Azido glycoside primer: a versatile building block for the biocombinatorial synthesis of glycosphingolipid analogues

In vitro synthesis of mucin-type O-glycans using saccharide primers comprising GalNAc-Ser and GalNAc-Thr residues

Mucin-type O-glycosylation of serine or threonine residue in proteins is known to be one of the major post-translational modifications. In this study, two novel alkyl glycosides, N^α-lauryl-O-(2-acetamido-2-deoxy-α-d-galactopyranosyl)-l-serineamide (GalNAc-Ser-C12) and N^α-lauryl-O-(2-acetamido-2-deoxy-α-d-galactopyranosyl)-l-threonineamide (GalNAc-Thr-C12) were synthesized as saccharide primers to prime mucin-type O-glycan biosynthesis in cells. Upon incubating human gastric cancer MKN45 cells with the saccharide primers, 22 glycosylated products were obtained, and their structures were analyzed using liquid chromatography-mass spectrometry and enzyme digestion. The amounts of glycosylated products were dependent on the amino acid residues in the saccharide primers. For example, in vitro synthesis of T antigen (Galβ1-3GalNAc), fucosyl-T (Fucα1-2Galβ1-3GalNAc), and sialyl-T (NeuAcα2-3Galβ1-3GalNAc) preferred a serine residue, whereas sialyl-Tn (NeuAcα2-6GalNAc) preferred a threonine residue. Furthermore, the glycosylated products derived from GalNAc-Ser/Thr-C12 and Gal-GalNAc-Ser/Thr-C12 using cell-free synthesis showed the same amino acid selectivity as those in the cell experiments. These results indicate that glycosyltransferases involved in the biosynthesis of mucin-type O-glycans distinguish amino acid residues conjugated to GalNAc. The saccharide primers developed in this study might be useful for comparing mucin-type oligosaccharides in cells and constructing oligosaccharide libraries to study cell function.

Comparative Quantification Method for Glycosylated Products Elongated on β-Xylosides Using a Stable Isotope-Labeled Saccharide Primer

The structures and amounts of glycosaminoglycan (GAG) produced by cells have attracted much interest because GAG biosynthesis activity can change in cellular processes such as disease and differentiation. β-Xylosides, also called saccharide primers, have been used as artificial acceptors not only to generate GAG oligosaccharides in cells and tissues but also to investigate their biosynthetic pathways. Various analytical methods have been applied to confirm the structure and amounts of GAG oligosaccharides elongated using saccharide primers, yet sample preparation processes such as solid-phase extraction in analysis can cause experimental error and disrupt accurate comparative quantification of glycosylated products. In this study, we developed a new quantification method using a deuterium-labeled saccharide primer. The "heavy" and "light" primers were chemically synthesized, and priming abilities were confirmed by liquid chromatography-tandem mass spectrometry. Relative peak areas of light/heavy products showed good linearity and were well correlated with the theoretical amounts of glycosylated products. Then, as a validation study, we carried out a biosynthesis inhibition assay using known GAG biosynthesis inhibitors. According to the relative quantification using saccharide primers, differences in the mode-of-action among the four GAG biosynthesis inhibitors were dependent on the GAG biosynthetic pathway. Our results indicate that the method will likely forge a new path for comparative glycosaminoglycomics using cultured cells and tissues.

AuBr3-catalyzed azidation of per-O-acetylated and per-O-benzoylated sugars

Herein we report, for the first time, the successful anomeric azidation of per-O-acetylated and per-O-benzoylated sugars by catalytic amounts of oxophilic AuBr3 in good to excellent yields. The method is applicable to a wide range of easily accessible per-O-acetylated and per-O-benzoylated sugars. While reaction with per-O-acetylated and per-O-benzoylated monosaccharides was complete within 1-3 h at room temperature, the per-O-benzoylated disaccharides needed 2-3 h of heating at 55 °C.

Glycosylation of Nα-lauryl-O-(β-D-xylopyranosyl)-L-serinamide as a saccharide primer in cells

N(α)-Lauryl-O-(β-D-xylopyranosyl)-L-serinamide (Xyl-Ser-C12) was synthesized as a saccharide primer to obtain oligosaccharides of glycosaminoglycan using the glycan biosynthetic potential of mouse osteosarcoma FBJ-S1 cells and Chinese hamster ovary (CHO) cells. The glycosylated products secreted into the culture medium were collected and analyzed by liquid chromatography-mass spectrometry and glycosidase digestion. The structure of the Xyl-Ser-C12 derivatives was investigated. Several glycosaminoglycan-type oligosaccharides, such as GalNAc-(GlcA-GlcNAc)(n)-GlcA-Gal-Gal-Xyl-Ser-C12, were detected, and identified as intermediates of the biosynthesis of heparan sulfate glycosaminoglycans. Xyl-Ser-C12 exhibited greater acceptor activity for the glycosylation of glycosaminoglycan-type oligosaccharides than p-nitrophenyl-β-D-xylopyranoside.

