Heparinase II from Flavobacterium heparinum. HPLC analysis of the saccharides generated from chemically modified heparins

Discovery of a class of glycosaminoglycan lyases with ultrabroad substrate spectrum and their substrate structure preferences

Glycosaminoglycan (GAG) lyases are often strictly substrate specific, and it is especially difficult to simultaneously degrade GAGs with different types of glycosidic bonds. Herein, we found a new class of GAG lyases (GAGases) from different bacteria. These GAGases belong to polysaccharide lyase 35 family and share quite low homology with the identified GAG lyases. The most surprising thing is that GAGases can not only degrade three types of GAGs: hyaluronan, chondroitin sulfate, and heparan sulfate but also even one of them can also degrade alginate. Further investigation of structural preferences revealed that GAGases selectively act on GAG domains composed of non/6-O-/N-sulfated hexosamines and d-glucoronic acids as well as on alginate domains composed of d-mannuronic acids. In addition, GAG lyases were once speculated to have evolved from alginate lyases, but no transitional enzymes have been found. The discovery of GAGases not only broadens the category of GAG lyases, provides new enzymatic tools for the structural and functional studies of GAGs with specific structures, but also provides candidates for the evolution of GAG lyases.

Comparative assessment of the effects of gender-specific heparan sulfates on mesenchymal stem cells

We compare here the structural and functional properties of heparan sulfate (HS) chains from both male or female adult mouse liver through a combination of molecular sieving, enzymatic cleavage, and strong anion exchange-HPLC. The results demonstrated that male and female HS chains are significantly different by a number of parameters; size determination showed that HS chain lengths were ∼100 and ∼22 kDa, comprising 30-40 and 6-8 disaccharide repeats, respectively. Enzymatic depolymerization and disaccharide composition analyses also demonstrated significant differences in domain organization and fine structure. N-Unsubstituted glucosamine (ΔHexA-GlcNH(3)(+), ΔHexA-GlcNH(3)(+)(6S), ΔHexA(2S)-GlcNH(3)(+), and N-acetylglucosamine (ΔHexA-GlcNAc) are the predominant disaccharides in male mouse liver HS. However, N-sulfated glucosamine (ΔHexA-GlcNSO(3)) is the predominant disaccharide found in female liver. These structurally different male and female liver HS forms exert differential effects on human mesenchymal cell proliferation and subsequent osteogenic differentiation. The present study demonstrates the potential usefulness of gender-specific liver HS for the manipulation of human mesenchymal cell properties, including expansion, multipotentiality, and subsequent matrix mineralization. Our results suggest that HS chains show both tissue- and gender-specific differences in biochemical composition that directly reflect their biological activity.

Catalytic mechanism of heparinase II investigated by site-directed mutagenesis and the crystal structure with its substrate

Heparinase II (HepII) is an 85-kDa dimeric enzyme that depolymerizes both heparin and heparan sulfate glycosaminoglycans through a beta-elimination mechanism. Recently, we determined the crystal structure of HepII from Pedobacter heparinus (previously known as Flavobacterium heparinum) in complex with a heparin disaccharide product, and identified the location of its active site. Here we present the structure of HepII complexed with a heparan sulfate disaccharide product, proving that the same binding/active site is responsible for the degradation of both uronic acid epimers containing substrates. The key enzymatic step involves removal of a proton from the C5 carbon (a chiral center) of the uronic acid, posing a topological challenge to abstract the proton from either side of the ring in a single active site. We have identified three potential active site residues equidistant from C5 and located on both sides of the uronate product and determined their role in catalysis using a set of defined tetrasaccharide substrates. HepII H202A/Y257A mutant lost activity for both substrates and we determined its crystal structure complexed with a heparan sulfate-derived tetrasaccharide. Based on kinetic characterization of various mutants and the structure of the enzyme-substrate complex we propose residues participating in catalysis and their specific roles.

Crystal structure of heparinase II from Pedobacter heparinus and its complex with a disaccharide product

