosidic and cross-ring cleavages depending on the position and the type of the charged group (sulphate, phosphate or carboxylate). When the above compounds were sulphated and phosphorylated, the ion found at m/z 79 was the only one that demonstrated a phosphate group on the structure. The data also suggested that when a sodium cation was present in a sulphated and phosphorylated structure, the phosphate group in most cases was neutralised by the sodium cation, and therefore cleaved off the molecule, while the sulphate group was carrying the negative charge.

Heparin Sequencing Using Enzymatic Digestion and ESI-MSn with HOST: A Heparin/HS Oligosaccharide Sequencing Tool

Mass spectrometry, and specifically sequential stages of mass spectrometry (MSn), is an established tool for the analysis of carbohydrates, proteins, and more recently glycosaminoglycans. As this trend continues, the development of algorithms for the rapid and automatic interpretation of mass spectra to identify glycan structure is also expected to grow as an active field of research. The methodology described herein utilizes a combination of enzymatic digestion, ESI-MS, and MSn for the sequencing of small heparin oligosaccharides. The heparin oligosaccharide sequencing tool (HOST) is a basic software application that was developed to aid in the integration and analysis of the data generated from these experiments, facilitating the process involved in arriving at sequence information. The sequences of several heparin oligosaccharides were determined using this method to illustrate proof of principle. Tandem MS is a very rapid and efficient tool for oligosaccharide analysis when limited amounts of material are available. Having a means, such as HOST, for automating the interpretation of the MSn data generated from glycosaminoglycans, provides a practical methodology for the future analysis of heparin/HS oligosaccharides of unknown structure.

Sheathless reverse-polarity capillary electrophoresis-electrospray-mass spectrometry for analysis of underivatized glycoconjugates

We report on the development of a novel methodology to extend the limits of capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) general applicability. A sheathless on-line CE-ESI-MS setup was optimized on standard monosaccharide mixture to operate in reverse polarity and negative ion mode for MS detection without pressure to assist the sample migration, coating of the capillaries, and/or sample derivatization. This approach was further applied for screening of a complex glycopeptide mixture obtained from the urine of a patient diagnosed with N-acetylhexosaminidase deficiency, known as Schindler's disease. The potential of this methodology in terms of high sensitivity, separation efficiency, resolution, and reproducibility is demonstrated. In combination with the high quality of MS data, a new, significantly improved insight into the sample heterogeneity is possible.

Quantification of isomers from a mixture of twelve heparin and heparan sulfate disaccharides using tandem mass spectrometry

Heparin/heparan sulfate-like glycosaminoglycans (HSGAGs) have been implicated in clinically relevant processes such as hemostasis, infection, development, and cancer progression, through their interactions with proteins. Electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MSn) were combined to identify and quantify 12 HSGAG disaccharides that can be generated by enzymatic depolymerization with heparin lyases. This technique includes free amine-containing disaccharides that had previously been observed in MSn but not quantified. Our methods use diagnostic product ions from MSn spectra of up to three isomeric disaccharides at once, and up to three sequential stages of MSn in tandem, for the quantitative analysis of the relative percentage of each of these isomers. The isomer quantification was validated using mock mixtures and showed acceptable accuracy and precision. These methods may be applied to the quantification of other isomers by MSn. While each of the 12 disaccharides alone had a linear response to an internal standard in the MS1 spectra, the individual response factors did not remain constant when the concentrations of the other 11 disaccharides in the mixtures fluctuated, due to competition for electrospray ionization. The absolute concentration of one fluctuating isomer was determined out of a constant mixture of the other disaccharides. The rapid, accurate, and sensitive quantification of all isomeric disaccharides may contribute to the eventual sequencing of longer saccharides by MSn, enabling the elucidation of the structure-function relationships of HSGAGs.