Preparation and high-performance liquid chromatography of 3'-phosphoadenosine-5'-phospho[35S]sulfate with a predetermined specific activity

Mice deficient in N-acetylgalactosamine 4-sulfate 6-o-sulfotransferase are unable to synthesize chondroitin/dermatan sulfate containing N-acetylgalactosamine 4,6-bissulfate residues and exhibit decreased protease activity in bone marrow-derived mast cells

Chondroitin sulfate (CS) and dermatan sulfate (DS) containing N-acetylgalactosamine 4,6-bissulfate (GalNAc(4,6-SO(4))) show various physiological activities through interacting with numerous functional proteins. N-Acetylgalactosamine 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST) transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate to position 6 of N-acetylgalactosamine 4-sulfate in CS or DS to yield GalNAc(4,6-SO(4)) residues. We here report generation of transgenic mice that lack GalNAc4S-6ST. GalNAc4S-6ST-null mice were born normally and fertile. In GalNAc4S-6ST-null mice, GalNAc(4,6-SO(4)) residues in CS and DS disappeared completely, indicating that GalNAc4S-6ST should be a sole enzyme responsible for the synthesis of GalNAc(4,6-SO(4)) residues in both CS and DS. IdoA-GalNAc(4,6-SO(4)) units that account for approximately 40% of total disaccharide units of DS in the liver of the wild-type mice disappeared in the liver DS of GalNAc4S-6ST-null mice without reduction of IdoA content. Bone marrow-derived mast cells (BMMCs) derived from GalNAc4S-6ST-null mice contained CS without GlcA-GalNAc(4,6-SO(4)) units. Tryptase and carboxypeptidase A activities of BMMCs derived from GalNAc4S-6ST-null mice were lower than those activities of BMMCs derived from wild-type mice, although mRNA expression of these mast cell proteases was not altered. Disaccharide compositions of heparan sulfate/heparin contained in the mast cells derived from BMMCs in the presence of stem cell factor were much different from those of heparan sulfate/heparin in BMMCs but did not differ significantly between wild-type mice and GalNAc4S-6ST-null mice. These observations suggest that CS containing GalNAc(4,6-SO(4)) residues in BMMCs may contribute to retain the active proteases in the granules of BMMCs but not for the maturation of BMMCs into connective tissue-type mast cells.

N-linked oligosaccharides are required to produce and stabilize the active form of chondroitin 4-sulphotransferase-1

C4ST-1 (chondroitin 4-sulphotransferase-1) transfers sulphate to position 4 of N-acetylgalactosamine in chondroitin. We showed previously that purified C4ST-1 from the culture medium of rat chondrosarcoma cells was a glycoprotein containing approx. 35% N-linked oligosaccharides. In the present paper, we investigated the functional role of the N-linked oligosaccharides attached to C4ST-1. We found that (i) treatment of recombinant C4ST-1 with peptide N-glycosidase F caused a marked decrease in activity, (ii) production of the active form of C4ST-1 by COS-7 cells transfected with cDNA of C4ST-1 was inhibited by tunicamycin, (iii) deletion of the N-glycosylation site located at the C-terminal region of C4ST-1 abolished activity, (iv) attachment of a single N-glycan at the C-terminal region supported production of the active form of C4ST-1, but the resulting recombinant enzyme was much more unstable at 37 degrees C than the control recombinant protein, and (v) truncation of C-terminal region up to the N-glycosylation site at the C-terminal region resulted in total loss of activity. These observations strongly suggest that N-linked oligosaccharides attached to C4ST-1 contribute to the production and stability of the active form of C4ST-1. In addition, the N-linked oligosaccharide at the C-terminal region appears to affect the glycosylation pattern of recombinant C4ST; a broad protein band of the wildtype protein resulting from microheterogeneity of N-linked oligosaccharides disappeared and four discrete protein bands with different numbers of N-linked oligosaccharides appeared when the N-linked oligosaccharide at the C-terminal region was deleted.

N-linked oligosaccharides on chondroitin 6-sulfotransferase-1 are required for production of the active enzyme, Golgi localization, and sulfotransferase activity toward keratan sulfate

