Convenient pre-separation method depends on negative charges suitable for glycan sequencing analysis.

For precise structural analysis of complex glycans, it is necessary to fractionate glycans based on acidity prior to liquid chromatography-mass spectrometry analysis. Conventional fractionation using high-performance liquid chromatography is time consuming and not high throughput. Therefore, we developed a rapid method for the fractionation using a small cartridge column. This enables rapid multi-sample processing for glycan sequencing.

Sequential modifications of glycans by linkage-specific alkylamidation of sialic acids and permethylation.

Permethylation is useful for glycosidic linkage analysis, but is often accompanied by a large proportion of by-products, especially for glycans containing sialic acids (Sia). Unlike hydroxyl groups of glycans, which are converted to stable methyl ethers by permethylation, the carboxylic acids on Sia are converted to methyl esters, which are easily reversible to carboxylate under alkaline conditions. To overcome this problem, we used linkage-specific alkylamidation to protect Sia prior to the permethylation. This method not only decreased the levels of by-products, but also enabled us to distinguish isomers of α2,3- and α2,6-Sia while simultaneously determining other glycosidic linkages.

Quantitative LC-MS and MS/MS analysis of sialylated glycans modified by linkage-specific alkylamidation.

Sialic acids (Sia) are involved in various biological and pathological processes, and are often found attached to non-reducing ends of glycans through either α2,3- or α2,6-linkages. To quantitatively analyze glycan structures with these linkage isoforms by liquid chromatography-mass spectrometry (LC-MS), we established a linkage-specific two-step alkylamidation method for N-glycans. Using this method, carboxyl groups of α2,3- and α2,6-linked Sia are derivatized with two kinds of alkylamines with different mass values in a linkage-specific manner, allowing products to be easily distinguished. The reaction efficiencies for di-, tri-, and tetra-sialyl PA-N-glycans were >94%, with few by-products. Mixtures of 2-aminopyridine (PA)-tagged N-glycans from human α1-acid glycoprotein were subjected to the method, and products were analyzed by LC-MS and MS/MS, and simultaneously monitored with a fluorescence detector. The relative content of Siaα2-3Gal and Siaα2-6Gal was estimated from the integrated fluorescence intensity of each peak. Moreover, MS/MS data clearly indicated characteristic B-ion fragments of N-glycan branches, such as the sialyl Lex sequence, with Sia linkage-specific alkylamidation, suggesting that this method also provides useful information of branch sequences. We optimized the method with the aim of (1) enabling high-throughput analysis and (2) maximizing the analysis of glycans from various types of samples, including highly heterogeneous glycans.

Structures and developmental alterations of N-glycans of zebrafish embryos.

Zebrafish is a model organism suitable for studying vertebrate development. We analyzed the N-glycan structures of zebrafish embryos and their alterations during zebrafish embryogenesis to obtain basic data for studying the roles of N-glycosylation. Multiple modes of high-performance liquid chromatography and multistage mass spectrometry were used for structural analysis of N-glycans. The N-glycans from deyolked embryos at 36 hours postfertilization, a mid-pharyngula stage, contained relatively higher amounts of complex- and hybrid-type glycans with LacNAc (Galß1-4GlcNAc) and/or sialyl LacNAc without additional ß1,4-Gal, which are commonly found in mammalian tissues, as well as abundant oligomannose-type glycans. Some of the complex- and hybrid-type glycans possessed various extended LacNAc structures, such as Galß1-4LacNAc, LacNAc-repeat or unique (+/- dHex)-GalNAcα1-GlcNAcß1-LacNAc. In contrast, the yolk of the embryo contains predominant oligomannose-type glycans and complex-type glycans with Galß1-4(Siaα2-3)Galß1-4(Fucα1-3)GlcNAc antennae. N-Glycan profiles obtained from deyolked embryos at different stages showed stage-dependent variation of complex- and hybrid-type glycans. At gastrula and early segmentation stages, complex- and hybrid-type glycans were minor components, and their antenna structures were mainly sialyl LacdiNAc (Siaα2-6GalNAcß1-4GlcNAc). From the mid-segmentation to pharyngula stages, those with LacNAc and/or α2,6-sialyl LacNAc antenna structures increased remarkably, and those with α2,3-sialyl LacNAc antenna, core α1,6-Fuc and bisecting GlcNAc modifications increased gradually. These results suggest the presence of mechanisms for regulating the antenna structures of complex/hybrid N-glycan biosynthesis in the phylotypic stage of vertebrate development.

