Purification and characterization of heparin lyases from Flavobacterium heparinum

Syndecan-1 and -4 synthesized simultaneously by mouse mammary gland epithelial cells bear heparan sulfate chains that are apparently structurally indistinguishable

Many of the biological functions attributed to cell surface heparan sulfate (HS) proteoglycans, including the Syndecan family, are elicited through the interaction of their HS chains with soluble extracellular molecules. Tightly controlled, cell-specific sulfation and epimerization of HS precursors endows these chains with highly sulfated, iduronate-rich regions, which are major determinants of cytokine and matrix-protein binding and which are interspersed by N-acetylated, poorly sulfated regions. Until this study, there have been no comprehensive structural comparisons made on HS chains decorating simultaneously expressed, but different, syndecan core proteins. In this paper we demonstrate that the HS chains on affinity-purified syndecan-1 and -4 from murine mammary gland cells are essentially identical by a number of parameters. Size determination, disaccharide analyses, enzymatic and chemical scission methods, and affinity co-electrophoresis all failed to reveal any significant differences in fine structure, domain organization, or ligand-binding properties of these HS species. These findings lead us to suggest that the imposition of the fine structure onto HS occurs independently of the core protein to which it is attached and that these core proteins, in addition to the HS chains, may play a pivotal role in the various biological functions ascribed to these macromolecules.

Heparin oligosaccharide sequence and size essential for inhibition of pulmonary artery smooth muscle cell proliferation

Heparin has a wide range of important biological activities including inhibition of pulmonary artery smooth muscle cell proliferation. To determine the minimum size of the heparin glycosaminoglycan chain essential for antiproliferative activity, porcine intestinal mucosal heparin was partially depolymerized with heparinase and fractionated to give oligosaccharides of different sizes. The structure of these oligosaccharides was fully characterized by 1D and 2D 1H NMR spectroscopy. These oligosaccharides were assayed for antiproliferative effects on cultured bovine pulmonary artery smooth muscle cells (PASMCs). The tetrasaccharide (4-mer) exhibited no heparin-like activity. Decasaccharides (10-mers) and dodecasaccharides (12-mers) displayed a reduced level of activity when compared to full-length heparin. Little effect on activity was observed in deca- and dodecasaccharides with one less 2-O-sulfo group. The 14-, 16-, and 18-mers showed comparable growth-inhibition effects on PAMSC as porcine intestinal mucosal heparin. These data suggest that a 14-mer is the minimum size of oligosaccharide that is essential for full heparin-like antiproliferative activity. Since the 14- to 18-mers have no 3-O-sulfo groups in their glucosamine residues, their full activity confirms that these 3-O-sulfonated glucosamine residues, which are required for heparin's anticoagulant activity, are not an essential requirement for antiproliferative activity.

Bacterial infection in cirrhosis impairs coagulation by a heparin effect: a prospective study

BACKGROUND

Bacterial infections have been postulated as a trigger for variceal bleeding in cirrhotic patients, and impair coagulation evaluated by thrombelastography (TEG). Endogenous heparinoids have been detected after variceal bleeding and during liver transplantation in some cirrhotics using heparinase-modified-TEG.

AIM

To assess if bacterial infection is associated with endogenous heparinoids in cirrhotics, thus impairing coagulation.

METHODS

Native and heparinase-modified-TEG (cleavage of heparin and heparan-sulphate) was performed in 60 cirrhotics (Grade A, 2; B, 30; C, 28): 30 infected [septicaemia, 6 (culture positive); 6 (culture negative); spontaneous bacterial peritonitis, 10; chest infection, 4; others, 4], 30 not infected, and five infected patients without liver diseases, comparing TEG parameters r, alpha, and ma. Eight cirrhotics were studied before and after infection. The diagnosis of presence and type of infection was based on international standard criteria.

RESULTS

A significant heparin effect was found only in infected cirrhotics (28 of 30) with significant changes in r (P=0.0003), alpha (P<0.0001), and ma (P<0.0001), but in none of those not infected. This effect completely reversed in the eight evaluated after resolution of infection. There was no heparin effect in infected non-cirrhotics.

CONCLUSIONS

A heparin effect was only found in cirrhotic patients with infection, further confirming that infection significantly modifies coagulation in cirrhotic patients.

Cloning, sequencing, and expression of the gene from bacillus circulans that codes for a heparinase that degrades both heparin and heparan sulfate

The gene, designated hep, coding for a heparinase that degrades both heparin and heparan sulfate, was cloned from Bacillus circulans HpT298. Nucleotide sequence analysis showed that the open reading frame of the hep gene consists of 3,150 bp, encoding a precursor protein of 1,050 amino acids with a molecular mass of 116.5 kDa. A homology search found that the deduced amino acid sequence has partial similarity with enzymes belonging to the family of acidic polysaccharide lyases that degrade chondroitin sulfate and hyaluronic acid. Recombinant mature heparinase (111.2 kDa) was produced by the addition of IPTG from Escherichia coli harboring pETHEP with an open reading frame of the mature hep gene and was purified to homogeneity by SDS-polyacrylamide gel electrophoresis. Analyses of substrate specificity and degraded disaccharides indicated that the recombinant enzyme acts on both heparin and HS, as does heparinase purified from the wild-type strain.

Expression system for high levels of GAG lyase gene expression and study of the hepA upstream region in Flavobacterium heparinum

A system for high-level expression of heparinase I, heparinase II, heparinase III, chondroitinase AC, and chondroitinase B in Flavobacterium heparinum is described. hepA, along with its regulatory region, as well as hepB, hepC, cslA, and cslB, cloned downstream of the hepA regulatory region, was integrated in the chromosome to yield stable transconjugant strains. The level of heparinase I and II expression from the transconjugant strains was approximately fivefold higher, while heparinase III expression was 10-fold higher than in wild-type F. heparinum grown in heparin-only medium. The chondroitinase AC and B transconjugant strains, grown in heparin-only medium, yielded 20- and 13-fold increases, respectively, in chondroitinase AC and B expression, compared to wild-type F. heparinum grown in chondroitin sulfate A-only medium. The hepA upstream region was also studied using cslA as a reporter gene, and the transcriptional start site was determined to be 26 bp upstream of the start codon in the chondroitinase AC transconjugant strain. The transcriptional start sites were determined for hepA in both the wild-type F. heparinum and heparinase I transconjugant strains and were shown to be the same as in the chondroitinase AC transconjugant strain. The five GAG lyases were purified from these transconjugant strains and shown to be identical to their wild-type counterparts.

Purification and characterization of heparinase that degrades both heparin and heparan sulfate from Bacillus circulans

A heparinase that degrades both heparin and heparan sulfate (HS) was purified to homogeneity from the cell-free extract of Bacillus circulans HpT298. The purified enzyme had a single band on SDS-polyacrylamide gel electrophoresis with an estimated molecular mass of 111,000. The enzyme showed optimal activity at pH 7.5 and 45 degrees C, and its activity was stimulated in the presence of 5 mM CaCl2, BaCl2, or MgCl2. Analysis of substrate specificity and degraded disaccharides demonstrated that the enzyme acts on both heparin and HS, similar to heparinase II from Flavobacterium heparinum.

