Toward robust N-glycomics of various tissue samples that may contain glycans with unknown or unexpected structures

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2021-2022

The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates is a well-established technique and this review is the 12th update of the original article published in 1999 and brings coverage of the literature to the end of 2022. As with previous review, this review also includes a few papers that describe methods appropriate to analysis by MALDI, such as sample preparation, even though the ionization method is not MALDI. The review follows the same format as previous reviews. It is divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of computer software for structural identification. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other general areas such as medicine, industrial processes, natural products and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. MALDI is still an ideal technique for carbohydrate analysis, particularly in its ability to produce single ions from each analyte and advancements in the technique and range of applications show little sign of diminishing.

Complexity and modification of the bull sperm glycocalyx during epididymal maturation

Mammalian spermatozoa have a surface covered with glycocalyx, consisting of heterogeneous glycoproteins and glycolipids. This complexity arises from diverse monosaccharides, distinct linkages, various isomeric glycans, branching levels, and saccharide sequences. The glycocalyx is synthesized by spermatozoa developing in the testis, and its subsequent alterations during their transit through the epididymis are a critical process for the sperm acquisition of fertilizing ability. In this study, we performed detailed analysis of the glycocalyx on the sperm surface of bull spermatozoa in relation to individual parts of the epididymis using a wide range (24) of lectins with specific carbohydrate binding preferences. Fluorescence analysis of intact sperm isolated from the bull epididymides was complemented by Western blot detection of protein extracts from the sperm plasma membrane fractions. Our experimental results revealed predominant sequential modification of bull sperm glycans with N-acetyllactosamine (LacNAc), followed by subsequent sialylation and fucosylation in a highly specific manner. Additionally, variations in the lectin detection on the sperm surface may indicate the acquisition or release of glycans or glycoproteins. Our study is the first to provide a complex analysis of the bull sperm glycocalyx modification during epididymal maturation.

Microheterogeneity and Individual Differences of Human Urinary N-Glycome under Normal Physiological Conditions

Urine is considered an outstanding biological fluid for biomarker discovery, reflecting both systemic and urogenital physiology. However, analyzing the N-glycome in urine in detail has been challenging due to the low abundance of glycans attached to glycoproteins compared to free oligosaccharides. Therefore, this study aims to thoroughly analyze urinary N-glycome using LC-MS/MS. The N-glycans were released using hydrazine and labeled with 2-aminopyridine (PA), followed by anion-exchange fractionation before LC-MS/MS analysis. A total of 109 N-glycans were identified and quantified, of which 58 were identified and quantified repeatedly in at least 80% of samples and accounted for approximately 85% of the total urinary glycome signal. Interestingly, a comparison between urine and serum N-glycome revealed that approximately 50% of the urinary glycome could originate from the kidney and urinary tract, where they were exclusively identified in urine, while the remaining 50% were common in both. Additionally, a correlation was found between age/sex and the relative abundances of urinary N-glycome, with more age-related changes observed in women than men. The results of this study provide a reference for human urine N-glycome profiling and structural annotations.

Mass Spectrometry-Based Glycoproteomic Workflows for Cancer Biomarker Discovery

Glycosylation has a clear role in cancer initiation and progression, with numerous studies identifying distinct glycan features or specific glycoproteoforms associated with cancer. Common findings include that aggressive cancers tend to have higher expression levels of enzymes that regulate glycosylation as well as glycoproteins with greater levels of complexity, increased branching, and enhanced chain length1. Research in cancer glycoproteomics over the last 50-plus years has mainly focused on technology development used to observe global changes in glycosylation. Efforts have also been made to connect glycans to their protein carriers as well as to delineate the role of these modifications in intracellular signaling and subsequent cell function. This review discusses currently available techniques utilizing mass spectrometry-based technologies used to study glycosylation and highlights areas for future advancement.

Synthesis of 2-Nitro-2,3-Unsaturated Glycosides by a Nanomagnetic Catalyst Fe3O4@C@Fe(III)

A sustainable magnetic core-shell nanocatalyst Fe₃O₄@C@Fe(III) was successfully applied in the synthesis of a series of 2-nitro-2,3-unsaturated O-glycosides with excellent yields (up to 89%) and high stereoselectivity (α:β > 19:1). The substrate ranges are widely applicable, including different kinds of alcohols and even structurally complex acceptors. In addition, phenols could be applied in good yields. Moreover, the catalyst could be easily separated from the reaction by the application of an external magnetic force and reused a minimum of five times without any significant decrease in catalytic performance.

Increased levels of acidic free-N-glycans, including multi-antennary and fucosylated structures, in the urine of cancer patients

We recently reported increased levels of urinary free-glycans in some cancer patients. Here, we focused on cancer related alterations in the levels of high molecular weight free-glycans. The rationale for this study was that branching, elongation, fucosylation and sialylation, which lead to increases in the molecular weight of glycans, are known to be up-regulated in cancer. Urine samples from patients with gastric cancer, pancreatic cancer, cholangiocarcinoma and colorectal cancer and normal controls were analyzed. The extracted free-glycans were fluorescently labeled with 2-aminopyridine and analyzed by multi-step liquid chromatography. Comparison of the glycan profiles revealed increased levels of glycans in some cancer patients. Structural analysis of the glycans was carried out by performing chromatography and mass spectrometry together with enzymatic or chemical treatments. To compare glycan levels between samples with high sensitivity and selectivity, simultaneous measurements by reversed-phase liquid chromatography-selected ion monitoring of mass spectrometry were also performed. As a result, three lactose-core glycans and 78 free-N-glycans (one phosphorylated oligomannose-type, four sialylated hybrid-type and 73 bi-, tri- and tetra-antennary complex-type structures) were identified. Among them, glycans with α1,3-fucosylation ((+/− sialyl) Lewis X), triply α2,6-sialylated tri-antennary structures and/or a (Man3)GlcNAc1-core displayed elevated levels in cancer patients. However, simple α2,3-sialylation and α1,6-core-fucosylation did not appear to contribute to the observed increase in the level of glycans. Interestingly, one tri-antennary free-N-glycan that showed remarkable elevation in some cancer patients contained a unique Glcβ1-4GlcNAc-core instead of the common GlcNAc2-core at the reducing end. This study provides further insights into free-glycans as potential tumor markers and their processing pathways in cancer.

