Hydrazinolysis of heparin and other glycosaminoglycans

Structural Characterization and Anticoagulant Activities of a Keratan Sulfate-like Polysaccharide from the Sea Cucumber Holothuria fuscopunctata

A sulfated polysaccharide (AG) was extracted and isolated from the sea cucumber H. fuscopunctata, consisting of GlcNAc, GalNAc, Gal, Fuc and lacking any uronic acid residues. Importantly, several chemical depolymerization methods were used to elucidate the structure of the AG through a bottom-up strategy. A highly sulfated galactose (oAG-1) and two disaccharides labeled with 2,5-anhydro-D-mannose (oAG-2, oAG-3) were obtained from the deaminative depolymerized product along with the structures of the disaccharide derivatives (oAG-4~oAG-6) identified from the free radical depolymerized product, suggesting that the repeating building blocks in a natural AG should comprise the disaccharide β-D-GalS-1,4-D-GlcNAc6S. The possible disaccharide side chains (bAG-1) were obtained with mild acid hydrolysis. Thus, a natural AG may consist of a keratan sulfate-like (KS-like) glycosaminoglycan with diverse modifications, including the sulfation types of the Gal residue and the possible disaccharide branches α-D-GalNAc4S6S-1,2-α/β-L-Fuc3S linked to the KS-like chain. Additionally, the anticoagulant activities of the AG and its depolymerized products (dAG1-9) were evaluated in vitro using normal human plasma. The AG could prolong activated partial thromboplastin time (APTT) in a dose-dependent manner, and the activity potency was positively related to the chain length. The AG and dAG1-dAG3 could prolong thrombin time (TT), while they had little effect on prothrombin time (PT). The results indicate that the AG could inhibit the intrinsic and common coagulation pathways.

Heparin and calreticulin interact on the surface of early G0/G1 dividing rat mesangial cells to regulate hyperglycemic glucose-induced responses

Heparin can block pathological responses associated with diabetic nephropathy in animal models and human patients. Our previous studies showed that the interaction of heparin on the surface of rat mesangial cells (RMCs) entering G1 of cell division in hyperglycemic glucose: 1) blocked glucose uptake by glucose transporter 4; 2) inhibited cytosolic uridine diphosphate-glucose elevation that would occur within 6 h from G0/G1; and 3) prevented subsequent activation of hyaluronan synthesis in intracellular compartments and subsequent inflammatory responses. However, specific proteins that interact with heparin are unresolved. Here, we showed by live cell imaging that fluorescent heparin was rapidly internalized into the cytoplasm and then into the endoplasmic reticulum, Golgi, and nuclei compartments. Biotinylated-heparin was applied onto the surface of growth arrested G0/G1 RMCs in order to extract heparin-binding protein(s). SDS-PAGE gels showed two bands at ∼70 kDa in the extract that were absent when unlabeled heparin was used to compete. Trypsin digests of the bands were analyzed by MS and identified as calreticulin and prelamin A/C. Immunostaining with their antibodies identified the presence of calreticulin on the G0/G1 RMC cell surface. Previous studies have shown that calreticulin can be on the cell surface and can interact with the LDL receptor-related protein, which has been implicated in glucose transport by interaction with glucose transporter 4. Thus, cell surface calreticulin can act as a heparin receptor through a mechanism involving LRP1, which prevents the intracellular responses in high glucose and reprograms the cells to synthesize an extracellular hyaluronan matrix after division.

Fucosylated Chondroitin Sulfate 9-18 Oligomers Exhibit Molecular Size-Independent Antithrombotic Activity while Circulating in the Blood

Fucosylated chondroitin sulfate (FCS) oligosaccharides extracted from sea cucumber and depolymerized exhibit potent anticoagulant activity. Knowledge of the antithrombotic activity of different size oligosaccharides and their fucose (Fuc) branch sulfation pattern should promote their development for clinical applications. We prepared highly purified FCS trisaccharide repeating units from hexasaccharide (6-mer) to octadecasaccharide (18-mer), including those with 2,4-disulfated and 3,4-disulfated Fuc branches. All 10 oligosaccharides were identified by their nuclear magnetic resonance structures and ESI-FTMS spectroscopy. In vitro anticoagulant activities and surface plasmon resonance binding tests indicated those of larger molecular sizes and 2,4-disulfated Fuc branches showed stronger anticoagulant effects with respect to anti-FXase activity, as well as stronger binding to FIXa among various clotting proteins. However, both types of FCS 9-mer to 18-mer exhibited molecular size-independent potent antithrombotic activity in vivo at the same dose. In addition, both types of the FCS 6-mer exhibited favorable antithrombotic activity in vivo, although they showed weak anticoagulant activity in vitro. Combining absorption and metabolism studies, we conclude that FCS 9-18 oligomers could remain in the circulation to interact with various clotting proteins to prevent thrombus formation, and appreciable quantities of these oligomers could be excreted through the kidneys. All FCS 9-18 oligomers also resulted in no bleeding, hypotension, or platelet aggregation risk during blood circulation. Thus, FCS 9-18 oligomers with 2,4-disulfated or 3,4-disulfated Fuc branches exhibit potent and safe antithrombotic activity needed for clinical applications.

Structure and heparanase inhibitory activity of a new glycosaminoglycan from the slug Limacus flavus

A new glycosaminoglycan (LF-GAG) was purified from the slug Limacus flavus. Its unique chemical structure and heparanase inhibitory activity were studied in this work. The native LF-GAG was composed of L-iduronic acid (L-IdoA) and N-acetyl-D-glucosamine (D-GlcNAc), with a Mw of 22,700 Da. To elucidate the precise structure and structure-activity relationship, its deacetylation-deaminative depolymerized product (dLF-GAG) was prepared, and from which four oligosaccharides were purified. Combining the NMR spectral analysis of LF-GAG and its derived oligosaccharides, the structure of LF-GAG was deduced to be -4)-L-IdoA_2R-(α1,4)-D-GlcNAc-(α1-, in which R was -OH (˜80%) or -OSO₃^- (˜20%). Bioactivity assays showed that LF-GAG could potently inhibit human heparanase (IC₅₀, 0.10 μM). dLF-GAG and LF-3 were less potent but also active for heparanase inhibition. Structure-activity relationship analysis indicated that the chain length and sulfate substitution of LF-GAG are essential for its heparanase inhibitory activity.