Heparinase II depolymerizes heparin and heparan sulfate glycosaminoglycans, yielding unsaturated oligosaccharide products through an elimination degradation mechanism. This enzyme cleaves the oligosaccharide chain on the nonreducing end of either glucuronic or iduronic acid, sharing this characteristic with a chondroitin ABC lyase. We have determined the first structure of a heparin-degrading lyase, that of heparinase II from Pedobacter heparinus (formerly Flavobacterium heparinum), in a ligand-free state at 2.15 A resolution and in complex with a disaccharide product of heparin degradation at 2.30 A resolution. The protein is composed of three domains: an N-terminal alpha-helical domain, a central two-layered beta-sheet domain, and a C-terminal domain forming a two-layered beta-sheet. Heparinase II shows overall structural similarities to the polysaccharide lyase family 8 (PL8) enzymes chondroitin AC lyase and hyaluronate lyase. In contrast to PL8 enzymes, however, heparinase II forms stable dimers, with the two active sites formed independently within each monomer. The structure of the N-terminal domain of heparinase II is also similar to that of alginate lyases from the PL5 family. A Zn2+ ion is bound within the central domain and plays an essential structural role in the stabilization of a loop forming one wall of the substrate-binding site. The disaccharide binds in a long, deep canyon formed at the top of the N-terminal domain and by loops extending from the central domain. Based on structural comparison with the lyases from the PL5 and PL8 families having bound substrates or products, the disaccharide found in heparinase II occupies the "+1" and "+2" subsites. The structure of the enzyme-product complex, combined with data from previously characterized mutations, allows us to propose a putative chemical mechanism of heparin and heparan-sulfate degradation.

Distinct Substrate Specificities of Bacterial Heparinases against N-Unsubstituted Glucosamine Residues in Heparan Sulfate

The rare N-unsubstituted glucosamine (GlcNH(3)(+)) residues in heparan sulfate have important biological and pathophysiological roles. In this study, four GlcNH(3)(+)-containing disaccharides were obtained from partially de-N-sulfated forms of heparin and the N-sulfated K5 polysaccharide by digestion with combined heparinases I, II, and III. These were identified as DeltaHexA-GlcNH(3)(+),DeltaHexA-GlcNH(3)(+)(6S),DeltaHexA(2S)-GlcNH(3)(+), and DeltaHexA(2S)-GlcNH(3)(+)(6S). Digestions with individual enzymes revealed that heparinase I did not cleave at GlcNH(3)(+) residues; however, heparinases II and III showed selective and distinct activities. Heparinase II generated DeltaHexA-GlcNH(3)(+)(6S),DeltaHexA(2S)-GlcNH(3)(+), and DeltaHexA(2S)-GlcNH(3)(+)(6S) disaccharides, whereas heparinase III yielded only the DeltaHexA-GlcNH(3)(+) unit. Thus, the action of heparinase II requires O-sulfation, whereas heparinase III acts only on the corresponding non-sulfated unit. These striking distinctions in substrate specificities of heparinases could be used to isolate oligosaccharides with novel sequences of GlcNH(3)(+) residues. Finally, heparinases were used to identify and quantify GlcNH(3)(+)-containing disaccharides in native bovine kidney and porcine intestinal mucosal heparan sulfates. The relatively high content of O-sulfated GlcNH(3)(+)-disaccharides in kidney HS raises questions about how these sequences are generated.

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.

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.

Effects of structural modification of calcium spirulan, a sulfated polysaccharide from Spirulina platensis, on antiviral activity

Calcium ion binding with the anionic part of a molecule was replaced with various metal cations and their inhibitory effects on the replication of herpes simplex virus type 1 were evaluated. Replacement of calcium ion with sodium and potassium ions maintained the antiviral activity while divalent and trivalent metal cations reduced the activity. Depolymerization of sodium spirulan with hydrogen peroxide decreased in antiviral activity as its molecular weight decreased.

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.

Mass spectrometric evidence for the enzymatic mechanism of the depolymerization of heparin-like glycosaminoglycans by heparinase II

Heparin-like glycosaminoglycans, acidic complex polysaccharides present on cell surfaces and in the extracellular matrix, regulate important physiological processes such as anticoagulation and angiogenesis. Heparin-like glycosaminoglycan degrading enzymes or heparinases are powerful tools that have enabled the elucidation of important biological properties of heparin-like glycosaminoglycans in vitro and in vivo. With an overall goal of developing an approach to sequence heparin-like glycosaminoglycans using the heparinases, we recently have elaborated a mass spectrometry methodology to elucidate the mechanism of depolymerization of heparin-like glycosaminoglycans by heparinase I. In this study, we investigate the mechanism of depolymerization of heparin-like glycosaminoglycans by heparinase II, which possesses the broadest known substrate specificity of the heparinases. We show here that heparinase II cleaves heparin-like glycosaminoglycans endolytically in a nonrandom manner. In addition, we show that heparinase II has two distinct active sites and provide evidence that one of the active sites is heparinase I-like, cleaving at hexosamine-sulfated iduronate linkages, whereas the other is presumably heparinase III-like, cleaving at hexosamine-glucuronate linkages. Elucidation of the mechanism of depolymerization of heparin-like glycosaminoglycans by the heparinases and mutant heparinases could pave the way to the development of much needed methods to sequence heparin-like glycosaminoglycans.