Heparin-protein interactions

Heparin, a sulfated polysaccharide belonging to the family of glycosaminoglycans, has numerous important biological activities, associated with its interaction with diverse proteins. Heparin is widely used as an anticoagulant drug based on its ability to accelerate the rate at which antithrombin inhibits serine proteases in the blood coagulation cascade. Heparin and the structurally related heparan sulfate are complex linear polymers comprised of a mixture of chains of different length, having variable sequences. Heparan sulfate is ubiquitously distributed on the surfaces of animal cells and in the extracellular matrix. It also mediates various physiologic and pathophysiologic processes. Difficulties in evaluating the role of heparin and heparan sulfate in vivo may be partly ascribed to ignorance of the detailed structure and sequence of these polysaccharides. In addition, the understanding of carbohydrate-protein interactions has lagged behind that of the more thoroughly studied protein-protein and protein-nucleic acid interactions. The recent extensive studies on the structural, kinetic, and thermodynamic aspects of the protein binding of heparin and heparan sulfate have led to an improved understanding of heparin-protein interactions. A high degree of specificity could be identified in many of these interactions. An understanding of these interactions at the molecular level is of fundamental importance in the design of new highly specific therapeutic agents. This review focuses on aspects of heparin structure and conformation, which are important for its interactions with proteins. It also describes the interaction of heparin and heparan sulfate with selected families of heparin-binding proteins.

Enzyme kinetics determined using calorimetry: a general assay for enzyme activity?

Two techniques for determining enzyme kinetic constants using isothermal titration microcalorimetry are presented. The methods are based on the proportionality between the rate of a reaction and the thermal power (heat/time) generated. (i) An enzyme can be titrated with increasing amounts of substrate, while pseudo-first-order conditions are maintained. (ii) Following a single injection, the change in thermal power as substrate is depleted can be continuously monitored. Both methods allow highly precise kinetic characterization in a single experiment and can be used to measure enzyme inhibition. Applicability is demonstrated using a representative enzyme from each EC classification, including (i) oxidation-reduction activity of DHFR (EC 1.5.1.3); (ii) transferase activity of creatine phosphokinase (EC 2.7.3.2) and hexokinase (EC 2.7.1.1); (iii) hydrolytic activity of Helicobacter pylori urease (EC 3.5.1.5), trypsin (EC 3.4.21.4), and the HIV-1 protease (EC 3.4.21.16); (iv) lyase activity of heparinase (EC 4.1.1.7); and (v) ligase activity of pyruvate carboxylate (EC 6.4.1.1). This nondestructive method is completely general, enabling precise analysis of reactions in spectroscopically opaque solutions, using physiological substrates. Such a universal assay may have wide applicability in functional genomics.

Analysis of glycosaminoglycans with polysaccharide lyases

Polysaccharide lyases are a class of enzymes useful for analysis of glycosaminoglycans (GAGs) and the glycosaminoglycan component of proteoglycans (PGs). These enzymes cleave specific glycosidic linkages present in acidic polysaccharides and result in depolymerization. The lyases are derived from a wide variety of pathogenic and nonpathogenic bacteria and fungi. This class of enzymes includes heparin lyases (heparinases), heparan sulfate lyases (heparanases or heparitinases), chondroitin lyases (chondroitinases), and hyaluronate lyases (hyaluronidases), all of which are described in this unit. Two protocols describe depolymerization of GAGs, and two support protocols describe assays to confirm and quantitate the activity of heparin and chondroitin ABC lyases.

Purification and characterization of acharan sulfate lyases, two novel heparinases, from Bacteroides stercoris HJ-15

Two novel acharan sulfate lyases (ASL1 and ASL2: no EC number) have been purified from Bacteroides stercoris HJ-15 which was isolated from human intestinal bacteria with glycosaminoglycan (GAG) degrading enzymes. These enzymes were purified to apparent homogeneity by a combination of QAE-cellulose, DEAE-cellulose, carboxymethyl-Sephadex C-50, hydroxyapatite and HiTrap SP Sephadex C-25 column chromatography with the final specific activity of 50.5 and 76.7 micromol.min-1.mg-1, respectively. Both acharan sulfate lyases are single subunits of 83 kDa by SDS/PAGE and gel filtration. ASL1 showed optimal activity at pH 7.2 and 45 degrees C. ASL1 activity was inhibited by Cu2+, Ni2+ and Co2+, but ASL2 activity was inhibited by Cu2+, Ni2+and Pb2. Both enzymes were slightly inhibited by some agents that modify histidine and cysteine residues, but activated by reducing agents such as DL-dithiothreitol and 2-mercaptoethanol. Both purified bacteroidal acharan sulfate lyases acted to the greatest extent on acharan sulfate, and to a lesser extents on heparan sulfate and heparin. They did not act on de-O-sulfated acharan sulfate. These findings suggest that the biochemical properties of these purified acharan sulfate lyases are different from those of the previously purified heparin lyases, but these enzymes belong to heparinase II.

Pressure-assisted capillary electrophoresis–electrospray ion trap mass spectrometry for the analysis of heparin depolymerised disaccharides

A pressure-assisted capillary electrophoresis-ion trap mass spectrometry method was developed for the analysis of eight heparin-derived disaccharides. A 30 mM formic acid buffer at pH 3.20 was selected as running electrolyte, and the separation was performed by the simultaneous application of a CE voltage of -30 kV and an overimposed pressure of 0.5 p.s.i. (3.45 kPa). The application of pressure assistance was needed to provide stable electrospray conditions for successful coupling. The linearity of the CE-MS and CE-MS-MS methods was checked under these conditions. Quality parameters such as run-to-run precision and limits of detection were established in both CE-MS and CE-MS-MS modes. Finally, enzymatically depolymerised bovine and porcine mucosal heparins were analysed in this CE-MS system and the characteristic relative molar percentages of major and minor disaccharides were calculated.

Development of a genetic system for the transfer of DNA into Flavobacterium heparinum

Flavobacterium heparinum (now Pedobacter heparinus) is a Gram-negative soil bacterium which can produce yellow pigments. It synthesizes five enzymes that degrade glycosoaminoglycan molecules. The study of this unique bacterium has been limited by the absence of a genetic manipulation system. In this paper, the construction of a conjugation/integration plasmid system and a broad-host-range plasmid, both of which contain a F. heparinum functional selective marker created by placing the trimethoprim resistance gene, dhfrII, under the control of the hepA regulatory region is described. Both plasmids were introduced into F. heparinum by conjugation and/or electroporation, and trimethoprim resistant colonies were obtained. Fifty electroporants were obtained per microgram covalently closed circular plasmid DNA. The existence of integrated plasmid DNA was confirmed by Southern hybridization and PCR. The existence of a derivative of the broad-host-range plasmid pBBR1 in F. heparinum was demonstrated by plasmid digestion and Southern hybridization, and by transformation of Escherichia coli.

Disaccharides derived from heparin or heparan sulfate regulate IL-8 and IL-1 beta secretion by intestinal epithelial cells

BACKGROUND & AIMS

Intestinal epithelial cells can produce cytokines and chemokines that play an important role in the mucosal immune response. Regulation of this secretion is important to prevent inflammatory tissue damage. Disaccharides derived from heparan sulfate and heparin have been shown to down-regulate inflammation in vivo. We tested the effect of such disaccharides on cytokine secretion by intestinal epithelial cells.

METHODS

Spontaneous and tumor necrosis factor (TNF)-alpha-stimulated interleukin (IL)-8 and IL-1 beta secretion and mRNA expression were assessed in HT-29 and Caco-2 intestinal epithelial cell lines in the presence of a panel of heparin and heparan sulfate disaccharides.

RESULTS

Specific disaccharides suppressed spontaneous and TNF-alpha-induced mediator secretion in a dose-dependent manner. Disaccharide activity was structurally restricted. Preincubation of cells with nonsuppressing disaccharides blocked the activity of suppressing disaccharides. The number of sulfate moieties determined the ability of nonsuppressing disaccharides to block the effect of suppressive disaccharides. No suppression of mRNA expression was noted, and intracellular mediator levels were not reduced.

