Characterization of glycosaminoglycans by 15N NMR spectroscopy and in vivo isotopic labeling

Ion Mobility Mass Spectrometry-Based Disaccharide Analysis of Glycosaminoglycans

Glycosaminoglycans (GAGs) are linear and acidic polysaccharides. They are ubiquitous molecules, which are involved in a wide range of biological processes. Despite being structurally simple at first glance, with a repeating backbone of alternating hexuronic acid and hexosamine dimers, GAGs display a highly complex structure, which predominantly results from their heterogeneous sulfation patterns. The commonly applied method for compositional analysis of all GAGs is "disaccharide analysis." In this process, GAGs are enzymatically depolymerized into disaccharides, derivatized with a fluorescent label, and then analysed through liquid chromatography. The limiting factor in the high throughput analysis of GAG disaccharides is the time-consuming liquid chromatography. To address this limitation, we here utilized trapped ion mobility-mass spectrometry (TIM-MS) for the separation of isomeric GAG disaccharides, which reduces the measurement time from hours to a few minutes. A full set of disaccharides comprises twelve structures, with eight possessing isomers. Most disaccharides cannot be differentiated by TIM-MS in underivatized form. Therefore, we developed chemical modifications to reduce sample complexity and enhance differentiability. Quantification is performed using stable isotope labelled standards, which are easily available due to the nature of the performed modifications.

NMR characterization of uniformly 13C- and/or 15N-labeled, unsulfated chondroitins with high molecular weights

Solution nuclear magnetic resonance (NMR) analysis of polysaccharides can provide valuable information not only on their primary structures but also on their conformation, dynamics, and interactions under physiological conditions. One of the main problems is that non-anomeric 1H signals typically overlap, and this often hinders detailed NMR analysis. Isotope enrichment, such as with 13C and 15N, will add a new dimension to the NMR spectra of polysaccharides, and spectral analysis can be performed with enhanced sensitivity using isolated peaks. For this purpose, here we have prepared uniformly 13C- and/or 15N-labeled chondroitin polysaccharides -4)-β-D-glucuronopyranosyl-(1-3)-2-acetamido-2-deoxy-β-D-galactopyranosyl-(1- with molecular weights in the range from 310 to 460 k by bacterial fermentation. The enrichment ratios for 13C and 15N were 98.9 and 99.8%, respectively, based on the mass spectrometric analysis of the constituent chondroitin disaccharides. 1H and 13C NMR signals were assigned mainly based on HSQC and 13C-detection experiments including INADEQUATE, HETCOR, and HETCOR-TOCSY. The carbonyl carbon signal of the N-acetyl-β-D-galactosamine residue was unambiguously distinguished from the C6 carbon of the β-D-glucuronic acid residue by the observation of 13C peak splitting due to 1JCN coupling in 13C- and 15N-labeled chondroitin. The T2* and T1 were measured and indicate that both rigid and mobile sites are present in the long sequence of chondroitin. The conformation, dynamics, and interactions of chondroitin and its derivatives will be further analyzed based on the results obtained in this study.

14N to 15N Isotopic Exchange of Nitrogen Heteroaromatics through Skeletal Editing

The selective modification of nitrogen heteroaromatics enables the development of new chemical tools and accelerates drug discovery. While methods that focus on expanding or contracting the skeletal structures of heteroaromatics are emerging, methods for the direct exchange of single core atoms remain limited. Here, we present a method for 14N → 15N isotopic exchange for several aromatic nitrogen heterocycles. This nitrogen isotope transmutation occurs through activation of the heteroaromatic substrate by triflylation of a nitrogen atom, followed by a ring-opening/ring-closure sequence mediated by 15N-aspartate to effect the isotopic exchange of the nitrogen atom. Key to the success of this transformation is the formation of an isolable 15N-succinyl intermediate, which undergoes elimination to give the isotopically labeled heterocycle. These transformations occur under mild conditions in high chemical and isotopic yields.

Production of isotopically enriched high molecular weight hyaluronic acid and characterization by solid-state NMR

Hyaluronic acid (HA) is a naturally occurring polysaccharide that is abundant in the extracellular matrix (ECM) of all vertebrate cells. HA-based hydrogels have attracted great interest for biomedical applications due to their high viscoelasticity and biocompatibility. In both ECM and hydrogel applications, high molecular weight (HMW)-HA can absorb a large amount of water to yield matrices with a high level of structural integrity. To understand the molecular underpinnings of structural and functional properties of HA-containing hydrogels, few techniques are available. Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for such studies, e.g. ¹³C NMR measurements can reveal the structural and dynamical features of (HMW) HA. However, a major obstacle to ¹³C NMR is the low natural abundance of ¹³C, necessitating the generation of HMW-HA that is enriched with ¹³C isotopes. Here we present a convenient method to obtain ¹³C- and ¹⁵N-enriched HMW-HA in good yield from Streptococcus equi subsp. zooepidemicus. The labeled HMW-HA has been characterized by solution and magic angle spinning (MAS) solid-state NMR spectroscopy, as well as other methods. These results will open new ways to study the structure and dynamics of HMW-HA-based hydrogels, and interactions of HMW-HA with proteins and other ECM components, using advanced NMR techniques.

