Structure of heparan sulfate and dermatan sulfate

Effects of different doses of soy isoflavones on bone tissue of ovariectomized rats

AIM

Studies report that hormone replacement prevents osteoporosis, but there are doubts whether isoflavones are really efficient in this process. The aim of this study was to evaluate the effects of different doses of soy isoflavones on bone tissue of ovariectomized rats.

METHODS

Forty female rats at the age of 6 months were ovariectomized and, after 3 months, the animals were divided into four groups: GI - Control (treated with drug vehicle); GII - treated with isoflavones (80 mg/kg per day); GIII - treated with isoflavones (200 mg/kg per day) and GIV - treated with isoflavones (350 mg/kg per day). Soy isoflavones were administered by gavage for 90 consecutive days. After treatment, the rats were euthanized and their distal femurs were removed for histological routine, histochemistry and biochemical study. Histological sections were stained with hematoxylin-eosin or subjected to picrosirius red and alcian blue methods. Shafts of femurs were submitted to biochemical assay and tibias were subjected to biophysical and biomechanical tests.

RESULTS

In distal femurs, the trabecular bone volume was higher in the groups treated with isoflavones, being higher in GIV, while the cortical bone width and the presence of mature type I collagen fibers were higher in GII. At the trabecular bone region, the percentage of total glycosaminoglycans (GAGs) was higher in GII and the percentage of only sulfated GAGs was higher in GIII, while the higher content of chondroitin sulfate in shafts of femurs was seen in GIV. Biophysical and biomechanical tests in tibias did not differ among the groups.

CONCLUSION

Our data indicate that soy isoflavones improve bone quality in femurs of rats by increasing histomorphometric parameters, the content of GAGs and mature type I collagen fibers. These positive effects are dose-dependent and it was different in cortical and trabecular bone.

Marine sulfated glycans with serpin-unrelated anticoagulant properties

Marine organisms are a rich source of sulfated polysaccharides with unique structures. Fucosylated chondroitin sulfate (FucCS) from the sea cucumber Ludwigothurea grisea and sulfated galactan from the red alga Botryocladia occidentalis are one of these unusual molecules. Besides their uncommon structures, they also exhibit high anticoagulant and antithrombotic effects. Earlier, it was considered that the anticoagulant activities of these two marine glycans were driven mainly by a catalytic serpin-dependent mechanism likewise the mammalian heparins. Its serpin-dependent anticoagulant action relies on promoting thrombin and/or factor Xa inhibition by their specific natural inhibitors (the serpins antithrombin and heparin cofactor II). However, as opposed to heparins, these two previously mentioned marine glycans were proved still capable in promoting coagulation inhibition using serpin-free plasmas. This puzzle observation was further investigated and clearly demonstrated that the cucumber FucCS and the red algal sulfated galactan have an unusual serpin-independent anticoagulant effect by inhibiting the formation of factor Xa and/or thrombin through the procoagulants tenase and prothrombinase complexes, respectively. These marine polysaccharides with unusual anticoagulant effects open clearly new perspectives for the development of new antithrombotic drugs as well as push the glycomics project.

Effects of soy isoflavones and mechanical vibration on rat bone tissue

OBJECTIVE

To investigate the effects of soy isoflavones (Iso) and mechanical vibration treatments alone or combined on bone extracellular matrix constituents of ovariectomized rats.

METHODS

Forty female Wistar rats at the age of 6 months were ovariectomized (Ovx) and ten were sham-operated (sham). After 3 months, the animals were divided into five groups: GI (sham); GII (Ovx); GIII, ovariectomized and orally treated with isoflavones (200 mg/kg) for 90 consecutive days; GIV, ovariectomized and submitted to vibration for 90 days (5 days/week); GV, ovariectomized and treated with isoflavones plus vibration. After treatments, the rats were euthanized, and their femurs were removed for histological routine and biochemical study. Histological sections were stained with hematoxylin-eosin, picrosirius red and alcian blue. Shaft of femurs were submitted to biochemical assay and tibias were subjected to biophysical and biomechanical tests.

