Molecular organization of heparan sulphate from human skin fibroblasts.

The molecular structure of human skin fibroblast heparan sulphate was examined by specific chemical or enzymic depolymerization and high-resolution separation of the resulting oligosaccharides and disaccharides. Important features of the molecular organization, disaccharide composition and O-sulphate disposition of this heparan sulphate were identified. Analysis of the products of HNO2 hydrolysis revealed a polymer in which 53% of disaccharide units were N-acetylated and 47% N-sulphated, with an N-/O-sulphate ratio of 1.8:1. These two types of disaccharide unit were mainly located in separate domains. Heparitinase and heparinase scission indicated that the iduronate residues (37% of total hexuronate) were largely present in contiguous disaccharide sequences of variable size that also contained the majority of the N-sulphate groups. Most of the iduronate residues (approx. 70%) were non-sulphated. About 8-10% of disaccharide units were cleaved by heparinase, but only a minority of these originated from contiguous sequences in the intact polymer. Trisulphated disaccharide units [alpha-N-sulpho-6-sulphoglucosaminyl-(1----4)-iduronate 2-sulphate], which are the major structural units in heparin, made up only 3% of the disaccharide units in heparan sulphate. O-Sulphate groups (approx. 26 per 100 disaccharide units) were distributed almost evenly among C-6 of N-acetylglucosamine, C-2 of iduronate and C-6 of N-sulphated glucosamine residues. The results indicate that the sulphated regions of heparan sulphate have distinctive and potentially variable structural characteristics. The high content of non-sulphated iduronate in this heparan sulphate species suggests a conformational versatility that could have important implications for the biological properties of the polymer.     

Distribution of sulphate and iduronic acid residues in heparin and heparan sulphate

1. A method was developed for determination of the uronic acid composition of heparin-like glycosaminoglycans. Polymers or oligosaccharides are degraded to monosaccharides by a combination of acid hydrolysis and deamination with HNO₂. The resulting uronic acid monosaccharides (accounting for about 70% of the uronic acid contents of the starting materials) are isolated and converted into the corresponding aldono-1,4-lactones, which are separated by g.l.c. The calculated ratios of glucuronic acid/iduronic acid are reproducible within 5%. 2. Samples of heparin from pig intestinal mucosa (molar ratio of sulphate/disaccharide unit, 2.40) and heparan sulphate from human aorta (sulphate/disaccharide ratio, 0.46) were subjected to uronic acid analysis. l-Iduronic acid constituted 77% and 19% respectively of the total uronic acid contents. 3. The correlation between the contents of sulphate and iduronic acid indicated by this finding also applied to the fractionated deamination products of the two polymers. The sulphated fragments varied in size from disaccharide to octasaccharide (or larger) and showed sulphate/disaccharide molar ratios in the range of 0.05–2.0. The proportion of iduronic acid increased with increasing ester sulphate contents of the oligosaccharides. 4. Previous studies on the biosynthesis of heparin in a cell-free system have shown that l-iduronic acid residues are formed by C-5 epimerization of d-glucuronic acid units at the polymer level; the process requires concomitant sulphation of the polymer. The results obtained in the present structural study conform to these findings, and suggest further that similar mechanisms may operate in the biosynthesis of heparan sulphate. The epimerization reaction appears to be linked to the sulphation of hydroxyl groups but does not seem to require sulphation of the target uronic acid residues. The significance of sulphamino groups in relation to the formation of iduronic acid is unknown.     

Thrombin-inhibitory activity of whale heparin oligosaccharides

Whale heparin was partially digested with a purified heparinase and the oligosaccharide fractions with 8-20 monosaccharide units were isolated from the digest by gel filtration on Sephadex G-50, followed by affinity chromatography on a column of antithrombin III immobilized on Sepharose 4B. A marked difference in the inhibitory activity for thrombin in the presence of antithrombin III was observed between the high-affinity fractions for antithrombin III of octasaccharide approximately hexadecasaccharide and those of octadecasaccharide approximately eicosasaccharide. The disaccharide compositions of these hexadeca-, octadeca-, and eicosasaccharides were analyzed by high-performance liquid chromatography after digestion with a mixture of purified heparitinases 1 and 2 and heparinase. The analytical data indicated that the proportions of trisulfated disaccharide (IdUA(2S)alpha 1----4GlcNS(6S)) and disulfated disaccharide (UA1----4GlcNS(6S)) increased with the manifestation of high thrombin-inhibitory activity, while that of monosulfated disaccharide (UA1----4GlcNS) decreased. The present observations, together with those so far reported, suggest that the presence of the former structural elements, specifically IdUA(2S)alpha 1----4GlcNS(6S), as well as the antithrombin III-binding pentasaccharide at the proper positions in the molecules of whale heparin oligosaccharides is essential for the manifestation of high inhibitory activity for thrombin in the presence of antithrombin III. The structural bases for the manifestation of the anticoagulant activity of whale and porcine heparins and their oligosaccharides are also discussed.     

