Structural identification of N-glycan isomers using logically derived sequence tandem mass spectrometry

Maximizing Glycoproteomics Results through an Integrated Parallel Accumulation Serial Fragmentation Workflow

Glycoproteins play important roles in numerous physiological processes and are often implicated in disease. Analysis of site-specific protein glycobiology through glycoproteomics has evolved rapidly in recent years thanks to hardware and software innovations. Particularly, the introduction of parallel accumulation serial fragmentation (PASEF) on hybrid trapped ion mobility time-of-flight mass spectrometry instruments combined deep proteome sequencing with separation of (near-)isobaric precursor ions or converging isotope envelopes through ion mobility separation. However, the reported use of PASEF in integrated glycoproteomics workflows to comprehensively capture the glycoproteome is still limited. To this end, we developed an integrated methodology using timsTOF Pro 2 to enhance N-glycopeptide identifications in complex mixtures. We systematically optimized the ion optics tuning, collision energies, mobility isolation width, and the use of dopant-enriched nitrogen gas (DEN). Thus, we obtained a marked increase in unique glycopeptide identification rates compared to standard proteomics settings, showcasing our results on a large set of glycopeptides. With short liquid chromatography gradients of 30 min, we increased the number of unique N-glycopeptide identifications in human plasma samples from around 100 identifications under standard proteomics conditions to up to 1500 with our optimized glycoproteomics approach, highlighting the need for tailored optimizations to obtain comprehensive data.

Preparation of natural high-mannose-type oligosaccharides (Glc1Man9GlcNAc2) with the asparagine-glycine-threonine as consensus sequence from chicken egg yolk

High-mannose-type glycan structure of N-glycoproteins plays important roles in the proper folding of proteins in sorting glycoprotein secretion and degradation of misfolded proteins in the endoplasmic reticulum (ER). The Glc1Man9GlcNAc2 (G1M9)-type N-glycan is one of the most important signaling molecules in the ER. However, current chemical synthesis strategies are laborious, warranting more practical approaches for G1M9-glycopeptide development. Wang et al. reported the procedure to give G1M9-Asn-Fmoc through chemical modifications and purifications from 40 chicken eggs, but only 3.3 mg of G1M9-glycopeptide was obtained. Therefore, better methods are needed to obtain more than 10 mg of G1M9-glycopeptide. In this study, we report the preparation of G1M9-glycopeptide (13.2 mg) linking Asn-Gly-Thr triad as consensus sequence from 40 chicken eggs. In this procedure, λ-carrageenan treatment followed by papain treatment was used to separate the Fc region of IgY antibody that harbors high-mannose glycans. Moreover, cotton hydrophilic interaction liquid chromatography was adapted for easy purification. The resulting G1M9-Asn(Fmoc)-Gly-Thr was identified by nuclear magnetic resonance and mass spectroscopy. G1M9-Asn(Fmoc)-Gly, G1M9-Asn(Fmoc), and G1M9-OH were also detected by mass spectroscopy. Here, our developed G1M9-tripeptide might be useful for the elucidation of glycoprotein functions as well as the specific roles of the consensus sequence.

Collision-Induced Dissociation of Fucose and Identification of Anomericity

Structural determination of carbohydrates using mass spectrometry remains challenging, particularly, the differentiation of anomeric configurations. In this work, we studied the collision-induced dissociation (CID) mechanisms of sodiated α- and β-l-fucose using an experimental method and quantum chemistry calculations. The calculations show that α-l-fucose is more likely to undergo dehydration due to the fact that O1 and O2 are on the same side of the sugar ring. In contrast, β-l-fucose is more prone to the ring-opening reaction because more OH groups are on the same side of the sugar ring as O1. These differences suggest a higher preference for the dehydration reaction in sodiated α-l-fucose but a lower preference for ring-opening compared to that of β-l-fucose. The calculation results, which are used to assign the CID mass spectra of α- and β-l-fucose separated by high-performance liquid chromatography, are supported by the fucose produced from the CID of disaccharides Fuc-β-(1 → 3)-GlcNAc and Fuc-α-(1 → 4)-GlcNAc. This study demonstrates that the correlation of cis- and trans-configurations of O1 and O2 to the relative branching ratios of dehydration and cross-ring dissociation in CID, observed in aldohexose and ketohexose in the pyranose form, can be extended to deoxyhexoses for anomericity determination.