Heparin-like structures on respiratory syncytial virus are involved in its infectivity in vitro

Addition of heparin to the virus culture inhibited syncytial plaque formation due to respiratory syncytial virus (RSV). Moreover, pretreatment of the virus with heparinase or an inhibitor of heparin, protamine, greatly reduced virus infectivity. Two anti-heparan sulfate antibodies stained RSV-infected cells, but not noninfected cells, by immunofluorescence. One of the antibodies was capable of neutralizing RSV infection in vitro. These results prove that heparin-like structures identified on RSV play a major role in early stages of infection. The RSV G protein is the attachment protein. Both anti-heparan sulfate antibodies specifically bound to this protein. Enzymatic digestion of polysaccharides in the G protein reduced the binding, which indicates that heparin-like structures are on the G protein. Such oligosaccharides may therefore participate in the attachment of the virus.

Ion-pair high-performance liquid chromatography for determining disaccharide composition in heparin and heparan sulphate

In this report we describe a convenient and sensitive HPLC method for separating and determining the non- and variously sulphated delta-disaccharides derived from heparan sulphate, heparin and Fragmin, using heparin- and heparan sulphate lyases. This method is superior to others since it can separate and determine twelve different non-, mono-, di- and trisulphated delta-disaccharides containing either N-sulphated, N-acetylated or unsubstituted glucosamine in a single HPLC run. The various types of delta-disaccharides are separated by an ion-pair reversed-phase chromatographic procedure on a Supelcosil LC-18 column, using a binary acetonitrile gradient system with tetrabutylammonium as the ion-pairing reagent. The eluted peaks were recorded by dual wavelength at 232 and 226 nm and a linear detector response was obtained over the entire interval tested, i.e., to 50 micrograms of delta-disaccharides. As little as 0.8-5 ng of delta-disaccharides can be reliably detected and accurately determined. Following separate digestion with the heparin- and heparan sulphate lyases (heparin lyases I, II and III), the characteristic heparin delta-disaccharides in the heparan sulphate chain, as well as the heparan sulphate delta-disaccharides in the heparin polymer, can be identified. Using combined digestions with these three lyases, the glycosaminoglycan chains are degraded almost completely (> 90%) to delta-disaccharides, which are then determined by direct injections into the HPLC system and thus an almost complete spectrum of disaccharide composition can be obtained. By this method, it is possible to analyse and confirm that the heparan sulphate chain is defined as a glycosaminoglycan dominated by GlcNAc(+/- 6S)-GlcA disaccharides and by some copolymeric disaccharides, such as GlcNS-IdoA2S and GlcNS6S-IdoA2S, otherwise most common in heparin. Fragmin, which is a controlled cepolymerized heparin fragment of M(r) 5000, is made up mainly of trisulphated disaccharides of the GlcNS6S-IdoA2S type (88.8%). Using separate digestions with the specific heparin lyases, one can also distinguish between heparin and heparan sulphate.

Heparinase-II-catalyzed degradation of N-propionylated heparin

Currently there is great interest in the preparation of modified heparins and heparin-like polymers that possess specific and useful bioactivities. This paper demonstrates the potential of a particularly versatile endopolysaccharide lyase (heparinase II) as an analytical tool with which to assess both the chemical modification occurring during synthesis of such polymers and the actual primary structure of the final product of the enzyme activity. Additionally, the work widens our knowledge of the specificity range of this enzyme. The study involved a novel derivative of heparin containing the unnatural N-propionyl group, which was prepared from de-N-sulfated heparin. The extent of the chemical modification was followed throughout the preparation process by incubating samples with heparinase II and analyzing, with HPLC, the products of degradation catalyzed by the enzyme.

High performance capillary electrophoresis method to characterize heparin and heparan sulfate disaccharides

A rapid, sensitive and accurate high-performance capillary electrophoresis method is described for the determination of the sulfation pattern of heparin and heparan sulfate disaccharides. The analysis, performed after enzymic degradation of the polysaccharides with heparinase and heparinases II and III in combination, yields highly UV-absorbing delta-disaccharides. The separation is performed with reversed polarity using 15 mM phosphate buffer, pH 3.50. This method is superior to others since all known 12 disaccharides carrying N-acetylated, N-sulfated or unsubstituent glucosamine can be separated in a single run of 15 min. At the highest sensitivity the analysis consumes only a few femtograms of glycosaminoglycan and allows a determination of delta-disaccharides at the attomole level.

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.