CONCLUSIONS

Disaccharides derived from heparin and heparan sulfate regulate proinflammatory mediator secretion from intestinal epithelial cells. Dose dependence and competition by structurally diverging disaccharides suggest a receptor-mediated mechanism. Unchanged mRNA and intracellular mediator levels suggest that the disaccharides act at posttranscriptional stages.

Heparin-like molecules inhibit pulmonary vascular pericyte proliferation in vitro

Proliferation of vascular pericytes (PCs), smooth muscle-like cells found in the distal microvasculature, contributes to vascular remodeling in pulmonary hypertension. The factors controlling lung PC quiescence in normal states are poorly understood. We demonstrate that exogenous heparin and heparan sulfate proteoglycans inhibit rat lung PC proliferation in vitro as does pulmonary vascular subendothelial matrix, particularly its heparan sulfate component. Heparin inhibits the intracellular alkalinization essential to proliferation, and we show that inhibition of alkalinization by 5-(N, N-dimethyl)amiloride also reduces PC proliferation. As shown by DNA staining and fluorescence-activated cell sorting analysis, heparin does not induce apoptosis in PCs. However, heparin maintains lung PCs in the G(0)/G(1) growth phase. Heparin induces production of p21, a potent inhibitor of cyclin-dependent kinases, thereby potentially identifying a fundamental mechanism by which heparin inhibits proliferation in smooth muscle-like cells. These studies establish additional similarities between lung PCs and smooth muscle cells and provide further understanding of growth control in the lung microvasculature. They also further support the rationale that heparin-like molecules might be therapeutically beneficial in pulmonary hypertension.

Cloning, expression, and purification of the K5 capsular polysaccharide lyase (KflA) from coliphage K5A: evidence for two distinct K5 lyase enzymes

The Escherichia coli K5 capsular polysaccharide [-4)-betaGlcA-(1, 4)-alphaGlcNAc-(1-] is a receptor for the capsule-specific bacteriophage K5A. Associated with the structure of bacteriophage K5A is a polysaccharide lyase which degrades the K5 capsule to expose the underlying bacterial cell surface. The bacteriophage K5A lyase gene (kflA) was cloned and sequenced. The kflA gene encodes a polypeptide with a predicted molecular mass of 66.9 kDa and which exhibits amino acid homology with ElmA, a K5 polysaccharide lyase encoded on the chromosome of E. coli SEBR 3282. There was only limited nucleotide homology between the kflA and elmA genes, suggesting that these two genes are distinct and either have been derived from separate progenitors or have diverged from a common progenitor for a considerable length of time. Southern blot analysis revealed that kflA was not present on the chromosome of the E. coli strains examined. In contrast, elmA was present in a subset of E. coli strains. Homology was observed between DNA flanking the kflA gene of bacteriophage K5A and DNA flanking a small open reading frame (ORF(L)) located 5' of the endosialidase gene of the E. coli K1 capsule-specific bacteriophage K1E. The DNA homology between these noncoding sequences indicated that bacteriophages K5A and K1E were related. The deduced polypeptide sequence of ORF(L) in bacteriophage K1E exhibited homology to the N terminus of KflA from bacteriophage K5A, suggesting that ORF(L) is a truncated remnant of KflA. The presence of this truncated kflA gene implies that bacteriophage K1E has evolved from bacteriophage K5A by acquisition of the endosialidase gene and subsequent loss of functional kflA. A (His)(6)-KflA fusion protein was overexpressed in E. coli and purified to homogeneity with a yield of 4.8 mg per liter of bacterial culture. The recombinant enzyme was active over a broad pH range and NaCl concentration and was capable of degrading K5 polysaccharide into a low-molecular-weight product.

Iduronic acid-containing glycosaminoglycans on target cells are required for efficient respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is an important human respiratory pathogen, particularly in infants. Glycosaminoglycans (GAGs) have been implicated in the initiation of RSV infection of cultured cells, but it is not clear what type of GAGs and GAG components are involved, whether the important GAGs are on the virus or the cell, or what the magnitude is of their contribution to infection. We constructed and rescued a recombinant green fluorescent protein (GFP)-expressing RSV (rgRSV) and used this virus to develop a sensitive system to assess and quantify infection by flow cytometry. Evaluation of a panel of mutant Chinese hamster ovary cell lines that are genetically deficient in various aspects of GAG synthesis showed that infection was reduced up to 80% depending on the type of GAG deficiency. Enzymatic removal of heparan sulfate and/or chondroitin sulfate from the surface of HEp-2 cells also reduced infection, and the removal of both reduced infection even further. Blocking experiments in which RSV was preincubated with various soluble GAGs revealed the relative blocking order of: heparin > heparan sulfate > chondroitin sulfate B. Iduronic acid is a component common to these GAGs. GAGs that do not contain iduronic acid, namely, chondroitin sulfate A and C and hyaluronic acid, did not inhibit infection. A role for iduronic acid-containing GAGs in RSV infection was confirmed by the ability of basic fibroblast growth factor to block infection, because basic fibroblast growth factor binds to GAGs containing iduronic acid. Pretreatment of cells with protamine sulfate, which binds and blocks GAGs, also reduced infection. In these examples, infection was reduced by pretreatment of the virus with soluble GAGs, pretreatment of the cells with GAG-binding molecules, pretreatment of the cells with GAG-destroying enzymes or in cells genetically deficient in GAGs. These results establish that the GAGs involved in RSV infection are present on the cell rather than on the virus particle. Thus, the presence of cell surface GAGs containing iduronic acid, like heparan sulfate and chondroitin sulfate B, is required for efficient RSV infection in cell culture.

Isolation and expression in Escherichia coli of cslA and cslB, genes coding for the chondroitin sulfate-degrading enzymes chondroitinase AC and chondroitinase B, respectively, from Flavobacterium heparinum

In medium supplemented with chondroitin sulfate, Flavobacterium heparinum synthesizes and exports two chondroitinases, chondroitinase AC (chondroitin AC lyase; EC 4.2.2.5) and chondroitinase B (chondroitin B lyase; no EC number), into its periplasmic space. Chondroitinase AC preferentially depolymerizes chondroitin sulfates A and C, whereas chondroitinase B degrades only dermatan sulfate (chondroitin sulfate B). The genes coding for both enzymes were isolated from F. heparinum and designated cslA (chondroitinase AC) and cslB (chondroitinase B). They were found to be separated by 5.5 kb on the chromosome of F. heparinum, transcribed in the same orientation, but not linked to any of the heparinase genes. In addition, the synthesis of both enzymes appeared to be coregulated. The cslA and cslB DNA sequences revealed open reading frames of 2,103 and 1,521 bp coding for peptides of 700 and 506 amino acid residues, respectively. Chondroitinase AC has a signal sequence of 22 residues, while chondroitinase B is composed of 25 residues. The mature forms of chondroitinases AC and B are comprised of 678 and 481 amino acid residues and have calculated molecular masses of 77,169 and 53,563 Da, respectively. Truncated cslA and cslB genes have been used to produce active, mature chondroitinases in the cytoplasm of Escherichia coli. Partially purified recombinant chondroitinases AC and B exhibit specific activities similar to those of chondroitinases AC and B from F. heparinum.