Family of Bioactive Heparin-Coated Iron Oxide Nanoparticles with Positive Contrast in Magnetic Resonance Imaging for Specific Biomedical Applications

Unfractionated heparin (UFH) and low-molecular-weight heparins (LMWH) are well-known for their anticoagulant properties. There is also currently a growing interest in using LMWH in targeted cancer therapy. In particular, several types inhibit heparanase, a key enzyme overexpressed in the tumor microenvironment that promotes angiogenesis progression and metastasis spreading. Here, we propose iron oxide nanoparticles (HEP-IONP) coated with different heparins of distinct anticoagulant/anti-heparanase activity ratios and suitable for positive contrast in magnetic resonance imaging. As a proof of concept, magnetic resonance angiography (MRA) was conducted in mice up to 3 h after intravenous administration. This new IONP-based positive contrast appropriate for clinic together with the long vascular circulating times can enable innovative theranostic applications if combined with the various bioactivities of the heparins. Indeed, we showed, using advanced in vitro tests, how HEP-IONP anticoagulant or anti-heparanase activities were maintained depending on the heparin species used for the coating. Overall, the study allowed presenting an IONP coated with a commercial LMWH (Lovenox) suggested as a theranostic translational probe for MRA diagnostic and treatment of thrombosis, and an antitumor IONP coated with a specific depolymerized heparin to be used in targeted therapy and diagnostic modalities.

A novel LC-MS/MS assay for heparan sulfate screening in the cerebrospinal fluid of mucopolysaccharidosis IIIA patients

AIMS

Heparan sulfate (HS) accumulates in the central nervous system in mucopolysaccharidosis III type A (MPS IIIA). A validated LC-MS/MS assay was developed to measure HS in human cerebrospinal fluid (CSF).

METHODS & RESULTS

HS was extracted and digested and the resultant disaccharides were derivatized with a novel label, 4-butylaniline, enabling isoform separation and isotope-tagged analog introduction as an internal standard for LC-MS/MS. The assay has a LLOQ for disaccharides of 0.1 μM, ±20% accuracy and ≤20% precision. CSF samples from patients with MPS IIIA showed elevated HS levels (mean 4.9 μM) compared with negative controls (0.37 μM).

CONCLUSION

This assay detected elevated HS levels in the CSF of patients with MPS IIIA and provides a method to assess experimental therapies.

Synthesis and detection of N-sulfonated oversulfated chondroitin sulfate in marketplace heparin

N-sulfonated oversulfated chondroitin sulfate (NS-OSCS), recently reported as a potential threat to the heparin supply, was prepared along with its intermediate derivatives. All compounds were spiked into marketplace heparin and subjected to United States Pharmacopeia (USP) identification assays for heparin (proton nuclear magnetic resonance [(1)H NMR], chromatographic identity, % galactosamine [%GalN], anti-factor IIa potency, and anti-factor Xa/IIa ratio). The U.S. Food and Drug Administration (FDA) strong-anionic exchange high-performance liquid chromatography (SAX-HPLC) method resolved NS-OSCS from heparin and OSCS and had a limit of detection of 0.26% (w/w) NS-OSCS. The %GalN test was sensitive to the presence of NS-OSCS in heparin. Therefore, current USP heparin monograph tests (i.e., SAX-HPLC and %GalN) detect the presence of NS-OSCS in heparin.

Role of Deacetylase Activity of N-Deacetylase/N-Sulfotransferase 1 in Forming N-Sulfated Domain in Heparan Sulfate

Heparan sulfate (HS) is a highly sulfated polysaccharide that plays important physiological roles. The biosynthesis of HS involves a series of enzymes, including glycosyltransferases (or HS polymerase), epimerase, and sulfotransferases. N-Deacetylase/N-Sulfotransferase isoform 1 (NDST-1) is a critical enzyme in this pathway. NDST-1, a bifunctional enzyme, displays N-deacetylase and N-sulfotransferase activities to convert an N-acetylated glucosamine residue to an N-sulfo glucosamine residue. Here, we report the cooperative effects between N-deacetylase and N-sulfotransferase activities. Using baculovirus expression in insect cells, we obtained three recombinant proteins: full-length NDST-1 and the individual N-deacetylase and N-sulfotransferase domains. Structurally defined oligosaccharide substrates were synthesized to test the substrate specificities of the enzymes. We discovered that N-deacetylation is the limiting step and that interplay between the N-sulfotransferase and N-deacetylase accelerates the reaction. Furthermore, combining the individually expressed N-deacetylase and N-sulfotransferase domains produced different sulfation patterns when compared with that made by the NDST-1 enzyme. Our data demonstrate the essential role of domain cooperation within NDST-1 in producing HS with specific domain structures.

Chemically modified N-acylated hyaluronan fragments modulate proinflammatory cytokine production by stimulated human macrophages

Low molecular mass hyaluronans are known to induce inflammation. To determine the role of the acetyl groups of low molecular mass hyaluronan in stimulating the production of proinflammatory cytokines, partial N-deacetylation was carried out by hydrazinolysis. This resulted in 19.7 ± 3.5% free NH2 functional groups, which were then acylated by reacting with an acyl anhydride, including acetic anhydride. Hydrazinolysis resulted in bond cleavage of the hyaluronan chain causing a reduction of the molecular mass to 30-214 kDa. The total NH2 and N-acetyl moieties in the reacetylated hyaluronan were 0% and 98.7 ± 1.5% respectively, whereas for butyrylated hyaluronan, the total NH2, N-acetyl, and N-butyryl moieties were 0, 82.2 ± 4.6, and 22.7 ± 3.8%, respectively, based on (1)H NMR. We studied the effect of these polymers on cytokine production by cultured human macrophages (THP-1 cells). The reacetylated hyaluronan stimulated proinflammatory cytokine production to levels similar to LPS, whereas partially deacetylated hyaluronan had no stimulatory effect, indicating the critical role of the N-acetyl groups in the stimulation of proinflammatory cytokine production. Butyrylated hyaluronan significantly reduced the stimulatory effect on cytokine production by the reacetylated hyaluronan or LPS but had no stimulatory effect of its own. The other partially N-acylated hyaluronan derivatives tested showed smaller stimulatory effects than reacetylated hyaluronan. Antibody and antagonist experiments suggest that the acetylated and partially butyrylated lower molecular mass hyaluronans exert their effects through the TLR-4 receptor system. Selectively N-butyrylated lower molecular mass hyaluronan shows promise as an example of a novel semisynthetic anti-inflammatory molecule.

Water ice is a soft matrix for the structural characterization of glycosaminoglycans by infrared matrix-assisted laser desorption/ionization

Glycosaminoglycans (GAGs) are a class of heterogeneous, often highly sulfated glycans that form linear chains consisting of up to 100 monosaccharide building blocks and more. GAGs are ubiquitous constituents of connective tissue, cartilage, and the extracellular matrix, where they have key functions in many important biological processes. For their characterization by mass spectrometry (MS) and tandem MS, the high molecular weight polymers are usually enzymatically digested to oligomers with a low degree of polymerization (dp), typically disaccharides. However, owing to their lability elimination of sulfate groups upon desorption/ionization is often encountered leading to a loss of information on the analyte. Here, we demonstrate that, in particular, water ice constitutes an extremely mild matrix for the analysis of highly sulfated GAG disaccharides by infrared matrix-assisted laser desorption/ionization (IR-MALDI) mass spectrometry. Depending on the degree of sulfation, next to the singly charged ionic species doubly- and even triply charged ions are formed. An unambiguous assignment of the sulfation sites becomes possible by subjecting sodium adducts of the GAGs to low-energy collision-induced dissociation tandem MS. These ionic species exhibit a remarkable stability of the sulfate substituents, allowing the formation of fragment ions retaining their sulfation that arise from either cross-ring cleavages or rupture of the glycosidic bonds, thereby allowing an unambiguous assignment of the sulfation sites.