RESULTS

Treatments did not have significant effects on the trabecular bone volume, but the combined treatments showed trophic effects on the cortical bone width and area. Bone density and the content of organic material of the tibias were higher in the GIV and GV groups. The GV group showed the highest presence of mature collagen fibers and content of total glycosaminoglycans, while the highest contents of chondroitin sulfate and other sulfated glycosaminoglycans were seen in the GIV group.

CONCLUSION

The mechanical vibration treatment is more efficient than soy isoflavones in improving bone quality by increasing the bone density, the content of sulfated glycosaminoglycans and the presence of mature collagen fibers. In addition, the combined interventions have partial trophic and synergistic effects that are bone site-specific in ovariectomized rats.

Fibrinogen, riboflavin, and UVA to immobilize a corneal flap--molecular mechanisms

PURPOSE

Tissue glue containing fibrinogen (FIB) and riboflavin (RF), upon exposure to long wavelength ultraviolet light (UVA, 365 nM) has been proposed potentially to solve long-standing problems presented by corneal wound and epithelial ingrowth side-effects from laser-assisted in situ keratomileuis (LASIK). Data presented in a previous study demonstrated an ability of FIB + RF + UVA to adhere two stromal surfaces; however, to our knowledge no molecular mechanisms have been proposed to account for interactions occurring between corneal extracellular matrix (ECM) and tissue glue molecules. Here, we document several covalent and noncovalent interactions between these classes of macromolecules.

METHODS

SDS-PAGE and Western blot techniques were used to identify covalent interactions between tissue glue molecules and corneal ECM molecules in either the presence or absence of RF and UVA, in vitro and ex vivo. Surface plasmon resonance (SPR) was used to characterize noncovalent interactions, and obtain k(a), k(d), and K(D) binding affinity values.

RESULTS

SDS-PAGE and Western blot analyses indicated that covalent interactions occurred between neighboring FIB molecules, as well as between FIB and collagen type I (Coll-I) proteins (in vitro and ex vivo). These interactions occurred only in the presence of RF and UVA. SPR data demonstrated the ability of FIB to bind noncovalently to corneal stroma molecules, Coll-I, decorin, dermatan sulfate, and corneal basement membrane molecules, laminin and heparan sulfate--only in the presence of Zn(2+).

CONCLUSIONS

Covalent and (zinc-mediated) noncovalent mechanisms involving FIB and stromal ECM molecules contribute to the adhesion created by FIB + RF + UVA.

Cloning, expression and characterization of acharan sulfate-degrading heparin lyase II from Bacteroides stercoris HJ-15

AIMS

This study focused on the cloning, expression and characterization of recombinant heparinase II (rHepII) from Bacteroides stercoris HJ-15.

METHODS AND RESULTS

The heparinase II gene from Bact. stercoris HJ-15 was identified by Southern blotting and the sequence was deposited in GenBank. The gene was cloned and overexpressed in Escherichia coli, and rHepII was purified using two simple ion-exchange column chromatography steps. Enzymatic properties and substrate specificities of rHepII were assessed and its kinetic constants were calculated. Heparin-like glycosaminoglycans (HLGAGs) were digested with rHepII under optimal reaction conditions, and the products were analysed by SAX-HPLC.

CONCLUSIONS

The heparinase II gene is 2322-bp long and consists of 773 amino acids. rHepII is most active in 50 mmol l(-1) sodium phosphate buffer with 75 mmol l(-1) NaCl (pH 7.4) at 32 degrees C, and the activity is stable at 4 degrees C for 15 days on storage. Acharan sulfate is the best substrate for rHepII, followed by heparan sulfate and heparin. The major degradation products were verified as highly sulfated disaccharides through SAX-HPLC analysis. It means that rHepII prefers iduronic acid over glucuronic acid on the HLGAG structure.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides easy and certain means for obtaining large amounts of pure rHepII and also provides important information regarding the tendencies of this enzyme and its digested products. rHepII digests HLGAGs in a different manner than heparinases from Flavobacterium heparinum; therefore, we anticipate that rHepII will be a powerful tool for studies of GAGs and GAGs lyases.