Heparan sulfate D-glucosaminyl 3-O-sulfotransferase-3A sulfates N-unsubstituted glucosamine residues

3-O-Sulfation of glucosamine by heparan sulfate D-glucosaminyl 3-O-sulfotransferase (3-OST-1) is the key modification in anticoagulant heparan sulfate synthesis. However, the heparan sulfates modified by 3-OST-2 and 3-OST-3A, isoforms of 3-OST-1, do not have anticoagulant activity, although these isoforms transfer sulfate to the 3-OH position of glucosamine residues. In this study, we characterize the substrate specificity of purified 3-OST-3A at the tetrasaccharide level. The 3-OST-3A enzyme was purified from Sf9 cells infected with recombinant baculovirus containing 3-OST-3A cDNA. Two 3-OST-3A-modified tetrasaccharides were purified from the 3-O-(35)S-sulfated heparan sulfate that was digested by heparin lyases. These tetrasaccharides were analyzed using nitrous acid and enzymatic degradation combined with matrix-assisted laser desorption/ionization-mass spectrometry. Two novel tetrasaccharides were discovered with proposed structures of DeltaUA2S-GlcNS-IdoUA2S-[(35)S]GlcNH(2)3S and DeltaUA2S-GlcNS-IdoUA2S-[3-(35)S]GlcNH(2)3S6S . The results demonstrate that 3-OST-3A sulfates N-unsubstituted glucosamine residues, and the 3-OST-3A modification sites are probably located in defined oligosaccharide sequences. Our study suggests that oligosaccharides with N-unsubstituted glucosamine are precursors for sulfation by 3-OST-3A. The intriguing linkage between N-unsubstituted glucosamine and the 3-O-sulfation by 3-OST-3A may provide a clue to the potential biological functions of 3-OST-3A-modified heparan sulfate.

Preparation and anticoagulant activity of fully O-sulphonated glycosaminoglycans

Glycosaminoglycans including dermatan sulphate, hyaluronan, heparan sulphate and heparin were chemically modified by O-sulphonation. By altering the reaction conditions, products having a different degree of O-sulphonation could be obtained. Glycosaminoglycan derivatives were prepared having no free hydroxyl groups, with sulphoester group/disaccharide unit ratios of 4.0 for dermatan sulphate and hyaluronan, and sulphoester and sulphamide group/disaccharide unit ratios of 4.22 and 4.88 for heparan sulphate and heparin, respectively. 1H NMR spectroscopy showed that the fully O-sulphonated hyaluronan derivative had a glucuronate residue with an altered conformation. Since glycosaminiglycans and their derivatives are often used as anticoagulant/antithrombotic agents, their anti-amidolytic activities were determined. The anti-factor IIa activity of fully O-sulphonated dermatan sulphate, hyaluronan and heparan sulphate ranged from 40 to 80 units/mg, while no anti-factor Xa activity of the fully O-sulphonated glycosaminoglycans was detected. These values are lower than those reported for low-molecular-weight heparins and are consistent with the requirement of an antithrombin III pentasaccharide binding site for anti-factor Xa activity. Interestingly, the anti-factor Xa of heparin is lost by chemical O-sulphonation.

Processing of the human heparanase precursor and evidence that the active enzyme is a heterodimer

Human platelet heparanase has been purified to homogeneity and shown to consist of two, non-covalently associated polypeptide chains of molecular masses 50 and 8 kDa. Protein sequencing provided the basis for determination of the full-length cDNA for this novel protein. Based upon this information and results from protein analysis and mass spectrometry, we propose a scheme to define the structural organization of heparanase in relation to its precursor forms, proheparanase and pre-proheparanase. The 8- and 50-kDa chains which make up the active enzyme reside, respectively, at the NH(2)- and COOH-terminal regions of the inactive precursor, proheparanase. The heparanase heterodimer is produced by excision and loss of an internal linking segment. This paper is the first to suggest that human heparanase is a two-chain enzyme.

Binding of xanthine oxidase to vascular endothelium. Kinetic characterization and oxidative impairment of nitric oxide-dependent signaling

Concentrations of up to 1.5 milliunits/ml xanthine oxidase (XO) (1.1 micrograms/ml) are found circulating in plasma during diverse inflammatory events. The saturable, high affinity binding of extracellular XO to vascular endothelium and the effects of cell binding on both XO catalytic activity and differentiated vascular cell function are reported herein. Xanthine oxidase purified from bovine cream bound specifically and with high affinity (Kd = 6 nM) at 4 degreesC to bovine aortic endothelial cells, increasing cell XO specific activity up to 10-fold. Xanthine oxidase-cell binding was not inhibited by serum or albumin and was partially inhibited by the addition of heparin. Pretreatment of endothelial cells with chondroitinase, but not heparinase or heparitinase, diminished endothelial binding by approximately 50%, suggesting association with chondroitin sulfate proteoglycans. Analysis of rates of superoxide production by soluble and cell-bound XO revealed that endothelial binding did not alter the percentage of univalent reduction of oxygen to superoxide. Comparison of the extent of CuZn-SOD inhibition of native and succinoylated cytochrome c reduction by cell-bound XO indicated that XO-dependent superoxide production was occurring in a cell compartment inaccessible to CuZn-SOD. This was further supported by the observation of a shift of exogenously added XO from extracellular binding sites to intracellular compartments, as indicated by both protease-reversible cell binding and immunocytochemical localization studies. Endothelium-bound XO also inhibited nitric oxide-dependent cGMP production by smooth muscle cell co-cultures in an SOD-resistant manner. This data supports the concept that circulating XO can bind to vascular cells, impairing cell function via oxidative mechanisms, and explains how vascular XO activity diminishes vasodilatory responses to acetylcholine in hypercholesterolemic rabbits and atherosclerotic humans. The ubiquity of cell-XO binding and endocytosis as a fundamental mechanism of oxidative tissue injury is also affirmed by the significant extent of XO binding to human vascular endothelial cells, rat lung type 2 alveolar epthelial cells, and fibroblasts.

Biochemical investigations and mapping of the calcium-binding sites of heparinase I from Flavobacterium heparinum

The heparinases from Flavobacterium heparinum are lyases that specifically cleave heparin-like glycosaminoglycans. Previously, amino acids located in the active site of heparinase I have been identified and mapped. In an effort to further understand the mechanism by which heparinase I cleaves its polymer substrate, we sought to understand the role of calcium, as a necessary cofactor, in the enzymatic activity of heparinase I. Specifically, we undertook a series of biochemical and biophysical experiments to answer the question of whether heparinase I binds to calcium and, if so, which regions of the protein are involved in calcium binding. Using the fluorescent calcium analog terbium, we found that heparinase I tightly bound divalent and trivalent cations. Furthermore, we established that this interaction was specific for ions that closely approximate the ionic radius of calcium. Through the use of the modification reagents N-ethyl-5-phenylisoxazolium-3'-sulfonate (Woodward's reagent K) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, we showed that the interaction between heparinase I and calcium was essential for proper functioning of the enzyme. Preincubation with either calcium alone or calcium in the presence of heparin was able to protect the enzyme from inactivation by these modifying reagents. In addition, through mapping studies of Woodward's reagent K-modified heparinase I, we identified two putative calcium-binding sites, CB-1 (Glu207-Ala219) and CB-2 (Thr373-Arg384), in heparinase I that not only are specifically modified by Woodward's reagent K, leading to loss of enzymatic activity, but also conform to the calcium-coordinating consensus motif.