Molecular engineering of glycosaminoglycan chemistry for biomolecule delivery

Glycosaminoglycans (GAGs) are linear, negatively charged polysaccharides that interact with a variety of positively charged growth factors. In this review article the effects of engineering GAG chemistry for molecular delivery applications in regenerative medicine are presented. Three major areas of focus at the structure-function-property interface are discussed: (1) macromolecular properties of GAGs; (2) effects of chemical modifications on protein binding; (3) degradation mechanisms of GAGs. GAG-protein interactions can be based on: (1) GAG sulfation pattern; (2) GAG carbohydrate conformation; (3) GAG polyelectrolyte behavior. Chemical modifications of GAGs, which are commonly performed to engineer molecular delivery systems, affect protein binding and are highly dependent on the site of modification on the GAG molecules. The rate and mode of degradation can determine the release of molecules as well as the length of GAG fragments to which the cargo is electrostatically coupled and eventually released from the delivery system. Overall, GAG-based polymers are a versatile biomaterial platform offering novel means to engineer molecular delivery systems with a high degree of control in order to better treat a range of degenerated or injured tissues.

Disaccharide analysis of glycosaminoglycans using hydrophilic interaction chromatography and mass spectrometry

Heparan sulfate (HS) and chondroitin sulfate/dermatan sulfate (CS/DS) glycosaminoglycans (GAGs) participate in many important biological processes. Quantitative disaccharide analysis of HS and CS/DS is essential for the characterization of GAGs and enables modeling of the GAG domain structure. Methods involving enzymatic digestion and chemical depolymerization have been developed to determine the type and location of sulfation/acetylation modifications as well as uronic acid epimerization. Enzymatic digestion generates disaccharides with Δ-4,5-unsaturation at the nonreducing end. Chemical depolymerization with nitrous acid retains the uronic acid epimerization. This work shows the use of hydrophilic interaction liquid chromatography mass spectrometry (HILIC-MS) for quantification of both enzyme-derived and nitrous acid depolymerization products for structural analysis of HS and CS/DS. This method enables biomedical researchers to determine complete disaccharide profiles on GAG samples using a single LC-MS platform.

Mass spectrometric method for determining the uronic acid epimerization in heparan sulfate disaccharides generated using nitrous acid

Heparan sulfate (HS) glycosaminoglycans (GAGs) regulate a host of biological functions. To better understand their biological roles, it is necessary to gain understanding about the structure of HS, which requires identification of the sulfation pattern as well as the uronic acid epimerization. In order to model HS structure, it is necessary to quantitatively profile depolymerization products. To date, liquid chromatography-mass spectrometry (LC-MS) methods for profiling heparin lyase decomposition products have been shown. These enzymes, however, destroy information about uronic acid epimerization. Deaminative cleavage using nitrous acid (HONO) is a classic method for GAG depolymerization that retains uronic acid epimerization. Several chromatographic methods have been used for analysis of deaminative cleavage products. The chromatographic methods have the disadvantage that there is no direct readout on the structures producing the observed peaks. This report demonstrates a porous graphitized carbon (PGC)-MS method for the quantification of HONO generated disaccharides to obtain information about the sulfation pattern and uronic acid epimerization. Here, we demonstrate the separation and identification of uronic acid epimers as well as geometric sulfation isomers. The results are comparable to those expected for benchmark HS and heparin samples. The data demonstrate the utility of PGC-MS for quantification of HS nitrous acid depolymerization products for structural analysis of HS and heparin.

Drosophila heparan sulfate, a novel design

Heparan sulfate (HS) proteoglycans play critical roles in a wide variety of biological processes such as growth factor signaling, cell adhesion, wound healing, and tumor metastasis. Functionally important interactions between HS and a variety of proteins depend on specific structural features within the HS chains. The fruit fly (Drosophila melanogaster) is frequently applied as a model organism to study HS function in development. Previous structural studies of Drosophila HS have been restricted to disaccharide composition, without regard to the arrangement of saccharide domains typically found in vertebrate HS. Here, we biochemically characterized Drosophila HS by selective depolymerization with nitrous acid. Analysis of the generated saccharide products revealed a novel HS design, involving a peripheral, extended, presumably single, N-sulfated domain linked to an N-acetylated sequence contiguous with the linkage to core protein. The N-sulfated domain may be envisaged as a heparin structure of unusually low O-sulfate content.

Identification of tubular heparan sulfate as a docking platform for the alternative complement component properdin in proteinuric renal disease

Properdin binds to proximal tubular epithelial cells (PTEC) and activates the complement system via the alternative pathway in vitro. Cellular ligands for properdin in the kidney have not yet been identified. Because properdin interacts with solid-phase heparin, we investigated whether heparan sulfate proteoglycans (HSPG) could be the physiological ligands of properdin. Kidneys from proteinuric rats showed colocalization of syndecan-1, a major epithelial HSPG, and properdin in the apical membranes of PTEC, which was not seen in control renal tissue. In vitro, PTEC did not constitutively express properdin. However, exogenous properdin binds to these cells in a dose-dependent fashion. Properdin binding was prevented by heparitinase pretreatment of the cells and was dose-dependently inhibited by exogenous heparin. ELISA and surface plasmon resonance spectroscopy (BIAcore) showed a strong dose-dependent interaction between heparan sulfate (HS) and properdin (K(d) = 128 nm). Pretreatment of HSPG with heparitinase abolished this interaction in ELISA. Competition assays, using a library of HS-like polysaccharides, showed that sulfation pattern, chain length, and backbone composition determine the interaction of properdin with glycosaminoglycans. Interestingly, two nonanticoagulant heparin derivatives inhibited properdin-HS interaction in ELISA and BIAcore. Incubation of PTEC with human serum as complement source led to complement activation and deposition of C3 on the cells. This C3 deposition is dependent on the binding of properdin to HS as shown by heparitinase pretreatment of the cells. Our data identify tubular HS as a novel docking platform for alternative pathway activation via properdin, which might play a role in proteinuric renal damage. Our study also suggests nonanticoagulant heparinoids may provide renoprotection in complement-dependent renal diseases.

Quantitation of surface-reducing-end covalently bound polysaccharides via hydrazinolysis and deamination

Depending on the method of deposition, reactive sites of polysaccharides on substrates may not be available when their reducing ends have been used to covalently bind them to the substrates. Here we present a method that allows surface density measurements of reducing-end covalently bound polysaccharides in a procedure that cleaves the polysaccharide chain from the surface via hydrazinolysis and deamination, leaving on the surface a disaccharide that is later radiolabeled with an aldehyde in a reaction with enamine formation. The method described has the advantage that it may be used with any polysaccharide patterned to any surface exposing an amino-terminated monolayer by reductive amination of their galactosamine or glucosamine repeating units. We illustrate the technique with the quantitation of glycosaminoglycans (GAGs) on silanized glass surfaces.