Chromatograms and Mass Spectra of High-Mannose and Paucimannose N-Glycans for Rapid Isomeric Identifications

N-Linked glycosylation is one of the most essential post-translational modifications of proteins. However, N-glycan structural determination remains challenging because of the small differences in structures between isomers. In this study, we constructed a database containing collision-induced dissociation MSn mass spectra and chromatograms of high-performance liquid chromatography for the rapid identification of high-mannose and paucimannose N-glycan isomers. These N-glycans include isomers by breaking of arbitrary numbers of glycosidic bonds at arbitrary positions of canonical Man9GlcNAc2 N-glycans. In addition, some GlcMannGlcNAc2 N-glycan isomers were included in the database. This database is particularly useful for the identification of the N-glycans not in conventional N-glycan standards. This study demonstrated the application of the database to structural assignment for high-mannose N-glycans extracted from bovine whey proteins, soybean proteins, human mammary epithelial cells, and human breast carcinoma cells. We found many N-glycans that are not expected to be generated by conventional biosynthetic pathways of multicellular eukaryotes.

Isomeric separation of native N-glycans using nano zwitterionic- hydrophilic interaction liquid chromatography column

Changes in the expression of glycan isomers have been implicated in the development and progression of several diseases. However, the analysis of structurally diverse isomeric N-glycans by LC-MS/MS is still a major analytical challenge, particularly due to their large number of possible isomeric conformations. Common approaches derivatized the N-glycans to increase their hydrophobicity and to gain better detection in the MS system. Unfortunately, glycan derivatization is time-consuming and, in many cases, adds complexity because of the multiple reaction and cleaning steps, incomplete chemical labeling, possible degradation, and unwanted side reactions. Thus, analysis of native glycans, especially for samples with low abundance by LC-MS/MS, is desirable. Normal phase chromatography, which employs HILIC stationary phase, has been commonly employed for the identification and separation of labeled glycans. In this study, we focused on achieving efficient isomeric separation of native N-glycans using a nano ZIC-HILIC column commonly employed to separate labeled glycans and glycopeptides. Underivatized sialylated and oligomannose N-glycans derived from bovine fetuin and Ribonuclease B were initially utilized to optimize chromatographic conditions, including column temperature, pH of mobile phases, and gradient elution time. The optimized condition was then applied for the isomeric separation of native N-glycans derived from alpha-1 acid glycoprotein, as well as from biological samples. Finally, we confirmed the stability and reproducibility of the ZIC-HILIC column by performing run-to-run comparisons of the full width at half height (FWHM) and retention time on different N-glycans. The variability in FWHM was less than 0.5 min, while that of retention time was less than 1.0 min with %RSD less than 1.0%.

The collision-induced dissociation mechanism of sodiated Hex-HexNAc disaccharides

Determining carbohydrate structures, such as their compositions, linkage positions, and in particular the anomers and stereoisomers, is a great challenge. Isomers of different anomers or stereoisomers have the same sequences of chemical bonds, but have different orientations of some chemical bonds which are difficult to be distinguished by mass spectrometry. Collision-induced dissociation (CID) tandem mass spectroscopy (MS/MS) is a widely used technique for characterizing carbohydrate structures. Understanding the carbohydrate dissociation mechanism is important for obtaining the structural information from MS/MS. In this work, we studied the CID mechanism of galactose-N-acetylgalactosamine (Gal-GalNAc) and glucose-N-acetylglucosamine (Glc-GlcNAc) disaccharides with 1→3 and 1→4 linkages. For Gal-GalNAc disaccharides, the CID mass spectra of sodium ion adducts show significant difference between the α- and β-anomers of GalNAc at the reducing end, while no difference in the CID mass spectra between two anomers of Glc-GlcNAc disaccharides was found. Quantum chemistry calculations show that for Gal-GalNAc disaccharides, the difference of the dissociation barriers between dehydration and glycosidic bond cleavage is significantly small in the β-anomer compared to that in the α-anomer; while these differences are similar between the α- and β-anomers of Glc-GlcNAc disaccharides. These differences can be attributed to the different orientations of hydroxyl and N-acetyl groups located at GalNAc and GlcNAc. The calculation results are consistent with the CID spectra of isotope labelled disaccharides. Our study provides an insight into the CID of 1→3 and 1→4 linked Gal-GalNAc and Glc-GlcNAc disaccharides. This information is useful for determining the anomeric configurations of GalNAc in oligosaccharides.