Use of reversed polarity and a pressure gradient in the analysis of disaccharide composition of heparin by capillary electrophoresis

A capillary electrophoresis method with reversed polarity, combining both the application of a voltage and a pressure gradient between the buffer vials, was developed for the analysis of eight heparin-derived delta-disaccharides obtained by enzymatic depolymerization. A 60 mM formic acid buffer at pH 3.40 was selected as running electrolyte, with an applied voltage of -15 kV and an over-imposed pressure gradient (3.45.10(-3) MPa) for 6 min from inlet to outlet starting at 20 min. Figures of merit such as run-to-run and day-to-day precision, and limits of detection were established. The electrophoretic method was applied to the analysis of depolymerization products of different kinds of heparins. The composition of the depolymerization buffer was selected in order to reduce baseline distortions in the electrophoretic separation, thus a buffer solution containing 20 mM Tris, 50 mM sodium chloride, and 3 mM calcium chloride at pH 7.10 was used. Percentages of molar disaccharide compositions for unfractionated heparins from porcine, bovine and ovine intestinal mucosa, and bovine lung were determined. In addition, low-molecular-mass heparins from bovine and porcine intestinal mucosa were analysed as well.

Degradation of acharan sulfate and heparin by Bacteroides stercoris HJ-15, a human intestinal bacterium

When glycosaminoglycan (GAG)-degrading enzymes were measured in normal human stool suspensions, all 5 tested different stools degraded titrable heparin and acharan sulfate. GAG-degrading bacteria were screened from the isolates of human stools. Among them, HJ-15 had the most potent activities of heparinases (GAGs-degrading enzymes). However, HJ-15 produced the enzyme even if in the media without heparin. Acharan sulfate lyase was induced by acharan sulfate and heparin. Heparinase production was also induced by these GAGs. These enzymes, acharan sulfate lyase and heparinase, were produced in exponential and stationary phase of HJ-15 growth, respectively. Optimal pHs of the acharan sulfate lyase and heparinase activities were 7.2 and 7.5, respectively. The biochemical properties of HJ-15 was similar to those of B. stercoris. However, difference from B. stercoris was utilization of raffinose. This HJ-15 also degraded chondroitin sulfates A and C.

Heparinase II from Flavobacterium heparinum. Role of cysteine in enzymatic activity as probed by chemical modification and site- directed mutagenesis

Heparinase II (no EC number) is one of three lyases isolated from Flavobacterium heparinum that degrade heparin-like complex polysaccharides. Heparinase II is unique among the heparinases in that it has broad substrate requirements and possesses the ability to degrade both heparin and heparan sulfate-like regions of glycosaminoglycans. This study set out to investigate the role of cysteines in heparinase II activity. Through a series of chemical modification experiments, it was found that one of the three cysteines in heparinase II is surface-accessible and possesses unusual chemical reactivity toward cysteine-specific chemical modifying reagents. Substrate protection experiments suggest that this surface-accessible cysteine is proximate to the active site, since addition of substrate shields the cysteine from modifying reagents. The cysteine, present in an ionic environment, was mapped by radiolabeling with N-[3H]ethylmaleimide and identified as cysteine 348. Site-directed mutagenesis of cysteine 348 to an alanine resulted in loss of activity toward heparin but not heparan sulfate, indicating that cysteine 348 is required for heparinase II activity toward heparin but is not essential for the breakdown of heparan sulfate. Furthermore, we show in this study that cysteine 164 and cysteine 189 are functionally unimportant for heparinase II.

Effect of depletion of glycosaminoglycans and non-collagenous proteins on interstitial hydraulic permeability in rabbit synovium

1. The hydraulic resistance of synovial interstitium helps to retain a lubricating fluid within the joint cavity. The contributions of sulphated glycosaminoglycans to resistance were assessed by selective depletion by chondroitinase ABC, keratanase and heparinases I, II and III in vivo. Also, since glycosaminoglycans do not account fully for the resistance, the contribution of non-collagenous, structural proteins in interstitium was assessed by treatment with chymopapain, a collagen-sparing protease. 2. Ringer solution containing enzyme was injected into the synovial cavity of the knee in anaesthetized rabbits. After >= 30 min the intra-articular pressure was raised and the relation between pressure (Pj) and trans-synovial outflow (Qs) determined. The slope dQs/dPj at low pressures, i.e. below yield pressure, represents the hydraulic conductance of the lining, i.e. 1/resistance. The contralateral joint received Ringer solution without enzyme as a control. Action of enzymes on the tissue was confirmed by histochemical and immunohistochemical studies. 3. Treatment with chondroitinase ABC (5 joints) increased the hydraulic conductance of the lining by 2.3 times (control, 1.34 +/- 0.22 microliter l min-1 cmH2O-1; post-enzyme, 3.11 +/- 0.45 microliter l min-1 cmH2O-1). This was significantly less than the effects of leech, Streptomyces and testicular hyaluronidases, which caused an average 4.7 times increase (P < 0.001, ANOVA). Analogous findings were made above yield pressure. 4. Treatment with keratanase (3 joints) or heparinases I, II and III (3 joints) caused no significant increase in trans-synovial flows or conductance, even though the concentration of heparan sulphate in synovium is higher than that of chondroitin sulphates or hyaluronan. 5. Treatment with chymopapain (7 joints) caused the greatest increases in trans-synovial flow, which exceeded control flow by an order of magnitude in one case. After 0.1 U chymopapain the average conductance was 6.6 times the control conductance below yield pressure. Immunohistochemical studies confirmed that chymopapain treatment removed the synovial proteoglycans. 6. It is concluded that, despite their similar resistivities in vitro, the different glycosaminoglycans do not contribute equally, weight for weight, to interstitial resistance in vivo. Hyaluronan is the dominant glycosaminoglycan governing synovial interstitial resistance. In addition, non-collagenous structural proteins contribute significantly to interstitial resistance.

Heparinase II from Flavobacterium heparinum. Role of histidine residues in enzymatic activity as probed by chemical modification and site-directed mutagenesis

The three heparinases derived from Flavobacterium heparinum are powerful tools for studying heparin-like glycosaminoglycans in major biological processes, including angiogenesis and development. Heparinase II is unique among the three enzymes because it is able to catalytically cleave both heparin and heparan sulfate-like regions of heparin-like glycosaminoglycans. Toward understanding the catalytic mechanism of heparin-like glycosaminoglycan degradation by heparinase II, we set out to investigate the role of the histidines of heparinase II in catalysis. We observe concentration-dependent inactivation of heparinase II in the presence of the reversible histidine-modifying reagent diethylpyrocarbonate (DEPC). With heparin as the substrate, the rate constant of inactivation was found to be 0.16 min-1 mM-1; with heparan sulfate as the substrate, the rate constant was determined to be 0.24 min-1 mM-1. Heparinase II activity is restored following hydroxylamine treatment. This, along with other experiments, strongly suggests that the inactivation of heparinase II by DEPC is specific for histidine residues and that three histidines are modified by DEPC. Substrate protection experiments show that heparinase II preincubation with heparin followed by the addition of DEPC resulted in a loss of enzymatic activity toward heparan sulfate but not heparin. However, heparinase II preincubation with heparan sulfate was unable to protect heparinase II from DEPC inactivation for either of the substrates. Proteolytic mapping studies with Lys-C were consistent with the chemical modification experiments and identified histidines 238, 451, and 579 as being important for heparinase II activity. Further mapping studies identified histidine 451 as being essential for heparin degradation. Site-directed mutagenesis experiments on the 13 histidines of heparinase II corroborated the chemical modification and the peptide mapping studies, establishing the importance of histidines 238, 451 and 579 in heparinase II activity.