Structural analysis of N-glycans in chicken trachea and lung reveals potential receptors of chicken influenza viruses

Although avian influenza A viruses (avian IAVs) bind preferentially to terminal sialic acids (Sia) on glycans that possess Siaα2-3Gal, the actual glycan structures found in chicken respiratory tracts have not been reported. Herein, we analyzed N-glycan structures in chicken trachea and lung, the main target tissues of low pathogenic avian IAVs. 2-Aminopyridine (PA)-labeled N-glycans from chicken tissues were analyzed by combined methods using reversed-phase liquid chromatography (LC), electrospray ionization (ESI)-mass spectrometry (MS), MS/MS, and multistage MS (MSⁿ), with or without modifications using exoglycosidases, sialic acid linkage-specific alkylamidation (SALSA), and/or permethylation. The results of SALSA indicated that PA-N-glycans in both chicken trachea and lung harbored slightly more α2,6-Sia than α2,3-Sia. Most α2,3-Sia on N-glycans in chicken trachea was a fucosylated form (sialyl Lewis X, sLe^x), whereas no sLe^x was detected in lung. By contrast, small amounts of N-glycans with 6-sulfo sialyl LacNAc were detected in lung but not in trachea. Considering previous reports that hemagglutinins (HAs) of avian IAVs originally isolated from chicken bind preferentially to α2,3-Sia with or without fucosylation and/or 6-sulfation but not to α2,6-Sia, our results imply that avian IAVs do not evolve to possess HAs that bind preferentially to α2,6-Sia, regardless of the abundance of α2,6-Sia.

Recent advances and trends in sample preparation and chemical modification for glycan analysis

Growing significance of glycosylation in protein functions has accelerated the development of methodologies for detection, identification, and characterization of protein glycosylation. In the past decade, glycobiology research has been advanced by innovative techniques with further progression in the post-genome era. Although significant technical progress has been made in terms of analytical throughput, comprehensiveness, and sensitivity, most methods for glycosylation analysis still require laborious and time-consuming sample preparation tasks. Additionally, sample preparation methods that are focused on specific glycan(s) require an in-depth understanding of various issues in glycobiology. In this review, modern sample preparation and chemical modification methods for the structural and quantitative glycan analyses together with the challenges and advantages of recent sample preparation methods are summarized. The techniques presented herein can facilitate the exploration of biomarkers, understanding of unknown glycan functions, and development of biopharmaceuticals.

Tissue N-Glycan Analysis Using LC-MS, MS/MS, and MSn

Tissue glycans usually contain various structures, from simple to highly complicated, in different quantities. N-Glycans are particularly heterogeneous, with up to pentaantennary structures, different branch sequences, and several isomeric structures. 2-Aminopyridine (PA) tagging on released N-glycans is useful for separating isomers and to quantitatively analyze both the major and minor glycan structures in tissues using reversed-phase liquid chromatography (LC)-mass spectrometry (MS) and MS/MS analysis. Because the structural differences of PA-N-glycans influence their retention on a reversed-phase C18 column, it is easy to deduce the core structure, including core Fuc and bisecting GlcNAc as well as the branching pattern of each PA-N-glycan, based on the results of elution position, full MS, and MS/MS analysis. If more detailed structural analysis is required, combining sequential exoglycosidase digestions, sialic acid linkage-specific alkylamidation (SALSA), and/or SALSA/permethylation is useful for determining glycosidic linkages of branches. This article includes detailed protocols for the preparation of N-glycans released from glycoproteins/glycopeptides by glycoamidase F or hydrazinolysis, PA-tagging of N-glycans, fractionation with anion-exchange chromatography, and chemical or enzymatic modifications of PA-N-glycans, as well as reversed-phase LC-MS, MS/MS, and MSⁿ analysis of PA-N-glycans from tissues. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Preparation of released N-glycans from tissue samples using glycoamidase F Alternate Protocol: Preparation of released N-glycans from tissue samples by hydrazinolysis Basic Protocol 2: PA-tagging of N-glycans and sample cleanup Support Protocol 1: Monitoring of PA-N-glycans using normal-phase HPLC Basic Protocol 3: Anion-exchange chromatography of PA-N-glycans Basic Protocol 4: Sequential exoglycosidase digestions Basic Protocol 5: Determination of Sia-linkages by SALSA Support Protocol 2: Cotton-HILIC solid-phase extraction to remove reagents for alkylamidation Basic Protocol 6: Sequential modifications of glycans with SALSA and permethylation Basic Protocol 7: LC-MS and MS/MS analysis of PA-N-glycans (before permethylation) Basic Protocol 8: LC-MS, MS/MS, and MSⁿ analysis of PA-N-glycans (after permethylation).