De novo glycan sequencing by electronic excitation dissociation MS2-guided MS3 analysis on an Omnitrap-Orbitrap hybrid instrument

Comprehensive de novo glycan sequencing remains an elusive goal due to the structural diversity and complexity of glycans. Present strategies employing collision-induced dissociation (CID) and higher energy collisional dissociation (HCD)-based multi-stage tandem mass spectrometry (MSⁿ) or MS/MS combined with sequential exoglycosidase digestions are inherently low-throughput and difficult to automate. Compared to CID and HCD, electron transfer dissociation (ETD) and electron capture dissociation (ECD) each generate more cross-ring cleavages informative about linkage positions, but electronic excitation dissociation (EED) exceeds the information content of all other methods and is also applicable to analysis of singly charged precursors. Although EED can provide extensive glycan structural information in a single stage of MS/MS, its performance has largely been limited to FTICR MS, and thus it has not been widely adopted by the glycoscience research community. Here, the effective performance of EED MS/MS was demonstrated on a hybrid Orbitrap-Omnitrap QE-HF instrument, with high sensitivity, fragmentation efficiency, and analysis speed. In addition, a novel EED MS²-guided MS³ approach was developed for detailed glycan structural analysis. Automated topology reconstruction from MS² and MS³ spectra could be achieved with a modified GlycoDeNovo software. We showed that the topology and linkage configurations of the Man₉GlcNAc₂ glycan can be accurately determined from first principles based on one EED MS² and two CID-EED MS³ analyses, without reliance on biological knowledge, a structure database or a spectral library. The presented approach holds great promise for autonomous, comprehensive and de novo glycan sequencing.

Identification of the High Mannose N-Glycan Isomers Undescribed by Conventional Multicellular Eukaryotic Biosynthetic Pathways

N-linked glycosylation is one of the most important post-translational modifications of proteins. Current knowledge of multicellular eukaryote N-glycan biosynthesis suggests high mannose N-glycans are generated in the endoplasmic reticulum and Golgi apparatus through conserved biosynthetic pathways. According to conventional biosynthetic pathways, four Man₇GlcNAc₂ isomers, three Man₆GlcNAc₂ isomers, and one Man₅GlcNAc₂ isomer are generated during this process. In this study, we applied our latest mass spectrometry method, logically derived sequence tandem mass spectrometry (LODES/MSⁿ), to re-examine high mannose N-glycans extracted from various multicellular eukaryotes which are not glycosylation mutants. LODES/MSⁿ identified many high mannose N-glycan isomers previously unreported in plantae, animalia, cancer cells, and fungi. A database consisting of retention time and CID MSⁿ mass spectra was constructed for all possible Man_nGlcNAc₂ (n = 5, 6, 7) isomers that include the isomers by removing arbitrary numbers and positions of mannose from canonical N-glycan, Man₉GlcNAc₂. Many N-glycans in this database are not found in current N-glycan mass spectrum libraries. The database is useful for rapid high mannose N-glycan isomeric identification.