Cloning, overexpression, and characterization of recombinant heparinase III from Bacteroides stercoris HJ-15

Recombinant heparinase III (rHepIII) from Bacteroides stercoris HJ-15 was cloned, expressed, and characterized. The full-length heparinase III gene from B. stercoris HJ-15 was identified by Southern blotting, and the sequence was deposited in GenBank. The heparinase III gene, which is 2,001-bp long, was cloned and overexpressed in Escherichia coli; highly active rHepIII was easily purified using only one step of immobilized Ni(2+) affinity column chromatography. Enzymatic properties and substrate specificities of rHepIII were assessed, and its kinetic constants were calculated. rHepIII was most active in 50 mM sodium phosphate buffer with 350 mM NaCl (pH 6.6) at 45 degrees C. Through amino acid modification studies and site-directed mutagenesis assay, cysteines and histidines were identified as crucial residues for enzymatic activity. Moreover, this enzyme digested not only heparan sulfate but also heparin and hyaluronic acid, and their degradation products were verified by strong anion exchange/high-performance liquid chromatography. These characteristics, including active residues and substrate specificities were interesting compared with those of existing heparinase III from other species. We anticipate that the convenience of purification and the characteristics of this enzyme will make it a powerful tool for studies of glycosaminoglycans and their lyases.

Thermodynamic studies and binding mechanisms of cell-penetrating peptides with lipids and glycosaminoglycans

Cell-penetrating peptides (CPPs) traverse the membrane of biological cells at low micromolar concentrations and are able to take various cargo molecules along with. Despite large differences in their chemical structure, CPPs share the structural similarity of a high cationic charge density. This property confers to them the ability to bind electrostatically membrane constituents such as anionic lipids and glycosaminoglycans (GAGs). Controversies exist, however, about the biological response after the interaction of CPPs with such membrane constituents. Present review compares thermodynamic binding studies with conditions of the biological CPP uptake. It becomes evident that CPPs enter biological cells by different and probably competing mechanisms. For example, some amphipathic CPPs traverse pure lipid model membranes at low micromolar concentrations--at least in the absence of cargos. In contrast, no direct translocation at these conditions is observed for non-amphipathic CPPs. Finally, CPPs bind GAGs at low micromolar concentrations with potential consequences for endocytotic pathways.

Analysis of plasma proteins that bind to glycosaminoglycans

Glycosaminoglycan-binding proteins, with specific emphasis on dermatan sulfate, have been investigated in human plasma by affinity chromatography, mass spectrometry and Western blotting. Diluted plasma was applied to affinity columns and bound protein was eluted with 500 mM NaCl. Dermatan sulfate and heparan sulfate bound 7% of the total protein. Heparin bound 22% of the total protein, but chondroitin sulfate A bound only 0.23%. Mass spectrometric analysis identified 20 proteins as dermatan-sulfate-binding proteins, most of which were confirmed by Western blotting. Some of these binding proteins, such as fibrinogen, fibronectin, apolipoprotein B, LMW kininogen, inter-alpha-trypsin inhibitor, and factor H, were degraded to various extents during the chromatography step, but this degradation could be prevented by the inclusion of a serine protease inhibitor. The protein fraction binding to the dermatan sulfate column showed amidase activity, whereas that binding to the heparan sulfate and heparin columns showed 1/2 and 1/20, respectively, of the activity of the dermatan sulfate binding fraction. Dermatan sulfate was similar to heparan sulfate with respect to its capacity to bind plasma proteins and its activation of protease, but differed from chondroitin sulfate and heparin in these properties.

Purification and characterization of heparin lyase I from Bacteroides stercoris HJ-15

Heparin lyase I was purified to homogeneity from Bacteroides stercoris HJ-15 isolated from human intestine, by a combination of DEAE-Sepharose, gel-filtration, hydroxyapatite, and CM-Sephadex C-50 column chromatography. This enzyme preferred heparin to heparan sulfate, but was inactive at cleaving acharan sulfate. The apparent molecular mass of heparin lyase I was estimated as 48,000 daltons by SDS-PAGE and its isoelectric point was determined as 9.0 by IEF. The purified enzyme required 500 mM NaCl in the reaction mixture for maximal activity and the optimal activity was obtained at pH 7.0 and 50 degrees C. It was rather stable within the range of 25 to 50 degrees C but lost activity rapidly above 50 degrees C. The enzyme was activated by Co(2+) or EDTA and stabilized by dithiothreitol. The kinetic constants, K(m) and V(max) for heparin were 1.3 10(-5) M and 8.8 micromol/min.mg. The purified heparin lyase I was an eliminase that acted best on porcine intestinal heparin, and to a lesser extent on porcine intestinal mucosa heparan sulfate. It was inactive in the cleavage of N-desulfated heparin and acharan sulfate. In conclusion, heparin lyase I from Bacteroides stercoris was specific to heparin rather than heparan sulfate and its biochemical properties showed a substrate specificity similar to that of Flavobacterial heparin lyase I.