Enzymatic preparation of heparin disaccharides as building blocks in glycosaminoglycan synthesis.

Pharmaceutical heparin and heparan sulfate, isolated from a side-stream of a commercial heparin manufacturing process, have been enzymatically depolymerzed with heparin lyases obtained from Flavobacterium heparinun. Heparin afforded a trisulfated disaccharide product that was recovered from the reaction mixture using gel permeation chromatography. Heparan sulfate afforded unsulfated disaccharide that was conveniently recovered from the product mixture by ion exchange chromatography. Both disaccharides were obtained in gram amounts at 90% or higher purity. Both enzymatically prepared disaccharides were chemically protected to prepare building blocks required for the future chemical synthesis of therapeutically valuable heparin oligosaccharides.     

Analysis of oligosaccharides from heparin by reversed-phase ion-pairing high-performance liquid chromatography

An ion-pairing high-pressure liquid chromatography procedure was developed for analysis of mixtures of oligosaccharides generated by nitrous acid cleavage of heparin. Oligosaccharides were eluted from a Hi-Chrom 5S ODS (C18) column using mixtures of acetonitrile and buffers containing 40 mM ammonium phosphate and 1 mM tetrabutylammonium phosphate. Isocratic conditions were developed for optimal separation of a number of individual disaccharides and tetrasaccharides that were characterized previously (M.J. Bienkowski and H.E. Conrad (1985) J. Biol. Chem. 260, 356-365). These isocratic conditions were then coupled to obtain gradient elution conditions for the ion-pairing separations of mixtures of disaccharides and mixtures of tetrasaccharides. A comparison of the elution profiles obtained in the ion-pairing chromatography procedure with profiles obtained by anion-exchange high-pressure liquid chromatography profiles showed markedly better overall resolution by the ion-pairing procedure. As a result of this improved resolution, the new procedure showed the presence of previously unidentified products in the heparin oligosaccharide mixtures.     

Oligosaccharide mapping of heparan sulphate by polyacrylamide-gradient-gel electrophoresis and electrotransfer to nylon membrane.

A new method that we have called 'oligosaccharide mapping' is described for the analysis of radiolabelled heparan sulphate and other glycosaminoglycans. The method involves specific enzymic or chemical scission of polysaccharide chains followed by high-resolution separation of the degradation products by polyacrylamide-gradient-gel electrophoresis. The separated oligosaccharides are immobilized on charged nylon membranes by electrotransfer and detected by fluorography. A complex pattern of discrete bands is observed covering an oligosaccharide size range from degree of polymerization (d.p.) 2 (disaccharide) to approximately d.p. 40. Separation is due principally to differences in Mr, though the method also seems to detect variations in conformation of oligosaccharide isomers. Resolution of oligosaccharides is superior to that obtained with isocratic polyacrylamide-gel-electrophoresis systems or gel chromatography, and reveals structural details that are not accessible by other methods. For example, in this paper we demonstrate a distinctive repeating doublet pattern of iduronate-rich oligosaccharides in heparitinase digests of mouse fibroblast heparan sulphate. This pattern may be a general feature of mammalian heparan sulphates. Oligosaccharide mapping should be a valuable method for the analysis of fine structure and sequence of heparan sulphate and other complex polysaccharides, and for making rapid assessments of the molecular distinctions between heparan sulphates from different sources.     

Heterogeneity of depolymerized heparin SEC fractions: to pool or not to pool?