A simple tandem mass spectrometry method for structural identification of pentose oligosaccharides

Differentiation of stereoisomers that are only dissimilar in the orientation of chemical bonds in space by mass spectrometry remains challenging. Structural determination of carbohydrates by mass spectrometry is difficult, mainly due to the large number of stereoisomers in carbohydrates. Arabinose and xylose are pentose stereoisomers typically present in plant polysaccharides and exist in α- and β-anomeric configurations of furanose and pyranose forms. Conventional methods used to determine the structures of polysaccharides include hydrolysis of polysaccharides into oligosaccharides followed by identification of these oligosaccharides' structures individually through nuclear magnetic resonance spectroscopy (NMR). Although the sensitivity of mass spectrometry is much higher than that of NMR, conventional mass spectrometry provides only limited useful information on oligosaccharide structure determination, only the linkage positions of glycosidic bonds. In this study, we demonstrated a mass spectrometry method for the identification of linkage positions, anomeric configurations, and monosaccharide stereoisomers of intact oligosaccharides consisting of arabinose and xylose. We separated arabinose and xylose monosaccharides into α-furanose, β-furanose, α-pyranose, and β-pyranose forms through high-performance liquid chromatography and obtained the corresponding collision-induced dissociation mass spectra. Using these monosaccharide spectra and a flow chart consisting of the proper CID sequences derived from the dissociation mechanisms of pentose, a simple multi-stage tandem mass spectrometry method for structural identification of intact oligosaccharides consisting of arabinose and xylose was developed. The new mass spectrometry method provides a simple method for determining the structure of polysaccharides consisting of arabinose and xylose. The flow chart can be used in computer coding for automation, an ultimate goal for oligosaccharide structure determination.

The Good, the Bad, and the Ugly Memories of Carbohydrate Fragments in Collision-Induced Dissociation

Collision-induced dissociation (CID) tandem mass spectrometry is commonly used for carbohydrate structural determinations. In the CID tandem mass spectrometry approach, carbohydrates are dissociated into fragments, and this is followed by the structural identification of fragments through subsequent CID. The success of the structural analysis depends on the structural correlation of fragments before and after dissociation, that is, structural memory of fragments. Fragments that completely lose the memory of their original structures cannot be used for structural analysis. By contrast, fragments with extremely strong correlations between the structures before and after fragmentation retain the information on their original structures as well as have memories of their precursors' entire structures. The CID spectra of these fragments depend on their own structures and on the remaining parts of the precursor structures, making structural analysis impractical. For effective structural analysis, the fragments produced from a precursor must have good structural memory, meaning that the structures of these fragments retain their original structure, and they must not be strongly affected by the remaining parts of the precursors. In this study, we found that most of the carbohydrate fragments produced by low-energy CID have good memory in terms of linkage position and anomericity. Fragments with ugly memory, where fragment structures change with the remaining parts of the precursors, can be attributed to C ion formation in a linear form. Fragments with ugly memory can be changed to have good memory by preventing linear C ion generation by using an alternative CID sequence, or the fragments of ugly memory can become useful in structural analysis when the contribution of linear C ions in fragmentation patterns is understood.

Recent Advances in Mass Spectrometry-Based Structural Elucidation Techniques

Mass spectrometry (MS) has become the central technique that is extensively used for the analysis of molecular structures of unknown compounds in the gas phase. It manipulates the molecules by converting them into ions using various ionization sources. With high-resolution MS, accurate molecular weights (MW) of the intact molecular ions can be measured so that they can be assigned a molecular formula with high confidence. Furthermore, the application of tandem MS has enabled detailed structural characterization by breaking the intact molecular ions and protonated or deprotonated molecules into key fragment ions. This approach is not only used for the structural elucidation of small molecules (MW < 2000 Da), but also crucial biopolymers such as proteins and polypeptides; therefore, MS has been extensively used in multiomics studies for revealing the structures and functions of important biomolecules and their interactions with each other. The high sensitivity of MS has enabled the analysis of low-level analytes in complex matrices. It is also a versatile technique that can be coupled with separation techniques, including chromatography and ion mobility, and many other analytical instruments such as NMR. In this review, we aim to focus on the technical advances of MS-based structural elucidation methods over the past five years, and provide an overview of their applications in complex mixture analysis. We hope this review can be of interest for a wide range of audiences who may not have extensive experience in MS-based techniques.