Heparin/heparan sulfate biosynthesis: processive formation of N-sulfated domains

Heparan sulfate (HS) proteoglycans influence embryonic development as well as adult physiology through interactions with various proteins, including growth factors/morphogens and their receptors. The interactions depend on HS structure, which is largely determined during biosynthesis by Golgi enzymes. A key step is the initial generation of N-sulfated domains, primary sites for further polymer modification and ultimately for functional interactions with protein ligands. Such domains, generated through action of a bifunctional GlcNAc N-deacetylase/N-sulfotransferase (NDST) on a [GlcUA-GlcNAc](n) substrate, are of variable size due to regulatory mechanisms that remain poorly understood. We have studied the action of recombinant NDSTs on the [GlcUA-GlcNAc](n) precursor in the presence and absence of the sulfate donor, 3'-phosphoadenosine 5'-phosphosulfate (PAPS). In the absence of PAPS, NDST catalyzes limited and seemingly random N-deacetylation of GlcNAc residues. By contrast, access to PAPS shifts the NDST toward generation of extended N-sulfated domains that are formed through coupled N-deacetylation/N-sulfation in an apparent processive mode. Variations in N-substitution pattern could be obtained by varying PAPS concentration or by experimentally segregating the N-deacetylation and N-sulfation steps. We speculate that similar mechanisms may apply also to the regulation of HS biosynthesis in the living cell.

Nitrous acid degradation of glycosaminoglycans

Glycosaminoglycans (GAGs) are made up of disaccharide units that are distinguished from each other by the monosaccharide units of which they are composed and by the degree and position of sulfation. These disaccharide units represent the monomeric units of the GAG; thus, measurement of the disaccharide composition of a GAG represents the first step in the characterization of the polymer. In this unit, cleavage of the glycosidic bonds of the N-sulfated GlcN residues in heparin and heparan sulfate is described, in addition to cleavage of the bonds between the N-acetylated amino sugar residues in heparin, heparan sulfate, chondroitin sulfate, dermatan sulfate, and keratan sulfate, and hyaluronic acid. Using these procedures involving, all GAGs can be converted completely to their constituent disaccharides and reduced with NaB[3H]4) to yield labeled disaccharides that can be assayed qualitatively or quantitatively. The procedure may also be used to analyze metabolically labeled GAGs (with or without the use of NaB[3H]4).

The effect of substitution of the N-acetyl groups of N-acetylgalactosamine residues in chondroitin sulfate on its degradation by chondroitinase ABC

Chondroitinase ABC is a lyase that degrades chondroitin sulfate, dermatan sulfate and hyaluronic acid into disaccharides. The purpose of this study was to determine the ability of chondroitinase ABC to degrade chondroitin sulfate in which the N-acetyl groups are substituted with different acyl groups. The bovine tracheal chondroitin sulfate A (bCSA) was N-deacetylated by hydrazinolysis, and the free amino groups derivatized into N-formyl, N-propionyl, N-butyryl, N-hexanoyl or N-benzoyl amides. Treatment of the N-acyl or N-benzoyl derivatives of bCSA with chondroitinase ABC and analysis of the products showed that the N-formyl, N-hexanoyl and N-benzoyl derivatives are completely resistant to the enzyme. In contrast, the N-propionyl or N-butyryl derivatives were degraded into disaccharides with slower kinetics compared to that of unmodified bCSA. The rate of degradation of bCSA derivatives by the enzyme was found to be in the order of N-acetyl>N-propionyl>>N-butyryl bCSA. These results have important implications for understanding the interaction of N-acetyl groups of glycosaminoglycans with chondroitinase ABC.

Determination of the substrate specificities of N-acetyl-d-glucosaminyltransferase

Heparan sulfate plays a wide range of physiological and pathological roles. Heparan sulfate consists of glucosamine and glucuronic/iduronic acid repeating disaccharides with various sulfations. Synthesis of structurally defined heparan sulfate oligosaccharides remains a challenge. Access to nonsulfated and unepimerized heparan sulfate backbone structures represents an essential step toward de novo enzymatic synthesis of heparan sulfate. The nonsulfated, unepimerized backbone heparan sulfate is similar to the capsular polysaccharide from Escherichia coli strain K5. The biosynthesis of this capsular polysaccharide involves in N-acetylglucosaminyltransferase (KfiA) and d-glucuronyltransferase (KfiC). In this study, we report the characterization of purified KfiA. KfiA was expressed in a C-terminal six-His fusion protein in BL21 star cells coexpressing chaperone proteins GroEL and GroES. The recombinant KfiA was purified to homogeneity with a Ni-agarose column. The binding affinities of various UDP-sugars for KfiA were determined using isothermal calorimetry titration, indicating that both the N-acetyl group and sugar type may be essential for donor substrates to bind KfiA. Kinetic analysis of KfiA toward different sizes of oligosaccharide revealed that KfiA is less sensitive to the size of the acceptor substrates. The results from this study open a new approach for the synthesis of the heparan sulfate backbone.

Structural basis for the adherence of Plasmodium falciparum-infected erythrocytes to chondroitin 4-sulfate and design of novel photoactivable reagents for the identification of parasite adhesive proteins

A dodecasaccharide motif of the low-sulfated chondroitin 4-sulfate (C4S) mediate the binding of Plasmodium falciparum-infected red blood cells (IRBCs) in human placenta. Here we studied the detailed C4S structural requirements by assessing the ability of chemically modified C4S to inhibit IRBC binding to the placental chondroitin sulfate proteoglycan. Replacement of the N-acetyl groups with bulky N-acyl or N-benzoyl substituents had no effect on the inhibitory activity of C4S, whereas reduction of the carboxyl groups abrogated the activity. Dermatan sulfates showed approximately 50% inhibitory activity when compared with C4Ss with similar sulfate contents. These data demonstrate that the C4S carboxyl groups and their equatorial orientation but not the N-acetyl groups are critical for IRBC binding. Conjugation of bulky substituents to the reducing end N-acetylgalactosamine residues of C4S dodecasaccharide had no effect on its inhibitory activity. Based on these results, we prepared photoaffinity reagents for the identification of the parasite proteins involved in C4S binding. Cross-linking of the IRBCs with a radioiodinated photoactivable C4S dodecasaccharide labeled a approximately 22-kDa novel parasite protein, suggesting strongly for the first time that a low molecular weight IRBC surface protein rather than a 200-400-kDa PfEMP1 is involved in C4S binding. Conjugation of biotin to the C4S dodecasaccharide photoaffinity probe afforded a strategy for the isolation of the labeled protein by avidin affinity precipitation, facilitating efforts to identify the C4S-adherent IRBC protein(s). Our results also have broader implications for designing oligosaccharide-based photoaffinity probes for the identification of proteins involved in glycosaminoglycan-dependent attachment of microbes to hosts.