Large scale biosynthesis of ganglioside analogues by RERF-LC-AI cells cultured in HYPERFlask

The efficient production of ganglioside analogues was accomplished using RERF-LC-AI cells cultured in HYPERFlask (High Yield PERformance Flask). Eight kinds of ganglioside analogues (GM3, GM2, sialylparagloboside, GD3, di-sialylated lacto-N-tetraose, and another three kinds of analogues with intricate structures) were synthesized by the saccharide primer method using lung squamous-cell carcinoma line RERF-LC-AI and 12-azidododecyl β-lactoside primer. The yield for each analogue obtained using HYPERFlask was higher than yields obtained from 100-mm dishes.

Involvement of Ext1 and heparanase in migration of mouse FBJ osteosarcoma cells

To know the involvement of glycosaminoglycans (GAGs) in the metastasis of mouse FBJ osteosarcoma cells, N(α)-lauroyl-O-(β-D-xylopyranosyl)-L-serinamide (Xyl-Ser-C12), which initiates elongation of GAG chains using the glycan biosynthesis system in cells, was administered to FBJ cells with different metastatic capacities. Production of glycosylated products derived from Xyl-Ser-C12, especially heparan sulfate (HS) GAG-type oligosaccharides such as GalNAc-GlcA-GlcNAc-GlcA-Gal-Gal-Xyl-Ser-C12, was indicated in poorly metastatic FBJ-S1 cells more than in highly metastatic FBJ-LL cells by LC-MS. The results of RT-PCR revealed that HS synthases, Ext1 and Ext2, were expressed in FBJ-S1 cells more than in FBJ-LL cells. Furthermore, siRNA against Ext1 suppressed the expression of HS and enhanced the motility of FBJ-S1 cells. In addition, the expression of heparanase (HPSE) was enhanced in Ext-1-knockdown FBJ-S1 cells, and responsible for the increase in cell motility caused by the down-regulation of Ext1 expression. Our data provide the first evidence that Ext1 regulates the expression of HPSE and also indicated that levels of Ext1 and HPSE influenced the motility of FBJ cells.

Incorporation of fluorous glycosides to cell membrane and saccharide chain elongation by cellular enzymes

A series of fluorous-tagged glycosides with different number of fluorine atoms are incorporated into the cells, transported to Golgi, elongated by cellular enzymes, and then released to the culture medium. Fluorine content strongly affects on the affinity for cell membrane and glycosylation. Essentially, the fluorocarbon chain in fluorous compound and the hydrocarbon chain are not miscible. However, the fluorous-tagged glycosides have affinity for cell membrane because of its amphiphilicity. The affinity of fluoro-amphiphilic compound for cell membrane is discussed using critical micelle concentration. The separation of glycosylated products by solvent extraction or fluorous solid phase extraction cartridges is also discussed.

Novel method for chase analysis of oligosaccharide metabolic error caused by xenobiotics

Saccharide primers, such as dodecyl beta-lactoside (Lac-C12), are unique artificial precursors of glycolipid synthesis. In culture media supplemented with saccharide primers, they are taken up by the cells in the culture media and glycosylated by cellular glycosyltransferases in the Golgi apparatus to form pseudo-glycolipids. In this study, we examine the effects of various xenobiotics on glycolipid synthesis by implementing a novel method to analyze pseudo-glycolipids, mainly gangliosides, produced by ONS-76 medulloblastoma cells in a culture medium containing various xenobiotics. The ganglioside group of pseudo-glycolipids was effectively purified by using strong anion-exchange cartridges. The production of pseudo-gangliosides was stimulated by N-(n-butyl)deoxygalactonojirimycin (NB-DGJ), but was inhibited by castanospermine, 2-deoxy-2-fluoro-d-galactose, tunicamycin, and brefeldin A. Because the cells in the culture medium are exposed to the saccharide primers and xenobiotics at the same time, and are secreted in the culture medium in their glycosylated form, our method can be used to effectively analyze the direct effects of xenobiotics on ganglioside synthesis.

