Deciphering the structure of isomeric oligosaccharides in a complex mixture by tandem mass spectrometry: Photon activation with vacuum ultra-violet brings unique information and enables definitive structure assignment

Radiation-Induced Transfer of Charge, Atoms, and Energy within Isolated Biomolecular Systems

In biological tissues, ionizing radiation interacts with a variety of molecules and the consequences include cell killing and the modification of mechanical properties. Applications of biological radiation action are for instance radiotherapy, sterilization, or the tailoring of biomaterial properties. During the first femtoseconds to milliseconds after the initial radiation action, biomolecular systems typically respond by transfer of charge, atoms, or energy. In the condensed phase, it is usually very difficult to distinguish direct effects from indirect effects. A straightforward solution for this problem is the use of gas-phase techniques, for instance from the field of mass spectrometry. In this review, we survey mainly experimental but also theoretical work, focusing on radiation-induced intra- and inter-molecular transfer of charge, atoms, and energy within biomolecular systems in the gas phase. Building blocks of DNA, proteins, and saccharides, but also antibiotics are considered. The emergence of general processes as well as their timescales and mechanisms are highlighted.

Specificity of a β-porphyranase produced by the carrageenophyte red alga Chondrus crispus and implications of this unexpected activity on red algal biology

The carrageenophyte red alga Chondrus crispus produces three family 16 glycoside hydrolases (CcGH16-1, CcGH16-2, and CcGH16-3). Phylogenetically, the red algal GH16 members are closely related to bacterial GH16 homologs from subfamilies 13 and 14, which have characterized marine bacterial β-carrageenase and β-porphyranase activities, respectively, yet the functions of these CcGH16 hydrolases have not been determined. Here, we first confirmed the gene locus of the ccgh16-3 gene in the alga to facilitate further investigation. Next, our biochemical characterization of CcGH16-3 revealed an unexpected β-porphyranase activity, since porphyran is not a known component of the C. crispus extracellular matrix. Kinetic characterization was undertaken on natural porphyran substrate with an experimentally determined molecular weight. We found CcGH16-3 has a pH optimum between 7.5 and 8.0; however, it exhibits reasonably stable activity over a large pH range (pH 7.0-9.0). CcGH16-3 has a K_M of 4.0 ± 0.8 μM, a k_cat of 79.9 ± 6.9 s^-1, and a k_cat/K_M of 20.1 ± 1.7 μM^-1 s^-1. We structurally examined fine enzymatic specificity by performing a subsite dissection. CcGH16-3 has a strict requirement for D-galactose and L-galactose-6-sulfate in its -1 and +1 subsites, respectively, whereas the outer subsites are less restrictive. CcGH16-3 is one of a handful of algal enzymes characterized with a specificity for a polysaccharide unknown to be found in their own extracellular matrix. This β-porphyranase activity in a carrageenophyte red alga may provide defense against red algal pathogens or provide a competitive advantage in niche colonization.

MS-based glycomics: An analytical tool to assess nervous system diseases

Neurological diseases affect millions of peopleochemistryorldwide and are continuously increasing due to the globe's aging population. Such diseases affect the nervous system and are characterized by a progressive decline in brain function and progressive cognitive impairment, decreasing the quality of life for those with the disease as well as for their families and loved ones. The increased burden of nervous system diseases demands a deeper insight into the biomolecular mechanisms at work during disease development in order to improve clinical diagnosis and drug design. Recently, evidence has related glycosylation to nervous system diseases. Glycosylation is a vital post-translational modification that mediates many biological functions, and aberrant glycosylation has been associated with a variety of diseases. Thus, the investigation of glycosylation in neurological diseases could provide novel biomarkers and information for disease pathology. During the last decades, many techniques have been developed for facilitation of reliable and efficient glycomic analysis. Among these, mass spectrometry (MS) is considered the most powerful tool for glycan analysis due to its high resolution, high sensitivity, and the ability to acquire adequate structural information for glycan identification. Along with MS, a variety of approaches and strategies are employed to enhance the MS-based identification and quantitation of glycans in neurological samples. Here, we review the advanced glycomic tools used in nervous system disease studies, including separation techniques prior to MS, fragmentation techniques in MS, and corresponding strategies. The glycan markers in common clinical nervous system diseases discovered by utilizing such MS-based glycomic tools are also summarized and discussed.