In the structural analysis of heparin and heparan sulfate, it is customary to combine or pool like-sized fractions obtained by size-exclusion chromatography (SEC) of enzymatically derived heparin oligosaccharides. In this study, we examine the heterogeneity of preparative-scale SEC fractions obtained from enzymatic digests of porcine intestinal mucosa heparin. Each fraction was profiled by capillary electrophoresis with UV detection (CE−UV) using a 60 mM formic acid running buffer at pH 3.43. Differences in the composition and relative concentration of components of the SEC fractions were observed for disaccharides and larger oligosaccharides. The heterogeneity of the fractions becomes more pronounced when heparin is digested using a heparin lyase cocktail. The heterogeneity of preparative SEC fractions was further investigated by reversed-phase ion-pairing ultraperformance liquid chromatography coupled with mass spectrometry (RPIP−UPLC−MS) using the ion-pairing reagent, tributylamine (Bu₃N). Our results suggest that preliminary profiling of preparative SEC fractions prior to pooling may simplify efforts to identify and/or isolate rare structures.     

Inactivation of unbound rat liver glucocorticoid receptor by N-alkylmaleimides at sub-zero temperatures

Biosynthetically radiolabelled heparan sulphate proteoglycans have been isolated from the growth medium and the cell lysate of a human neuroblastoma cell line (CHP100). Chromatography on Sepharose CL-4B identified two heparan sulphate proteoglycans in the medium (Kav 0.220 and 0.389), whereas in the cell lysate the major proteoglycan species were more heterogenous and of a smaller overall molecular size (Kav 0.407) than the medium-derived counterparts. Chromatography on Sepharose CL-6B of free heparan sulphate glycosaminoglycan chains showed that the majority of cell-layer-derived material heparan sulphate 2, Kav = 0.509) was smaller than medium heparan sulphates (heparan sulphate 1 and heparan sulphate 2, Kav 0.230 and 0.317). Analysis of the patterns of polymer sulphation by nitrous acid treatment, gel chromatography and high-voltage electrophoresis established that in each heparan sulphate fraction there was on average 1.1 sulphate residues per disaccharide with an N:O sulphate ratio of 1.1. Heparan sulphate in the medium had a high proportion of di-O-sulphated disaccharides in regions of the chain with repeat disaccharide sequences of structure GlcA-GlcNSO3, whereas cell-associated material was enriched in di-O-sulphated tetrasaccharides of alternating sequences GlcA-GlcNAc-GlcA-GlcNSO3. The identification of several populations of heparan sulphate proteoglycans differing in molecular size and glycosaminoglycan fine structure may reflect the functional diversity of this family of macromolecules in the nervous system.     

Interactions between glycosaminoglycans and blood coagulation factors: 1. Affinity chromatography of glycosaminoglycans on thrombin-substituted agarose

Various glycosaminoglycans have been subjected to affinity chromatography on immobilized bovine thrombin. Chondroitin sulphate, dermatan sulphate and heparan sulphate variants with a sulphate-to-hexosamine molar ratio of ～ 1 exhibited weak affinities. Heparan sulphate/heparin fractions of higher sulphate content could be separated into material with high and low affinity for thrombin. Removal of N-sulphate followed by N-acetylation did not affect binding, whereas oxidation and cleavage of non-sulphated hexuronate abolished the interaction. Heparan-related molecules of high thrombin-affinity comprised sequences where large blocks of sulphated iduronate-containing repeats were joined via a few repeats carrying non-sulphated iduronate or glucuronate to form continuous segments that were larger than decasaccharide.     

New oligosaccharides from heparin and heparan sulfate and their use as substrates for heparin-degrading enzymes

Oligosaccharides were isolated from heparin and heparan sulfate by a procedure consisting of three major steps: (a) acid hydrolysis; (b) gel chromatography; and (c) cation exchange chromatography on an amino acid analyzer. To date, six new oligosaccharides have been isolated by this procedure and have been sequenced by a combination of NaB3H4-labeling and deaminative cleavage with nitrous acid. The structures of these oligosaccharides were as follows: 1. GlcN-GlcUA-GlcN 2. GlcN-IdUA-GlcN 3. GlcN-GlcUA-GlcN-GlcUA-GlcN 4. GlcN-IdUA-GlcN-GlcUA-GlcN 5. GlcN-GlcUA-GlcN-IdUA-GlcN 6. GlcN-IdUA-GlcN-IdUA-GlcN The linkage positions and anomeric configurations were assumed to be the same as in the polysaccharides from which the oligosaccharides originated. The usefulness of some of these oligosaccharides as enzyme substrates was tested after appropriate modifications and radioactive labeling. Oligosaccharides 2 and 3 were N-[35S]sulfated and were found to serve as substrates for heparan N-sulfate sulfatase (heparin sulfamidase), with a homogenate of cultured skin fibroblasts as enzyme source. Similarly, reduction of oligosaccharide 2 with NaB3H4 yielded a substrate for acetyl-CoA:alpha-D-glucosaminide N-acetyltransferase. Finally, the previously known disaccharide, 4-O-alpha-D-glucosaminyl-L-iduronic acid, which was isolated in the course of this work, was N-acetylated with [3H] acetic anhydride and was shown to be a substrate for N-acetyl-alpha-D-glucosaminidase.     