Mass spectrometry imaging spatially identifies complex-type N-glycans as putative cartilage degradation markers in human knee osteoarthritis tissue

N-Glycan alterations contribute to the pathophysiology and progression of various diseases. However, the involvement of N-glycans in knee osteoarthritis (KOA) progression at the tissue level, especially within articular cartilage, is still poorly understood. Thus, the aim of this study was to spatially map and identify KOA-specific N-glycans from formalin-fixed paraffin-embedded (FFPE) osteochondral tissue of the tibial plateau relative to cadaveric control (CTL) tissues. Human FFPE osteochondral tissues from end-stage KOA patients (n=3) and CTL individuals (n=3), aged >55 years old, were analyzed by matrix‐assisted laser desorption/ionization mass spectrometry imaging (MALDI‐MSI) and liquid chromatography–tandem mass spectrometry (LC-MS/MS). Overall, it was revealed that 22 N-glycans were found in the cartilage region of KOA and CTL tissue. Of those, 15 N-glycans were more prominent in KOA cartilage than CTL cartilage. We then compared sub-regions of KOA and CTL tissues based on the Osteoarthritis Research Society International (OARSI) histopathological grade (1 to 6), where 1 is an intact cartilage surface and 6 is cartilage surface deformation. Interestingly, three specific complex-type N-glycans, (Hex)₄(HexNAc)₃, (Hex)₄(HexNAc)₄, and (Hex)₅(HexNAc)₄, were found to be localized to the superficial fibrillated zone of degraded cartilage (KOA OARSI 2.5-4), compared to adjacent cartilage with less degradation (KOA OARSI 1-2) or relatively healthy cartilage (CTL OARSI 1-2). Our results demonstrate that N-glycans specific to degraded cartilage in KOA patients have been identified at the tissue level for the first time. The presence of these N-glycans could further be evaluated as potential diagnostic and prognostic biomarkers.

Highly sensitive characterization of non-human glycan structures of monoclonal antibody drugs utilizing tandem mass spectrometry

Glycosylation is an important attribute of monoclonal antibodies (mAbs) for assessing manufacturing quality. Analysis of non-human glycans containing terminal galactose-α1,3-galactose and N-glycolylneuraminic acid is essential due to the potential immunogenicity and insufficient efficacy caused by mAb expression in non-human mammalian cells. Using parallel sequencing of isobaric glycopeptides and isomeric glycans that were separated by reversed-phase and porous graphitic carbon LC, we report a highly sensitive LC MS/MS method for the comprehensive characterization of low-abundance non-human glycans and their closely related structural isomers. We demonstrate that the straightforward use of high-abundance diagnostic ions and complementary fragments under the positive ionization low-energy collision-induced dissociation is a universal approach to rapidly discriminate branch-linkage structures of biantennary glycans. Our findings reveal the structural diversity of non-human glycans and sulfation of α-galactosylated glycans, providing both an analytical method and candidate structures that could potentially be used in the crucial quality control of therapeutic mAb products.

Egg yolk sialylglycopeptide: purification, isolation and characterization of N-glycans from minor glycopeptide species

Sialylglycopeptide (SGP) is a readily available naturally occurring glycopeptide obtained from hen egg yolk which is now commercially available. During SGP extraction, other minor glycopeptide species are identified, bearing N-glycan structures that might be of interest, such as asymmetrically branched and triantennary glycans. As the scale of SGP production increases, recovery of minor glycopeptides and their N-glycans can become more feasible. In this paper, we aim to provide structural characterization of the N-glycans derived from these minor glycopeptides.