Structural characterization of human milk oligosaccharides using ultrahigh performance liquid chromatography-helium charge transfer dissociation mass spectrometry

The combination of helium charge transfer dissociation mass spectrometry (He-CTD-MS) with ultrahigh performance liquid chromatography (UHPLC) is presented for the analysis of a complex mixture of acidic and neutral human milk oligosaccharides (HMOs). The research focuses on the identification of the monosaccharide sequence, the branching patterns, the sialylation/fucosylation arrangements, and the differentiation of isomeric oligosaccharides in the mixture. Initial studies first optimized the conditions for the UHPLC separation and the He-CTD-MS conditions. Results demonstrate that He-CTD is compatible with UHPLC timescales and provides unambiguous glycosidic and cross-ring cleavages from both the reducing and the nonreducing ends, which is not typically possible using collision-induced dissociation. He-CTD produces informative fragments, including 0,3An and 0,4An ions, which have been observed with electron transfer dissociation, electron detachment dissociation, and ultraviolet photodissociation (UVPD) and are crucial for differentiating the α-2,3- versus α-2,6-linked sialic acid (Neu5Ac) residues present among sialyllacto-N-tetraose HMOs. In addition to the linkage positions, He-CTD is able to differentiate structural isomers for both sialyllacto-N-tetraoses and lacto-N-fucopentaoses structures by providing unique, unambiguous cross-ring cleavages of types 0,2An, 0,2Xn, and 1,5An while preserving most of the labile Neu5Ac and fucose groups.

Charge transfer dissociation of a branched glycan with alkali and alkaline earth metal adducts

Alkali and alkaline earth metal adducts of a branched glycan, XXXG, were analyzed with helium charge transfer dissociation (He-CTD) and low-energy collision-induced dissociation (LE-CID) to investigate if metalation would impact the type of fragments generated and the structural characterization of the analyte. The studied adducts included 1+ and 2+ precursors involving one or more of the cations: H⁺ , Na⁺ , K⁺ , Ca²⁺ , and Mg²⁺ . Regardless of the metal adduct, He-CTD generated abundant and numerous glycosidic and cross-ring cleavages that were structurally informative and able to identify the 1,4-linkage and 1,6-branching patterns. In contrast, the LE-CID spectra mainly contained glycosidic cleavages, consecutive fragments, and numerous neutral losses, which complicated spectral interpretation. LE-CID of [M + K + H]²⁺ and [M + Na]⁺ precursors generated a few cross-ring cleavages, but they were not sufficient to identify the 1,4-linkage and 1,6-branching pattern of the XXXG xyloglucan. He-CTD predominantly generated 1+ fragments from 1+ precursors and 2+ product ions from 2+ precursors, although both LE-CID and He-CTD were able to generate 1+ product ions from 2+ adducts of magnesium and calcium. The singly charged fragments derive from the loss of H⁺ from the metalated product ions and the formation of a protonated complementary product ion; such observations are similar to previous reports for magnesium and calcium salts undergoing electron capture dissociation (ECD) activation. However, during He-CTD, the [M + Mg]²⁺ precursor generated more singly charged product ions than [M + Ca]²⁺ , either because Mg has a higher second ionization potential than Ca or because of conformational differences and the locations of the charging adducts during fragmentation. He-CTD of the [M + 2Na]²⁺ and the [M + 2 K]²⁺ precursors generated singly charged product ions from the loss of a sodium ion and potassium ion, respectively. In summary, although the metal ions influence the mass and charge state of the observed product ions, the metal ions had a negligible effect on the types of cross-ring cleavages observed.