Effects of chemically modified heparin on Chlamydia trachomatis serovar L2 infection of eukaryotic cells in culture

The mechanism and inhibitors of Chlamydia trachomatis serovar L2 infection of eukaryotic host cells were studied using a tissue culture model infection system. Potent inhibition of infectivity was observed when elementary bodies (EBs) were exposed to heparin or when HeLa 229 cells were treated with heparinase. No significant inhibition was seen the other way around. The same potent inhibition was observed when EBs were exposed to chemically 2-O-desulfated heparin (2-ODS heparin), which is composed of repeating disaccharide units of IdoA-GlcNS(6S), but not when exposed to chemically 6-ODS heparin or completely desulfated and N-resulfated heparin, which is composed of repeating disaccharide units of IdoA(2S)-GlcNS or IdoA-GlcNS, respectively. The inhibitory effects of 2-ODS heparin could be seen only with oligosaccharides longer than dodecasaccharides. The mutant Chinese hamster ovary (CHO) cell line 677, which is deficient in the biosynthesis of heparan sulfate, was less sensitive to C. trachomatis infection than were wild-type CHO cells. F-17 cells, deficient in 2-O-sulfation of heparan sulfate, had the same sensitivity to infection as wild-type CHO cells did. These data suggest that infection of host cells by EBS results from the specific binding of ligand molecules with affinity for heparin on the EB surface to heparan sulfate proteoglycans on the host cell surface. This binding may depend on host cell heparan sulfate chains that are 6-O-sulfated and longer than dodecasaccharides. The 2-ODS heparin oligosaccharides may be a potential agent for the prevention of C. trachomatis infection.     

Microbial heparin/heparan sulphate lyases: potential and applications

Heparin/heparan sulphate glycosaminoglycans (HSGAGs) are composed of linear chains of 20–100 disaccharide units of N-acetylated d-glucosamine α (1–4) linked to glucuronic acid. HSGAGs are widely distributed on the cell surface and extracellular cell matrix of virtually every mammalian cell type and play critical role in regulating numerous functions of blood vessel wall, blood coagulation, inflammation response and cell differentiation. These glycosaminoglycans present in this extracellular environment very significantly influence the blood coagulation system and cardiovascular functions. Recent studies have investigated the mechanism by which cancer causes thrombosis and emphasizes the importance of the coagulation system in angiogenesis and tumour metastasis. Heparan sulphate/heparin lyases or heparinases are a class of enzymes that are capable of specifically cleaving the (1–4) glycosidic linkages in heparin and heparan sulphate to generate biologically active oligosaccharides with substantially significant and distinct clinical, pharmaceutical and prophylactic/therapeutic applications. Bioavailability and pharmacokinetic behaviour and characteristics of these oligosaccharides vary significantly depending on the origin/nature of the substrate (heparin or heparan sulphate-like glycosaminoglycans), the source of enzyme and method of preparation. Various microorganisms are reported/patented to produce these enzymes with different properties. Heparinases are commercially used for the depolymerization of unfractionated heparin to produce low molecular weight heparins (LMWHs), an effective anticoagulant. Individual LMWHs are chemically different and unique and thus cannot be interchanged therapeutically. Heparinases and LMWHs are reported to control angiogenesis and metastasis also. This review catalogues the degradation of HSGAGs by microbial heparin/heparan sulphate lyases and their potential either specific to the enzymes or with the dual role for generation of oligosaccharides for a new generation of compounds, as shown by various laboratory or clinical studies.     