Effects of low molecular weight chondroitin sulfate on type II collagen-induced arthritis in DBA/1J mice

In order to evaluate the improvement in the treatment of chronic arthritis, we investigated chondroitin sulfate depolymerization product (low molecular weight chondroitin sulfate, LMWCS) and intact chondroitin sulfate (CS) in vitro and in vivo. LMWCS was prepared by a chemical depolymerization process induced by hydrogen peroxide in the presence of copper salts. LMWCS (300 mg/kg) and CS (1200 mg/kg) were orally administered to DBA/1J mice once daily for 14 d prior to initial immunization with type II collagen. Their elastase activities and the production of cytokines in sera were examined on type II collagen-induced arthritis in DBA/1J mice. We also compared the paracellular transport of LMWCS and CS across Caco-2 cell monolayers and examined the inhibitory effects on elastase activities. LMWCS inhibited elastase activity slightly, but CS did not show inhibition. Hind paw edema was significantly decreased by LMWCS treatment. Levels of anti-type II collagen antibody and tumor necrosis factor-alpha (TNF-alpha) in sera were also reduced by LMWCS treatment but not in case of CS, although no significant difference was observed between LMWCS and CS on interleukin-6 (IL-6) induction. The LMWCS preparation showed preventive effects on the type II collagen-induced arthritis in DBA/1J mice and better permeability through Caco-2 cells.

Effect of heparin on antigen-induced airway responses and pulmonary leukocyte accumulation in neonatally immunized rabbits

The effect of single administrations of aerosolized heparin, low molecular weight heparin (LMWH) and the linear polyanionic molecule, polyglutamic acid (PGA) were examined on antigen-induced airway hyperresponsiveness and leukocyte accumulation in neonatally immunized rabbits. Adult litter-matched NZW rabbits immunized within 24 h of birth with Alternaria tenuis antigen were treated with heparin, LMWH or PGA prior to or following antigen challenge (Alternaria tenuis). For each drug-treated group, a parallel group of rabbits were treated with the appropriate vehicle. In all groups, airway responsiveness to inhaled histamine and bronchoalveolar lavage (BAL) was performed 24 h prior to and following antigen challenge. Basal lung function in terms of resistance (R(L)) and dynamic compliance (C(dyn)) and acute bronchoconstriction was unaltered by pre-treatment with heparin, LMWH or PGA compared to their respective vehicles 24 h prior to or following antigen challenge. In vehicle-treated animals, airway hyperresponsiveness to inhaled histamine was indicated by an increase in the maximal responses of the cumulative concentration-effect curves to histamine and reductions in R(L)PC(50) and C(dyn)PC(35) values 24 h following antigen challenge. Heparin and LMWH given prior to antigen challenge significantly inhibited the development of airway hyperresponsiveness, whereas PGA did not. When given following antigen challenge, all three drugs failed to inhibit the development of airway hyperresponsiveness. Eosinophil and neutrophil cell numbers in BAL fluid increased significantly 24 h following antigen challenge. Heparin, LMWH and PGA failed to inhibit the increase in cell numbers following antigen challenge whether given prior to or following antigen challenge.

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.

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.