Ultra-high-performance liquid chromatography charge transfer dissociation mass spectrometry (UHPLC-CTD-MS) as a tool for analyzing the structural heterogeneity in carrageenan oligosaccharides

Ultra-high-performance liquid chromatography (UHPLC) with charge transfer dissociation mass spectrometry (CTD-MS) is presented for the analysis of a mixture of complex sulfated oligosaccharides. The mixture contained kappa (κ), iota (ι), and lambda (λ) carrageenans that contain anhydro bridges, different degrees of sulfation ranging from one to three per dimer, different positioning of the sulfate groups along the backbone, and varying degrees of polymerization (DP) between 4 and 12. Optimization studies using standard mixtures of carrageenans helped establish the optimal conditions for online UHPLC-CTD-MS/MS analysis. Optimization included (1) UHPLC conditions; (2) ion source conditions, such as the capillary voltage, drying gas and nebulizing gas temperature, and flow rate; and (3) CTD-MS conditions, including data-dependent CTD-MS. The UHPLC-CTD results were contrasted with UHPLC-CID results of the same mixture on the same instrument. Whereas CID tends to produce B/Y and C/Z ions with many neutral losses, CTD produced more abundant A/X ions and less abundant neutral losses, which enabled more confident structural detail. The results demonstrate that He-CTD is compatible with the timescale of UHPLC and provides more structural information about carrageenans compared to state-of-the-art methods like UHPLC-CID analysis.

Anomeric Retention of Carbohydrates in Multistage Cyclic Ion Mobility (IMSn): De Novo Structural Elucidation of Enzymatically Produced Mannosides

Carbohydrates are complex structures that still challenge analysts today because of their different levels of isomerism, notably the anomerism of the glycosidic bond. It has been shown recently that anomerism is preserved upon gas-phase fragmentation and that high-resolution ion mobility (IMS) can distinguish anomers. However, these concepts have yet to be applied to complex biological products. We have used high-resolution IMS on a cyclic device to characterize the reaction products of Uhgb_MS, a novel mannoside synthase of the GH130 family. We designed a so-called IMSⁿ sequence consisting of (i) separating and isolating specific IMS peaks, (ii) ejecting ions to a pre-array store cell depending on their arrival time, (iii) inducing collisional activation upon reinjection, and (iv) performing multistage IMS analysis of the fragments. First, we applied IMS² sequences to purely linked α1,2- and β1,2-mannooligosaccharides, which provided us with reference drift times for fragments of known conformation. Then, we performed IMSⁿ analyses of enzymatically produced mannosides and, by comparison with the references, we succeeded in determining the intrachain anomerism of a α1,2-mannotriose and a mix-linked β/α1,2-mannotetraose-a first for a crude biological medium. Our results show that the anomerism of glycosides is maintained through multiple stages of collisional fragmentation, and that standalone high-resolution IMS and IMSⁿ can be used to characterize the intrachain anomerism in tri- and tetrasaccharides in a biological medium. This is also the first evidence that a single carbohydrate-active enzyme can synthesize both α- and β-glycosidic linkages.

Structural Characterization of Isomeric Oligogalacturonan Mixtures Using Ultrahigh-Performance Liquid Chromatography-Charge Transfer Dissociation Mass Spectrometry

Pectins are natural polysaccharides made from galacturonic acid residues, and they are widely used as an excipient in food and pharmaceutical industries. The degree of methyl-esterification, the monomeric composition, and the linkage pattern are all important factors that influence the physical and chemical properties of pectins, such as the solubility. This work focuses on the successful online coupling of charge transfer dissociation-mass spectrometry (CTD-MS) with ultrahigh-performance liquid chromatography (UHPLC) to differentiate isomers of oligogalacturonans derived from citrus pectins. This work employed CTD fragmentation of the pectin mixtures in data-dependent acquisition mode. Compared to the UHPLC with collision-induced dissociation mass spectrometry (UHPLC-CID-MS), UHPLC-CTD-MS yielded fewer ambiguous ions and more structurally informative results. The developed UHPLC-CTD-MS method resulted in abundant cross-ring cleavages-and especially ^1,4X_n, ^1,5X_n, and ^2,4X_n ions-which helped to identify most of the isomers. The Gal A isomers differed only in the methyl group position along the galacturonic acid backbone. The combination of CTD in real time with UHPLC provides a new tool for the structural characterization of complex mixtures of oligogalacturonans and potentially other classes of oligosaccharides.

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.