The disaccharide repeating-units of heparan sulfate

Five disaccharides have been isolated after degradation of heparan sulfate by heparinase (heparin lyase) and heparitinase (heparan sulfate lyase) and are suggested to represent the repeating units of the polysaccharide. They all contain a 4,5-unsaturated uronic acid residue and are: (a) A trisulfated disaccharide that is apparently identical to a disaccharide repeating-unit of heparin; (b) a disulfated disaccharide that seems unique for heparan sulfate and contains 2-deoxy-2-sulfamidoglucose and uronic acid sulfate residues; (c) a nonsulfated disaccharide containing a 2-acetamido-2-deoxyglucose residue; (d) a monosulfated disaccharide containing a 2-acetamido-2-deoxyglucose sulfate residue; and (e) a monosulfated disaccharide containing a 2-deoxy-2-sulfamidoglucose residue. Yields of these disaccharides from different heparan sulfate fractions are discussed in relation to possible arrangements of these units in the intact polymer.     

Binding of heparin/heparan sulfate to fibroblast growth factor receptor 4

Fibroblast growth factors (FGFs) are heparin-binding polypeptides that affect the growth, differentiation, and migration of many cell types. FGFs signal by binding and activating cell surface FGF receptors (FGFRs) with intracellular tyrosine kinase domains. The signaling involves ligand-induced receptor dimerization and autophosphorylation, followed by downstream transfer of the signal. The sulfated glycosaminoglycans heparin and heparan sulfate bind both FGFs and FGFRs and enhance FGF signaling by mediating complex formation between the growth factor and receptor components. Whereas the heparin/heparan sulfate structures involved in FGF binding have been studied in some detail, little information has been available on saccharide structures mediating binding to FGFRs. We have performed structural characterization of heparin/heparan sulfate oligosaccharides with affinity toward FGFR4. The binding of heparin oligosaccharides to FGFR4 increased with increasing fragment length, the minimal binding domains being contained within eight monosaccharide units. The FGFR4-binding saccharide domains contained both 2-O-sulfated iduronic acid and 6-O-sulfated N-sulfoglucosamine residues, as shown by experiments with selectively desulfated heparin, compositional disaccharide analysis, and a novel exoenzyme-based sequence analysis of heparan sulfate oligosaccharides. Structurally distinct heparan sulfate octasaccharides differed in binding to FGFR4. Sequence analysis suggested that the affinity of the interaction depended on the number of 6-O-sulfate groups but not on their precise location.     

The nature of the non-ultrafilterable glycosaminoglycans of normal human urine

1. The non-ultrafilterable acidic glycosaminoglycans from pooled urine of normal men, aged about 20, were isolated and characterized. The isolation procedure included digestion with sialidase and pronase, and fractionation by stepwise elution from an ECTEOLA-cellulose column. The glycosaminoglycans in each fraction were separated from each other by preparative electrophoresis in sodium barbital buffer and in barium acetate. 2. Approximate relative amounts of the different glycosaminoglycans were: chondroitin sulphate 60%, chondroitin 2%, hyaluronic acid 4%, dermatan sulphate 1%, heparan sulphate 15% and keratan sulphate 18%. Chondroitin sulphate-dermatan sulphate hybrids seemed to occur in trace amounts. 3. Chondroitin sulphate, heparan sulphate and keratan sulphate were heterogeneous with respect to degree of sulphation. Two distinct groups of chondroitin sulphate fractions were found, with sulphate/hexosamine molar ratios of about 0.5 and 1 respectively. The sulphate/hexosamine molar ratios in the heparan sulphate fractions varied from 0.5 to 0.9; the N-sulphate/hexosamine ratio was about 0.5 in all fractions. The sulphate/hexosamine molar ratios in the keratan sulphate fractions varied from 0.2 to 0.7.     

The carbohydrate moiety of band-3 glycoprotein of human erythrocyte membranes.

