Synthesis and glycosaminoglycan priming activity of three disaccharides related to the linkage region tetrasaccharide of proteoglycans

'Click'-xylosides as initiators of the biosynthesis of glycosaminoglycans: Comparison of mono-xylosides with xylobiosides

Different mono-xylosides and their corresponding xylobiosides obtained by a chemo-enzymatic approach featuring various substituents attached to a triazole ring were probed as priming agents for glycosaminoglycan (GAG) biosynthesis in the xylosyltransferase-deficient pgsA-745 Chinese hamster ovary cell line. Xylosides containing a hydrophobic aglycone moiety were the most efficient priming agents. Mono-xylosides induced higher GAG biosynthesis in comparison with their corresponding xylobiosides. The influence of the degree of polymerization of the carbohydrate part on the priming activity was investigated through different experiments. We demonstrated that in case of mono-xylosides, the cellular uptake as well as the affinity and the catalytic efficiency of β-1,4-galactosyltransferase 7 were higher than for xylobiosides. Altogether, these results indicate that hydrophobicity of the aglycone and degree of polymerization of glycone moiety were critical factors for an optimal priming activity for GAG biosynthesis.

β-Xylopyranosides: synthesis and applications

In recent years, β-xylopyranosides have attracted interest due to the development of biomass-derived molecules. This review focuses on general routes for the preparation of β-xylopyranosides by chemical and enzymatic pathways and their main uses.

Glycan antagonists and inhibitors: a fount for drug discovery

Glycans, the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids, represent a relatively unexploited area for drug development compared with other macromolecules. This review describes the major classes of glycans synthesized by animal cells, their mode of assembly, and available inhibitors for blocking their biosynthesis and function. Many of these agents have proven useful for studying the biological activities of glycans in isolated cells, during embryological development, and in physiology. Some are being used to develop drugs for treating metabolic disorders, cancer, and infection, suggesting that glycans are excellent targets for future drug development.

Temperature-sensitive glycosaminoglycan biosynthesis in a Chinese hamster ovary cell mutant containing a point mutation in glucuronyltransferase I

In previous studies, we reported the isolation and characterization of a Chinese hamster ovary cell mutant (pgsG) defective in glucuronyltransferase I (GlcATI). This enzyme adds the terminal GlcA residue in the core protein-linkage tetrasaccharide (GlcAbeta1,3Galbeta1,3Galbeta1, 4Xylbeta-O-) on which glycosaminoglycan assembly occurs (Bai, X. M., Wei, G., Sinha, A., and Esko, J. D. (1999) J. Biol. Chem. 274, 13017-13024; Wei, G., Bai, X. M., Sarkar, A. K., and Esko, J. D. (1999) J. Biol. Chem. 274, 7857-7864). Here we show that incorporation of 35SO4 into glycosaminoglycans in the mutant is temperature-sensitive, with greater synthesis occurring at 33 degrees C compared with 37 degrees C. Wild-type cells show the opposite thermal dependence. Rabbit antiserum to hamster GlcATI failed to detect cross-reactive material in pgsG cells by immunofluorescence and Western blotting. Furthermore, expression of chimeric proteins composed of mutant GlcATI fused to IgG binding domain of protein A or to green fluorescent protein did not yield the proteins at the expected mass. The green fluorescent protein-tagged version appeared as a truncated protein, and immunofluorescence showed large perinuclear bodies at 30 degrees C. At 37 degrees C, the fusion protein was not readily detectable. Sequencing cDNAs from mutant and wild-type cells revealed a single base transition (G331A) in the open reading frame in pgsG cells, which resulted in a Val-111-->Met substitution. These data suggest that pgsG cells contain a labile form of GlcATI that causes conditional expression of glycosaminoglycans dependent on temperature.

Age-related changes in the sulphation of the chondroitin sulphate linkage region from human articular cartilage aggrecan

The chondroitin sulphate (CS) linkage regions have been isolated from human articular cartilage aggrecan (from 10- to 72-year-olds) by chondroitin ABC endolyase digestion and size-exclusion chromatography. Linkage region hexasaccharides have been characterized and their abundance estimated by high-pH anion-exchange chromatography. The basic structure for the CS linkage region oligosaccharides identified from human aggrecan is as follows: DeltaUA(beta1-3)GalNAc[0S/4S/6S](beta1-4)GlcA(beta1-3)Gal[0S/6S](beta1-3)Gal(beta1-4)Xyl, where DeltaUA represents 4,5-unsaturated hexuronic acid, 4S and 6S represent an O-ester sulphate group on C-4 and C-6 respectively, and 0S represents zero sulphation. There are significant age-related changes in the abundance of the various N-acetylgalactosamine (GalNAc) sulphation forms identified, occurring up to approx. 20 years old. During the period from 10 to 20 years old the level of GalNAc 6-sulphation at the linkage region increases from approx. 43% to approx. 75%, while there is a corresponding reduction in unsulphated (approx. 30% to approx. 20%) and 4-sulphated (approx. 25% to approx. 6%) GalNAc residues. There is also an increase in the incidence of linkage region galactose 6-sulphation (approx. 2% to approx. 10%) which was only observed in linkage regions with GalNAc 6-sulphation. Beyond 20 years old there are few changes in the relative abundance of these GalNAc sulphation variants; however, there is a slight increase in the abundance of 6-sulphation between approx. 20 years old and approx. 40 years old and a slight decrease in its abundance beyond approx. 40 years old. Our data show that in the majority of chains from tissues of all ages the GalNAc residue closest to the linkage region is 6-sulphated, but the level of GalNAc 6-sulphation within the linkage region is lower than the average level observed within the repeat region.