Metabolic labeling of hyaluronan: Biosynthesis and quantitative analysis of 13C,15N-enriched hyaluronan by NMR and MS-based methods

Hyaluronan (HA), a member of the GAG family of glycans, has many diverse biological functions that vary a lot depending on the length of the HA chain and its concentration. A better understanding of the structure of different-sized HA at the atomic level is therefore crucial to decipher these biological functions. NMR is a method of choice for conformational studies of biomolecules, but there are limitations due to the low natural abundance of the NMR active nuclei ¹³C and ¹⁵N. We describe here the metabolic labeling of HA using the bacterium Streptococcus equi subsp. Zooepidemicus and the subsequent analysis by NMR and mass spectrometry. The level of ¹³C and ¹⁵N isotope enrichment at each position was determined quantitatively by NMR spectroscopy and was further confirmed by high-resolution mass spectrometry analysis. This study provides a valid methodological approach that can be applied to the quantitative assessment of isotopically labeled glycans and will help improve detection capabilities and facilitate future structure-function relationship analysis of complex glycans.

Determination of Amide Cis/Trans Isomers in N-Acetyl-d-glucosamine: Tailored NMR Analysis of the N-Acetyl Group Conformation

N‐Acetyl‐d‐glucosamine (GlcNAc) is one of the most common amino sugars in nature, but the conformation of its N‐acetyl group has drawn little attention. We report herein the first identification of NH protons of the amide cis forms of α‐ and β‐GlcNAc by NMR spectroscopy. Relative quantification and thermodynamic analysis of both cis and trans forms was carried out in aqueous solution. The NH protons were further utilized by adapting protein NMR experiments to measure eight J‐couplings within the N‐acetyl group, of which six are sensitive to the H2‐NH conformation and two are sensitive to the amide conformation. For amide cis and trans forms, the orientation between H2 and NH was determined as anti conformation, while a small percentage of syn conformation was predicted for the amide trans form of β‐GlcNAc. This approach holds great promise for the detailed conformational analysis of GlcNAc in larger biomolecules, such as glycoproteins and polysaccharides.

Fluorescence sensing of heparin and heparin-like glycosaminoglycans by stabilizing intramolecular charge transfer state of dansyl acid-labeled AG73 peptides with glutathione-capped gold nanoclusters

Sensors that can specifically and accurately detect glycosaminoglycans are rare. Here, a dual-mode platform for fluorescence intensity and lifetime sensing of plasma heparin and fluorescence imaging of heparan sulfate proteoglycan-expressed cancer cells was developed by stabilizing the intramolecular charge transfer (ICT) state of dansyl acid-labeling AG73 (DA-AG73) peptide with glutathione-capped gold nanoclusters (GSH-AuNCs). DA-AG73 peptides, including an electron-donor dimethylamino group and an electron-withdrawing sulfonamide moiety in the labeled DA molecules, emitted weak fluorescence due to the formation of the twisted ICT excited state. The complexation of heparin with DA-AG73 peptides followed by interacting with the GSH-AuNCs could restrict the rotation of the dimethylamino groups of the labeled DA molecules, triggering the transition from their twisted ICT state to ICT excited state. As a result, the fluorescence intensity and lifetime of the labeled DA molecules in DA-AG73 peptides were gradually enhanced with increasing the heparin concentration. The proposed platform provided excellent selectivity toward heparin and heparan sulfate and exhibited two linear calibration curves for quantifying 20-800 nM and 20-1000 nM heparin in the fluorescence intensity and lifetime modes, respectively. The proposed platform was practically applied for the fluorescence intensity and lifetime determination of plasma heparin and for the selective imaging of heparan sulfate proteoglycan-expressed cells.