No change in glomerular heparan sulfate structure in early human and experimental diabetic nephropathy

Heparan sulfate (HS) proteoglycans are major anionic glycoconjugates of the glomerular basement membrane and are thought to contribute to the permeability properties of the glomerular capillary wall. In this study we evaluated whether the development of (micro) albuminuria in early human and experimental diabetic nephropathy is related to changes in glomerular HS expression or structure. Using a panel of recently characterized antibodies, glomerular HS expression was studied in kidney biopsies of type I diabetic patients with microalbuminuria or early albuminuria and in rat renal tissue after 5 months diabetes duration. Glomerular staining, however, revealed no differences between control and diabetic specimens. A significant (p < 0.05) approximately 60% increase was found in HS N-deacetylase activity, a key enzyme in HS sulfation reactions, in diabetic glomeruli. Structural analysis of glomerular HS after in vivo and in vitro radiolabeling techniques revealed no changes in HS N-sulfation or charge density. Also HS chain length, protein binding properties, as well as disaccharide composition did not differ between control and diabetic glomerular HS samples. These results indicate that in experimental and early human diabetic nephropathy, increased urinary albumin excretion is not caused by loss of glomerular HS expression or sulfation and suggest other mechanisms to be responsible for increased glomerular albumin permeability.

Isolation and characterization of low sulfated heparan sulfate sequences with affinity for lipoprotein lipase

Lipoprotein lipase (LPL), which is an important enzyme in lipid metabolism, binds to heparan sulfate (HS) proteoglycans. This interaction is crucial for several aspects of LPL function, such as intracellular/extracellular transport and high capacity attachment to cell surfaces. Retention of LPL on the capillary walls, and elsewhere, via HS chains is most likely affected by the quality and quantity of HS present. Earlier studies have demonstrated that LPL interacts with highly sulfated HS and heparin oligosaccharides. Since such structures are relatively rare in endothelial HS, we have re-addressed the question of physiological ligand structures for LPL by affinity purification of end-labeled oligosaccharides originating from heparin and HS on immobilized LPL. By a combination of chemical modification and fragmentation of the bound material we identified that the bound fraction contained modestly sulfated oligosaccharides with an average sulfation of one O-sulfate per disaccharide unit and tolerates N-acetylated glucosamine residues. Therefore LPL, containing several clusters of positive charges on each subunit, may constitute an ideal structure for a protein that needs to bind with reasonable affinity to a variety of modestly sulfated sequences of the type that is abundant in HS chains.

Overexpression of heparan sulfate 6-O-sulfotransferases in human embryonic kidney 293 cells results in increased N-acetylglucosaminyl 6-O-sulfation

Heparan sulfate (HS) interacts with a variety of proteins and thus mediates numerous complex biological processes. These interactions critically depend on the patterns of O-sulfate groups within the HS chains that determine binding sites for proteins. In particular the distribution of 6-O-sulfated glucosamine residues influences binding and activity of HS-dependent signaling molecules. The protein binding domains of HS show large structural variability, potentially because of differential expression patterns of HS biosynthetic enzymes along with differences in substrate specificity. To investigate whether different isoforms of HS glucosaminyl 6-O-sulfotransferase (6-OST) give rise to differently sulfated domains, we have introduced mouse 6-OST1, 6-OST2, and 6-OST3 in human embryonic kidney 293 cells and compared the effects of overexpression on HS structure. High expression of any one of the 6-OST enzymes resulted in appreciably increased 6-O-sulfation of N-sulfated as well as N-acetylated glucosamine units. The increased 6-O-sulfation was accompanied by a decrease in nonsulfated as well as in iduronic acid 2-O-sulfated disaccharide structures. Furthermore, overexpression led to an altered HS domain structure, the most striking effect was the formation of extended 6-O-sulfated predominantly N-acetylated HS domains. Although the effect was most noticeable in 6-OST3-expressing cells, these results were largely independent of the particular 6-OST isoform expressed and mainly influenced by the level of overexpression.

Identification of L-selectin Binding Heparan Sulfates Attached to Collagen Type XVIII

L-selectin is a C-type lectin expressed on leukocytes that is involved in both lymphocyte homing to the lymph node and leukocyte extravasation during inflammation. Known L-selectin ligands include sulfated Lewis-type carbohydrates, glycolipids, and proteoglycans. Previously, we have shown that in situ detection of different types of L-selectin ligands is highly dependent on the tissue fixation protocol used. Here we use this knowledge to specifically examine the expression of L-selectin binding proteoglycans in normal mouse tissues. We show that L-selectin binding chondroitin/dermatan sulfate proteoglycans are present in cartilage, whereas L-selectin binding heparan sulfate proteoglycans are present in spleen and kidney. Furthermore, we show that L-selectin only binds a subset of renal heparan sulfates, attached to a collagen type XVIII protein backbone and predominantly present in medullary tubular and vascular basement membranes. As L-selectin does not bind other renal heparan sulfate proteoglycans such as perlecan, agrin, and syndecan-4, and not all collagen type XVIII expressed in the kidney binds L-selectin, this indicates that there is a specific L-selectin binding domain on heparan sulfate glycosaminoglycan chains. Using an in vitro L-selectin binding assay, we studied the contribution of N-sulfation, O-sulfation, C5-epimerization, unsubstituted glucosamine residues, and chain length in L-selectin binding to heparan sulfate/heparin glycosaminoglycan chains. Based on our results and the accepted model of heparan sulfate domain organization, we propose a model for the interaction of L-selectin with heparan sulfate glycosaminoglycan chains. Interestingly, this opens the possibility of active regulation of L-selectin binding to heparan sulfate proteoglycans, e.g. under inflammatory conditions.

Sepharose-bound, highly sulfated glycosaminoglycans can capture HIV-1 from culture medium

In the search for new strategies against HIV-1 and on the basis of a number of previous studies reporting on the capacity of certain polyanionic compounds to influence the replication of HIV-1, we prepared a few chemically oversulfated dermatan and chondroitin sulfates. Four of these compounds and two samples of heparin were bound to activated Sepharose through either their carboxylic groups, or their aldehydic groups, or their deacetylated primary amino groups. Some of these so-derivatised resins, packed into columns, proved able to remove HIV-1 IIIB, a laboratory adapted strain, and one clinical primary isolate from an AIDS patient, from infected cell culture medium. The resins bind the virus very tightly and could be useful for capturing the virus from infected fluids.