Heparan sulfate undergoes specific structural changes during the progression from human colon adenoma to carcinoma in vitro

We report a detailed analysis of heparan sulfate (HS) structure using a model of human colon carcinogenesis. Metabolically radiolabeled HS was isolated from adenoma and carcinoma cells. The chain length of HS was the same in both cell populations (Mr 20,000; 45-50 disaccharides), and the chains contained on average of two sulfated domains (S domains), identified by heparinase I scission. This enzyme produced fragments of approximate size 7 kDa, suggesting that the S domains were evenly spaced in the intact HS chain. The degree of polymer sulfation and the patterns of sulfation were strikingly different between the two HS species. When compared with adenoma HS, the iduronic acid 2-O-sulfate content of the carcinoma-derived material was reduced by 33%, and the overall level of N-sulfation was reduced by 20%. However, the level of 6-O-sulfation was increased by 24%, and this was almost entirely attributable to an enhanced level of N-sulfated glucosamine 6-O-sulfate, a species whose data implied was mainly located in the mixed sequences of alternating N-sulfated and N-acetylated disaccharides. The results indicate that in the transition to malignancy in human colon adenoma cells, the overall molecular organization of HS is preserved, but there are distinct modifications in both the S domains and their flanking mixed domains that may contribute to the aberrant behavior of the cancer cell.

Heparinase I from Flavobacterium heparinum. Role of positive charge in enzymatic activity

Heparinases are bacterial enzymes that are powerful tools to study the physiological roles of heparin-like complex polysaccharides. In addition, heparinases have significant therapeutic applications. We had proposed earlier that cysteine 135 and histidine 203 together form the catalytic domain in heparinase I. We had also identified a heparin binding domain in heparinase I containing two positively charged clusters HB-1 and HB-2 in a primary heparin binding site and other positively charged residues in the vicinity of cysteine 135. In this study, through systematic site-directed mutagenesis studies, we show that the alteration of the positive charge of the HB-1 region has a pronounced effect on heparinase I activity. More specifically, site-directed mutagenesis of K199A (contained in HB-1) results in a 15-fold reduction in catalytic activity, whereas a K198A mutation (also in HB-1) results in only a 2- to 3-fold reduction in heparinase I activity. A K132A mutation, in close proximity to cysteine 135, also resulted in reduced (8-fold) activity. Heparin affinity chromatography experiments indicated moderately lowered binding affinities for the K132A, K198A, and the K199A mutant enzymes. The above results, taken together with our previous observations, lead us to propose that the positively charged heparin binding domain provides the necessary microenvironment for the catalytic domain of heparinase I. The dominant effect of lysine 199 suggests an additional, more direct, role in catalysis for this residue.

Chemical microdetermination of heparin in plasma

A new, simple, and highly sensitive method for the determination of heparin has been established. Heparin was first converted into unsaturated disaccharides through the action of heparin lyases I, II, and III. A major trisulfated unsaturated disaccharide product results, consistent with structural analysis of a number of pharmaceutical heparins using one- and two-dimensional 1H NMR spectroscopy. This disaccharide was analyzed by HPLC using fluorometric postcolumn derivatization. The correlation between the amount of this trisulfated unsaturated disaccharide and anticoagulant activity of heparin as measured by anti-IIa was determined. The analysis of these pharmaceutical heparins showed a linear correlation between both HPLC and bioassay. This HPLC method was then applied to a pharmacokinetic study of heparin intravenously administered to rabbits.

Heparanase and a synthetic peptide of heparan sulfate-interacting protein recognize common sites on cell surface and extracellular matrix heparan sulfate

Heparanase is an endo-beta-D-glucuronidase that degrades the glycosaminoglycan chains of heparan sulfate (HS) proteoglycans at specific sites. Elevated levels of heparanase are associated with the metastatic potential of melanoma and other types of tumor cells. We previously reported heparanase degradation of cell surface HS subpopulations of the human adenocarcinoma cell line RL95. In the present study, heparanase activity was examined on RL95 cell surface HS subpopulations in the presence of a synthetic peptide (CRPKAKAKAKAKDQTK) of heparin/heparan sulfate-interacting protein (HIP; Liu, S., Smith, S. E., Julian, J., Rohde, L. H., Karin, N. J., and Carson, D. D. (1996) J. Biol. Chem. 271, 11817-11823). Heparanase digestion generated HS fragments from cell surface- or extracellular matrix-derived HS of approximately 25 and 9 kDa, respectively. In contrast, HS of various size classes isolated from proteoglycans secreted or released by RL95 and endothelial cells in culture were not susceptible to heparanase digestion. Incubation of heparanase-containing melanoma cellular extracts or partially purified heparanase preparations with cell surface- or ECM-derived HS and HIP peptide, but not a scrambled sequence of this peptide or other HS-binding proteins present in ECM, completely inhibited heparanase action. Conversely, predigestion of cell surface HS with either heparanase-containing cellular extracts or with secreted or partially purified heparanase destroyed binding to HIP peptide. Preincubation of HS with HIP peptide prevented subsequent heparanase digestion. Collectively, these data demonstrate that HIP peptide and heparanase recognize specific, common motifs within HS chains at cell surfaces and in ECM and may mutually modulate HS-dependent activities.

VEGF145, a secreted vascular endothelial growth factor isoform that binds to extracellular matrix

A vascular endothelial growth factor (VEGF) mRNA species containing exons 1-6 and 8 of the VEGF gene was found to be expressed as a major VEGF mRNA form in several cell lines derived from carcinomas of the female reproductive system. This mRNA is predicted to encode a VEGF form of 145 amino acids (VEGF145). Recombinant VEGF145 induced the proliferation of vascular endothelial cells and promoted angiogenesis in vivo. VEGF145 was compared with previously characterized VEGF species with respect to interaction with heparin-like molecules, cellular distribution, VEGF receptor recognition, and extracellular matrix (ECM) binding ability. VEGF145 shares with VEGF165 the ability to bind to the KDR/flk-1 receptor of endothelial cells. It also binds to heparin with an affinity similar to that of VEGF165. However, VEGF145 does not bind to two additional endothelial cell surface receptors that are recognized by VEGF165 but not by VEGF121. VEGF145 is secreted from producing cells as are VEGF121 and VEGF165. However, VEGF121 and VEGF165 do not bind to the ECM produced by corneal endothelial cells, whereas VEGF145 binds efficiently to this ECM. Basic fibroblast growth factor (bFGF)-depleted ECM containing bound VEGF145 induces proliferation of endothelial cells, indicating that the bound VEGF145 is active. The mechanism by which VEGF145 binds to the ECM differs from that of bFGF. Digestion of the ECM by heparinase inhibited the binding of bFGF to the ECM and released prebound bFGF, whereas the binding of VEGF145 was not affected by heparinase digestion. It therefore seems that VEGF145 possesses a unique combination of biological properties distinct from those of previously characterized VEGF species.

Enzymatic preparation of heparin oligosaccharides containing antithrombin III binding sites