Peracylation Coupled with Tandem Mass Spectrometry for Structural Sequencing of Sulfated Glycosaminoglycan Mixtures without Depolymerization

The structures of glycosaminoglycans (GAGs), especially the patterns of modification, are crucial to modulate interactions with various protein targets. It is very challenging to determine the fine structures using liquid chromatography-mass spectrometry (LC-MS) due in large part to the gas-phase sulfate losses upon collisional activation. Previously, our group reported a method for fine structure analysis that required permethylation of the GAG oligosaccharide. However, uncontrolled depolymerization during the permethylation process due to esterification of uronic acid lowers the reliability of the method to resolve structures of GAGs, especially for larger oligosaccharides. Here, we describe a simplified derivatization method using propionylation and desulfation. The oligosaccharides have all hydroxyl and amine groups protected with propionyl groups and then have sulfate groups removed to generate unprotected hydroxyl and amine groups at all sites that were previously sulfated. This derivatized oligosaccharide generates informative fragments during collision-induced dissociation that resolve the original sulfation patterns. This method is demonstrated to enable accurate determination of sulfation patterns of even the highly sulfated pentasaccharide fondaparinux by MS² and MS³. Using a mixture of dp6 from porcine heparin, we demonstrate that this method allows for structural characterization of complex mixtures, including clear chromatographic separation and sequencing of structural isomers, all at high yields without evidence of depolymerization. This represents a marked improvement in the reliability to structurally characterize GAG oligosaccharides over permethylation-based derivatization schemes.

Advances in the preparation and synthesis of heparin and related products

Heparin is a naturally occurring glycosaminoglycan from livestock, principally porcine intestine, and is clinically used as an anticoagulant drug. A limitation to heparin production is that it depends on a single animal species and potential problems have been associated with animal-derived heparin. The contamination crisis in 2008 led to a search for new animal sources and the investigation of non-animal sources of heparin. Over the past 5 years, new animal sources, chemical, and chemoenzymatic methods have been introduced to prepare heparin-based drugs. In this review, we describe advances in the preparation and synthesis of heparin and related products.

Biocompatibility and structural characterization of glycosaminoglycans isolated from heads of silver-banded whiting (Sillago argentifasciata Martin & Montalban 1935)

Glycosaminoglycans (GAGs) were extracted from heads of silver-banded whiting (SBW) fish and subjected to preliminary biocompatibility testing per ISO 10993: intracutaneous irritation, maximization sensitization, systemic toxicity, and cytotoxicity. When the GAG solution was injected intradermally, the observed irritation was within ISO limits and comparable to a marketed control. There was no evidence of sensitization, systemic toxicity, or cellular toxicity on the test organisms treated with the GAG mixture from SBW fish heads. Fractionation by size-exclusion chromatography has shown three distinct fractions: F1 as low molecular weight hyaluronic acid (190 kDa), F2 (82 kDa) and F3 (64 kDa), both as chondroitin sulfates. Structural characterization by 1D and 2D nuclear magnetic resonance spectroscopy and disaccharide analysis have shown sulfation ratios at positions C4:C6 of the F2 and F3 fractions respectively as 70:20% and 50:30%, and the balance of non-sulfated and 4,6-di-sulfated units. The preliminary results here suggest that GAG-based extracts from SBW fish heads are suitable alternative products to be used in soft tissue augmentation, although further long-term biocompatibility studies are still required.

Galactosaminoglycans: Medical Applications and Drawbacks

Galactosaminoglycans (GalAGs) are sulfated glycans composed of alternating N-acetylgalactosamine and uronic acid units. Uronic acid epimerization, sulfation patterns and fucosylation are modifications observed on these molecules. GalAGs have been extensively studied and exploited because of their multiple biomedical functions. Chondroitin sulfates (CSs), the main representative family of GalAGs, have been used in alternative therapy of joint pain/inflammation and osteoarthritis. The relatively novel fucosylated chondroitin sulfate (FCS), commonly found in sea cucumbers, has been screened in multiple systems in addition to its widely studied anticoagulant action. Biomedical properties of GalAGs are directly dependent on the sugar composition, presence or lack of fucose branches, as well as sulfation patterns. Although research interest in GalAGs has increased considerably over the three last decades, perhaps motivated by the parallel progress of glycomics, serious questions concerning the effectiveness and potential side effects of GalAGs have recently been raised. Doubts have centered particularly on the beneficial functions of CS-based therapeutic supplements and the potential harmful effects of FCS as similarly observed for oversulfated chondroitin sulfate, as a contaminant of heparin. Unexpected components were also detected in CS-based pharmaceutical preparations. This review therefore aims to offer a discussion on (1) the current and potential therapeutic applications of GalAGs, including those of unique features extracted from marine sources, and (2) the potential drawbacks of this class of molecules when applied to medicine.

Heavy Heparin: A Stable Isotope-Enriched, Chemoenzymatically-Synthesized, Poly-Component Drug

Heparin is a highly sulfated, complex polysaccharide and widely used anticoagulant pharmaceutical. In this work, we chemoenzymatically synthesized perdeuteroheparin from biosynthetically enriched heparosan precursor obtained from microbial culture in deuterated medium. Chemical de-N-acetylation, chemical N-sulfation, enzymatic epimerization, and enzymatic sulfation with recombinant heparin biosynthetic enzymes afforded perdeuteroheparin comparable to pharmaceutical heparin. A series of applications for heavy heparin and its heavy biosynthetic intermediates are demonstrated, including generation of stable isotope labeled disaccharide standards, development of a non-radioactive NMR assay for glucuronosyl-C5-epimerase, and background-free quantification of in vivo half-life following administration to rabbits. We anticipate that this approach can be extended to produce other isotope-enriched glycosaminoglycans.