Enzymatic degradation of glycosaminoglycans

Glycosaminoglycans (GAGs) play an intricate role in the extracellular matrix (ECM), not only as soluble components and polyelectrolytes, but also by specific interactions with growth factors and other transient components of the ECM. Modifications of GAG chains, such as isomerization, sulfation, and acetylation, generate the chemical specificity of GAGs. GAGs can be depolymerized enzymatically either by eliminative cleavage with lyases (EC 4.2.2.-) or by hydrolytic cleavage with hydrolases (EC 3.2.1.-). Often, these enzymes are specific for residues in the polysaccharide chain with certain modifications. As such, the enzymes can serve as tools for studying the physiological effect of residue modifications and as models at the molecular level of protein-GAG recognition. This review examines the structure of the substrates, the properties of enzymatic degradation, and the enzyme substrate-interactions at a molecular level. The primary structure of several GAGs is organized macroscopically by segregation into alternating blocks of specific sulfation patterns and microscopically by formation of oligosaccharide sequences with specific binding functions. Among GAGs, considerable dermatan sulfate, heparin and heparan sulfate show conformational flexibility in solution. They elicit sequence-specific interactions with enzymes that degrade them, as well as with other proteins, however, the effect of conformational flexibility on protein-GAG interactions is not clear. Recent findings have established empirical rules of substrate specificity and elucidated molecular mechanisms of enzyme-substrate interactions for enzymes that degrade GAGs. Here we propose that local formation of polysaccharide secondary structure is determined by the immediate sequence environment within the GAG polymer, and that this secondary structure, in turn, governs the binding and catalytic interactions between proteins and GAGs.

Disaccharide composition of heparan sulfates: brain, nervous tissue storage organelles, kidney, and lung

We have characterized the structural properties of heparan sulfates from brain and other tissues after depolymerization with a mixture of three heparin and heparan sulfate lyases from Flavobacterium heparinum. The resulting disaccharides were separated by HPLC and identified by comparison with authentic standards. In rat, rabbit, and bovine brain, 46-69% of the heparan sulfate disaccharides are N-acetylated and unsulfated, and 17-21% contain a single sulfate residue in the form of a sulfoamino group. In rabbit, bovine, and 1-day postnatal rat brain, disaccharides containing both a sulfated uronic acid and N-sulfate account for an additional 10-14%, together with smaller and approximately equal proportions (5-9%) of mono-, di-, and trisulfated disaccharides having sulfate at the 6-position of the glucosamine residue. Kidney and lung heparan sulfates are distinguished by high concentrations of disaccharides containing 6-sulfated N-acetylglucosamine residues. In chromaffin granules, the catecholamine- and peptide-storing organelles of adrenal medulla, where heparan sulfate accounts for a minor portion (5-10%) of the glycosaminoglycans, we have determined that bovine chromaffin granule membranes contain heparan sulfate in which almost all of the disaccharides are either unsulfated (71%) or monosulfated (18%). In sympathetic nerves, norepinephrine is stored in large dense cored vesicles that in biochemical composition and properties closely resemble adrenal chromaffin granules. However, in contrast to chromaffin granules, heparan sulfate accounts for approximately 75% of the total glycosaminoglycans in large dense-cored vesicles and more closely resembles heparin, insofar as it contains only 21% unsulfated disaccharides, 10% mono- and disulfated disaccharides, and 69% trisulfated disaccharides.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of heparins with different relative molecular masses (from 11,600 to 1600) by various analytical techniques

Heparin was extracted and purified from beef intestinal mucosa, and its structure and physico-chemical properties, e.g. disaccharide pattern (by specific enzymatic cleavage), relative molecular mass and sulfate-to-carboxyl ratio, were evaluated by different techniques. Heparin fractions with different relative molecular mass (from M(r) = 7560 to M(r) = 1600) were prepared by chemical degradation and gel-permeation chromatography. The fractions were characterized with respect to relative molecular mass, disaccharide pattern, sulfate-to-carboxyl ratio and percentage of slow moving and fast moving components by agarose-gel electrophoresis. The percentage of the two heparin species was calculated by densitometric analysis and specific calibration curves. The amount of the slow moving component decreases with relative molecular mass. The disaccharide pattern is different for the two heparin fractions. The percentage of trisulfated disaccharide decreases and the amount of mono- and disulfated disaccharides increases with a decrease of the relative molecular mass. The charge density, evaluated as the sulfate-to-carboxyl ratio, also decreases with the molecular mass of the fractions. This study confirms the heterogeneity of the structure, as evaluated by the constituent disaccharides, of the physico-chemical properties, such as relative molecular mass and charge density, and of the relative amount of the two heparin components also for low molecular mass heparins particularly produced by chemical depolymerization in the presence of free radicals.