A quantitative method to detect non-antithrombin-binding 3-O-sulfated units in heparan sulfate.

Heparan sulfate is synthesized by most animal cells and interacts with numerous proteins via specific sulfation motifs to regulate various physiological processes. Various 3-O-sulfated motifs are considered to be key in controlling the binding specificities to the functional proteins. One such motif synthesized by 3-O-sulfotransferase-1 (3OST-1) serves as a binding site for antithrombin (AT) and has been thoroughly studied because of its pharmacological importance. However, the physiological roles of 3-O-sulfates produced by other 3OST isoforms, which do not bind AT, remain obscure, in part due to the lack of a standard method to analyze this rare modification. This study aims to establish a method for quantifying 3-O-sulfated components of heparan sulfate, focusing on non-AT-binding units. We previously examined the reaction products of human 3OST isoforms and identified five 3-O-sulfated components, including three non-AT-binding disaccharides and two AT-binding tetrasaccharides, as digestion products of heparin lyases. In this study, we prepared these five components as a standard saccharide for HPLC analysis. Together with eight non-3-O-sulfated disaccharides, a standard mixture of 13 units was prepared. Using reverse-phase ion-pair HPLC with a postcolumn fluorescent labeling system, the separation conditions were optimized to quantify the 13 units. Finally, we analyzed the compositional changes of 3-O-sulfated units in heparan sulfate from P19 cells before and after neuronal differentiation. We successfully detected the 3-O-sulfated units specifically expressed in the differentiated neurons. This is the first report that shows the quantification of three non-AT-binding 3-O-sulfated units and establishes a new approach to explore the physiological functions of 3-O-sulfate.

Heparosan-glucuronate 5-epimerase: Molecular cloning and characterization of a novel enzyme.

Iduronic acid (IdoA) is a critical component of heparan sulfate in its interaction with functional proteins. Heparosan-N-sulfate-glucuronate 5-epimerase (HNSG-5epi) converts d-glucuronic acid (GlcA) residues in N-sulfated heparosan (NS-heparosan), as an intermediate in heparan sulfate biosynthesis, to IdoA. In the present study, the authors discovered a different 5-epimerase, designated HG-5epi (heparosan-glucuronate 5-epimerase), that is involved in acharan sulfate biosynthesis and possesses novel substrate specificity. A candidate cDNA of HG-5epi was cloned from the cDNA library of Achatina fulica. The cloned cDNA contained a whole coding region that predicts a type II transmembrane protein composed of 601 amino acid residues. The amino acid sequence of HG-5epi is homologous to that of HNSG-5epi. Recombinant HG-5epi was expressed in insect cells and its enzymatic properties characterized. As expected, HG-5epi epimerizes GlcA residues in heparosan, but not in NS-heparosan. Conversion of IdoA to GlcA was also catalyzed by HG-5epi when completely desulfated N-acetylated heparin was used as the substrate, indicating a reversible reaction mechanism. At equilibrium of the epimerization, the proportion of IdoA in the reaction product reached up to 30% of total hexuronic acid. To our knowledge, this is the first report to describe an enzyme that catalyzes the epimerization of non-sulfated heparosan. This new enzyme may be applied to the study of synthetic heparan sulfate-related polysaccharides having certain biological and pharmacological activities. In addition, a new method using anion-exchange HPLC connected to a post-column fluorescent labeling system was developed for analyzing hexuronic acid isomers.

Modification of di- and tetrasaccharides from shark cartilage keratan sulphate by refined anhydromethanolic hydrochloric acid-treatments and evaluation of their specific desulphation.