1H NMR characterization of chitin tetrasaccharide in binary H2O:DMSO solution: Evidence for anomeric end-effect propagation

Chitin oligosaccharides, composed of homogeneous β(1 → 4)-linked N-acetyl-D-glucosamine (GlcNAc) sequences, is a well-known elicitor of plant immune defense, and also occur as structural elements of chitosan and nodulation (Nod) factor. Detailed microstructure characterization is required for understanding the function mode of these bioactive molecules. Herein, experimental conditions for detection and elucidation of the ¹H NMR resonances of amide groups in chitin oligosaccharides are presented. The binary mixture of 70% H₂O: 30% DMSO‑d₆ was found to be the optimal solvent for amide proton measurements in homogeneous GlcNAc sequences, facilitating differentiation of the local chemical microenvironments of all four amide groups of the chitin tetrasaccharide. Experimental evidence that anomeric end-effect triggers amide proton resonance differentiation at the adjacent residue has potential to provide important insights into the solution structure of chitin and other amino sugars containing GlcNAc sequences.

Glycosaminoglycan-Protein Interactions by Nuclear Magnetic Resonance (NMR) Spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy is one of the most utilized and informative analytical techniques for investigating glycosaminoglycan (GAG)-protein complexes. NMR methods that are commonly applied to GAG-protein systems include chemical shift perturbation, saturation transfer difference, and transferred nuclear Overhauser effect. Although these NMR methods have revealed valuable insight into the protein-GAG complexes, elucidating high-resolution structural and dynamic information of these often transient interactions remains challenging. In addition, preparation of structurally homogeneous and isotopically enriched GAG ligands for structural investigations continues to be laborious. As a result, understanding of the structure-activity relationship of GAGs is still primitive. To overcome these deficiencies, several innovative NMR techniques have been developed lately. Here, we review some of the commonly used techniques along with more novel methods such as waterLOGSY and experiments to examine structure and dynamic of lysine and arginine side chains to identify GAG-binding sites. We will also present the latest technology that is used to produce isotopically enriched as well as paramagnetically tagged GAG ligands. Recent results that were obtained from solid-state NMR of amyloid’s interaction with GAG are also presented together with a brief discussion on computer assisted modeling of GAG-protein complexes using sparse experimental data.

A microbial-enzymatic strategy for producing chondroitin sulfate glycosaminoglycans

Chondroitin sulfate has been widely used in both medical and clinical applications. Commercial chondroitin sulfate has been mainly acquired from animal tissue extraction. Here we report a new two-step biological strategy for producing chondroitin sulfate A and chondroitin sulfate C. First, the chondroitin biosynthesis pathway in a recombinant Bacillus subtilis strain using sucrose as carbon source was systematically optimized and the titer of chondroitin was significantly enhanced to 7.15 g/L. Then, specific sulfation transformation systems were successfully constructed and optimized by combining the purified aryl sulfotransferase IV (ASST IV), chondroitin 4-sulfotransferase (C4ST) and chondroitin 6-sulfotransferase (C6ST). Chondroitin sulfate A and C were enzymatically transformed from chondroitin at conversion rates of 98% and 96%, respectively. The present biological strategy has great potential to be scaled up for biosynthesis of chondroitin sulfate A and C from cheap carbon sources.

One-pot analysis of sulfated glycosaminoglycans

Routine isolation, estimation, and characterization of glycosaminoglycans (GAGs) is quite challenging. This is compounded by the fact that the analysis is technique-intensive and more often there will be a limitation on the quantity of GAGs available for various structural, functional and biological studies. In such a scenario, the sample which can be made available for estimation and elucidation of disaccharide composition and species composition as well remains a challenge. In the present study, we have determined the feasibility where isolated sulfated GAGs (sGAG) that is estimated by metachromasia is recovered for further analysis. sGAG-DMMB complex formed after estimation of sGAG by DMMB dye-binding assay was decomplexed and sGAGs were recovered. Recovered sGAGs were analysed by cellulose acetate membrane electrophoresis and taken up for disaccharide composition analysis by HPLC after fluorescent labelling. Good recovery of sGAGs after metachromasia was observed in all samples of varying levels of purity by this protocol. Further analysis using cellulose acetate membrane electrophoresis showed good separation between species of sGAGs namely chondroitin/dermatan sulfate and heparan sulfate, with comparatively lesser interference from hyaluronic acid, a non-sulfated GAG. Analysis of recovered sGAGs, specifically heparan sulfate by HPLC showed characteristic disaccharide composition akin to that of GAG obtained by the conventional protocol. Thus, in the present paper, we show that sGAG can be recovered in comparatively purer form after routine estimation and can be used for further analysis thus saving up on the precious sample.