Easy production of a glycolipid analogue using animal cells in culture

A glycolipid analogue, GM4-type ganglioside, was obtained by a combination of chemical synthesis and biosynthetic processes in animal cells with dodecyl beta-D-galactoside (Gal C12) as primer. The primer was conveniently prepared in two steps: glycosylation, followed by deacetylation. The primer was introduced to mouse melanoma B16 cells to serve as substrate for cellular, enzyme-catalyzed glycosylation. Incubation of the cells in the presence of the primer resulted in sialylation of the galactose residue to afford a GM4 analogue that was released from the cells to the culture medium. The strategy of preparation of the GM4 analogue described in this study is a viable alternative to the existing methods. The saccharide-primer method is fast, convenient, not requiring expensive enzymes and glycosyl donors, and highly stereoselective.

Synthesis of fluorescent alkyl lactoside derivatives

Fluorescent-labeled alkyl lactoside (NBD-alkyl lactoside) derivatives were synthesized by the reaction of NBD alkyl alcohol with heptaacetyllactosyl trichloroacetimidate in the presence of BF(3).Et(2)O.

Alternative methods of globotrioside production using Vero cells: a microcarrier system procedure

Background

Glycolipids are one component of cell membranes, and are found most prevalently at the surface of the plasma membrane. Animal cells take in amphipathic glycosides, which are later glycosylated after assimilation in biosynthetic pathways. Gycosylated glycosides are released outside of cells to the surrounding culture medium. This represents an accessible method of obtaining complex glycosides.

Results

Vero cells are sensitive to Shiga toxins and are known to express the glycosides globotriaosyl ceramide (Gb3) and globotetraosyl ceramide (Gb4) on the surface of the plasma membrane. By administering amphipathic lactosides to Vero cells, the above mentioned glycolipids could be produced by the action of cellular enzymes. In our study, the optimum conditions (seeded cell number, incubated time period, 12-azidododecyl lactoside concentration and medium volume) for the production of Gb3 analogue were investigated. The 87.9 μg/100 mm dish (11.7 % yield) Gb3 analogue was produced under appropriate conditions. The large-scale culture of Vero cells using a microcarrier culture method with repetitions produced about 30 mg of the Gb3 analogue.

Conclusion

The mass production of glycosides in Vero cells was carried out on a microcarrier with repeated administration of 12-azidododecyl lactoside. The results indicated that the use of both a microcarrier culture and repetition were highly effective in the production of Gb3, Gb4 and sialyl lactoside (GM3) type-oligosaccharides.

Ganglioside GD1a regulation of caveolin-1 and Stim1 expression in mouse FBJ cells: augmented expression of caveolin-1 and Stim1 in cells with increased GD1a content

GD1a was previously shown responsible for regulating cell motility, cellular adhesiveness to vitronectin, phosphorylation of c-Met and metastatic ability of mouse FBJ osteosarcoma cells. To determine the particular molecules regulated by GD1a, FBJ cells were assessed for tumor-related gene expression by semi-quantitative RT-PCR. Caveolin-1 and stromal interaction molecule 1 (Stim1) expression in FBJ-S1 cells, rich in GD1a, were found to be 6 and 4 times as much, respectively, than in FBJ-LL cells devoid of GD1a. Enhanced production of caveolin-1 in protein was confirmed by Western blotting. A low-metastatic FBJ-LL cell variant, having high GD1a expression through beta1-4GalNAcT-1 (GM2/GD2 synthase) cDNA transfection (Hyuga S, et al, Int J Cancer 83: 685-91, 1999), showed enhanced production of caveolin-1 and Stim1 in mRNA and protein, compared to mock-transfectant M5. Incubation of FBJ-M5 cells with exogenous GD1a augmented the expression of caveolin-1 in mRNA and protein and Stim1 in mRNA as well. Treatment of FBJ-S1 with fumonisin B1, an inhibitor of N-acylsphinganine synthesis, for 15 days caused the complete depletion of gangliosides and suppressed the expression of caveolin-1 and Stim1. St3gal5 siRNA transfected cells showed decreased expression of caveolin-1 and Stim1 mRNA, as well as St3gal5 mRNA. These findings clearly indicate ganglioside GD1a to be involved in the regulation of the transformation suppressor genes, caveolin-1 and Stim1. Moreover, treatment with GD1a of mouse melanoma B16 cells and human hepatoma HepG2 cells brought about elevated expression of caveolin-1 and Stim1.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update covering the period 1999-2000

This review describes the use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates and continues coverage of the field from the previous review published in 1999 (D. J. Harvey, Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates, 1999, Mass Spectrom Rev, 18:349-451) for the period 1999-2000. As MALDI mass spectrometry is acquiring the status of a mature technique in this field, there has been a greater emphasis on applications rather than to method development as opposed to the previous review. The present review covers applications to plant-derived carbohydrates, N- and O-linked glycans from glycoproteins, glycated proteins, mucins, glycosaminoglycans, bacterial glycolipids, glycosphingolipids, glycoglycerolipids and related compounds, and glycosides. Applications of MALDI mass spectrometry to the study of enzymes acting on carbohydrates (glycosyltransferases and glycosidases) and to the synthesis of carbohydrates, are also covered.