Structural characterization and functional effects of a circulating heparan sulfate in a patient with hepatocellular carcinoma

A circulating anticoagulant was isolated from the plasma of a 42-year-old man with cirrhosis and hepatocellular carcinoma who had an unusual coagulation test profile. The patient developed a fatal coagulopathy, unresponsive to protamine therapy or plasma exchange following liver biopsy. However, at presentation, routine hemostasis assays were normal. The patient had mucocutaneous bleeding but the sole laboratory abnormality was a prolonged thrombin time (TT = 99 s, normal 25-35 s). Protamine titration indicated activity equivalent to a heparin concentration of 6-7 U/ml. Antithrombin III (AT III) antigen and activity were markedly elevated. The anticoagulant activity, purified from plasma by DEAE chromatography, was identified as a glycosaminoglycan (GAG). GAG anti-thrombin activity was completely abolished by heparin lyase III. Based on the degree of sulfation and HPLC pattern, the GAG was classified as heparan sulfate. Low levels (4 microM) of purified GAG markedly prolonged the TT (>120 s) but not the activated partial thromboplastin time (PTT) (31.4 s). In a Factor Xa assay, the GAG exhibited a potency equivalent to 0.06 U of low molecular weight heparin per nmol of uronic acid. Patients with endogenous circulating glycosaminoglycans can present with unusual laboratory coagulation test profiles. These reflect complex dysfunction of hemostasis, leading to difficulty in providing diagnosis and effective care.

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.

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.

Fluorescence and circular dichroism studies during the interactions of sulfated polysaccharides with antithrombin III

The changes in relative fluorescence of antithrombin III (AT-III) during its interaction with sulfated xylans were compared with that of sulfated glycosaminoglycans by measuring the ratio of the increase in fluorescence of AT-III in the presence of sulfated polysaccharide to the fluorescence of AT-III alone for various mass ratios. Interactions of corn cob xylan sulfate (CCXS) and sodium pentosan polysulfate (SP-54) with AT-III resulted in enhancements of relative fluorescence which were lower than commercial heparin. At mass ratios below 1, heparan sulfate and low molecular weight heparin (LMWH) gave increases in the relative fluorescence higher than that of commercial heparin, while highly sulfated semisynthetic chondroitin sulfates A and C gave much smaller increases. The relative fluorescence enhancements of AT-III by heparan sulfate, commercial heparin, LMWH and heparin derived pentasaccharide (HDP) increased with increasing mass ratios while the enhancements by CCXS, SP-54 and the highly sulfated chondroitin sulfates A and C were reversed at higher mass ratios. The estimated dissociation constants (kd) for the interaction of AT-III and the heparin-related compounds showed that heparin sulfate and LMWH gave the lowest kd values indicating a higher affinity for AT-III while commercial heparin and HDP gave higher kd values, indicating a lower affinity for AT-III. SP-54 gave a kd value lower than CCXS, indicating a greater affinity for AT-III. A comparison of the near ultraviolet (UV) circular dichroism (CD) spectrum of AT-III alone and during its interaction with oat spelts xylan sulfate (OSXS) showed enhancements of the two aromatic amino acid regions corresponding to phenylalanine and tryptophan.

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.

A stereochemical approach to pyranose ring flexibility: its implications for the conformation of dermatan sulfate

Glycosaminoglycans, such as heparin, heparan sulfate, and dermatan sulfate, are characterized by a disaccharide repeating unit of a uronate and a hexosamine and are increasingly understood to be important physiologically as soluble components of the extracellular matrix. The secondary structure of this class of acidic polysaccharides is believed to play a key role in determining the wide range of biological specificities. Central to the structural diversity of the glycosaminoglycans is the experimentally documented conformational flexibility of the iduronate residue. Here, we outline an approach to explore the iduronate conformational flexibility by imposing stereochemical criteria of nonbonded contact distances. By performing a complete search of all possible torsions that define the iduronate ring geometry, we eliminate any prior bias with regard to minimum energy conformers. The approach led to alternative feasible conformers for the iduronate ring that are stereochemically satisfactory and are consistent with the available physico-chemical data.

Preliminary chemical, biochemical, and pharmacological characterization of a low molecular weight dermatan sulphate

The aim of this study was to set up a depolymerization process which resulted in the formation of a low molecular weight dermatan sulphate (LMWDS), retaining the chemical properties possessed by native dermatan sulphate (DS), fundamental for the expression of its specific biological activity. The depolymerization of DS by a beta elimination process led to the production of oligosaccharide chains having a 4,5 unsaturated uronic acid at the nonreducing end. The chemical evaluation has shown that the most important parameters (degree of sulphation, sulphate to carboxyl ratio, and specific rotation) have not undergone any particular modification compared to native DS. The biochemical results demonstrate that the LMWDS obtained retains most, if not all, of the specific biological activity. The reduction in molecular weight significantly enhanced the bioavailability of the product after subcutaneous administration.