Determination of galactosamine impurities in heparin sodium using fluorescent labeling and conventional high-performance liquid chromatography.

Heparin is a sulfated glycosaminoglycan (GAG), which contains N-acetylated or N-sulfated glucosamine (GlcN). Heparin, which is generally obtained from the healthy porcine intestines, is widely used as an anticoagulant during dialysis and treatments of thrombosis such as disseminated intravascular coagulation. Dermatan sulfate (DS) and chondroitin sulfate (CS), which are galactosamine (GalN)-containing GAGs, are major process-related impurities of heparin products. The varying DS and CS contents between heparin products can be responsible for the different anticoagulant activities of heparin. Therefore, a test to determine the concentrations of GalN-containing GAG is essential to ensure the quality and safety of heparin products. In this study, we developed a method for determination of relative content of GalN from GalN-containing GAG in heparin active pharmaceutical ingredients (APIs). The method validation and collaborative study with heparin manufacturers and suppliers showed that our method has enough specificity, sensitivity, linearity, repeatability, reproducibility, and recovery as the limiting test for GalN from GalN-containing GAGs. We believe that our method will be useful for ensuring quality, efficacy, and safety of pharmaceutical heparins. On July 30, 2010, the GalN limiting test based on our method was adopted in the heparin sodium monograph in the Japanese Pharmacopoeia.

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.

One-step purification method for pyridylamino glycans.

Pyridylamino derivatization is suitable for the microanalysis of glycans but there is a problem in that by-products of the labeling reaction and fluorescent substances from samples occasionally interfere with the detection of pyridylamino glycans. We have reported a three-step purification method (S. Natsuka et al., FEBS J., 278, 452-460 (2011)). That method gives high purity and high yield for various glycans, but it is rather complicated. In this study I checked the efficiency of a one-step method with a spin column for the purification of pyridylamino glycans and found that it was excellent in respect of throughput. High-throughput analysis of N-glycans is desirable in glycomics.

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, sLex), whereas no sLex 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.

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 Glcß1-4GlcNAc-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.

ß-galactosidases from jack bean and Streptococcus have different cleaving abilities towards fucose-containing sugars.

We examined the sugar-cleaving abilities of ß-galactosidases from jack bean and Streptococcus towards sugars containing fucose residues, and found that jack bean ß-galactosidase has an ability to cleave the ß1-3 linkage between galactose (Gal) and fucose (Fuc) residues, but not ß1-4 linkage. On the other hand, streptococcal ß-galactosidase was found to cleave the linkage in both Galß1-4Fuc and Galß1-3Fuc disaccharide units. Such a difference in sugar-cleaving abilities between these 2 ß-galactosidases will be useful for structural analysis of glycans, especially those from species belonging to Protostomia, such as Caenorhabditis elegans.

A convenient purification method for pyridylamino monosaccharides.

Pyridylamino derivatization is suitable for the microanalysis of sugars, but there is a problem in that by-products of the labeling reaction and fluorescent substances from samples occasionally interfere with the detection of pyridylamino sugars. Especially, interference by them is serious in monosaccharide analysis. I have developed a convenient purification method for pyridylamino monosaccharides by the use of a spin column with boronate-conjugated resin.

A comparative study of monosaccharide composition analysis as a carbohydrate test for biopharmaceuticals.