Efficient Sialylation on Azidododecyl Lactosides by Using B16 Melanoma Cells

Lactoside primers (dodecyl lactoside derivatives) resemble intermediates in the biosynthetic pathway of glycolipids and, therefore, act as substrates for cellular enzyme-catalyzed glycosylation. To establish the optimal condition for the bioproduction of a large amount of valuable materials containing GM3-type oligosaccharides, two kinds of lactoside primers having the azido group in different positions were synthesized and introduced into B16 melanoma cells. The saccharide chains of both primers were elongated by cells to give GM3-type oligosaccharide derivatives, which were released to the culture medium. The amount of glycosylated product from newly synthesized 2-azidododecyl beta-lactoside (primer II) was almost twice that from 12-azidododecyl beta-lactoside (primer I). The effects of seeded cell number, primer concentration, and length of incubation time on the glycosylation efficiency were also investigated. The results showed that the higher the seeded cell number, the larger the amount of sialylated products obtained. The optimum concentrations of primers I and II were found to be 200 and 100 microM, respectively. Above these concentrations, productivity and cell viability decreased. As regards the length of incubation time, the sialylated products increased linearly until 48 h, but productivity did not advance thereafter. These results represent the optimal conditions that are necessary for the mass production of GM3-type oligosaccharide using azidododecyl lactoside primers and B16 cells.

Synthesis of 5a-carba-hexopyranoses and hexopyranosylamines, as well as 5a,5a′-dicarbadisaccharides, from 3,8-dioxatricyclo[4.2.1.02,4]nonan-9-ol: glycosidase inhibitory activity of N-substituted 5a-carba-β-gluco- and β-galactopyranosylamines, and derivatives thereof

Since glycosidase and glycosyltransferase inhibitors, composed of carba-sugars, have recently attracted much attention, it is desirable to develop effective preparative routes for provision of new carba-sugar derivatives of potential biological interest. 1,2:3,6-Dianhydro-5a-carba-alpha-glucopyranose was here chosen for study of synthetic utility, and demonstrated to be a promising intermediate for supplying several carba-beta-glycosylamines and N-linked dicarba-oligosaccharides. An N-linked 5a,5a'-dicarbalactose derivative obtained here was found to be a strong alpha-galactosidase inhibitor (IC50 1.2 microM, green coffee beans).

Fluorous-tagged compound: a viable scaffold to prime oligosaccharide synthesis by cellular enzymes

Fluorous-tagged saccharide primers could be viable scaffolds for the synthesis of oligosaccharides. This research demonstrates that a fluorine-containing saccharide derivative could actually be taken up by the cell, the saccharide chain elongated by cellular enzymes, and the elongated product released by the cells to the culture medium. A fluorous-tagged lactoside primer, 6-(perfluorohexyl)hexyl-4-O-(beta-D-galactopyranosyl)-beta-D-glucopyranoside, was chemically synthesized and introduced in mouse B16 cells to prime oligosaccharide synthesis. Uptake of the primer by B16 cells resulted in the sialylation of the terminal galactose residue to afford an oligosaccharide with the same glycan structure as ganglioside GM3. The presence of many fluorine atoms did not have any adverse effects to the cells. Moreover, the number of fluorine atoms did not pose a steric barrier and instead, their presence possibly increased the hydrophobicity of the primer and enhanced membrane permeability. This strategy of using a fluorous-tagged primer and cells can pave the way for an easier way of preparing oligosaccharides via an environment-friendly approach that eliminates the use of large amounts of organic solvents.

Synthesis of an ether-linked alkyl 5a-carba-beta-D-glucoside, a 5a-carba-beta-D-galactoside, a 2-acetamido-2-deoxy-5a-carba-beta-D-glucoside, and an alkyl 5a'-carba-beta-lactoside

For the purpose of providing biologically stable building blocks for the biocombinatorial synthesis using a living cell, some ether-linked alkyl 5a-carba-beta-D-glycoside primers were prepared. The key step of the synthesis was coupling of 1-bromo-n-alkanes with the 1-OH unprotected derivatives of 5a-carba-sugar analogues of D-glucose, D-galactose, and 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine), in DMF in the presence of sodium hydride. Alternatively, alkyl carba-lactoside was synthesized by incorporation of a 5a-carba-beta-D-galactose residue into the 4-position of dodecyl beta-D-glucopyranoside. A strong and specific inhibition of beta-galactosidase (K(i) 0.67 microM, bovine liver) was found for dodecyl 5a-carba-beta-D-galactopyranoside.