Simple and Efficient Purification of Recombinant Proteins Using the Heparin-Binding Affinity Tag

Heparin, a member of the glycosaminoglycan family, is known to interact with more than 400 different types of proteins. For the past few decades, significant progress has been made to understand the molecular details involved in heparin-protein interactions. Based on the structural knowledge available from the FGF1-heparin interaction studies, we have designed a novel heparin-binding peptide (HBP) affinity tag that can be used for the simple, efficient, and cost-effective purification of recombinant proteins of interest. HBP-tagged fusion proteins can be purified by heparin Sepharose affinity chromatography using a simple sodium chloride gradient to elute the bound fusion protein. In addition, owing to the high density of positive charges on the HBP tag, recombinant target proteins are preferably expressed in their soluble forms. The purification of HBP-fusion proteins can also be achieved in the presence of chemical denaturants, including urea. Additionally, polyclonal antibodies raised against the affinity tag can be used to detect HBP-fused target proteins with high sensitivity. © 2017 by John Wiley & Sons, Inc.

Single Stage Tandem Mass Spectrometry Assignment of the C-5 Uronic Acid Stereochemistry in Heparan Sulfate Tetrasaccharides using Electron Detachment Dissociation

The analysis of heparan sulfate (HS) glycosaminoglycans presents many challenges, due to the high degree of structural heterogeneity arising from their non-template biosynthesis. Complete structural elucidation of glycosaminoglycans necessitates the unambiguous assignments of sulfo modifications and the C-5 uronic acid stereochemistry. Efforts to develop tandem mass spectrometric-based methods for the structural analysis of glycosaminoglycans have focused on the assignment of sulfo positions. The present work focuses on the assignment of the C-5 stereochemistry of the uronic acid that lies closest to the reducing end. Prior work with electron-based tandem mass spectrometry methods, specifically electron detachment dissociation (EDD), have shown great promise in providing stereo-specific product ions, such as the B3´ -CO2, which has been found to distinguish glucuronic acid (GlcA) from iduronic acid (IdoA) in some HS tetrasaccharides. The previously observed diagnostic ions are generally not observed with 2-O-sulfo uronic acids or for more highly sulfated heparan sulfate tetrasaccharides. A recent study using electron detachment dissociation and principal component analysis revealed a series of ions that correlate with GlcA versus IdoA for a set of 2-O-sulfo HS tetrasaccharide standards. The present work comprehensively investigates the efficacy of these ions for assigning the C-5 stereochemistry of the reducing end uronic acid in 33 HS tetrasaccharides. A diagnostic ratio can be computed from the sum of the ions that correlate to GlcA to those that correlate to IdoA. Graphical Abstract ᅟ.

¹H and (15)N NMR Analyses on Heparin, Heparan Sulfates and Related Monosaccharides Concerning the Chemical Exchange Regime of the N-Sulfo-Glucosamine Sulfamate Proton

Heparin and heparan sulfate are structurally related glycosaminoglycans (GAGs). Both GAGs present, although in different concentrations, N-sulfo-glucosamine (GlcNS) as one of their various composing units. The conditional fast exchange property of the GlcNS sulfamate proton in these GAGs has been pointed as the main barrier to its signal detection via NMR experiments, especially ¹H-¹⁵N HSQC. Here, a series of NMR spectra is collected on heparin, heparan sulfate and related monosaccharides. The N-acetyl glucosamine-linked uronic acid types of these GAGs were properly assigned in the ¹H-¹⁵N HSQC spectra. Dynamic nuclear polarization (DNP) was employed in order to facilitate 1D spectral acquisition of the sulfamate ¹⁵N signal of free GlcNS. Analyses on the multiplet pattern of scalar couplings of GlcNS ¹⁵N has helped to understand the chemical properties of the sulfamate proton in solution. The singlet peak observed for GlcNS happens due to fast chemical exchange of the GlcNS sulfamate proton in solution. Analyses on kinetics of alpha-beta anomeric mutarotation via ¹H NMR spectra have been performed in GlcNS as well as other glucose-based monosaccharides. 1D ¹H and 2D ¹H-¹⁵N HSQC spectra recorded at low temperature for free GlcNS dissolved in a proton-rich solution showed signals from all exchangeable protons, including those belonging to the sulfamate group. This work suits well to the current grand celebration of one-century-anniversary of the discovery of heparin.