We have shown previously that purified chondroitin 6-sulfotransferase-1 (C6ST-1) was a glycoprotein abundant in N-linked oligosaccharides and could sulfate both chondroitin (C6ST activity) and keratan sulfate (KSST activity); however, functional roles of the N-glycans have remained unclear. In the present study, we show essential roles of N-glycans attached to C6ST-1 in the generation of the active enzyme and in its KSST activity. Treatment with tunicamycin of COS-7 cells transfected with C6ST-1 cDNA totally abolished production of the active C6ST-1. A nearly complete removal of N-glycans of the recombinant C6ST-1 by peptide N-glycosidase F increased the C6ST activity but decreased the KSST activity. Among six potential N-glycosylation sites, deletion of the fourth or sixth site from the amino terminus inhibited production of the active C6ST-1, whereas deletion of the fifth site resulted in a marked loss of the KSST activity. Wild-type recombinant C6ST-1 showed a typical Golgi localization, whereas M-4 recombinant C6ST-1, in which the fourth N-glycosylation site was deleted, colocalized with calnexin, an endoplasmic reticulum-resident protein. Unlike wildtype recombinant C6ST-1, M-4 recombinant C6ST-1 showed a weak affinity toward wheat germ agglutinin and was converted completely to the nonglycosylated form by endoglycosidase H. These observations suggest that N-glycan attached to the fourth N-glycosylation site may function in the proper processing of N-glycans required for the Golgi localization, thereby causing the production of the active C6ST-1, and that N-glycan attached to the fifth N-glycosylation site may contribute to the KSST activity of C6ST-1.

Recognition of Sulfation Pattern of Chondroitin Sulfate by Uronosyl 2-O-Sulfotransferase

We have shown previously that a highly sulfated sequence, GalNAc(4,6-SO(4))-GlcA(2SO(4))-GalNAc(6SO(4)), is present at the nonreducing terminal of chondroitin sulfate (CS), and this structure was synthesized from a unique sequence, GalNAc(4SO(4))-GlcA(2SO(4))-GalNAc(6SO(4)), by sulfation with N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase. Uronosyl 2-O-sulfotrasferase (2OST), which transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to position 2 of the GlcA residue of CS, is expected to be involved in synthesis of these structures; however, the specificity of 2OST concerning recognition of the sulfation pattern of the acceptor has largely remained unclear. In the present study, we examined the specificity of 2OST in terms of recognition of the sulfation pattern around the targeting GlcA residue. The recombinant 2OST could sulfate CS-A, CS-C, and desulfated dermatan sulfate. When [(35)S]glycosaminoglycans formed from CS-A after the reaction with the recombinant 2OST and [(35)S]PAPS were subjected to limited digestion with chondroitinase ACII, a radioactive tetrasaccharide (Tetra A) was obtained as a sole intermediate product. The sequence of Tetra A was found to be DeltaHexA-GalNAc(4SO(4))-GlcA(2SO(4))-GalNAc(6SO(4)) by enzymatic and chemical reactions. These observations indicate that 2OST transfers sulfate preferentially to the GlcA residue located in a unique sequence, -GalNAc(4SO(4))-GlcA-GalNAc(6SO(4))-. When oligosaccharides with different sulfation patterns were used as the acceptor, GalNAc(4SO(4))-GlcA-GalNAc(6SO(4)) and GlcA-GalNAc(4SO(4))-GlcA-GalNAc(6SO(4)) were the best acceptors for 2OST among trisaccharides and tetrasaccharides, respectively. These results suggest that 2OST may be involved in the synthesis of the highly sulfated structure found in CS-A.

Chondroitin 4-sulphotransferase-1 and chondroitin 6-sulphotransferase-1 are affected differently by uronic acid residues neighbouring the acceptor GalNAc residues

C4ST-1 (chondroitin 4-sulphotransferase-1) and C6ST-1 (chondroitin 6-sulphotransferase-1) transfer sulphate from PAPS (adenosine 3'-phosphate 5'-phosphosulphate) to positions 4 and 6 respectively of the GalNAc residues of chondroitin. We showed previously that C4ST-1 purified from rat chondrosarcoma and recombinant C4ST-1 both transfer sulphate efficiently to position 4 of the GalNAc residues of DSDS (desulphated dermatan sulphate). We report here the specificity of C4ST-1 and C6ST-1 in terms of uronic acid residue recognition around the GalNAc residue to which sulphate is transferred. When [35S]glycosaminoglycans formed from DSDS after incubation with [35S]PAPS and C4ST-1 were digested with chondroitinase ACII, a major part of the radioactivity was recovered in disaccharide fractions and the remainder distributed to tetrasaccharides and larger fractions, indicating that C4ST-1 mainly transferred sulphate to position 4 of the GalNAc residue located at the GlcA-GalNAc-GlcA sequence. Structural analysis of tetrasaccharide and larger oligosaccharide fractions indicated that C4ST-1 mainly transferred sulphate to the GalNAc residue adjacent to the reducing side of the GlcA residue. On the other hand, when [35S]glycosaminoglycans formed from DSDS after incubation with [35S]PAPS and C6ST-1 were digested with chondroitinase ACII, a major part of the radioactivity was recovered in fractions larger than hexasaccharides, indicating that C6ST-1 transferred sulphate to the GalNAc residues located in the L-iduronic acid-rich region. Structural analysis of the tetrasaccharide and larger oligosaccharide fractions indicated that C6ST-1 showed very little preference for the GalNAc residue neighbouring the GlcA residue. These results indicate that C4ST-1 and C6ST-1 differ from each other in the recognition of uronic acid residues adjacent to the targeted GalNAc residue.