The various monosaccharide composition analysis methods were evaluated as monosaccharide test for glycoprotein-based pharmaceuticals. Neutral and amino sugars were released by hydrolysis with 4-7N trifluoroacetic acid. The monosaccharides were N-acetylated if necessary, and analyzed by high-performance liquid chromatography (HPLC) with fluorometric or UV detection after derivatization with 2-aminopyridine, ethyl 4-aminobenzoate, 2-aminobenzoic acid or 1-phenyl-3-methyl-5-pyrazolone, or high pH anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Sialic acids were released by mild acid hydrolysis or sialidase digestion, and analyzed by HPLC with fluorometric detection after derivatization with 1,2-diamino-4,5-methylenedioxybenzene, or HPAEC-PAD. These methods were verified for resolution, linearity, repeatability, and accuracy using a monosaccharide standard solution, a mixture of epoetin alfa and beta, and alteplase as models. It was confirmed that those methods were useful for ensuring the consistency of glycosylation. It is considered essential that the analytical conditions including desalting, selection of internal standards, release of monosaccharides, and gradient time course should be determined carefully to eliminate interference of sample matrix. Various HPLC-based monosaccharide analysis methods were evaluated as a carbohydrate test for glycoprotein pharmaceuticals by an inter-laboratory study.

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

Glycans in tissues are structurally diverse and usually include a large number of isomers that cannot be easily distinguished by mass spectrometry (MS). To address this issue, we developed a combined method that can efficiently separate and identify glycan isomers. First, we separated 2-aminopyridine (PA)-derivatized N-glycans from chicken colon by reversed-phase liquid chromatography (LC) and directly analyzed them by electrospray ionization (ESI)-MS and MS/MS to obtain an overview of the structural features of tissue glycans. Next, we deduced the structures of isomers based on their elution positions, full MS, and MS/MS data, before or after digestions with several exoglycosidases. In this method, the elution position differed greatly depending on the core structure and branching pattern, allowing multiantennary N-glycan structures to be easily distinguished. To further determine linkages of branch sequences, we modified PA-N-glycans with sialic acid linkage-specific alkylamidation and/or permethylation, and analyzed the products by LC-MS and multistage MS. We determined the relative abundances of core structures, branching patterns, and branch sequences of N-glycans from chicken colon, and confirmed presence of characteristic branch sequences such as Lex, sialyl Lex, sulfated LacNAc, LacNAc repeat, and LacdiNAc. The results demonstrated that our method is useful for comparing N-glycomes among various tissue samples.

Involvement of murine ß-1,4-galactosyltransferase V in lactosylceramide biosynthesis.

Human ß-1,4-galactosyltransferase (ß-1,4-GalT) V was shown to be involved in the biosynthesis of N-glycans, O-glycans and lactosylceramide (Lac-Cer) by in vitro studies. To determine its substrate specificity, enzymatic activity and its products were analyzed using mouse embryonic fibroblast (MEF) cells from ß-1,4-GalT V (B4galt5)-mutant mice. Analysis of expression levels of the ß-1,4-GalT I-VI genes revealed that the expression of the ß-1,4-GalT V gene in B4galt5 ( +/- ) - and B4galt5 ( -/- ) -derived MEF cells are a half and null when compared to that of B4galt5 ( +/+ )-derived MEF cells without altering the expression levels of other ß-1,4-GalT genes. These MEF cells showed no apparent difference in their growth. When ß-1,4-GalT activities were determined towards GlcNAcß-S-pNP, no significant difference in its specific activity was obtained among B4galt5 ( +/+ )-, B4galt5 ( +/- ) - and B4galt5 ( -/- ) -derived MEF cells. No significant differences were obtained in structures and amounts of N-glycans and lectin bindings to membrane glycoproteins among B4galt5 ( +/+ )-, B4galt5 ( +/- ) - and B4galt5 ( -/- ) -derived MEF cells. However, when cell homogenates were incubated with glucosylceramide in the presence of UDP-[(3)H]Gal, Lac-Cer synthase activity in B4galt5 ( +/- ) - and B4galt5 ( -/- ) -derived MEF cells decreased to 41% and 11% of that of B4galt5 ( +/+ )-derived MEF cells. Consistent with this, amounts of Lac-Cer and its derivative GM3 in B4galt5 ( -/- ) -derived MEF cells decreased remarkably when compared with those of B4galt5 ( +/+ )-derived MEF cells. These results indicate that murine ß-1,4-GalT V is involved in Lac-Cer biosynthesis.