Highly sulphated keratan di- and tetrasaccharides were prepared from keratan sulphate (KS) of shark cartilage by enzymatic digestion with keratanase II and subsequent chromatography. The tetrasaccharide fraction carrying four sulphate groups was completely desulphated by 100 mM anhydromethanolic hydrochloric acid (MeOH-HCl) treatment at room temperature for 16 h. The conditions for the desulphation reaction by MeOH-HCl treatment were examined using sulphated keratan di- and tetrasaccharides as substrates by means of reversed phase high performance liquid chromatography (HPLC) and/or capillary electrophoresis, followed by the preparation of partially desulphated keratan oligosaccharides. Sulphate substitution patterns of monosulphated keratan disaccharide and trisulphated keratan tetrasaccharide were evaluated by methylation analysis. The results suggested that 6-O-sulphate groups of Gal moieties are cleaved faster than those of GlcNAc moieties under the present conditions adopted for the MeOH-HCl treatment of KS-derived oligosaccharides.

Tetrasulfated disaccharide unit in heparan sulfate: enzymatic formation and tissue distribution.

We previously reported that the heparan sulfate 3-O-sulfotransferase (3OST)-5 produces a novel component of heparan sulfate, i.e. the tetrasulfated disaccharide (Di-tetraS) unit ( Mochizuki, H., Yoshida, K., Gotoh, M., Sugioka, S., Kikuchi, N., Kwon, Y.-D., Tawada, A., Maeyama, K., Inaba, N., Hiruma, T., Kimata, K., and Narimatsu, H. (2003) J. Biol. Chem. 278, 26780-26787 ). In the present study, we investigated the potential of other 3OST isoforms to produce Di-tetraS with heparan sulfate and heparin as acceptor substrates. 3OST-2, 3OST-3, and 3OST-4 produce Di-tetraS units as a major product from both substrates. 3OST-5 showed the same specificity for heparin, but the production from heparan sulfate was very low. Di-tetraS production by 3OST-1 was negligible. We then investigated the presence of Di-tetraS units in heparan sulfates from various rat tissues. Di-tetraS was detected in all of the tissues analyzed. Liver and spleen contain relatively high levels of Di-tetraS, 1.6 and 0.95%, respectively. However, the content of this unit in heart, large intestine, ileum, and lung is low, less than 0.2%. We further determined the expression levels of 3OST transcripts by quantitative real time PCR. The 3OST-3 transcripts are highly expressed in spleen and liver. The 3OST-2 and -4 are specifically expressed in brain. These results indicate that the Di-tetraS unit is widely distributed throughout the body as a rare and unique component of heparan sulfate and is synthesized by tissue-specific 3OST isoforms specific for Di-tetraS production.

Purification, characterization, and molecular cloning of a novel keratan sulfate hydrolase, endo-beta-N-acetylglucosaminidase, from Bacillus circulans.

Keratan sulfate (KS) is degraded by various enzymes including endo-beta-galactosidase, keratanase, and keratanase II, which are used for the structural analysis of KS. We purified a novel KS hydrolase, endo-beta-N-acetylglucosaminidase, from the cell pellet and conditioned medium of Bacillus circulans, by sequential chromatography using DE52 and phenyl-Sepharose columns with approximately 63- and 180-fold purity and 58 and 12.5% recovery, respectively. Like keratanase II of Bacillus sp. Ks36, the enzyme, designated Bc keratanase II, hydrolyzed KS between the 4GlcNAcbeta1-3Gal1 structure (endo-beta-N-acetylglucosaminidase), but not hyaluronan, heparan sulfate, heparin, and chondroitin sulfate C, demonstrating a strict specificity to KS. The enzyme digested shark cartilage KS to disaccharides and tetrasaccharides and bovine cornea KS to hexasaccharide, indicating that it prefers highly sulfated KS. Distinct from keratanase II of strain Ks36, the enzyme digested shark cartilage KS at an optimal temperature of 55 degrees C. Based on partial peptide sequencing of the enzyme, we molecularly cloned the gene, which encodes a protein with a predicted molecular mass of approximately 200 kDa. From the deduced protein sequence, Bc keratanase II contained a domain at the C terminus, homologous to the S-layer-like domain of pullulanase from Thermoanaerobacterium thermosulfurigenes and endoxylanase from Thermoanaerobacterium saccharolyticum, and a carbohydrate-binding domain, which may serve to specifically recognize KS chains. A full-length recombinant enzyme showed keratanase II activity. These results may prove useful for the structural analysis of KS toward achieving an understanding of its function.