Band-3 glycoprotein was purified from human blood-group-A erythrocyte membranes by selective solubilization and gel chromatography on Sepharose 6B in the presence of sodium dodecyl sulphate. The purified glycoprotein was subjected to hydrazinolysis in order to release the carbohydrate moiety. The released oligosaccharides were N-acetylated and applied to a column of DEAE-cellulose. Most of the band-3 oligosaccharides obtained were found to be free of sialic acids. When this neutral fraction was subjected to gel chromatography on a column of Sephadex G-50, two broad peaks were observed indicating that the band-3 glycoprotein was heterogeneous in the size of the oligosaccharide moieties. All fractions from gel chromatography were found to contain galactose, mannose, N-acetylglucosamine and fucose. The higher-molecular-weight (mol.wt. 3000-8000) peak consisted of fucose, mannose, galactose, N-acetylglucosamine and N-acetylgalactosamine in a molar proportion of 1.6:3.0:8.4:10.5:0.2. Most of these oligosaccharides were digested with a mixture of beta-galactosidase and beta-N-acetylhexosaminidase after alpha-L-fucosidase treatment to give a small oligosaccharide with the structure alpha Man2-beta Man-beta GlcNAc-GlcNAc. Methylation studies and limited degradation by nitrous acid deamination showed that the oligosaccharides contained the repeating disaccharide Gal beta 1----4GlcNAc beta 1----3, with branching points at C-6 of some of the galactose residues. These results indicate that a major portion of the band-3 oligosaccharide has a common core structure, with heterogeneity in the numbers of the repeating disaccharides, and contains fucose residues both in the peripheral portion and in the core portion. Haemagglutination tests were also carried out to determine the blood-group specificities of the glycoprotein and the results demonstrated the presence of both blood-group-H and I antigenic activities.     

Structural features in heparin which modulate specific biological activities mediated by basic fibroblast growth factor

The biological activity of basic fibroblast growth factor (bFGF)is influenced greatly by direct binding to heparin and heparansulphate (HS). Heparin-derived oligosaccharides have been utilizedto determine the structural requirements present in the polymerthat account for bind ing to bFGF. We had previously demonstratedthat fragments >6 mer can inhibit the interaction betweencell surface heparan sulphate proteoglycan (HSPG) and bFGF,and bFGF-induced proliferation of adrenocortical endothelial(ACE) cells. In contrast, oligosaccharides > 10 mer can enhancethe binding of bFGF to its high-affinity receptor or supportbFGF-induced mitogenesis in ACE cells (Ishihara et al., J. Biol.Chem., 268, 4675–4683, 1993). We have extended these studiesto size- and structure-defined oligosaccharides from heparin,2-O-desulphated (2-O-DS-) heparin, 6-O-desulphated (6-O-DS-)heparin, carboxyreduced (CR-) heparin and carboxy-amidomethylsulphonated(AMS-) heparin. Oligosaccharides from these polymers were fractionatedon a bFGF-affinity column and were assessed as inhibitors orenhancers of specific bFGF-derived biological activities. Theresults of these studies indicate that both 2-O-sulphate andthe negative charge of the carboxy group [L-iduronic acid (IdoA)residues] are required for specific interactions of heparin-derivedoligosaccharides with bFGF and for modulation of bFGF mitogenicactivity. In addition, the charge of the carboxy groups in uronicacids can be replaced by other functional groups with a negativecharge, such as the amidomethyl sulphonate moiety describedhere. basic fibroblast growth factor heparan sulphate heparin oligosaccharides     

Identification of N-sulphated disaccharide units in heparin-like polysaccharides.

1. Preparations of heparin and heparan sulphate were degraded with HNO2. The resulting disaccharides were isolated by gel chromatography, reduced with either NaBH4 or NaB3H4 and were then fractionated into non-sulphated, monosulphated and disulphated species by ion-exchange chromatography or by paper electrophoresis. The non-sulphated disaccharides were separated into two, and the monosulphated disaccharides into three, components by paper chromatography. 2. The uronic acid moieties of the various non- and mono-sulphated disaccharides were identified by means of radioactive labels selectively introduced into uronic acid residues (3H and 14C in D-glucuronic acid, 14C only in L-iduronic acid units) during biosynthesis of the polysaccharide starting material. Labelled uronic acids were also identified by paper chromatography, after liberation from disaccharides by acid hydrolysis or by glucuronidase digestion. Similar procedures, applied to disaccharides treated with NaB3H4, indicated 2,5-anhydro-D-mannitol as reducing terminal unit. On the basis of these results, and the known positions and configurations of the glycosidic linkages in heparin, the two non-sulphated disaccharides were identified as 4-O-(beta-D-glucopyranosyluronic acid)-2,5-anhydro-D-mannitol and 4-O-(alpha-L-idopyranosyluronic acid)-2,5-anhydro-D-mannitol. 3. The three monosulphated [1-3H]anhydromannitol-labelled disaccharides were subjected to Smith degradation or to digestion with homogenates of human skin fibroblasts, and the products were analysed by paper electrophoresis. The results, along with the 1H n.m.r. spectra of the corresponding unlabelled disaccharides, permitted the allocation of O-sulphate groups to various positions in the disaccharides. These were thus identified as 4-O-(beta-D-glucopyranosyl-uronic acid)-2,5-anhydro-D-mannitol 6-sulphate, 4-O-(alpha-L-idopyranosyluronic acid)-2,5-anhydro-D-mannitol 6-sulphate and 4-O-(alpha-L-idopyranosyluronic acid 2-sulphate)-2,5-anhydro-D-mannitol. The last-mentioned disaccharide was found to be a poor substrate for the iduronate sulphatase of human skin fibroblasts, as compared with the disulphated species, 4-O-(alpha-L-idopyranosyluronic acid 2-sulphate)-2,5-anhydro-D-mannitol 6-sulphate. 4. The identified [1-3H]anhydromannitol-labelled disaccharides were used as reference standards in a study of the disaccharide composition of heparins and heparan sulphates. Low N-sulphate contents, most pronounced in the heparin sulphates, were associated with high ratios of mono-O-sulphated/di-O-sulphated (N-sulphated) disaccharide units, and in addition, with relatively large amounts of 2-sulphated L-iduronic acid residues bound to C-4 of N-sulpho-D-glucosamine units lacking O-sulphate substituents.     