N-Glycosylation patterns of hemolymph glycoproteins from Biomphalaria glabrata strains expressing different susceptibility to Schistosoma mansoni infection.

Comparative analyses of the N-glycosylation pattern of hemolymph glycoproteins from Biomphalaria glabrata strains Puerto Rico (BgPR) and Salvador (BgBS-90), differing in their susceptibility towards Schistosoma mansoni infection, were performed by Western blotting, enzyme-linked immunosorbent assays, two-dimensional high-performance liquid chromatography and mass spectrometry. Obtained data demonstrated an enhanced expression of serologically cross-reacting, fucosylated carbohydrate epitopes by the highly susceptible BgPR-strain in comparison to the resistant BgBS-90-strain. In particular, glycoproteins of BgPR snails exhibited larger amounts of glycans with (ß1-2)-linked xylose or terminal Fuc(α1-3)GalNAc(ß1-4)[±Fuc(α1-3)]GlcNAc(ß1-)-units which are known to mediate cross-reactivity with schistosomal glycoconjugates. This finding could be corroborated by immunohistochemical studies showing again an enhanced expression of such carbohydrate epitopes in BgPR tissue. Hence, our results provide evidence for a correlation of B. glabrata susceptibility towards S. mansoni infection and the expression of carbohydrate determinants shared by the parasite and its intermediate host.

The och1 mutant of Schizosaccharomyces pombe produces galactosylated core structures of N-linked oligosaccharides.

Unlike the budding yeast Saccharomyces cerevisiae, the fission yeast Schizosaccharomyces pombe synthesizes large outer chains on the N-linked oligosaccharides that consist mainly of D-Gal and D-Man residues. The fission yeast och1(+) gene product has alpha1,6-mannosyltransferase activity, and Och1p is the key enzyme in the initiation of outer chain elongation. Although the in vitro substrate specificity of S. pombe Och1p has been reported (Yoko-o et al., FEBS Lett., 489, 75-80 (2001)), the structure of the N-linked oligosaccharides of och1Delta cells has not been investigated. In this study, we report a structural analysis of S. pombe N-linked oligosaccharides. Lectin blot analysis indicated that galactose residues were attached to the cell surface glycoproteins of the och1Delta cells. We conducted a structural analysis of pyridylaminated N-linked oligosaccharides prepared from galactomannoproteins by HPLC and (1)H NMR. These analyses revealed that the N-linked oligosaccharides of the och1Delta cells displayed heterogeneity in the glycan consisting of Hex(11-15)GlcNAc(2). The structural heterogeneity arose mainly from the addition of alpha1,2- and alpha1,3-Gal residues to the Man(9)GlcNAc(2) core structure.

Characterisation of N-glycans in the epithelial-like tissue of the rat cochlea.

Membrane proteins (such as ion channels, transporters, and receptors) and secreted proteins are essential for cellular activities. N-linked glycosylation is involved in stability and function of these proteins and occurs at Asn residues. In several organs, profiles of N-glycans have been determined by comprehensive analyses. Nevertheless, the cochlea of the mammalian inner ear, a tiny organ mediating hearing, has yet to be examined. Here, we focused on the stria vascularis, an epithelial-like tissue in the cochlea, and characterised N-glycans by liquid chromatography with mass spectrometry. This hypervascular tissue not only expresses several ion transporters and channels to control the electrochemical balance in the cochlea but also harbours different transporters and receptors that maintain structure and activity of the organ. Seventy-nine N-linked glycans were identified in the rat stria vascularis. Among these, in 55 glycans, the complete structures were determined; in the other 24 species, partial glycosidic linkage patterns and full profiles of the monosaccharide composition were identified. In the process of characterisation, several sialylated glycans were subjected sequentially to two different alkylamidation reactions; this derivatisation helped to distinguish α2,3-linkage and α2,6-linkage sialyl isomers with mass spectrometry. These data should accelerate elucidation of the molecular architecture of the cochlea.

Preparation of a Molecular Library of Branched ß-Glucan Oligosaccharides Derived from Laminarin.