A New Strategy Coupling Ion-Mobility-Selective CID and Cryogenic IR Spectroscopy to Identify Glycan Anomers

Determining the primary structure of glycans remains challenging due to their isomeric complexity. While high-resolution ion mobility spectrometry (IMS) has recently allowed distinguishing between many glycan isomers, the arrival-time distributions (ATDs) frequently exhibit multiple peaks, which can arise from positional isomers, reducing-end anomers, or different conformations. Here, we present the combination of ultrahigh-resolution ion mobility, collision-induced dissociation (CID), and cryogenic infrared (IR) spectroscopy as a systematic method to identify reducing-end anomers of glycans. Previous studies have suggested that high-resolution ion mobility of sodiated glycans is able to separate the two reducing-end anomers. In this case, Y-fragments generated from mobility-separated precursor species should also contain a single anomer at their reducing end. We confirm that this is the case by comparing the IR spectra of selected Y-fragments to those of anomerically pure mono- and disaccharides, allowing the assignment of the mobility-separated precursor and its IR spectrum to a single reducing-end anomer. The anomerically pure precursor glycans can henceforth be rapidly identified on the basis of their IR spectrum alone, allowing them to be distinguished from other isomeric forms.

Collision-Induced Dissociation of Cellobiose and Maltose

Structure determination is a longstanding bottleneck of carbohydrate research. Tandem mass spectrometry (MS/MS) is one of the most widely used methods for carbohydrate structure determination. However, the effectiveness of MS/MS depends on how the precursor structures are derived from the observed fragments. Understanding the dissociation mechanisms is crucial for MS/MS-based structure determination. Herein, we investigate the collision-induced dissociation mechanism of β-cellobiose and β-maltose sodium adducts using quantum chemical calculations and experimental measurements. Four dissociation channels are studied. Dehydration mainly occurs through the transfer of an H atom to O1 of the sugar at the reducing end, followed by a C1-O1 bond cleavage; cross-ring dissociation starts with a ring-opening reaction, which occurs through the transfer of an H atom from O1 to O5 of the sugar at the reducing end. These two dissociation channels are analogous to that of glucose monosaccharide. The third channel, generation of B₁ and Y₁ ions, occurs through the transfer of an H atom from O3 (cellobiose) or O2 (maltose) to O1 of the sugar at the nonreducing end, followed by a glycosidic bond cleavage. The fourth channel, C₁-Z₁ fragmentation, has two mechanisms: (1) the transfer of an H atom from O3 or O2 to O4 of the sugar at the reducing end to generate C ions in the ring form and (2) the transfer of an H atom from O3 of the sugar at the reducing end to O5 of the sugar at the nonreducing end to produce C ions in the linear form. The results of calculations are supported by experimental collision-induced dissociation spectral measurements.

High-Throughput Multiplexed Infrared Spectroscopy of Ion Mobility-Separated Species Using Hadamard Transform

Coupling vibrational ion spectroscopy with high-resolution ion mobility separation offers a promising approach for detailed analysis of biomolecules in the gas phase. Improvements in the ion mobility technology have made it possible to separate isomers with minor structural differences, and their interrogation with a tunable infrared laser provides vibrational fingerprints for unambiguous database-enabled identification. Nevertheless, wide analytical application of this technique requires high-throughput approaches for acquisition of vibrational spectra of all species present in complex mixtures. In this work, we present a novel multiplexed approach and demonstrate its utility for cryogenic ion spectroscopy of peptides and glycans in mixtures. Since the method is based on Hadamard transform multiplexing, it yields infrared spectra with an increased signal-to-noise ratio compared to a conventional signal averaging approach.

Structural Determination of Polysaccharides Lichenin Using Logically Derived Sequence Tandem Mass Spectrometry

A new mass spectrometry method, logically derived sequence (LODES) tandem mass spectrometry (MSⁿ), was applied to determine the primary structure of polysaccharide lichenin. Conventional polysaccharide structural analysis requires complex processes, including derivation, permethylation, gas chromatography-mass spectrometry, and nuclear magnetic resonance spectrometry. Many of these processes can be replaced by LODES/MSⁿ. In this new method, polysaccharides are hydrolyzed into monosaccharides, disaccharides, and oligosaccharides, and structures of these molecules are determined using LODES/MSⁿ. The application of LODES/MSⁿ for determination of primary structure of polysaccharide lichenin was demonstrated. The repeating unit of lichenin was determined to be An-Bn, where A represents β-Glc-(1 → 4)-β-Glc-(1 → 4)-β-Glc-(1 → 3)-Glc, B represents β-Glc-(1 → 4)-β-Glc-(1 → 4)-β-Glc-(1 → 4)-β-Glc-(1 → 3)-Glc, n is an integral, and n ≥ 2 exists but n = 1 cannot be excluded. LODES/MSⁿ, which substantially reduces the time, effort, and sample quantity necessary for structural determination of oligosaccharides, is a powerful tool for polysaccharide primary structural determination.