Distinctive Expression Patterns of Heparan Sulfate O-Sulfotransferases and Regional Differences in Heparan Sulfate Structure in Chick Limb Buds

The skeletal tissue development and patterning in chick limb buds are known to be under the spacio-temporal control of various heparin-binding cell growth factors such as fibroblast growth factors and bone morphogenetic proteins. Different structural regions on heparan sulfate (HS) chains of proteoglycans could be implicated in regional differences in the binding capacities of these cell growth factors, by which they could selectively interact with targeted cells and regulate their signaling in those processes. In this study we first demonstrated by cDNA cloning that one heparan sulfate 2-O-sulfotransferase (HS2ST) and two isoforms of heparan sulfate 6-O-sulfotransferase (HS6ST-1 and -2) occurred in chick embryos and had different substrate specificities each other. We next showed by whole mount in situ hybridization that the HS6ST-1 and HS6ST-2 transcripts were preferentially localized to the anterior proximal region and at the posterior proximal region of the limb bud, respectively, whereas the HS2ST transcript was distributed rather uniformly throughout the bud. Analyses of the structures of HS from different regions of the wing buds have shown variation in that 6-O-sulfated residues are more abundant in the proximal than distal region, whereas iduronosyl 6-O-sulfated residues are abundant in the anterior proximal region and glucuronosyl 6-O-sulfated residues in the posterior proximal region. These results suggest that HS with different sulfation patterns created with multiple sulfotransferase activities provides an appropriate extracellular environment for morphogenetic signal transduction.

A unique nonreducing terminal modification of chondroitin sulfate by N-acetylgalactosamine 4-sulfate 6-o-sulfotransferase

N-Acetylgalactosamine 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST) transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to position 6 of N-acetylgalactosamine 4-sulfate (GalNAc(4SO4)). We previously identified human GalNAc4S-6ST cDNA and showed that the recombinant GalNAc4S-6ST could transfer sulfate efficiently to the nonreducing terminal GalNAc(4SO4) residues. We here present evidence that GalNAc4S-6ST should be involved in a unique nonreducing terminal modification of chondroitin sulfate A (CSA). From the nonreducing terminal of CS-A, a GlcA-containing oligosaccharide (Oligo I) that could serve as an acceptor for GalNAc4S-6ST was obtained after chondroitinase ACII digestion. Oligo I was found to be GalNAc(4SO4)-GlcA(2SO4)-GalNAc(6SO4) because GalNAc(4SO4) and deltaHexA(2SO4)-GalNAc(6SO4) were formed after chondroitinase ABC digestion. When Oligo I was used as the acceptor for GalNAc4S-6ST, sulfate was transferred to position 6 of GalNAc(4SO4) located at the nonreducing end of Oligo I. Oligo I was much better acceptor for GalNAc4S-6ST than GalNAc(4SO4)-GlcAGalNAc(6SO4). An oligosaccharide (Oligo II) whose structure is identical to that of the sulfated Oligo I was obtained from CS-A after chondroitinase ACII digestion, indicating that the terminal modification occurs under the physiological conditions. When CS-A was incubated with [35S]PAPS and GalNAc4S-6ST and the 35S-labeled product was digested with chondroitinase ACII, a 35S-labeled trisaccharide (Oligo III) containing [35S]GalNAc(4,6-SO4) residue at the nonreducing end was obtained. Oligo III behaved identically with the sulfated Oligos I and II. These results suggest that GalNAc4S-6ST may be involved in the terminal modification of CS-A, through which a highly sulfated nonreducing terminal sequence is generated.

Heparan sulfate 6-o-sulfotransferase is essential for muscle development in zebrafish

Heparan sulfate proteoglycans function in development and disease. They consist of a core protein with attached heparan sulfate chains that are altered by a series of carbohydrate-modifying enzymes and sulfotransferases. Here, we report on the identification and characterization of a gene encoding zebrafish heparan sulfate 6-O-sulfotransferase (hs6st) that shows high homology to other heparan sulfate 6-O-sulfotransferases. When expressed as a fusion protein in cultured cells, the protein shows specific 6-O-sulfotransferase activity and preferentially acts on the iduronosyl N-sulfoglycosamine. In the developing embryo, hs6st is expressed in the brain, the somites, and the fins; the same structures that were affected upon morpholino-mediated functional knockdown. Morpholino injections significantly inhibited 6-O- but not 2-O-sulfation as assessed by HPLC. Morphants display disturbed somite specification independent of the somite oscillator mechanism and have impaired muscle differentiation. In conclusion, our results show that transfer of sulfate to specific positions on glycosaminoglycans is essential for muscle development.