In vitro polymerization of heparan sulfate backbone by the EXT proteins

Multiple exosotoses is a dominantly inherited bone disorder caused by defects in EXT1 and EXT2, genes encoding glycosyltransferases involved in heparan sulfate chain elongation. Heparan sulfate polymerization occurs by the alternating addition of glucuronic acid and N-acetylglucosamine units to the nonreducing end of the polysaccharide. EXT1 and EXT2 are suggested to be dual glucuronyl/N-acetylglucosaminyltransferases, and a heterooligomeric complex of EXT1 and EXT2 (EXT1/2) is considered to be the biological functional polymerization unit. Here, we have investigated the in vitro polymerization capacities of recombinant soluble EXT1, EXT2, and EXT1/2 complex on exogenous oligosaccharide acceptors derived from Escherichia coli K5 capsular polysaccharide. Incubations of recombinant EXT1 or EXT1/2 complex with 3H-labeled oligosaccharide acceptors and the appropriate nucleotide sugars resulted in conversion of the acceptors to higher molecular weight compounds but with different efficacies for EXT1 and EXT1/2. In contrast, incubations with recombinant EXT2 resulted in the addition of a single glucuronic acid but no further polymerization. These results indicate that EXT1 alone and the EXT1/2 heterocomplex can act as heparan sulfate polymerases in vitro without the addition of additional auxiliary proteins.

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.

New cross-linked and sulfated derivatives of partially deacetylated hyaluronan: synthesis and preliminary characterization

Partial chemical deacetylation of hyaluronan (HA) has been carried out using known procedures and carefully controlled experimental conditions in order to minimize chain degradation. The sample described herein (deHA) has a degree of deacetylation of about 17%, which corresponds to what required for its further use, but a molecular weight of about 1/25 with respect to the native, starting material. Chemical gels have been prepared with different degrees of cross-linking by means of a Ugi multicomponent condensation reaction involving aqueous deHA, formaldehyde, and cyclohexylisocyanide: the gels are mechanically stable and exhibit good water uptake strongly dependent on the extent of cross-linking, as expected. deHA samples have also been selectively N-sulfated or O-sulfated: the former exhibit anticoagulant properties well exceeding those of the latter and not too inferior to heparin.

Substrate specificity of the heparan sulfate hexuronic acid 2-O-sulfotransferase

The interaction of heparan sulfate with different ligand proteins depends on the precise location of O-sulfate groups in the polysaccharide chain. We have previously shown that overexpression in human kidney 293 cells of a mouse mastocytoma 2-O-sulfotransferase (2-OST), previously thought to catalyze the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate to C2 of L-iduronyl residues, preferentially increases the level of 2-O-sulfation of D-glucuronyl units [Rong, J., Habuchi, H., Kimata, K., Lindahl, U., and Kusche-Gullberg, M. (2000) Biochem. J. 346, 463-468]. In the study presented here, we further investigated the substrate specificity of the mouse mastocytoma 2-OST. Different polysaccharide acceptor substrates were incubated with cell extracts from 2-OST-transfected 293 cells together with the sulfate donor 3'-phosphoadenosine 5'-phospho[(35)S]sulfate. Incubations with O-desulfated heparin, predominantly composed of [(4)alphaIdoA(1)-(4)alphaGlcNSO(3)(1)-](n)(), resulted in 2-O-sulfation of iduronic acid. When, on the other hand, an N-sulfated capsular polysaccharide from Escherichia coli K5, with the structure [(4)betaGlcA(1)-(4)alphaGlcNSO(3)(1)-](n)(), was used as an acceptor, sulfate was transferred almost exclusively to C2 of glucuronic acid. Substrates containing both iduronic and glucuronic acid residues in about equal proportions strongly favored sulfation of iduronic acid. In agreement with these results, the 2-OST was found to have a approximately 5-fold higher affinity for iduronic acid-containing substrate disaccharide units (K(m) approximately 3.7 microM) than for glucuronic acid-containing substrate disaccharide units (K(m) approximately 19.3 microM).

Overexpression of different isoforms of glucosaminyl N-deacetylase/N-sulfotransferase results in distinct heparan sulfate N-sulfation patterns

Functional interactions of heparan sulfate (HS) with selected proteins depend on distinct saccharide sequences which are generated during biosynthesis of the polysaccharide. Glucosaminyl N-deacetylase/N-sulfotransferases (NDSTs) catalyze both the N-deacetylation and N-sulfation reactions that initiate the modification of the (GlcNAc-GlcA)(n) polysaccharide backbone. The N-acetyl/N-sulfate exchange is restricted to certain regions of the polysaccharide chains, and only these can be further modified by glucuronyl C5-epimerization and O-sulfation at various positions. To investigate whether NDST isoforms influenced differently the structure of HS, murine NDST-1 was overexpressed in human kidney 293 cells, and the structure of the HS produced was compared to HS from NDST-2 overexpressing cells [Cheung, W. F., Eriksson, I., Kusche-Gullberg M., Lindahl, U., and Kjellén, L. (1996) Biochemistry 35, 5250-5256]. The level of N-sulfation increased from 40% in control cells to 60% and 80%, respectively, in NDST-1 and NDST-2 transfected cells. Interestingly, the increase in N-sulfation was accompanied by an increased chain length, while no effect on IdoA content or O-sulfation was seen. The most extended N-sulfated domains were found in HS synthesized by NDST-2 transfected cells. Since both the N-deacetylase and the N-sulfotransferase activities were lower in these cells than in the NDST-1 overexpressing cells, we conclude that, in addition to the level of enzyme expression, the NDST isoform also is important in determining the N-sulfation pattern in HS.

Disaccharide analysis and molecular mass determination to microgram level of single sulfated glycosaminoglycan species in mixtures following agarose-gel electrophoresis

The separation of sulfated glycosaminoglycans in mixtures by agarose-gel electrophoresis and the recovery of single polysaccharide bands has been applied to the characterization of polysaccharides extracted from tissues without previous purification of single species. Sulfated glycosaminoglycans, heparin with its two components, slow-moving and fast-moving, heparan sulfate, dermatan sulfate, and chondroitin sulfate, were separated to microgram level by conventional agarose-gel electrophoresis. After their separation, they were fixed in the agarose-gel matrix by precipitation in a cetyltrimethylammonium bromide solution, making them visible on a dark background. After recovery of gel containing the fixed bands, high temperatures (90 degrees C for 15 min) were necessary to dissolve the gel matrix, and a solution of NaCl (3 M) was used to release sulfated polysaccharides from the complex with cetyltrimethylammonium. After precipitation of glycosaminoglycans in the presence of ethanol, the recovery of slow-moving heparin, fast-moving heparin, heparan sulfate, dermatan sulfate, and chondroitin sulfate was from 1 to 10 microg, with a percentage greater than 45% and a purity above 90%. Sulfated glycosaminoglycans in mixtures recovered from gel matrix as single species were evaluated for purity and characterized for unsaturated disaccharides after treatment with bacterial lyases (heparinases for heparin and heparan sulfate samples, and chondroitinases for dermatan sulfate and chondroitin sulfate) and molecular mass. Bovine lung and heart Glycosaminoglycans were extracted and separated into single species by agarose-gel electrophoresis and recovered from gel matrix after treatment in cetyltrimethylammonium solution. Unsaturated disaccharides pattern, the sulfate to carboxyl ratio, and the molecular mass of each single polysaccharide species were determined.