Ultraviolet Photodissociation Mass Spectrometry for Analysis of Biological Molecules

The development of new ion-activation/dissociation methods continues to be one of the most active areas of mass spectrometry owing to the broad applications of tandem mass spectrometry in the identification and structural characterization of molecules. This Review will showcase the impact of ultraviolet photodissociation (UVPD) as a frontier strategy for generating informative fragmentation patterns of ions, especially for biological molecules whose complicated structures, subtle modifications, and large sizes often impede molecular characterization. UVPD energizes ions via absorption of high-energy photons, which allows access to new dissociation pathways relative to more conventional ion-activation methods. Applications of UVPD for the analysis of peptides, proteins, lipids, and other classes of biologically relevant molecules are emphasized in this Review.

VUV Photodissociation Induced by a Deuterium Lamp in an Ion Trap

Tandem mass spectrometry represents an important analytical tool to unravel molecular structures and to study the gas-phase behavior of organic molecules. Besides commonly used methods like collision-induced dissociation and electron capture or transfer dissociation, new ultraviolet light-based techniques have the potential to synergistically add to the activation methods. Here, we present a new simple, yet robust, experimental design for polychromatic activation of trapped ions using the 115-160 nm output of a commercially available deuterium lamp. The resulting continuous dissociative excitation with photons of a wide energy range from 7.7 to 10.8 eV is studied for a comprehensive set of analyte classes in both positive and negative ion modes. While being simple, affordable, compact, and of low maintenance, the new setup initiates fragmentation of most precursor ions via their known dissociation pathways. Additionally, some new fragmentation patterns were discovered. Especially, electron loss and electron capture reactions with subsequent fragmentations were observed. For oligonucleotides, peptides, carbohydrates, and organic dyes, in comparison to collision-induced dissociation, a significantly wider fragment distribution was obtained, resulting in an information increase. Since the individual photons carry enough energy to post-ionize the nascent fragments, a permanent vacuum ultraviolet light exposure inside the ion trap potentially goes along with a general increase in detection capability.

Cyclic Ion Mobility Mass Spectrometry Distinguishes Anomers and Open-Ring Forms of Pentasaccharides

There is increasing biopharmaceutical interest in oligosaccharides and glycosylation. A key requirement for these sample types is the ability to characterize the chain length, branching, type of monomers, and importantly stereochemistry and anomeric configuration. Herein, we showcase the multi-function capability of a cyclic ion mobility (cIM) separator embedded in a quadrupole/time-of-flight mass spectrometer (Q-ToF MS). The instrument design enables selective activation of mobility-separated precursors followed by cIM separation of product ions, an approach analogous to MSⁿ. Using high cIM resolution, we demonstrate the separation of three isomeric pentasaccharides and, moreover, that three components are present for each compound. We show that structural differences between product ions reflect the precursor differences in some cases but not others. These findings are corroborated by a heavy oxygen labelling approach. Using this methodology, the identity of fragment ions may be assigned. This enables us to postulate that the two main components observed for each pentasaccharide are anomeric forms. The remaining low abundance component is assigned as an open-ring form.

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.

The agar-specific hydrolase ZgAgaC from the marine bacterium Zobellia galactanivorans defines a new GH16 protein subfamily

Agars are sulfated galactans from red macroalgae and are composed of a d-galactose (G unit) and l-galactose (L unit) alternatively linked by α-1,3 and β-1,4 glycosidic bonds. These polysaccharides display high complexity, with numerous modifications of their backbone (e.g. presence of a 3,6-anhydro-bridge (LA unit) and sulfations and methylation). Currently, bacterial polysaccharidases that hydrolyze agars (β-agarases and β-porphyranases) have been characterized on simple agarose and more rarely on porphyran, a polymer containing both agarobiose (G-LA) and porphyranobiose (GL6S) motifs. How bacteria can degrade complex agars remains therefore an open question. Here, we studied an enzyme from the marine bacterium Zobellia galactanivorans (ZgAgaC) that is distantly related to the glycoside hydrolase 16 (GH16) family β-agarases and β-porphyranases. Using a large red algae collection, we demonstrate that ZgAgaC hydrolyzes not only agarose but also complex agars from Ceramiales species. Using tandem MS analysis, we elucidated the structure of a purified hexasaccharide product, L6S-G-LA2Me-G(2Pentose)-LA2S-G, released by the activity of ZgAgaC on agar extracted from Osmundea pinnatifida By resolving the crystal structure of ZgAgaC at high resolution (1.3 Å) and comparison with the structures of ZgAgaB and ZgPorA in complex with their respective substrates, we determined that ZgAgaC recognizes agarose via a mechanism different from that of classical β-agarases. Moreover, we identified conserved residues involved in the binding of complex oligoagars and demonstrate a probable influence of the acidic polysaccharide's pH microenvironment on hydrolase activity. Finally, a phylogenetic analysis supported the notion that ZgAgaC homologs define a new GH16 subfamily distinct from β-porphyranases and classical β-agarases.