De novo structural determination of oligosaccharide isomers in glycosphingolipids using logically derived sequence tandem mass spectrometry

Despite the importance of carbohydrates in biological systems, structural determination of carbohydrates remains difficult because of the large number of isomers. In this study, a new mass spectrometry method, namely logically derived sequence tandem mass spectrometry (LODES/MSⁿ), was developed to characterize oligosaccharide structures. In this approach, sequential collision-induced dissociation (CID) of oligosaccharides is performed in an ion trap mass spectrometer to identify the linkage position, anomeric configuration, and stereoisomers of each monosaccharide in the oligosaccharides. The CID sequences are derived from carbohydrate dissociation mechanisms. LODES/MSⁿ does not require oligosaccharide standards or the prior knowledge of the rules and principles of biosynthetic pathways; thus LODES/MSⁿ is particularly useful for the investigation of undiscovered oligosaccharides. We demonstrated that the structure of core oligosaccharides in glycosphingolipids can be identified from more than 500 000 isomers using LODES/MSⁿ. The same method can be applied for determining the structures of other oligosaccharides, such as N-, and O-glycans, and free oligosaccharides in milk.

The glycosylation in SARS-CoV-2 and its receptor ACE2

Coronavirus disease 2019 (COVID-19), a highly infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has infected more than 235 million individuals and led to more than 4.8 million deaths worldwide as of October 5 2021. Cryo-electron microscopy and topology show that the SARS-CoV-2 genome encodes lots of highly glycosylated proteins, such as spike (S), envelope (E), membrane (M), and ORF3a proteins, which are responsible for host recognition, penetration, binding, recycling and pathogenesis. Here we reviewed the detections, substrates, biological functions of the glycosylation in SARS-CoV-2 proteins as well as the human receptor ACE2, and also summarized the approved and undergoing SARS-CoV-2 therapeutics associated with glycosylation. This review may not only broad the understanding of viral glycobiology, but also provide key clues for the development of new preventive and therapeutic methodologies against SARS-CoV-2 and its variants.

Identification of Anomericity and Linkage of Arabinose and Ribose through Collision-Induced Dissociation

Arabinose and ribose are two common pentoses that exist in both furanose and pyranose forms in plant and bacteria oligosaccharides. In this study, each pentose isomer, namely α-furanose, β-furanose, α-pyranose, and β-pyranose, was first separated through high-performance liquid chromatography followed by an investigation of collision-induced dissociation in an ion trap mass spectrometer. The major dissociation channels, dehydration and cross-ring dissociation, were analyzed by using high-level quantum chemistry calculations and transition state theory. The branching ratio of major dissociation channels was governed by two geometrical features: one being the cis or trans configuration of O1 and O2 atoms determining dehydration preferability and the other being the number of hydroxyl groups on the same side of the ring as the O1 atom determining the preferability of cross-ring dissociation. The relative branching ratios of the major channels were used to identify anomericity and the linkages of arabinose and ribose. Arabinose in the β-configuration and ribose in the α-configuration are predicted to have larger relative dehydration branching ratios than arabinose in the α-configuration and ribose in the β-configuration, respectively. Arabinose and ribose at the reducing end of oligosaccharides with 1 → 2 (pyranose and furanose), 1 → 3 (pyranose and furanose), 1 → 4 (pyranose only), and 1 → 5 (furanose only) linkages are predicted to undergo ^0,2X, ^0,3X, ^0,2A, and ^0,2A/^0,3A cross-ring dissociation, respectively. Application of the dissociation mechanism to the disaccharide linkage determination is demonstrated.