Characterization of a neutrophil cell surface glycosaminoglycan that mediates binding of platelet factor 4

Platelet factor 4 (PF-4) is a platelet-derived alpha-chemokine that binds to and activates human neutrophils to undergo specific functions like exocytosis or adhesion. PF-4 binding has been shown to be independent of interleukin-8 receptors and could be inhibited by soluble chondroitin sulfate type glycosaminoglycans or by pretreatment of cells with chondroitinase ABC. Here we present evidence that surface-expressed neutrophil glycosaminoglycans are of chondroitin sulfate type and that this species binds to the tetrameric form of PF-4. The glycosaminoglycans consist of a single type of chain with an average molecular mass of approximately 23 kDa and are composed of approximately 85-90% chondroitin 4-sulfate disaccharide units type CSA (-->4GlcAbeta1-->3GalNAc(4-O-sulfate)beta1-->) and of approximately 10-15% di-O-sulfated disaccharide units. A major part of these di-O-sulfated disaccharide units are CSE units (-->4GlcAbeta1-->3GalNAc(4,6-O-sulfate)beta1-->). Binding studies revealed that the interaction of chondroitin sulfate with PF-4 required at least 20 monosaccharide units for significant binding. The di-O-sulfated disaccharide units in neutrophil glycosaminoglycans clearly promoted the affinity to PF-4, which showed a Kd approximately 0.8 microM, as the affinities of bovine cartilage chondroitin sulfate A, porcine skin dermatan sulfate, or bovine cartilage chondroitin sulfate C, all consisting exclusively of monosulfated disaccharide units, were found to be 3-5-fold lower. Taken together, our data indicate that chondroitin sulfate chains function as physiologically relevant binding sites for PF-4 on neutrophils and that the affinity of these chains for PF-4 is controlled by their degree of sulfation.

Expression of heparan sulfate D-glucosaminyl 3-O-sulfotransferase isoforms reveals novel substrate specificities

The 3-O-sulfation of glucosamine residues is an important modification during the biosynthesis of heparan sulfate (HS). Our previous studies have led us to purify and molecularly clone the heparan sulfate D-glucosaminyl 3-O-sulfotransferase (3-OST-1), which is the key enzyme converting nonanticoagulant heparan sulfate (HSinact) to anticoagulant heparan sulfate (HSact). In this study, we expressed and characterized the full-length cDNAs of 3-OST-1 homologous genes, designated as 3-OST-2, 3-OST-3A, and 3-OST-3B as described in the accompanying paper (Shworak, N. W., Liu, J., Petros, L. M., Zhang, L., Kobayashi, M., Copeland, N. G., Jenkins, N. A., and Rosenberg, R. D. (1999) J. Biol. Chem. 274, 5170-5184). All these cDNAs were successfully expressed in COS-7 cells, and heparan sulfate sulfotransferase activities were found in the cell extracts. We demonstrated that 3-OST-2, 3-OST-3A, and 3-OST-3B are heparan sulfate D-glucosaminyl 3-O-sulfotransferases because the enzymes transfer sulfate from adenosine 3'-phosphophate 5'-phospho-[35S]sulfate ([35S]PAPS) to the 3-OH position of glucosamine. 3-OST-3A and 3-OST-3B sulfate an identical disaccharide. HSact conversion activity in the cell extract transfected by 3-OST-1 was shown to be 300-fold greater than that in the cell extracts transfected by 3-OST-2 and 3-OST-3A, suggesting that 3-OST-2 and 3-OST-3A do not make HSact. The results of the disaccharide analysis of the nitrous acid-degraded [35S]HS suggested that 3-OST-2 transfers sulfate to GlcA2S-GlcNS and IdoA2S-GlcNS; 3-OST-3A transfers sulfate to IdoA2S-GlcNS. Our results demonstrate that the 3-O-sulfation of glucosamine is generated by different isoforms depending on the saccharide structures around the modified glucosamine residue. This discovery has provided evidence for a new cellular mechanism for generating a defined saccharide sequence in structurally complex HS polysaccharide.

Chemical sulfonation and anticoagulant activity of acharan sulfate

Acharan sulfate is a glycosaminoglycan prepared from the giant African snail, Achatina fulica. This polysaccharide has a repeating disaccharide structure of -->4)-2-deoxy-2-acetamido-alpha-D-glucopyranose (1-->4)-2-sulfo-alpha-L-idopyranosyluronic acid (1-->). Its structure is related to heparin and heparan sulfate but is distinctly different from all known members of these classes of glycosaminoglycans. Because of its structural similarities to heparin, chemically modified acharan sulfate was studied to understand the chemical structure effected its anticoagulant activity. After de-N-acetylation, acharan sulfate was N-sulfonated using either chlorosulfonic acid-pyridine or sulfur trioxide-trimethylamine complex. The sulfate level in these products ranged from 22 to 24%(w/w), significantly less than that of heparin at 36%. The molecular weight of both N-sulfoacharan sulfates were comparable with that of heparin. In vitro anticoagulant activity assays showed that N-sulfoacharan sulfate derivatives were moderately active for the inhibition of thrombin and neither product showed any measurable anti-factor Xa activity. The differences in the activities of N-sulfoacharan sulfates produced by these two methods are probably ascribable to a small level of concomitant O-sulfonation obtained when using chlorosulfonic acid-pyridine.

Defining the interleukin-8-binding domain of heparan sulfate

Interleukin-8, a member of the CXC chemokine family, has been shown to bind to glycosaminoglycans. It has been suggested that heparan sulfate on cell surfaces could provide specific ligand sites on endothelial cells to retain the highly diffusible inflammatory chemokine for presentation to leukocytes. By using selectively modified heparin and heparan sulfate fragments in a nitrocellulose filter trapping system, we have analyzed sequence requirements for interleukin-8 binding to heparin/heparan sulfate. We demonstrate that the affinity of a monomeric interleukin-8 molecule for heparin/heparan sulfate is too weak to allow binding at physiological ionic strength, whereas the dimeric form of the protein mediates binding to two sulfated domains of heparan sulfate. These domains, each an N-sulfated block of approximately 6 monosaccharide units, are contained within an approximately 22-24-mer sequence and are separated by a region of </=14 monosaccharide residues that may be fully N-acetylated. Binding to interleukin-8 correlates with the occurrence of the di-O-sulfated disaccharide unit -IdceA(2-OSO3)-GlcNSO3(6-OSO3)-. We suggest that the heparan sulfate sequence binds in horseshoe fashion over two antiparallel-oriented helical regions on the dimeric protein.