Advances in mass spectrometry-based glycomics

The diversification of the chemical properties and biological functions of proteins is attained through posttranslational modifications, such as glycosylation. Glycans, which are covalently attached to proteins, play a vital role in cell activities. The microheterogeneity and complexity of glycan structures associated with proteins make comprehensive glycomic analysis challenging. However, recent advancements in mass spectrometry (MS), separation techniques, and sample preparation methods have primarily facilitated structural elucidation and quantitation of glycans. This review focuses on describing recent advances in MS-based techniques used for glycomic analysis (2012-2018), including ionization, tandem MS, and separation techniques coupled with MS. Progress in glycomics workflow involving glycan release, purification, derivatization, and separation will also be highlighted here. Additionally, the recent development of quantitative glycomics through comparative and multiplex approaches will also be described.

Lasers and ion mobility: new additions to the glycosaminoglycanomics toolkit

Glycosaminoglycans are biopolymers present in mammalian cells or in the extracellular matrix. To address their structure, the nature of the hexuronic acids and the position of sulfate groups must be determined. Tandem mass spectrometry using collision induced dissociation or electron-based fragmentation techniques, is a well-established approach for the identification of glycans but suffers from the frequent lack of diagnostic fragments in the case of glycosaminoglycans. This review presents alternative fragmentation techniques, namely photofragmentation in the IR and the UV ranges. Alternative approaches based on the direct analysis of the molecular structure, including ion mobility spectrometry and ion spectroscopies are reviewed. The potential of future multidimensional workflows for glycosaminoglycanomics is discussed.

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

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

De Novo Glycan Sequencing by Electronic Excitation Dissociation and Fixed-Charge Derivatization

Detailed glycan structural characterization is frequently achieved by collisionally activated dissociation (CAD) based sequential tandem mass spectrometry (MS ⁿ) analysis of permethylated glycans. However, it is challenging to implement MS ⁿ ( n > 2) during online glycan separation, and this has limited its application to analysis of complex glycan mixtures from biological samples. Further, permethylation can reduce liquid chromatographic (LC) resolution of isomeric glycans. Here, we studied the electronic excitation dissociation (EED) fragmentation behavior of native glycans with a reducing-end fixed charge tag and identified key spectral features that are useful for topology and linkage determination. We also developed a de novo glycan sequencing software that showed remarkable accuracy in glycan topology elucidation based on the EED spectra of fixed charge-derivatized glycans. The ability to obtain glycan structural details at the MS² level, without permethylation, via a combination of fixed charge derivatization, EED, and de novo spectral interpretation, makes the present approach a promising tool for comprehensive and rapid characterization of glycan mixtures.

Glycan analysis by ion mobility-mass spectrometry and gas-phase spectroscopy

Due to the existence of numerous isomers, the in-depth analysis of glycans represents a major challenge. Currently, the majority of glycans are analysed using mass spectrometry (MS)-based techniques, which can provide information on regioisomers but usually fail to differentiate stereoisomers. A promising approach to overcome this limitation is to implement ion mobility spectrometry (IMS) as an additional gas-phase separation dimension. This review highlights recent developments in which IM-MS was used as a tool for comprehensive glycan analysis or as rapid screening method for glycan feature analysis. Furthermore, we summarize a series of very recent investigations in which gas-phase spectroscopy is applied to study glycans and discuss the potential of the hyphenation between IM-MS and infrared (IR) spectroscopy as a future tool for glycomics and glycoproteomics.