To study the structure of ß-glucans, we developed a separation method and molecular library of ß-glucan oligosaccharides. The oligosaccharides were prepared by partial acid hydrolysis from laminarin, which is a ß-glucan of Laminaria digitata. They were labeled with the 2-aminopyridine fluorophore and separated to homogeneity by size-fractionation and reversed phase high-performance liquid chromatography (HPLC). Branching structures of all isomeric oligosaccharides from trimers to pentamers were determined, and a two-dimensional (2D)-HPLC map of the ß-glucan oligosaccharides was made based on the data. Next, structural analysis of the longer ß-glucan oligosaccharide was performed using the 2D-HPLC map. A branched decamer oligosaccharide was isolated from the ß-glucan and cleaved to smaller oligosaccharides by partial acid hydrolysis. The structure of the longer oligosaccharide was successfully elucidated from the fragment structures determined by the 2D-HPLC map. The molecular library and the 2D-HPLC map described in this study will be useful for the structural analysis of ß-glucans.

Free oligosaccharides with Lewis x structure expressed in the segmentation period of zebrafish embryo.

We previously reported that zebrafishalpha1-3fucosyltrasferase 1 (zFT1) was expressed in embryos at the segmentation period, and was capable of synthesizing the Lewis x epitope [Gal beta1-4(Fuc alpha1-3)GlcNAc] [Kageyama et.al, J. Biochem., 125, 838-845 (1999)]. In the current study, we attempted to detect the enzyme products of zFT1 in zebrafish embryos. Oligosaccharides were prepared from the zebrafish embryos at 12, 18 and 48 h after fertilization and labelled with a fluorophore, 2-aminopyridine, for highly sensitive detections. Pyridylamino (PA)-oligosaccharides that were alpha1-3/4fucosidase sensitive and time-dependently expressed at 18 h after fertilization were identified as candidates for the in vivo products synthesized by zFT1. Structures of these oligosaccharides were determined by a combination of exoglycosidase digestions and two-dimensional HPLC sugar mapping to be the biantennary complex-type structures with two Lewis x epitopes: (Gal beta1-4)(0,1,2)-{Gal beta1-4(Fuc alpha1-3)GlcNAc beta1-2Man alpha1-6[Gal beta1-4(Fuc alpha1-3)GlcNAc beta1-2Man alpha1-3]}Man beta1-4GlcNAc, and (Gal beta1-4)(0,1)-{Gal beta1-4(Fuc alpha1-3)GlcNAc beta1-2Man alpha1-6[Gal beta1-4(Fuc alpha1-3)GlcNAc beta1-2Man alpha1-3]} Man beta1-4GlcNAc beta1-4GlcNAc. The presence of Lewis x structure of these oligosaccharides together with their expression time suggests that they are products of zFT1. Remarkably, most of these oligosaccharides were free form. Furthermore, we detected an endo-beta-N-acetylglucosaminidase activity in the 18 h embryo. These results suggest that the oligosaccharides synthesized by zFT1 are present in the embryo at the segmentation period in free form, owing to the liberation from glycoproteins with endo-beta-N-acetylglucosaminidase(s) and/or glycoamidase(s).

Comparative biochemical study of N-linked glycans from skin of a squid, Todarodes pacificus.

For comparative biochemical interest, we analyzed the structures of N-glycans in a squid belonging to the Lophotrochozoa, one of the protostome clades. N-Glycans were prepared from squid skin by hydrazinolysis and re-N-acetylation followed by fluorescent tagging with 2-aminopyridine. The labeled N-glycans were purified, and their structures were determined by the two-dimensional HPLC mapping method combined with glycosidase digestions and mass spectrometry. We found that high mannose-type glycans, paucimannose-type glycans and complex-type glycans with a type-1 structure (Galbeta1-3GlcNAc) were dominant in squid skin. The complex-type glycans detected in the squid were similar to those in vertebrates, but have not yet been found in the Ecdysozoa, which is another protostome clade. However, paucimannose-type glycans are commonly found in the Ecdysozoa. Thus, the N-glycan structures of the squid belonging to the Lophotrochozoa have features common to those in vertebrates and the Ecdysozoa including insects and nematodes.