Effective extraction and purification of beta-xylosidase from Trichoderma koningii fermentation culture by aqueous two-phase partitioning

Effective extraction of protein from bulk medium is an important technique in bioresearch. In the present study, we describe an extracellular beta-xylosidase from the fermentation supernatant of Trichoderma koningii G-39 that was successfully extracted and purified simultaneously in a single step by using an aqueous two-phase partitioning method. This two-phase system was prepared by dissolving suitable amount of poly(ethylene glycol) (PEG) and sodium dihydrogenphosphate (NaH(2)PO(4)) in aqueous solution. beta-Xylosidase was recovered with high yield and high concentration in the bottom salt-rich phase when 25% (w/v) PEG 1500 and 20-25% (w/v) NaH(2)PO(4) were applied. Based on a 1-liter scale extraction, the purity of the enzyme was enhanced at least 33-fold. The total activity increased 422% in comparison with that in the untreated filtrate. The effectiveness and simplicity may make this technique potentially useful in various applications. The transxylosylation activity of the enzyme purified by this technique was also investigated.

Increased incidence of unsulphated and 4-sulphated residues in the chondroitin sulphate linkage region observed by high-pH anion-exchange chromatography

We report the isolation, characterization and quantification of five octasaccharides, four hexasaccharides and two tetrasaccharides, derived from the chondroitin sulphate (CS) linkage region of 6-8-year-old bovine articular cartilage aggrecan, following digestion with chondroitin ABC endolyase. Using a novel high-pH anion-exchange chromatography (HPAEC) method, in conjunction with one- and two-dimensional (1)H-NMR spectroscopy, we have identified the following basic structure for the CS linkage region of aggrecan: DeltaUA(beta1-3)GalNAc[0S/4S/6S](beta1-4)GlcA(beta1-3)GalNAc[0S/4S/6S](beta1-4)GlcA(beta1-3)Gal[0S/6S](beta1-3)Gal(beta1-4)Xyl, where DeltaUA represents 4,5-unsaturated hexuronic acid, and 4S and 6S represent an O-ester sulphate group on C-4 and C-6 respectively. The octa-, hexa- and tetra-saccharide linkage region fragments were used to develop a HPAEC fingerprinting method, with detection at A(232 nm), and a linear response to approx. 0.1 nmol of substance. The sulphation patterns of CS linkage regions, of up to octasaccharide in size, from articular and tracheal cartilage aggrecan were examined. The results show that in articular cartilage, for the majority (53%) of octasaccharides the 2-deoxy-2-N-acetyl amino-D-galactose (GalNAc) residues closest to the linkage region are both 6-sulphated; however, in a significant portion (34%), one or more of these GalNAc residues are unsulphated, and in 8% both are unsulphated. Approximately 10-18% of the chains have a 4-sulphated GalNAc in the first disaccharide, and 12% have a sulphated linkage region Gal residue. No evidence was found for uronic acid sulphation. These data show that there is a significant increase in the incidence of unsulphated and 4-sulphated GalNAc residues adjacent to the linkage region compared with the rest of the chain. Bovine tracheal cartilage linkage regions displayed very similar sulphation profiles to those from articular cartilage, despite the presence of a higher level of GalNAc 4-sulphation within the repeat region of the main CS chain.

Characterization of recombinant human glucuronyltransferase I involved in the biosynthesis of the glycosaminoglycan-protein linkage region of proteoglycans

We characterized the recombinant glucuronyltransferase I (GlcAT-I) involved in the glycosaminoglycan-protein linkage region biosynthesis. The enzyme showed strict specificity for Galbeta1-3Galbeta1-4Xyl, exhibiting negligible incorporation into other galactoside substrates including Galbeta1-3Galbeta1-O-benzyl, Galbeta1-4GlcNAc and Galbeta1-4Glc. A comparison of the GlcAT-I with another beta1,3-glucuronyltransferase involved in the HNK-1 epitope biosynthesis revealed that the two beta1,3-glucuronyltransferases exhibited distinct and no overlapping acceptor substrate specificities in vitro. Nevertheless, the transfection of the GlcAT-I cDNA into COS-1 cells induced the significant expression of the HNK-1 epitope. These results suggested that the high expression of the GlcAT-I gene rendered the cells capable of synthesizing the HNK-1 epitope.