Morphological and biochemical analyses of amyloid plaque core proteins purified from Alzheimer disease brain tissue

Amyloid plaque cores were purified from Alzheimer disease brain tissue. Plaque core proteins were solubilized in formic acid which upon dialysis against guanidinium hydrochloride (GuHCl) partitioned into soluble (approximately 15%) and insoluble (approximately 85%) components. The GuHCl-soluble fraction contained beta-amyloid1-40, whereas the GuHCl-insoluble fraction was fractionated into six components by size exclusion HPLC: S1 (> 200 kDa), S2 (200 kDa), S3 (45 kDa), S4 (15 kDa), S5 (10 kDa), and S6 (5 kDa). Removal of the GuHCl reconstituted 10-nm filaments composed of two intertwined 5-nm strands. Fractions S5 and S6 also yielded filamentous structures when treated similarly, whereas fractions S1-S4 yielded amorphous aggregates. Chemical analysis identified S4-S6 as multimeric and monomeric beta-amyloid. Immunochemical analyses revealed alpha 1-antichymotrypsin and non-beta-amyloid segments of the beta-amyloid precursor protein within fractions S1 and S2. Several saccharide components were identified within plaque core protein preparations by fluorescence and electron microscopy, as seen with fluorescein isothiocyanate- and colloidal gold-conjugated lectins. We have shown previously that this plaque core protein complex is more toxic to neuronal cultures than beta-amyloid. The non-beta-amyloid components likely mediate this additional toxicity, imposing a significant influence on the pathophysiology of Alzheimer disease.

"Fast moving" and "slow moving" heparins, dermatan sulfate, and chondroitin sulfate: qualitative and quantitative analysis by agarose-gel electrophoresis

Heparin from beef intestinal mucosa, dermatan sulfate from beef intestinal mucosa, and chondroitin sulfate from bovine trachea were extracted and purified, and their structures and physico-chemical properties were evaluated by different techniques (disaccharide patterns by specific enzymatic cleavage, relative molecular mass by high-performance size-exclusion chromatography, sulfate-to-carboxyl ratio by potentiometric determination). Heparin was fractionated into "slow moving" and "fast moving" fractions by selective precipitation as the barium salt at different temperatures. The "fast moving" and "slow moving" components of heparin, dermatan sulfate, and chondroitin sulfate were utilized to run calibration curves in agarose-gel electrophoresis. Mixtures containing different amounts of these glycosaminoglycans were made and separated by agarose-gel electrophoresis, and these were analyzed quantitatively. For analysis of relative amounts, the area of each individual component of mixtures, obtained by photodensitometric readings, was divided by the sum of the areas of all glycosaminoglycans and expressed as a percentage. For analysis of absolute amounts, the area under the curve for each component of mixtures was fitted to specific calibration curves, and the amount of each glycosaminoglycan was calculated in micrograms. The quantitative procedure performed by analysing absolute amounts was used to obtain an accurate quantitative evaluation of each component in mixtures of glycosaminoglycans utilized for pharmaceutical purposes. A sensitive method was developed for the evaluation of very small amounts (0.2% w/w) of possible glycosaminoglycans as contaminants in preparations of a single species of glycosaminoglycan. This technique requires specific enzymatic degradation by bacterial lyases, separation in agarose-gel electrophoresis, and quantitative analysis by photodensitometric analysis and specific calibration curves.

Glycosaminoglycans and proteins: different behaviours in high-performance size-exclusion chromatography

The influence of the conformation of globular proteins and glycosaminoglycans in high-performance size-exclusion chromatography (HPSEC) was studied. Glycosaminoglycans (heparin, chondroitin sulphate and dermatan sulphate) with different primary structures, sulphate-to-carboxyl ratios and physico-chemical properties were extracted and purified. Their physico-chemical properties and purity were evaluated by several analytical techniques. Glycosaminoglycans with different relative molecular masses (M(r)) were prepared by a chemical depolymerization process. These heteropolysaccharides were evaluated by HPSEC and compared with globular proteins of known relative molecular mass. The two third-degree polynomial regression curves for proteins and glycosaminoglycans have different coefficients and the columns present different exclusion limits. In particular, under the experimental conditions, the M(r) exclusion limits for high M(r) are 44,000 for glycosaminoglycans and 240,000 for globular proteins. In contrast, the behaviours of these two classes of macromolecules are similar for lower M(r). In fact, the two third-degree polynomial curves show the same regression below about M(r) = 1000. The behaviour in HPSEC is discussed in relation to the different steric conformations for proteins and glycosaminoglycans with different relative molecular masses.