Substrate specificities of mouse heparan sulphate glucosaminyl 6-O-sulphotransferases

Glycosaminoglycan heparan sulphate interacts with a variety of proteins, such as growth factors, cytokines, enzymes and inhibitors and, thus, influences cellular functions, including adhesion, motility, differentiation and morphogenesis. The interactions generally involve saccharide domains in heparan sulphate chains, with precisely located O-sulphate groups. The 6-O-sulphate groups on glucosamine units, supposed to be involved in various interactions of functional importance, occur in different structural contexts. Three isoforms of the glucosaminyl 6-O-sulphotransferase (6-OST) have been cloned and characterized [H. Habuchi, M. Tanaka, O. Habuchi, K. Yoshida, H. Suzuki, K. Ban and K. Kimata (2000) J. Biol. Chem. 275, 2859-2868]. We have studied the substrate specificities of the recombinant enzymes using various O-desulphated poly- and oligo-saccharides as substrates, and using adenosine 3'-phosphate 5'-phospho[(35)S]sulphate as sulphate donor. All three enzymes catalyse 6-O-sulphation of both -GlcA-GlcNS- and -IdoA-GlcNS- (where GlcA represents D-glucuronic acid, NS the N-sulphate group and IdoA the L-iduronic acid) sequences, with preference for IdoA-containing targets, with or without 2-O-sulphate substituents. 6-OST1 showed relatively higher activity towards target sequences lacking 2-O-sulphate, e.g. the -GlcA-GlcNS- disaccharide unit. Sulphation of such non-O-sulphated acceptor sequences was generally favoured at low acceptor polysaccharide concentrations. Experiments using partially O-desulphated antithrombin-binding oligosaccharide as the acceptor revealed 6-O-sulphation of N-acetylated as well as 3-O-sulphated glucosamine residues with each of the three 6-OSTs. We conclude that the three 6-OSTs have qualitatively similar substrate specificities, with minor differences in target preference.

Biosynthesis of heparan sulphate with diverse structures and functions: two alternatively spliced forms of human heparan sulphate 6-O-sulphotransferase-2 having different expression patterns and properties

Heparan sulphate 6- O -sulphotransferase (HS6ST) catalyses the transfer of sulphate from adenosine 3'-phosphate, 5'-phosphosulphate to the 6th position of the N -sulphoglucosamine residue in HS. We previously described the occurrence of three isoforms of mouse HS6ST, mHS6ST-1, -2, and -3 [Habuchi, Tanaka, Habuchi, Yoshida, Suzuki, Ban and Kimata (2000) J. Biol. Chem. 275, 2859-2868]. In the present study, we have characterized HS6ST-2 and HS6ST-1 human isologues, including their chromosomal localizations. In the process of their cDNA cloning, we found two forms of HS6ST-2: the original (hHS6ST-2) and a short form (hHS6ST-2S) with 40 amino acids deleted. Both hHS6ST-2 and hHS6ST-2S catalysed the same sulphation reaction, but their preferences for sulphation sites in HS substrates were different. Dot-blot analysis of the two forms showed that the original form was exclusively expressed in adult and foetal brain tissues, whereas the short form was expressed preferentially in ovary, placenta and foetal kidney, suggesting that the expression of two forms of hHS6ST-2 is strictly regulated to yield tissue-dependent differences in the fine structure of HS. A refined analysis of their reaction products has led us to another finding, that HS6STs could also transfer sulphate to N -sulphoglucosamine residues located at the non-reducing terminal of HS with high affinity.

Enzymatic synthesis of chondroitin sulfate E by N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase purified from squid cartilage

Chondroitin sulfate E (CS-E), a chondroitin sulfate isomer containing GlcAbeta1-3GalNAc(4,6-SO(4)) repeating unit, was found in various mammalian cells in addition to squid cartilage and is predicted to have several physiological functions in various mammalian systems such as mast cell maturation, regulation of procoagulant activity of monocytes, and binding to midkine or chemokines. To clarify the physiological functions of GalNAc(4,6-SO(4)) repeating unit, preparation of CS-E with a defined content of GalNAc(4,6-SO(4)) residues is important. We report here the in vitro synthesis of CS-E from chondrotin sulfate A (CS-A) by the purified squid N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST) which catalyzed transfer of sulfate from 3(')-phosphoadenosine-5(')-phosphosulfate to position 6 of GalNAc(4SO(4)) residues of CS-A and dermatan sulfate (DS). When CS-A was used as an acceptor, about half of GalNAc(4SO(4)) residues, on average, were converted to GalNAc(4,6-SO(4)) residues. Anion exchange chromatography of the CS-E synthesized in vitro showed marked heterogeneity in negative charge; the proportion of GalNAc(4,6-SO(4)) in the most negative fraction exceeded 70% of the total sulfated repeating units. GalNAc4S-6ST also catalyzed the synthesis of oversulfated DS with GalNAc(4,6-SO(4)) residues from DS. Squid GalNAc4S-6ST thus should provide a useful tool for preparing CS-E and oversulfated DS with a defined proportion of GalNAc(4,6-SO(4)) residues.