Types of oligosaccharide sulphation, depending on mucus glycoprotein source, corpus or antral, in rat stomach.

Radiolabelled mucus glycoprotein was obtained from tissue and a culture medium each of the corpus and antrum of rat stomach incubated with [35S]sulphate in vitro. Gel-filtration analysis of oligosaccharides liberated by alkaline-borohydride treatment from glycoproteins indicated that 35S-labelled oligosaccharides from the corpus vary considerably with respect to chain length whereas those from antral mucus glycoprotein are composed of small oligosaccharides. Examination of the reduced radiolabelled products obtained by HNO2 cleavage of the hydrazine-treated oligosaccharides indicated sulphate esters of N-acetylglucosamine to be present at three locations on a carbohydrate unit: [35S]sulphated monosaccharide (2,5-anhydromannitol 6-sulphate), [35S]sulphated disaccharide [galactosyl(beta 1-4)-2,5-anhydromannitol 6-sulphate] and [35S]sulphated trisaccharide [fucosyl(alpha 1-2)-galactosyl(beta 1-4)-2,5-anhydromannitol 6-sulphate]. Sulphated disaccharide and trisaccharide, possibly originating from the N-acetyl-lactosamine and fucosyl-N-acetyl-lactosamine sequences respectively, were detected in the corpus, especially as large oligosaccharides, but were present in the antrum in only very small amounts. The sulphated monosaccharide, however, most probably originating from 6-sulphated N-acetylglucosamine residues at non-reducing termini, was present in all oligosaccharide fractions in both the corpus and antrum.     

Heterogeneity of cell-associated and secretory heparan sulphate proteoglycans produced by cultured human neuroblastoma cells

Biosynthetically radiolabelled heparan sulphate proteoglycans have been isolated from the growth medium and the cell lysate of a human neuroblastoma cell line (CHP100). Chromatography on Sepharose CL-4B identified two heparan sulphate proteoglycans in the medium (K_av 0.220 and 0.3890, whereas in the cell lysate the major proteoglycan species were more heterogenous and of a smaller overall molecular size (K_av 0.407) than the medium-derived counterparts. Chromatography on Sepharose CL-6B of free heparan sulphate glycosaminoglycan chains showed that the majority of cell-layer-derived material heparan sulphate 2, K_av=0.509) was smaller than medium heparan sulphates (heparan sulphate 1 and heparan sulphate 2, K_av 0.230 and 0.317). Analysis of the patterns of polymer sulphation by nitrous acid treatment, gel chromatography and high-voltage electrophoresis established that in each heparan sulphate fraction there was on average 1.1 sulphate residues per disaccharide with an N:O sulphate ratio of 1.1 Heparan sulphate in the medium had a high proportion of di-O-sulphated disaccharides in regions of the chain with repeat disaccharide sequences of structure GlcA-GlcNSO₃, whereas cell-associated material was enriched in di-O-sulphated tetrasaccharides of alternating sequences GlcA-GlcNAc-GlcA-GlcNSO₃. The identification of several populations of heparan sulphate proteoglycans differing in molecular size and glycosaminoglycan fine structure may reflect the functional diversity of this family of macromolecules in the nervous system.