Gas-Phase Intercluster Thiyl-Radical Induced C-H Bond Homolysis Selectively Forms Sugar C2-Radical Cations of Methyl D-Glucopyranoside: Isotopic Labeling Studies and Cleavage Reactions

A suite of isotopologues of methyl D-glucopyranosides is used in conjunction with multistage mass spectrometry experiments to determine the radical site and cleavage reactions of sugar radical cations formed via a recently developed 'bio-inspired' method. In the first stage of CID (MS²), collision-induced dissociation (CID) of a protonated noncovalent complex between the sugar and S-nitrosocysteamine, [H₃NCH₂CH₂SNO + M]⁺, unleashes a thiyl radical via bond homolysis to give the noncovalent radical cation, [H₃NCH₂CH₂S^• + M]⁺. CID (MS³) of this radical cation complex results in dissociation of the noncovalent complex to generate the sugar radical cation. Replacement of all exchangeable OH and NH protons with deuterons reveals that the sugar radical cation is formed in a process involving abstraction of a hydrogen atom from a C-H bond of the sugar coupled with proton transfer to the sugar, to form [M - H^• + D⁺]. Investigation of this process using individual C-D labeled sugars reveals that the main site of H/D abstraction is the C2 position, since only the C2-deuterium labeled sugar yields a dominant [M - D^• + H⁺] product ion. The fragmentation reactions of the distonic sugar radical cation, [M - H^•+ H⁺], were studied by another stage of CID (MS⁴). ¹³C-labeling studies revealed that a series of three related fragment ions each contain the C1-C3 atoms; these arise from cross-ring cleavage reactions of the sugar. Graphical Abstract ᅟ.

Negative Polarity Helium Charge Transfer Dissociation Tandem Mass Spectrometry: Radical-Initiated Fragmentation of Complex Polysulfated Anions

This work provides the first use of helium charge transfer dissociation (He-CTD) tandem mass spectrometry (MS/MS) in negative polarity mode. Three sulfated oligosaccharides of natural origin were chosen as representative structures that are difficult to solve by conventional MS/MS approaches. Negative polarity He-CTD provided a full set of structurally informative fragments, which permitted the unambiguous determination of the complete structures of these molecules, including the characterization of labile sulfated functional groups. Despite close structural features, the three molecules led to distinct fragmentation patterns depending on the position of the sulfate group in the heterocycle. The observed fragments showed a consistent radical-initiated mechanism of dissociation, which shares similarities with fragment types produced in electron detachment dissociation (EDD), negative electron transfer dissociation (NETD), or extreme UV photodissociation (XUV-PD). Short times of data collection and the fact that the technique can be affordably implementable in any standard laboratory and with a classical ion trap mass spectrometer were other remarkable characteristics of negative polarity He-CTD.

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.

The Deconstruction of Pectic Rhamnogalacturonan I Unmasks the Occurrence of a Novel Arabinogalactan Oligosaccharide Epitope

Rhamnogalacturonan I (RGI) is a pectic polysaccharide composed of a backbone of alternating rhamnose and galacturonic acid residues with side chains containing galactose and/or arabinose residues. The structure of these side chains and the degree of substitution of rhamnose residues are extremely variable and depend on species, organs, cell types and developmental stages. Deciphering RGI function requires extending the current set of monoclonal antibodies (mAbs) directed to this polymer. Here, we describe the generation of a new mAb that recognizes a heterogeneous subdomain of RGI. The mAb, INRA-AGI-1, was produced by immunization of mice with RGI oligosaccharides isolated from potato tubers. These oligomers consisted of highly branched RGI backbones substituted with short side chains. INRA-AGI-1 bound specifically to RGI isolated from galactan-rich cell walls and displayed no binding to other pectic domains. In order to identify its RGI-related epitope, potato RGI oligosaccharides were fractionated by anion-exchange chromatography. Antibody recognition was assessed for each chromatographic fraction. INRA-AGI-1 recognizes a linear chain of (1→4)-linked galactose and (1→5)-linked arabinose residues. By combining the use of INRA-AGI-1 with LM5, LM6 and INRA-RU1 mAbs and enzymatic pre-treatments, evidence is presented of spatial differences in RGI motif distribution within individual cell walls of potato tubers and carrot roots. These observations raise questions about the biosynthesis and assembly of pectin structural domains and their integration and remodeling in cell walls.