Two new oligosaccharides were prepared from heparin by its partial depolymerization using heparin lyase I (EC 4.2.2.7) in an attempt to prepare oligosaccharides having intact antithrombin III binding sites. The oligosaccharides were purified by chromatography on the basis of both size and charge and demonstrated a high level of purity by capillary electrophoresis. One- and two-dimensional 1H NMR spectroscopy at 500 MHz revealed the structure of each oligosaccharide. The octasaccharide and decasaccharide are DeltaUAp2S(1-->4)-alpha-DGlcNpS6S(1-->4)-alpha-L-IdoAp (1-->4)-alpha-D -GlcNpAc6S(1-->4)-betaD-GlcAp(1-->4)-alpha-D-GlcNpS 3S6S(1-->4)-alpha- L-IdoAp2S(1-->4)alpha-D-GlcNpS6S (where DeltaUAp is 4-deoxy-alpha-L-threo-hex-enopyranosyluronic acid, GlcNp is 2-amino-2-deoxy-glucopyranose, GlcAp is glucopyranosyluronic acid, S is sulfate and Ac is acetate) and DeltaUAp2S(1-->4)-alpha-D-GlcNpS6S(1-->4)-alpha-L-IdoAp++ +(1-->4)-alpha- D-GlcNpAc6S (1-->4)-beta-D-GlcAp(1-->4)-alpha-D-GlcNpS3S6S(1-->4)-alpha- L-IdoAp2S (1-->4)-alpha-D-GlcNpS6S(1-->4)-alpha-L-IdoAp2S(1-->4)-alpha -D-GlcNpS 6S, respectively. A hexasaccharide containing a similar structural motif to that found in the antithrombin III binding site and having greatly reduced anticoagulant activity was also isolated. The structure of the hexasaccharide is DeltaUAp2S(1-->4)-alpha-D-GlcNpAc6S(1-->4)-beta-D-GlcAp++ +(1-->4)-alpha- D-GlcNpS3S6S(1-->4)-alpha-L-IdoAp(1-->4)-alpha-D-GlcNpS6S . The octasaccharide and decasaccharide correspond to the predominant structural motif found in porcine intestinal mucosal heparin. Sufficient quantities of the decasaccharide were obtained to examine its interaction with antithrombin III using microtitration calorimetry. This decasaccharide bound to antithrombin III with similar avidity as heparin and showed comparable anticoagulant activity, as determined using an antithrombin III dependent anti-factor Xa assay. Interestingly, while both decasaccharide and heparin bound to antithrombin with nanomolar affinity, very little heat of binding was observed.

Isolation and expression in Escherichia coli of hepB and hepC, genes coding for the glycosaminoglycan-degrading enzymes heparinase II and heparinase III, respectively, from Flavobacterium heparinum

Upon induction with heparin, Flavobacterium heparinum synthesizes and secretes into its periplasmic space heparinase I (EC 4.2.2.7), heparinase II, and heparinase III (heparitinase; EC 4.2.2.8). Heparinase I degrades heparin, and heparinase II degrades both heparin and heparan sulfate, while heparinase III degrades heparan sulfate predominantly. We isolated the genes encoding heparinases II and III (designated hepB and hepC, respectively). These genes are not contiguous with each other or with the heparinase I gene (designated hepA). hepB and hepC were found to contain open reading frames of 2,316 and 1,980 bp, respectively. Enzymatic removal of pyroglutamate groups permitted sequence analysis of the amino termini of both mature proteins. It was determined that the mature forms of heparinases II and III contain 746 and 635 amino acids, respectively, and have calculated molecular weights of 84,545 and 73,135, respectively. The preproteins have signal sequences consisting of 26 and 25 amino acids. Truncated hepB and hepC genes were used to produce active, mature heparinases II and III in the cytoplasm of Escherichia coli. When these enzymes were expressed at 37 degrees C, most of each recombinant enzyme was insoluble, and most of the heparinase III protein was degraded. When the two enzymes were expressed at 25 degrees C, they were both present predominantly in a soluble, active form.

A new glycosaminoglycan from the giant African snail Achatina fulica

A new glycosaminoglycan has been isolated from the giant African snail Achatina fulica. This polysaccharide had a molecular weight of 29,000, calculated based on the viscometry, and a uniform repeating disaccharide structure of -->4)-2-acetyl,2-deoxy-alpha-D-glucopyranose (1-->4)-2-sulfo-alpha-L-idopyranosyluronic acid (1-->. This polysaccharide represents a new, previously undescribed glycosaminoglycan. It is related to the heparin and heparan sulfate families of glycosaminoglycans but is distinctly different from all known members of these classes of glycosaminoglycans. The structure of this polysaccharide, with adjacent N-acetylglucosamine and 2-sulfo-iduronic acid residues, also poses interesting questions about how it is made in light of our current understanding of the biosynthesis of heparin and heparan sulfate. This glycosaminoglycan represents 3-5% of the dry weight of this snail's soft body tissues, suggesting important biological roles for the survival of this organism, and may offer new means to control this pest. Snail glycosaminoglycan tightly binds divalent cations, such as copper(II), suggesting a primary role in metal uptake in the snail. Finally, this new polysaccharide might be applied, like the Escherichia coli K5 capsular polysaccharide, to the study of glycosaminoglycan biosynthesis and to the semisynthesis of new glycosaminoglycan analogs having important biological activities.

Heparinase I from Flavobacterium heparinum. Mapping and characterization of the heparin binding domain

In this study we have identified the primary heparin binding site of heparinase I (EC 4.2.2.7). Chemical and proteolytic digests of heparinase I were used in direct binding and competition assays, to map the regions of heparinase I that interact specifically with heparin. We find the heparin binding site contains two Cardin-Weintraub heparin binding consensus sequences and a calcium co-ordination consensus motif. We show that heparin binding to heparinase I is independent of calcium (Kd of 60 nm) and that calcium is able to activate heparinase I catalytically. We find that sulfhydryl selective labeling of cysteine 135 of heparinase I protects the lysines of the heparin binding sequence from proteolytic cleavage, suggesting the close proximity of the heparin binding site to the active site. Site-directed mutagenesis of H203A (contained in the heparin binding site) inactivated heparinase I; however, a H203D mutant retained marginal activity, indicating a role for this residue in catalysis. The above results taken together suggest that histidine 203 (hence the heparin binding site) is immediately adjacent to the scissile bond. We propose that the heparin binding site and active site are in close proximity to each other and that the calcium coordination motif, contained in the heparin binding site, may bridge heparin to heparinase I through calcium in a ternary complex during catalysis.

High-performance liquid chromatographic analysis of glycosaminoglycan-derived oligosaccharides

High-performance liquid chromatography of glycosaminoglycan (GAG)-derived oligosaccharides has been employed for the structural analysis and measurement of hyaluronan, chondroitin sulphate, dermatan sulphate, keratan sulphate, heparan sulphate and heparin. Recent developments in the separation and detection of unsaturated disaccharides and oligosaccharides derived from GAGs by enzymatic or chemical degradation are reviewed.

Isolation and characterization of heparan sulfate from crude porcine intestinal mucosal peptidoglycan heparin

A method for the preparation of heparan sulfate from peptidoglycan heparin is described. The objective of this research was to provide a basis for the development and validation of an industrial process to support the preclinical development of heparan sulfate and/or heparan sulfate derivatives. In the preparation of heparan sulfate, heparin was recovered by alcohol fractionation and dermatan sulfate was isolated by selective precipitation. The remaining crude heparan sulfate was fractionated by anion-exchange chromatography into five subfractions. The biological activities of these subfractions were examined by anticoagulant and amidolytic assays. Molecular weight and molecular size were determined using capillary viscometry and polyacrylamide gel electrophoresis. Charge density and degree of sulfation were determined by cellulose acetate electrophoresis and elemental analysis. Oligosaccharide and disaccharide analysis relied on enzymatic depolymerization using heparin lyases followed by polyacrylamide gel and capillary electrophoresis. 1H NMR analysis provided detailed structural information on each subfraction. Crude heparin sulfate and its subfractions showed significant differences in physical, structural and biological properties.

Polysaccharide lyases

Polysaccharide lyases are the products of various microorganisms, bacteriophage and some eukaryotes. All such enzymes cleave a hexose-1,4-alpha- or beta-uronic acid sequence by beta-elimination. They are in some examples, the only known type of enzymes degrading their polyanionic substrates. Although only a small number of these enzymes have been exhaustively studied, the pectin lyases of bacterial origin have proved to be of interesting crystal structure containing a parallel beta-helix domain. Alginate and heparin lyases may yield products with biotechnological potential.