Human N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase cDNA is related to human B cell recombination activating gene-associated gene

N-Acetylgalactosamine 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST) transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate to position 6 of N-acetylgalactosamine 4-sulfate (GalNAc(4SO(4))) in chondroitin sulfate and dermatan sulfate. We have previously purified the enzyme to apparent homogeneity from the squid cartilage. We report here cloning and characterization of human GalNAc4S-6ST. The strategy for identification of human GalNAc4S-6ST consisted of: 1) determination of the amino acid sequences of peptides derived from the purified squid GalNAc4S-6ST, 2) amplification of squid DNA by polymerase chain reaction, and 3) homology search using the amino acid sequence deduced from the squid DNA. The human GalNAc4S-6ST cDNA contains a single open reading frame that predicts a type II transmembrane protein composed of 561 amino acid residues. The recombinant protein expressed from the human GalNAc4S-6ST cDNA transferred sulfate from 3'-phosphoadenosine 5'-phosphosulfate to position 6 of the nonreducing terminal and internal GalNAc(4SO(4)) residues contained in chondroitin sulfate A and dermatan sulfate. When a trisaccharide and a pentasaccharide having sulfate groups at position 4 of N-acetylgalactosamine residues were used as acceptors, only nonreducing terminal GalNAc(4SO(4)) residues were sulfated. The nucleotide sequence of the human GalNAc4S-6ST cDNA was nearly identical to the sequence of human B cell recombination activating gene-associated gene.

Drosophila heparan sulfate 6-O-sulfotransferase (dHS6ST) gene. Structure, expression, and function in the formation of the tracheal system

Heparan sulfate, one of the most abundant components of the cell surface and the extracellular matrix, is involved in a variety of biological processes such as growth factor signaling, cell adhesion, and enzymatic catalysis. The heparan sulfate chains have markedly heterogeneous structures in which distinct sequences of sulfate groups determine specific binding properties. Sulfation at each different position of heparan sulfate is catalyzed by distinct enzymes, sulfotransferases. In this study, we identified and characterized Drosophila heparan sulfate 6-O-sulfotransferase (dHS6ST). The deduced primary structure of dHS6ST exhibited several common features found in those of mammalian HS6STs. We confirmed that, when the protein encoded by the cDNA was expressed in COS-7 cells, it showed HS6ST activity. Whole mount in situ hybridization revealed highly specific expression of dHS6ST mRNA in embryonic tracheal cells. The spatial and temporal pattern of dHS6ST expression in these cells clearly resembles that of the Drosophila fibroblast growth factor (FGF) receptor, breathless (btl). RNA interference experiments demonstrated that reduced dHS6ST activity caused embryonic lethality and disruption of the primary branching of the tracheal system. These phenotypes were reminiscent of the defects observed in mutants of FGF signaling components. We also show that FGF-dependent mitogen-activated protein kinase activation is significantly reduced in dHS6ST double-stranded RNA-injected embryos. These findings indicate that dHS6ST is required for tracheal development in Drosophila and suggest the evolutionally conserved roles of 6-O-sulfated heparan sulfate in FGF signaling.

Molecular cloning and characterization of GalNAc 4-sulfotransferase expressed in human pituitary gland

We have previously cloned chondroitin-4-sulfotransferase (C4ST) cDNA from mouse brain. In this paper, we report cloning and characterization of GalNAc 4-sulfotransferase (GalNAc4ST), which transfers sulfate to position 4 of the nonreducing terminal GalNAc residue. The obtained cDNA contains a single open reading frame that predicts a type II transmembrane protein composed of 424 amino acid residues. Identity of the amino acid sequence between GalNAc4ST and human C4ST was 30%. When the cDNA was transfected in COS-7 cells, sulfotransferase activity toward carbonic anhydrase VI was overexpressed but no sulfotransferase activity toward chondroitin or desulfated dermatan sulfate was increased over the control. Sulfation of carbonic anhydrase VI by the recombinant GalNAc4ST occurred at position 4 of the GalNAc residue of N-linked oligosaccharides. The recombinant GalNAc4ST transferred sulfate to position 4 of GalNAc residue of p-nitrophenyl GalNAc, indicating that this sulfotransferase transfers sulfate to position 4 at the nonreducing terminal GalNAc residue. Dot blot analysis showed that the message of GalNAc4ST was expressed strongly in the human pituitary, suggesting that the cloned GalNAc4ST may be involved in the synthesis of the nonreducing terminal GalNAc 4-sulfate residues found in the N-linked oligosaccharides of pituitary glycoprotein hormones.