Pharmacological profile of a native dermatan sulfate

We performed different "in vivo" investigations to study the pharmacological properties of a native DS: anti-thrombosis by the stasis model, bleeding potential by tail transection bleeding time and template bleeding time, and profibrinolysis by a growing thrombus model and by an established thrombus model. The results suggest that DS is a safe antithrombotic drug by i.v. administration without bleeding potential, even at very high doses (up to 16 mg/Kg). DS has shown a protective index of at least 4 in contrast to heparin that has shown a protective index of 1. The profibrinolytic models so far studied did not evidence a clear profibrinolytic contribution to the antithrombotic properties of DS, but showed a prolonged antithrombotic action that cannot be explained only by the heparin cofactor II potentiation.

Recombinant human thrombomodulin. Regulation of cofactor activity and anticoagulant function by a glycosaminoglycan side chain

Two glycoforms of a secretable human thrombomodulin mutant [TMD1-105 and TMD1-75; Parkinson, Grinnell, Moore, Hoskins, Vlahos & Bang (1990) J. Biol. Chem. 265, 12602-12610] were expressed in human 293 cells and used to study the role of glycosylation in the functions of this endothelial-cell thrombin receptor. Carbohydrate content analysis and intrinsic labelling with [3H]glucosamine and [35S]sulphate showed that TMD1-105 contained a chondroitin sulphate whereas TMD1-75 did not. Other than chondroitin sulphate, the carbohydrate contents of the two glycoforms were identical, indicating similar glycosylation patterns at other O-linked and N-linked sites in the two glycoforms. The properties of TMD1-105 were converted into those of TMD1-75 by chondroitin ABC lyase digestion. Trypsin digestion of labelled TMD1-105 permitted isolation of two overlapping peptides that contained chondroitin sulphate, spanned the entire O-glycosylation domain and had O-glycosylation sites at Ser-492, Ser-498, Thr-500, Thr-504 and Thr-506. The chondroitin sulphate-attachment site was assigned to Ser-492 as this residue is conserved in mouse and bovine thrombomodulin and lies within a sequence Ser-Gly-Ser-492-Gly-Glu-Pro, which has strong similarity to chondroitin sulphate attachment sites in other proteoglycans. Five peptides with N-linked carbohydrate were also isolated and contained glycosylation sites in the lectin-like domain (Asn-47, Asn-115, Asn-116) and in the fourth (Asn-382) and fifth (Asn-409) epidermal growth factor domains. The role of N-linked and simple O-linked carbohydrates in the functions of human thrombomodulin remain unclear. The present studies demonstrate, however, that the presence of chondroitin sulphate in human thrombomodulin has profound effects on all of the anticoagulant properties of this important anticoagulant thrombin receptor.

Complex carbohydrates in drug development

Recent advances in carbohydrate chemistry and biochemistry afford the opportunity to develop bioactive complex carbohydrates, per se, as drugs or as lead compounds in drug development. Complex carbohydrates are unique among biopolymers in their inherent potential to generate diverse molecular structures. While proteins vary only in the linear sequence of their monomer constituents, individual monosaccharides can combine at any of several sites on each carbohydrate ring, in linear or branched arrays, and with varied stereochemistry at each linkage bond. This chapter addresses some salient features of mammalian glycoconjugate structure and biosynthesis, and presents examples of the biological activities of complex carbohydrates. The chapter presents selected examples that will provide an accurate introduction to their pharmacological potential. In addition to their independent functions, oligosaccharides can modify the activities of proteins to which they are covalently attached. Many glycoprotein enzymes and hormones require glycosylation for expression and function. The chapter discusses the ancillary role of carbohydrates that is of great importance to the use of engineered glycoproteins as pharmaceuticals.