Oligosaccharides from the 3-linked 2-sulfated alpha-L-fucan and alpha-L-galactan show similar conformations but different dynamics

Here we have performed an nuclear magnetic resonance-based study on the ring and chain conformations as well as dynamics of oligosaccharides generated by acid hydrolysis on two structurally related glycans, a 3-linked 2-sulfated alpha-L-galactan and a 3-linked 2-sulfated alpha-L-fucan. Results derived from scalar couplings have confirmed the ¹C₄ chair configuration to both alpha-L-fucose and alpha-L-galactose, and a similar solution 3D structure for the oligosaccharide chains of both sulfated glycans as seen on the basis of NOE patterns. Measurements of spin-relaxation rates have suggested, however, a slight difference dynamical property to these glycans. The fucose-based oligosaccharides showed an enhanced dynamical property if compared to the galactose-based oligosaccharides of same anomericity, sugar configuration, glycosidic bond and sulfation type. This distinction solely on the dynamical aspect has been driven therefore by the different sugar composition of the two studied sulfated glycans.

De Novo Sequencing of Complex Mixtures of Heparan Sulfate Oligosaccharides

Here, we describe the first sequencing method of a complex mixture of heparan sulfate tetrasaccharides by LC-MS/MS. Heparin and heparan sulfate (HS) are linear polysaccharides that are modified in a complex manner by N- and O-sulfation, N-acetylation, and epimerization of the uronic acid. Heparin and HS are involved in various essential cellular communication processes. The structural analysis of these glycosaminoglycans is challenging due to the lability of their sulfate groups, the high heterogeneity of modifications, and the epimerization of the uronic acids. While advances in liquid chromatography (LC) and mass spectrometry (MS) have enabled compositional profiling of HS oligosaccharide mixtures, online separation and detailed structural analysis of isomeric and epimeric HS mixtures has not been achieved. Here, we report the development and evaluation of a chemical derivatization and tandem mass spectrometry method that can separate and identify isomeric and epimeric structures from complex mixtures. A series of well-defined synthetic HS tetrasaccharides varying in sulfation patterns and uronic acid epimerization were analyzed by chemical derivatization and LC-MS/MS. These synthetic compounds made it possible to establish relationships between HS structure, chromatographic behavior and MS/MS fragmentation characteristics. Using the analytical characteristics determined through the analysis of the synthetic HS tetrasaccharide standards, an HS tetrasacharide mixture derived from natural sources was successfully sequenced. This method represents the first sequencing of complex mixtures of HS oligosaccharides, an essential milestone in the analysis of structure-function relationships of these carbohydrates.

Impact of sulfation pattern on the conformation and dynamics of sulfated fucan oligosaccharides as revealed by NMR and MD

Sulfated fucans from sea urchin egg jelly express well-defined chemical structures that vary with species. This species specificity regulates the sperm acrosome reaction, a critical step to assure intra-specific fertilization. In addition, these polysaccharides are involved in other biological activities such as anticoagulation. Although sulfation patterns are relevant to the levels of response in both activities, conformation and dynamics of these glycans are also contributing factors. However, data about these features of sulfated fucans are very rare. To address this, we have employed nuclear magnetic resonance experiments combined with molecular dynamics on structurally defined oligosaccharides derived from two sulfated fucans. The results have indicated that the oligosaccharides are flexible in solution. Ring conformation of their composing units displays just the (1)C4 chair configuration. In a particular octasaccharide, composed of two tetrasaccharide sequences, inter-residual hydrogen bonds play a role to decrease dynamics in these repeating units. Conversely, the linking disaccharide [-3)-α-L-Fucp-2(OSO3(-))-(1-3)-α-L-Fucp-4(OCO3(-))-(1-] located right between the two tetrasaccharide units has amplified motions suggested to be promoted by electrostatic repulsion of sulfates on opposite sides of the central glycosidic bond. This conjunction of information about conformation and dynamics of sulfated fucan oligosaccharides provides new insights to explain how these glycans behave free in solution and influenced by sulfation patterns. It may also serve for future studies concerning structure-function relationship of sulfated fucans, especially those involving sea urchin fertilization and anticoagulation.

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.

Characterizing the microstructure of heparin and heparan sulfate using N-sulfoglucosamine 1H and 15N NMR chemical shift analysis