Purification and characterization of N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase from the squid cartilage

N-Acetylgalactosamine 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST), which transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to position 6 of N-acetylgalactosamine 4-sulfate in chondroitin sulfate and dermatan sulfate, was purified 19,600-fold to apparent homogeneity from the squid cartilage. SDS-polyacrylamide gel electrophoresis of the purified enzyme showed a broad protein band with a molecular mass of 63 kDa. The protein band coeluted with GalNAc4S-6ST activity from Toyopearl HW-55 around the position of 66 kDa, indicating that the active form of GalNAc4S-6ST may be a monomer. The purified enzyme transferred sulfate from PAPS to chondroitin sulfate A, chondroitin sulfate C, and dermatan sulfate. The transfer of sulfate to chondroitin sulfate A and dermatan sulfate occurred mainly at position 6 of the internal N-acetylgalactosamine 4-sulfate residues. Chondroitin sulfate E, keratan sulfate, heparan sulfate, and completely desulfated N-resulfated heparin were not efficient acceptors of the sulfotransferase. When a trisaccharide or a pentasaccharide having sulfate groups at position 4 of N-acetylgalactosamine was used as acceptor, efficient sulfation of position 6 at the nonreducing terminal N-acetylgalactosamine 4-sulfate residue was observed.

The occurrence of three isoforms of heparan sulfate 6-O-sulfotransferase having different specificities for hexuronic acid adjacent to the targeted N-sulfoglucosamine

We previously cloned heparan sulfate 6-O-sulfotransferase (HS6ST) (Habuchi, H., Kobayashi, M., and Kimata, K. (1998) J. Biol. Chem. 273, 9208-9213). In this study, we report the cloning and characterization of three mouse isoforms of HS6ST, a mouse homologue to the original human HS6ST (HS6ST-1) and two novel HS6STs (HS6ST-2 and HS6ST-3). The cDNAs have been obtained from mouse brain cDNA library by cross-hybridization with human HS6ST cDNA. The three cDNAs contained single open reading frames that predicted type II transmembrane proteins composed of 401, 506, and 470 amino acid residues, respectively. Amino acid sequence of HS6ST-1 was 51 and 57% identical to those of HS6ST-2 and HS6ST-3, respectively. HS6ST-2 and HS6ST-3 had the 50% identity. Overexpression of each isoform in COS-7 cells resulted in about 10-fold increase of HS6ST activity. The three isoforms purified with anti-FLAG antibody affinity column transferred sulfate to heparan sulfate and heparin but not to other glycosaminoglycans. Each isoform showed different specificity toward the isomeric hexuronic acid adjacent to the targeted N-sulfoglucosamine; HS6ST-1 appeared to prefer the iduronosyl N-sulfoglucosamine while HS6ST-2 had a different preference, depending upon the substrate concentrations, and HS6ST-3 acted on either substrate. Northern analysis showed that the expression of each message in various tissues was characteristic to the respective isoform. HS6ST-1 was expressed strongly in liver, and HS6ST-2 was expressed mainly in brain and spleen. In contrast, HS6ST-3 was expressed rather ubiquitously. These results suggest that the expression of these isoforms may be regulated in tissue-specific manners and that each isoform may be involved in the synthesis of heparan sulfates with tissue-specific structures and functions.

Purification and characterization of chondroitin 4-sulfotransferase from the culture medium of a rat chondrosarcoma cell line

Chondroitin 4-sulfotransferase, which transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate to position 4 of N-acetylgalactosamine in chondroitin, was purified 1900-fold to apparent homogeneity with 6.1% yield from the serum-free culture medium of rat chondrosarcoma cells by affinity chromatography on heparin-Sepharose CL-6B, Matrex gel red A-agarose, 3',5'-ADP-agarose, and the second heparin-Sepharose CL-6B. SDS-polyacrylamide gel electrophoresis of the purified enzyme showed two protein bands. Molecular masses of these protein were 60 and 64 kDa under reducing conditions and 50 and 54 kDa under nonreducing conditions. Both the protein bands coeluted with chondroitin 4-sulfotransferase activity from Toyopearl HW-55 around the position of 50 kDa, indicating that the active form of chondroitin 4-sulfotransferase is a monomer. Dithiothreitol activated the purified chondroitin 4-sulfotransferase. The purified enzyme transferred sulfate to chondroitin and desulfated dermatan sulfate. Chondroitin sulfate A and chondroitin sulfate C were poor acceptors. Chondroitin sulfate E from squid cartilage, dermatan sulfate, heparan sulfate, and completely desulfated N-resulfated heparin hardly served as acceptors of the sulfotransferase. The transfer of sulfate to the desulfated dermatan sulfate occurred preferentially at position 4 of the N-acetylgalactosamine residues flanked with glucuronic acid residues on both reducing and nonreducing sides.