Endothelial heparan sulfate proteoglycans that bind to L-selectin have glucosamine residues with unsubstituted amino groups

We earlier reported calcium-dependent, heparin-like L-selectin ligands in cultured bovine endothelial cells (Norgard-Sumnicht, K. E., Varki, N. M., and Varki, A. (1993) Science 261,480-483). Here we show that these are heparan sulfate proteoglycans (HSPGs) associated either with the cultured cells or secreted into the medium and extracellular matrix. Activation of the endothelial cells with bacterial lipopolysaccharide (LPS) does not markedly alter the amount or distribution of this material. A major portion of the glycosaminoglycan (GAG) chains released from these HSPGs by alkaline beta-elimination rebinds to L-selectin in the presence of calcium, indicating that these saccharides alone can mediate the high affinity recognition. Heparin lyase digestions indicate that these GAG chains are enriched in heparan sulfate, not heparin sequences. Current understanding of the biosynthesis of heparan sulfate chains indicates that all glucosamine amino groups must be either N-acetylated or N-sulfated. However, nitrous acid deamination at pH 4.0 suggests the presence of some unsubstituted amino groups in these L-selectin-binding GAG chains from endothelial cell HSPGs. This is confirmed by chemical N-reacetylation and by reactivity with sulfo-N-hydroxysuccinimide-biotin. These unsubstituted amino groups are also found on HSPGs from human umbilical vein endothelial cells, but are not detected in those from Chinese hamster ovary cells. In both bovine and human endothelial cells, these novel groups are enriched for in the HS-GAG chains which bind to L-selectin. Despite this, studies with N-reacetylation and nitrous acid deamination do not show conclusive evidence for the direct involvement of the unsubstituted amino groups in L-selectin binding. This may be because the chemical reactions used to modify the amino groups do not go to completion. Alternatively, the unsubstituted amino groups may only be indirectly involved in generating binding, by dictating the biosynthesis of another critical group. Regardless, these studies shown that HSPGs from cultured endothelial cells which can bind to L-selectin are enriched with unsubstituted amino groups on their GAG chains. The possible biochemical mechanisms for generation of these novel groups are discussed.

CXC chemokines connective tissue activating peptide-III and neutrophil activating peptide-2 are heparin/heparan sulfate-degrading enzymes

Heparan sulfate proteoglycans at cell surfaces or in extracellular matrices bind diverse molecules, including growth factors and cytokines, and it is believed that the activities of these molecules may be regulated by the metabolism of heparan sulfate. In this study, purification of a heparan sulfate-degrading enzyme from human platelets led to the discovery that the enzymatic activity residues in at least two members of the platelet basic protein (PBP) family known as connective tissue activating peptide-III (CTAP-III) and neutrophil activating peptide-2. PBP and its N-truncated derivatives, CTAP-III and neutrophil activating peptide-2, are CXC chemokines, a group of molecules involved in inflammation and wound healing. SDS-polyacrylamide gel electrophoresis analysis of the purified heparanase resulted in a single broad band at 8-10 kDa, the known molecular weight of PBP and its truncated derivatives. Gel filtration chromatography of heparanase resulted in peaks of activity corresponding to monomers, dimers, and tetramers; these higher order aggregates are known to form among the chemokines. N-terminal sequence analysis of the same preparation indicated that only PBP and truncated derivatives were present, and commercial CTAP-III from three suppliers had heparanase activity. Antisera produced in animals immunized with a C-terminal synthetic peptide of PBP inhibited heparanase activity by 95%, compared with activity of the purified enzyme in the presence of the preimmune sera. The synthetic peptide also inhibited heparanase by 95% at 250 microM, compared to the 33% inhibition of heparanase activity by two other peptides. The enzyme was determined to be an endoglucosaminidase, and it degraded both heparin and heparan sulfate with optimal activity at pH 5.8. Chromatofocusing of the purified heparanase resulted in two protein peaks: an inactive peak at pI7.3, and an active peak at pI 4.8-5.1. Sequence analysis showed that the two peaks contained identical protein, suggesting that a post-translational modification activates the enzyme.

Low molecular weight dermatan sulfate as an antithrombotic agent. Structure-activity relationship studies

A structure-activity relationship of low molecular weight dermatan sulfate was undertaken to understand better this new non-heparin, glycosaminoglycan-based antithrombotic agent. A dermatan sulfate prepared from bovine intestinal mucosa [average molecular weight (MWavg) 25,000], and currently in clinical trials as an antithrombotic agent, was used in this study. Dermatan sulfate was partially depolymerized using hydrogen peroxide and copper(II) as catalyst to MWavg 5600 to obtain a low molecular weight dermatan sulfate. This low molecular weight dermatan sulfate was then fractionated by gel permeation chromatography to obtain four subfractions having MWavg 7800, 5500, 4200 and 1950. The dermatan sulfate, low molecular weight dermatan sulfate and its subfractions showed substantially different optical rotations. The 1H-NMR spectroscopic analysis of dermatan sulfate samples showed some differences including increased content of GalpNAc4S6S residues and improved resolution in ring resonances for low molecular weight dermatan sulfate fractions, primarily the result of reduced molecular weight and lowered heterogeneity. Saccharide compositional analysis relied on chondroitin ABC lyase treatment followed by capillary electrophoresis. Polyacrylamide gel-based oligosaccharide mapping was also performed by treating dermatan sulfate samples with chondroitin B, AC and ABC lysases. These analyses showed increased amounts of sulfation as the MWavg decreased. In vitro bioassay showed maximum anti-Xa activity in the 4.2 kDa fraction and maximum heparin cofactor II-mediated anti-IIa activity in the 5.5 kDa fraction. The in vivo antithrombotic activity of these fractions was measured using a modified Wessler stasis thrombosis model. The 4.2 kDa fraction showed greater antithrombotic activity than the other low molecular weight dermatan sulfate fractions, dermatan sulfate, and low molecular weight dermatan sulfate. This enhanced activity may result from several structural features of the 4.2 kDa fraction including: a high content of 4,6- and 2,4-disulfated disaccharide sequences; the requirement of specific chain length; a change in the ratio of iduronic to glucuronic acid; and the presence of chondroitin ABC lyase resistant material.

Molecular weight of low molecular weight heparins by 13C nuclear magnetic resonance spectroscopy

Heparin and low molecular weight heparins are polydisperse polysaccharides with a degree of polymerization ranging from 4 to approximately 40. The determination of their average molecular weights has traditionally relied on size exclusion chromatography involving the use of oligosaccharides of known size and molecular weight as standards. 13C NMR spectroscopy is applied for the first time to obtain the molecular weights of low molecular weight heparins. The signal intensities of the reducing end and internal anomeric carbons, having distinctive chemical shifts in the 13C NMR spectrum, are measured to determine the molecular weight. Compared to techniques utilizing broad band decoupling or selective decoupling of anomeric protons, distortionless enhancement polarization transfer pulse sequence gave better quantitation of signal intensities of anomeric carbons. Molecular weight was calculated from the calibrated ratio of signal intensities of the anomeric carbons of reducing end groups and internal residues, and the disaccharide compositional analysis. The calibrated signal intensity ratio is determined using the T1 relaxation rates of anomeric carbons of model oligosaccharides. The disaccharide composition of low molecular weight-heparins is obtained using capillary electrophoresis. Signal averaging over 40,000-90,000 transients, requiring a total of 12-18 h on a 360-MHz NMR spectrometer was adequate to measure molecular weights in the range of 3000-7000. The measured molecular weights of twelve low molecular weight heparins, analyzed by this 13C NMR spectroscopic technique, correlated well with the number average molecular weights obtained using high performance-gel permeation chromatography and gradient polyacrylamide gel electrophoresis. In addition to establishing the number average molecular weight, the 13C NMR spectra helped distinguish the structural properties of different commercially prepared low molecular weight heparins.