Heparin and heparan sulfate (HS) are members of a biologically important group of highly anionic linear polysaccharides called glycosaminoglycans (GAGs). Because of their structural complexity, the molecular-level characterization of heparin and HS continues to be a challenge. The work presented herein describes an emerging approach for the analysis of unfractionated and low molecular weight heparins, as well as porcine and human-derived HS. This approach utilizes the untapped potential of (15)N NMR to characterize these preparations through detection of the NH resonances of N-sulfo-glucosamine residues. The sulfamate group (1)H and (15)N chemical shifts of six GAG microenvironments were assigned based on the critical comparison of selectively modified heparin derivatives, NMR measurements for a library of heparin-derived oligosaccharide standards, and an in-depth NMR analysis of the low molecular weight heparin enoxaparin through systematic investigation of the chemical exchange properties of NH resonances and residue-specific assignments using the [(1)H,(15)N] HSQC-TOCSY experiment. The sulfamate microenvironments characterized in this study include GlcNS(6S)-UA(2S), ΔUA(2S)-GlcNS(6S), GlcNS(3S)(6S)-UA(2S), GlcNS-UA, GlcNS(6S)-red(α), and 1,6-anhydro GlcNS demonstrating the utility of [(1)H,(15)N] HSQC NMR spectra to provide a spectroscopic fingerprint reflecting the composition of intact GAGs and low molecular weight heparin preparations.

Chemokine oligomerization in cell signaling and migration

Chemokines are small proteins best known for their role in controlling the migration of diverse cells, particularly leukocytes. Upon binding to their G-protein-coupled receptors on the leukocytes, chemokines stimulate the signaling events that cause cytoskeletal rearrangements involved in cell movement, and migration of the cells along chemokine gradients. Depending on the cell type, chemokines also induce many other types of cellular responses including those related to defense mechanisms, cell proliferation, survival, and development. Historically, most research efforts have focused on the interaction of chemokines with their receptors, where monomeric forms of the ligands are the functionally relevant state. More recently, however, the importance of chemokine interactions with cell surface glycosaminoglycans has come to light, and in most cases appears to involve oligomeric chemokine structures. This review summarizes existing knowledge relating to the structure and function of chemokine oligomers, and emerging methodology for determining structures of complex chemokine assemblies in the future.

Residual keratan sulfate in chondroitin sulfate formulations for oral administration

Chondroitin sulfate is a biomedical glycosaminoglycan (GAG) mostly used as a dietary supplement. We undertook analysis on some formulations of chondroitin sulfates available for oral administration. The analysis was based on agarose-gel electrophoresis, strong anion-exchange chromatography, digestibility with specific GAG lyases, uronic acid content, NMR spectroscopy, and size-exclusion chromatography. Keratan sulfate was detected in batches from shark cartilage, averaging ∼16% of the total GAG. Keratan sulfate is an inert material, and hazardous effects due to its presence in these formulations are unlikely to occur. However, its unexpected high percentage compromises the desired amounts of the real ingredient specified on the label claims, and forewarns the pharmacopeias to update their monographs. The techniques they recommended, especially cellulose acetate electrophoresis, are inefficient in detecting keratan sulfate in chondroitin sulfate formulations. In addition, this finding also alerts the manufacturers for improved isolation procedures as well as the supervisory agencies for better audits. Analysis based on strong anion-exchange chromatography is shown to be more reliable than the methods presently suggested by standard pharmacopeias.

Fucanomics and galactanomics: marine distribution, medicinal impact, conceptions, and challenges

Glycomics turned out to be a very extensive project where its subdivision is consequently emerging. This is seen by the growing number of terminologies used to define subprojects concerning particular classes of bioactive carbohydrates. Sulfated fucans (SFs) and sulfated galactans (SGs) are relatively new classes of sulfated polysaccharides (SPs) that occur mostly in marine organisms, and exhibit a broad range of medicinal effects. Their structures are taxonomically dependent, and their therapeutic actions include benefits in inflammation, coagulation, thrombosis, angiogenesis, cancer, oxidation, and infections. Some red algae, marine angiosperm and invertebrates express SPs of unique structures composed of regular repeating oligomeric units of well-defined sulfation patterns. This fine pattern of structural regularity is quite rare among any naturally occurring long SPs, and enables accurate structure-biofunction correlations. Seeing that, fucanomics and galactanomics may comprise distinguished glycomics subprojects. We hereby discuss the relevance that justifies the international recognition of these subprojects in the current glycomics age associated with the beneficial outcomes that these glycans may offer in drug development.

A closer look at the nitrogen next door: 1H-15N NMR methods for glycosaminoglycan structural characterization

Recently, experimental conditions were presented for the detection of the N-sulfoglucosamine (GlcNS) NHSO(3)(-) or sulfamate (1)H and (15)N NMR resonances of the pharmaceutically and biologically important glycosaminoglycan (GAG) heparin in aqueous solution. In the present work, we explore further the applicability of nitrogen-bound proton detection to provide structural information for GAGs. Compared to the detection of (15)N chemical shifts of aminosugars through long-range couplings using the IMPACT-HNMBC pulse sequence, the more sensitive two-dimensional (1)H-(15)N HSQC-TOCSY experiments provided additional structural data. The IMPACT-HNMBC experiment remains a powerful tool as demonstrated by the spectrum measured for the unsubstituted amine of 3-O-sulfoglucosamine (GlcN(3S)), which cannot be observed with the (1)H-(15)N HSQC-TOCSY experiment due to the fast exchange of the amino group protons with solvent. The (1)H-(15)N HSQC-TOCSY NMR spectrum reported for the mixture of model compounds GlcNS and N-acetylglucosamine (GlcNAc) demonstrate the broad utility of this approach. Measurements for the synthetic pentasaccharide drug Arixtra® (Fondaparinux sodium) in aqueous solution illustrate the power of this NMR pulse sequence for structural characterization of highly similar N-sulfoglucosamine residues in GAG-derived oligosaccharides.