Deacetylation of chitin oligosaccharides of dp 2-4 by chitin deacetylase from Colletotrichum lindemuthianum

Chitin oligosaccharides of degree of polymerization 2-4 were deacetylated by purified chitin deacetylase isolated from Colletotrichum lindemuthianum to give their corresponding breakdown products after purification by liquid chromatography. Data from FABMS analyses suggested that N,N',N",N"'-tetraacetylchitotetraose and N,N',N"-triacetylchitotriose were converted into fully-deacetylated corresponding chitosan oligomers. Conversely, N,N'-diacetylchitobiose [(GlcNAc)2] was deacetylated to give a product which showed an [M + H]+ pseudomolecular ion at m/z 383, suggesting that either of the two acetyl groups were removed. Further data from 1H NMR analyses confirmed that the reaction product was 2-acetamido-4-O-(2-amino-2-deoxy-beta-D-glucopyranosyl)-2-deoxy-D-glucos e [GlcN-GlcNAc]. The enzymatic method has three advantageous characteristics over chemical methods: (i) it does not cause unexpected degradation of the sugar chain, (ii) it is highly reproducible, and (iii) unique compounds such as GlcN-GlcNAc may be produced.

Mouse mastocytoma cells synthesize undersulfated heparin and chondroitin sulfate in the presence of brefeldin A

In order to study the subcellular localization and organization of the enzymes involved in the glycosylation of the hybrid proteoglycan serglycin, mouse mastocytoma cells were metabolically labeled with [35S]sulfate or [3H]glucosamine in the absence or presence of brefeldin A. This drug is known to induce a disassembly of the proximal part of the Golgi complex, resulting in a redistribution of cis-, medial-, and trans-Golgi resident enzymes back to the endoplasmic reticulum, and to block the anterograde transport of proteins to the trans-Golgi network. Although the total incorporation of [3H]glucosamine into glycosaminoglycan chains was reduced to about 25% in brefeldin A-treated cells compared to control cells, both control cells and cells treated with brefeldin A synthesized heparin as well as chondroitin sulfate chains. Therefore, enzymes involved in the biosynthesis of both types of glycosaminoglycan chains seem to be present proximal to the trans-Golgi network in these cells. Chondroitin sulfate and heparin synthesized in cells exposed to brefeldin A were undersulfated, as demonstrated by ion-exchange chromatography, compositional analyses of disaccharides, as well as by a lower [35S]sulfate/[3H]glucosamine ratio compared to controls. In heparin biosynthesis, both N- and O-sulfation reactions were impaired, with a larger relative decrease in 2-O-sulfation than in 6-O-sulfation. Despite undersulfation, the heparin chains synthesized in the presence of brefeldin A were larger (30 kDa) than the heparin synthesized by control cells (20 kDa). The reduced [3H]glucosamine incorporation in brefeldin A-treated cells was partly due to decreased number of glycosaminoglycan chains synthesized, but also to the biosynthesis of chondroitin sulfate chains of smaller molecular size (8 versus 15 kDa in control cells). Brefeldin A had no effect on the glycosaminoglycan synthesis when used in a cell-free, microsomal fraction, indicating that brefeldin A does not interfere directly with the enzymes involved in the biosynthesis of glycosaminoglycans.

N-Acetylated domains in heparan sulfates revealed by a monoclonal antibody against the Escherichia coli K5 capsular polysaccharide. Distribution of the cognate epitope in normal human kidney and transplant kidney with chronic vascular rejection

The Escherichia coli K5 capsular polysaccharide has the same (GlcUA-->GlcNAc)n structure as the nonsulfated heparan sulfate/heparin precursor polysaccharide. A monoclonal antibody (mAb 865) against the K5 polysaccharide has been described (Peters, H., Jürs, M., Jann, B., Jann, K., Timmis, K. N., and Bitter-Sauermann, D. (1985) Infect. Immun. 50, 459-466). In this report, we demonstrate the binding of anti-K5 mAb 865 to N-acetylated sequences in heparan sulfates and heparan sulfate proteoglycans but not to heparin. This is shown by direct binding and fluid phase inhibition of mAb 865 in an enzyme-linked immunosorbent assay. In this system we found that the binding of the mAb decreased with increasing sulfate content of the polysaccharide. By testing chemically modified K5 and heparin polysaccharides, we found that each of the modifications that occur during heparan sulfate (HS) synthesis (N-sulfation, C-5 epimerization, and O-sulfation) prevents recognition by mAb 865. Samples of heparan sulfate from human aorta (HS-II) were selectively degraded so as to allow the separate isolation of N-sulfated and N-acetylated block structures. N-Sulfated oligosaccharides (obtained after N-deacetylation by hydrazinolysis followed by nitrous acid deamination at pH 3.9) were not recognized by mAb 865, in contrast to N-acetylated oligosaccharides (obtained after nitrous acid deamination at pH 1.5), although the reactivity was lower than for intact HS-II. Analysis of the latter's pH 1.5 deamination products by gel filtration indicated that a minimal size of 18 saccharide units was necessary for antibody binding. These results lead us to propose bivalent antibody-heparan sulfate interaction, in which both F(ab) domains of the mAb interact with their epitopes, both of which are present in a single large (>/=18 saccharide units) N-acetylated domain and additionally with single epitopes present in two N-acetylated sequences (each <18 saccharide units) bridged by a short N-sulfated domain. Immunohistochemistry with mAb 865 on cryostat sections of normal human kidney tissue, revealed its binding to most but not all renal basement membranes. However, all renal basement membranes contain heparan sulfate, as shown by a mAb against heparitinase-digested heparan sulfate stubs (mAb 3G10). This finding indicates that not all heparan sulfate chains present in basement membranes express the mAb 865 epitopes. Besides the normal distribution, mAb 865 staining was found in fibrotic and sclerotic lesions in vessels, interstitium, and mesangium in transplant kidneys with chronic vascular rejection. Occasionally, a decrease of staining was observed within tubulo-interstitium and glomeruli. These findings show that N-acetylated sequences in heparan sulfates can be demonstrated by anti-K5 mAb 865 in normal and diseased kidneys.

Domain structure of heparan sulfates from bovine organs

Samples of heparan sulfate, isolated from bovine aorta, lung, intestine, and kidney, were degraded by digestion with a mixture of heparitinases or by treatment with nitrous acid, with or without previous N-deacetylation. Analysis of the resulting oligosaccharides showed that the various heparan sulfate samples all contained regions of up to 8 or 9 consecutive N-acetylated glucosamine residues, as well as contiguous N-sulfated sequences. L-Iduronic acid accounted for a remarkably constant proportion, 50-60%, of the total hexuronic acid units within the latter structures. Of the total iduronic acid units, 36-55% were located outside the contiguous N-sulfated regions, presumably in sequences composed of alternating N-acetylated and N-sulfated disaccharide residues. While most of the iduronic acid units within the N-sulfated blocks were 2-O-sulfated, those located outside were almost exclusively nonsulfated. The heparan sulfate preparations differed markedly with regard to the content of 6-O-sulfated glucosamine units, more than half of which were located outside the N-sulfated block regions. These findings suggest that the formation of iduronic acid residues and their subsequent 2-O-sulfation are coupled within but not outside the contiguous N-sulfated regions of the heparan sulfate chains and, furthermore, that the 2-O- and 6-O-sulfotransferase reactions are differentially regulated during heparan sulfate biosynthesis.