Molecular cloning and characterization of human keratan sulfate Gal-6-sulfotransferase

We have previously cloned chondroitin 6-sulfotransferase (C6ST) cDNA from chick embryo chondrocytes. C6ST catalyzes sulfation of chondroitin, keratan sulfate, and sialyl N-acetyllactosamine oligosaccharides. In this study, we report the cloning and characterization of a novel sulfotransferase that catalyzes sulfation of keratan sulfate. This new sulfotransferase cDNA clone was obtained from a human fetal brain library by cross-hybridization with chick C6ST cDNA. The cDNA clone obtained contains a single open reading frame that predicts a type II transmembrane protein composed of 411 amino acid residues. When the cDNA was introduced into a eukaryotic expression vector and transfected in COS-7 cells, keratan sulfate sulfotransferase activity was overexpressed, but C6ST activity was not increased over that of the control. Structural analysis of 35S-labeled glycosaminoglycan, which was formed from keratan sulfate by the reaction with 35S-labeled 3'-phosphoadenosine 5'-phosphosulfate and the recombinant sulfotransferase, showed that keratan sulfate was sulfated at position 6 of Gal residues. On the basis of the acceptor substrate specificity, we propose keratan sulfate Gal-6-sulfotransferase (KSGal6ST) for the name of the newly cloned sulfotransferase. KSGal6ST was assigned to chromosome 11p11. 1-11.2 by fluorescence in situ hybridization. Among various human adult tissues, a 2.8-kilobase message of KSGal6ST was expressed mainly in the brain. When poly(A)+ RNAs from the chick embryo cornea and brain were probed with the human KSGal6ST cDNA in Northern hybridization, a clear band with about 2.8 kilobases was detected. These observations suggest that KSGal6ST may participate in the biosynthesis of keratan sulfate in the brain and cornea.

Purification and characterization of heparan sulfate 2-sulfotransferase from cultured Chinese hamster ovary cells

Heparan sulfate 2-sulfotransferase, which catalyzes the transfer of sulfate from adenosine 3'-phosphate 5'-phosphosulfate to position 2 of L-iduronic acid residue in heparan sulfate, was purified 51,700-fold to apparent homogeneity with a 6% yield from cultured Chinese hamster ovary cells. The isolation procedure included a combination of affinity chromatography on heparin-Sepharose CL-6B and 3',5'-ADP-agarose, which was repeated twice for each, and finally gel chromatography on Superose 12 . Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme showed two protein bands with molecular masses of 47 and 44 kDa. Both proteins appeared to be glycoproteins, because their molecular masses decreased after N-glycanase digestion. When completely desulfated and N-resulfated heparin and mouse Engelbreth-Holm-Swarm tumor heparan sulfate were used as acceptors, the purified enzyme transferred sulfate to position 2 of L-iduronic acid residue but did not transfer sulfate to the amino group of glucosamine residue or to position 6 of N-sulfoglucosamine residue. Heparan sulfates from pig aorta and bovine liver, however, were poor acceptors. The enzyme showed no activities toward chondroitin, chondroitin sulfate, dermatan sulfate, and keratan sulfate. The optimal pH for the enzyme activity was around 5.5. The enzyme activity was minimally affected by dithiothreitol and was stimulated strongly by protamine. The Km value for adenosine 3'-phosphate 5'-phosphosulfate was 0.20 microM.

Purification and characterization of heparan sulfate 6-sulfotransferase from the culture medium of Chinese hamster ovary cells

Heparan sulfate 6-sulfotransferase, which catalyzes the transfer of sulfate from 3'-phosphoadenylyl sulfate to position 6 of N-sulfoglucosamine in heparan sulfate, was purified 10,700-fold to apparent homogeneity with a 40% yield from the serum-free culture medium of Chinese hamster ovary cells. The isolation procedure included affinity chromatography of the first heparin-Sepharose CL-6B column (stepwise elution), 3',5'-ADP-agarose, and the second heparin-Sepharose CL-6B column (gradient elution). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme showed two protein bands with molecular masses of 52 and 45 kDa. Both proteins appeared to be glycoproteins, because their molecular masses decreased after N-glycanase digestion. When completely desulfated and N-resulfated heparin was used as acceptor, the purified enzyme transferred sulfate to position 6 of N-sulfoglucosamine residue but did not transfer sulfate to the amino group of glucosamine residue or to position 2 of the iduronic acid residue. Heparan sulfate was also sulfated by the purified enzyme at position 6 of N-sulfoglucosamine residue. Chondroitin and chondroitin sulfate did not serve as acceptors. The optimal pH for enzyme activity was around 6.3. The enzyme activity was inhibited by dithiothreitol and was stimulated strongly by protamine. The Km value for adenosine 3'-phosphate 5'-phosphosulfate was 0.44 microM.