Exploiting enzyme specificities in digestions of chondroitin sulfates A and C: production of well-defined hexasaccharides

Interactions between proteins and glycosaminoglycans (GAGs) of the extracellular matrix are important to the regulation of cellular processes including growth, differentiation and migration. Understanding these processes can benefit greatly from the study of protein-GAG interactions using GAG oligosaccharides of well-defined structure. Materials for such studies have, however, been difficult to obtain because of challenges in synthetic approaches and the extreme structural heterogeneity in GAG polymers. Here, it is demonstrated that diversity in structures of oligosaccharides derived by limited enzymatic digestion of materials from natural sources can be greatly curtailed by a proper selection of combinations of source materials and digestive enzymes, a process aided by an improved understanding of the specificities of certain commercial preparations of hydrolases and lyases. Separation of well-defined oligosaccharides can then be accomplished by size-exclusion chromatography followed by strong anion-exchange chromatography. We focus here on two types of chondroitin sulfate (CS) as starting material (CS-A, and CS-C) and the use of three digestive enzymes with varying specificities (testicular hyaluronidase and bacterial chondroitinases ABC and C). Analysis using nuclear magnetic resonance and mass spectrometry focuses on isolated CS disaccharides and hexasaccharides. In all, 15 CS hexasaccharides have been isolated and characterized. These serve as useful contributions to growing libraries of well-defined GAG oligosaccharides that can be used in further biophysical assays.

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.

LC-MS(n) analysis of isomeric chondroitin sulfate oligosaccharides using a chemical derivatization strategy

Improved methods for structural analyses of glycosaminoglycans (GAGs) are required to understand their functional roles in various biological processes. Major challenges in structural characterization of complex GAG oligosaccharides using liquid chromatography-mass spectrometry (LC-MS) include the accurate determination of the patterns of sulfation due to gas-phase losses of the sulfate groups upon collisional activation and inefficient on-line separation of positional sulfation isomers prior to MS/MS analyses. Here, a sequential chemical derivatization procedure including permethylation, desulfation, and acetylation was demonstrated to enable both on-line LC separation of isomeric mixtures of chondroitin sulfate (CS) oligosaccharides and accurate determination of sites of sulfation by MS(n). The derivatized oligosaccharides have sulfate groups replaced with acetyl groups, which are sufficiently stable to survive MS(n) fragmentation and reflect the original sulfation patterns. A standard reversed-phase LC-MS system with a capillary C18 column was used for separation, and MS(n) experiments using collision-induced dissociation (CID) were performed. Our results indicate that the combination of this derivatization strategy and MS(n) methodology enables accurate identification of the sulfation isomers of CS hexasaccharides with either saturated or unsaturated nonreducing ends. Moreover, derivatized CS hexasaccharide isomer mixtures become separable by LC-MS method due to different positions of acetyl modifications.

Getting to know the nitrogen next door: HNMBC measurements of amino sugars

Long-range ¹H-¹⁵N correlations detected by the heteronuclear multiple-bond correlation (HMBC) experiment are explored for the characterization of amino sugars. The gradient-enhanced HMBC, IMPACT-HMBC, and a modified pulse sequence with the ¹J-filters removed, IMPACT-HNMBC, are compared for sensitivity and resolution. ¹⁵N chemical shifts and long-range proton correlations are reported using the IMPACT-HNMBC experiment for N-acetyl-glucosamine, N-acetyl-galactosamine, and for a series of glucosamine analogs with an N-sulfo substitution, unmodified amino group, and 6-O-sulfonation. As is common with sugars, for all the compounds examined both anomeric forms are present in solution. For each compound studied, the ¹⁵N chemical shifts of the α anomer are downfield of the β form. For the N-acetylated sugars, the β anomer has a unique long-range ¹⁵N correlation to the anomeric proton not observed for the α anomer. Though N-sulfonation results in a significant change in the ¹⁵N chemical shift of the glucosamine analogs, 6-O sulfo substitution has no significant effect on the local environment of the amino nitrogen. For N-acetylated sugars in D₂O solution, peaks in the ¹⁵N projection of the HMBC spectrum appear as triplets as a result of J-modulation due to ²H-¹⁵N coupling.

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.