Characterization of a heparan sulfate 3-O-sulfotransferase-5, an enzyme synthesizing a tetrasulfated disaccharide.

Heparan sulfate d-glucosaminyl 3-O-sulfotransferases (3-OSTs) catalyze the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to position 3 of the glucosamine residue of heparan sulfate and heparin. A sixth member of the human 3-OST family, named 3-OST-5, was recently reported (Xia, G., Chen, J., Tiwari, V., Ju, W., Li, J.-P., Malmstrom, A., Shukla, D., and Liu, J. (2002) J. Biol. Chem. 277, 37912-37919). In the present study, we cloned putative catalytic domain of the human 3-OST-5 and expressed it in insect cells as a soluble enzyme. Recombinant 3-OST-5 only exhibited sulfotransferase activity toward heparan sulfate and heparin. When incubated heparan sulfate with [35S]PAPS, the highest incorporation of35S was observed, and digestion of the product with a mixture of heparin lyases yielded two major35S-labeled disaccharides, which were determined as DeltaHexA-GlcN(NS,3S,6S) and DeltaHexA(2S)-GlcN(NS,3S) by further digestion with 2-sulfatase and degradation with mercuric acetate. However, when used heparin as acceptor, we identified a highly sulfated disaccharide unit as a major product. This had a structure of DeltaHexA(2S)-GlcN(NS,3S,6S). Quantitative real-time PCR analysis revealed that 3-OST-5 was highly expressed in fetal brain, followed by adult brain and spinal cord, and at very low or undetectable levels in the other tissues. Finally, we detected a tetrasulfated disaccharide unit in bovine intestinal heparan sulfate. To our knowledge, this is the first report to describe not only the natural occurrence of tetrasulfated disaccharide unit but also the enzymatic formation of this novel structure.

Molecular cloning and characterization of a novel chondroitin sulfate glucuronyltransferase that transfers glucuronic acid to N-acetylgalactosamine.

We found a novel human gene (GenBank accession number, Kazusa DNA Research Institute KIAA1402) that possesses homology with chondroitin synthase. The full-length open reading frame consists of 772 amino acids and encodes a typical type II membrane protein. This enzyme had a domain containing beta 3-glycosyltransferase motifs, which might be a beta3-glucuronyltransferase domain, but no domain with beta 4-glycosyltransferase motifs, although both are found in chondroitin synthase. The putative catalytic domain was expressed in COS-7 cells as a soluble enzyme. Its glucuronyltransferase activity was observed when chondroitin and chondroitin sulfate polysaccharides and oligosaccharides were used as acceptor substrates. However, it was not detected when dermatan sulfate, hyaluronan, heparan sulfate, heparin, N-acetylheparosan, lactosamine tetrasaccharide, and linkage tri- and tetrasaccharide acceptors were employed. The reaction product, which was speculated to exhibit a GlcA beta 1-3GalNAc linkage structure at its non-reducing terminus, showed the following characteristics. 1) It was catabolized by beta-glucuronidase. 2) It was an acceptor for Escherichia coli K4 chondroitin polymerase (K4 chondroitin polymerase). 3) The product of K4 chondroitin polymerase was cleaved by chondroitinase ACII. On the other hand, no N-acetylgalactosaminyltransferase activity was detected toward any acceptors. Quantitative real time PCR analysis revealed that its transcripts were highly expressed in the placenta, small intestine, and pancreas, although they were ubiquitously expressed in various tissues and cell lines. This enzyme could play a role in the synthesis of chondroitin sulfate as a glucuronyltransferase.