Secretion of chondroitin 6-sulfotransferase and chondroitin 4-sulfotransferase from cultured chick embryo chondrocytes

We found that chondroitin 6-sulfotransferase and chondroitin 4-sulfotransferase were released into the culture medium from the cultured chick embryo chondrocytes. Since the release of the sulfotransferases was observed not only in serum-supplemented medium but also in serum-free medium, the released sulfotransferases were unlikely to be derived from serum. Addition of ascorbate to the serum-free medium supported the continuous release of the sulfotransferases. Monensin, which is known to cause dilatation of the Golgi apparatus and to inhibit sulfation of proteoglycan, was found to affect the release of the sulfotransferases. In the presence of 10(-6) M monensin, chondroitin 6-sulfotransferase activity in the cell layer was decreased to less than one tenth of the control, and the rate of the release of the activity became much smaller than the control after the initial rapid release. The activity of chondroitin 4-sulfotransferase was also affected by monensin, but the reduction of the chondroitin 4-sulfotransferase activity in the cell layer was not so great as the reduction of chondroitin 6-sulfotransferase activity. Unlike to the microsomal sulfotransferases, both chondroitin 6-sulfotransferase and chondroitin 4-sulfotransferase released into the culture medium were retained in the soluble fraction after centrifugation at 100,000 x g for 60 min, and were not activated by detergent. pH optimum and requirements for sulfhydryl compounds of the released sulfotransferases were similar to those observed previously in the chondroitin sulfotransferases from chick embryo cartilage and from cultured chick embryo chondrocytes. These results suggest that chondroitin sulfotransferases, which are localized in the Golgi apparatus, may be secreted to the extracellular space in a soluble form under the culture conditions.

Synthesis and utilization of a nonhydrolyzable phosphoadenosine phosphosulfate analog

3'-Phosphoadenosine 5'-phosphosulfate (PAPS) functions as the high-energy sulfate donor for sulfate ester synthesis in all higher organisms. This activated sulfate, like its adenosine 5'-phosphosulfate precursor, is both chemically labile and vulnerable to sulfohydrolase degradation. These obstacles have limited the utility of the native PAPS in the purification and mechanistic description of the numerous PAPS-utilizing enzymes. This paper describes the synthesis of the 2'- and 3'-isomers of a nonhydrolysable, and thus stable, PAPS analog, beta-methylene-PAPS, from the previously described beta-methylene-APS (L. Callahan et al., Anal. Biochem. 177, 67-71, 1989). The method involves phosphorylation of beta-methylene-APS with trimetaphosphate and separation of the resulting mixed 2'(3')-isomers by ion-pair reverse-phase HPLC. The utilization of this analog as an inhibitor of APS kinase and PAPS translocase, two of the numerous PAPS-utilizing activities, as well as an affinity ligand for purification of APS kinase, is described.

Preparation and quantification of 3'-phosphoadenosine 5'-phospho[35S]sulfate with high specific activity

The synthesis and quantitation of the sulfate donor 3'-phosphoadenosine 5'-phospho[35S]sulfate (PAP35S), prepared from inorganic [35S]sulfate and ATP, were studied. An enzymatic transfer method based upon the quantitative transfer of [35S]sulfate from PAP35S to 2-naphthol and 4-methylumbelliferone by the action of phenolsulfotransferase activity from rat brain cytosol was also developed. The 2-naphthyl[35S]sulfate or 35S-methylumbelliferone sulfate formed was isolated by polystyrene bead chromatography. This method allows the detection of between 0.1 pmol and 1 nmol/ml of PAP35S. PAP35S of high specific activity (75 Ci/mmol) was prepared by incubating ATP and carrier-free Na2 35SO4 with a 100,000g supernatant fraction from rat spleen. The product was purified by ion-exchange chromatography. The specific activity and purity of PAP35S were estimated by examining the ratios of Km values for PAP35S of the tyrosyl protein sulfotransferase present in microsomes from rat cerebral cortex. The advantage and applications of these methods for the detection of femtomole amounts, and the synthesis of large scale quantities of PAP35S with high specific activity are discussed.