Differential roles of two N-acetylgalactosaminyltransferases, CSGalNAcT-1, and a novel enzyme, CSGalNAcT-2. Initiation and elongation in synthesis of chondroitin sulfate.

By a tblastn search with beta 1,4-galactosyltransferases as query sequences, we found an expressed sequence tag that showed similarity in beta 1,4-glycosyltransferase motifs. The full-length complementary DNA was obtained by a method of 5'-rapid amplification of complementary DNA ends. The predicted open reading frame encodes a typical type II membrane protein comprising 543 amino acids, the sequence of which was highly homologous to chondroitin sulfate N-acetylgalactosaminyltransferase (CSGalNAcT-1), and we designated this novel enzyme CSGalNAcT-2. CSGalNAcT-2 showed much stronger N-acetylgalactosaminyltransferase activity toward glucuronic acid of chondroitin poly- and oligosaccharides, and chondroitin sulfate poly- and oligosaccharides with a beta 1-4 linkage, i.e. elongation activity for chondroitin and chondroitin sulfate, but showed much weaker activity toward a tetrasaccharide of the glycosaminoglycan linkage structure (GlcA-Gal-Gal-Xyl-O-methoxyphenyl), i.e. initiation activity, than CSGalNAcT-1. Transfection of the CSGalNAcT-1 gene into Chinese hamster ovary cells yielded a change of glycosaminoglycan composition, i.e. the replacement of heparan sulfate on a syndecan-4/fibroblast growth factor-1 chimera protein by chondroitin sulfate, however, transfection of the CSGalNAcT-2 gene did not. The above results indicated that CSGalNAcT-1 is involved in the initiation of chondroitin sulfate synthesis, whereas CSGalNAcT-2 participates mainly in the elongation, not initiation. Quantitative real-time PCR analysis revealed that CSGalNAcT-2 transcripts were highly expressed in the small intestine, leukocytes, and spleen, however, both CSGalNAcTs were ubiquitously expressed in various tissues.

Enzymatic synthesis of chondroitin with a novel chondroitin sulfate N-acetylgalactosaminyltransferase that transfers N-acetylgalactosamine to glucuronic acid in initiation and elongation of chondroitin sulfate synthesis.

We found a novel glycosyltransferase gene having a hypothetical beta 1,4-galactosyltransferase motif (GenBank accession number ) by a BLAST search and cloned its full-length open reading frame using the 5'-rapid amplification of cDNA ends method. The truncated form was expressed in insect cells as a soluble enzyme. It transferred N-acetylgalactosamine, not galactose, to para-nitrophenyl-beta-glucuronic acid. The N-acetylgalactosamine-glucuronic acid linkage has been identified only in chondroitin sulfate; therefore, we examined its chondroitin elongation and initiation activities. N-Acetylgalactosaminyltransferase activity was observed toward chondroitin poly- and oligosaccharides, chondroitin sulfate oligosaccharides, and linkage tetrasaccharide (GlcA-Gal-Gal-Xyl-O-methoxyphenyl), and the chondroitin polysaccharide and linkage tetrasaccharide were better acceptor substrates than the others. Northern blot analysis and quantitative real-time PCR analysis revealed that its 4-kb transcripts were highly expressed in thyroid and placenta, although they were ubiquitously expressed in various tissues and cells. These results suggest that this enzyme has N-acetylgalactosaminyltransferase activity in both the elongation and initiation of chondroitin sulfate synthesis. Furthermore, we performed enzymatic synthesis of chondroitin pentasaccharide in vitro. In one tube reaction with four enzymes, beta 1,4-galactosyltransferase-VII, beta 1,3-galactosyltransferase-VI, glucuronyltransferase-I, and this enzyme, and a synthetic xylose-peptide acceptor, the structure GalNAc-GlcA-Gal-Gal-Xyl-peptide was constructed. This is the first report of a chondroitin pentasaccharide constructed with recombinant glycosyltransferases in vitro.