A simple and rapid electrophoretic method for the separation of glucuronic acid and iduronic acid.
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Animals↗
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Urinary glycosaminoglycans bearing glucuronic acid or iduronic acid residue at the reducing terminals.
The urinary glycosaminoglycan was reduced with NaB[3H]4, and was separated into three fractions according to molecular size by column chromatography on Sephadex G-200. The hexuronic acid residues at the reducing terminals of each fraction were quantified by the method of preferential quantitation of hexuronic acid at the reducing terminals. This method consisted of hydrolysis with trifluoroacetic acid and nitrous acid, lactonization, and paper chromatographic analysis. Both radioactive gulonolactone and idonolactone were detected in the fractions with a lower molecular size, but not in those with a higher molecular size. These observations demonstrated that the glucuronide and iduronide linkages at other-than-terminal sites of carbohydrate chains were cleaved by the processes of depolymerization of glycosaminoglycans in tissues. Therefore, it is highly likely that endo-beta-glucuronidase(s) and endo-alpha-iduronidase(s) which belong to the glycosidase of endo type such as hyaluronidase are involved in the catabolic degradation of glycosaminoglycans in tissues.
Carbohydrate Sequence↗
Metal binding to heparin monosaccharides: D-glucosamine-6-sulphate, D-glucuronic acid, and L-iduronic acid.
In order to ascertain which residues in heparin may be responsible for its metal binding capacities we have investigated metal binding to some of its component monosaccharides by 1H and 13C NMR. The diamagnetic Zn ion and the paramagnetic Ni ion were used as probes. 4-Methylumbelliferyl-2-deoxy-2-acetamido-6-O-sulpho-D-glucosamine was used as a model for O-sulphates. Only weak interactions with the sulphate group were found. The 4C1 ring conformation of sodium methyl-beta-D-glucopyranosiduronate was not perturbed by binding to its carboxylate and little evidence exists for chelation. By contrast, the ring conformation of the sodium methyl-alpha-L-idopyranosiduronate is affected by the addition of Zn greater than Pb greater than Cd greater than Ca much greater than K ions. The sodium salt is suggested to be an equilibrium mixture of the 2SO and 1C4 ring conformations. Cation binding to the carboxylate group shifts this equilibrium towards the 1C4 conformation and suggests additional binding to O5 or, less likely, O4. This effect appears to be electrostatic in nature, as excess Na and protonation produce similar shifts. Lead complexation is different from the other ions and suggests some covalent character. The control of the ring conformation of iduronic acid by metal ions may have biological implications for the action of heparin and heparin-like compounds.
Cadmium↗
Biosynthesis of dermatan sulfate. I. Formation of L-iduronic acid residues.
L-[14C]Iduronic acid-containing sulfated galactosaminoglycans were formed by incubation of a fibroblast particulate fraction with UDP-D[14C]glucuronic acid, UDP-N-acetylgalactosamine, and sulfate donor (3'-phosphoadenylylsulfate). The formation of L-iduronic acid was strongly promoted by concomitant sulfation of the polymer. In the absence of sulfate donor 5 to 10% of the [14C]uronic acid residues were L-iduronic acid. However, when 3'-phosphoadenylylsulfate was included in the incubation mixture the amount of L-iduronic acid in the product increased 3 to 5-fold. Furthermore, approximately the same quantity of L-[14C]iduronic acid was recovered from the product formed in a pulse-chase experiment where incorporation of 14C-isotope preceded sulfation. It was therefore concluded that C-5 inversion of D-glucuronic acid to L-iduronic acid occurred on the polymer level as shown previously for the biosynthesis of heparin (Hook, M., Lindahl, U., Backstrom, G., Malmstrom, A., AND Fransson, L-A., J. Biol. Chem. (1974) 249, 3908). This conclusion was supported by the finding that no L[14C]iduronic acid could be detected in the UDP-hexuronic acid pool during this experiment. Nonsulfated and sulfated [14C]galactosaminoglycan products were degraded separately with chondroitinase-AC. The non-sulfated products afforded primarily disaccharide and a small amount of tetrasaccharide, while the sulfated products yielded, in addition, a considerable amount of larger oligosaccharides. Tetrasaccharides from nonsulfated products contained L-iduronic acid indicating that C-5 inversion at solitary sites can occur in the absence of sulfation of adjacent hexosamine moieties. The larger oligosaccharides obtained after chondroitinase-AC digestion of sulfated products yielded L-iduronic acid upon acid hydrolysis and were susceptible to chondroitinase-ABC digestion. The split products were almost exclusively 4-sulfated disaccharides. These results demonstrate that formation of blocks of L-iduronic acid-containing repeat periods is associated with 4-sulfation of adjacent hexosamine moieties.
Chondroitin↗
Distribution of sulphate and iduronic acid residues in heparin and heparan sulphate.
1. A method was developed for determination of the uronic acid composition of heparin-like glycosaminoglycans. Polymers or oligosaccharides are degraded to monosaccharides by a combination of acid hydrolysis and deamination with HNO(2). The resulting uronic acid monosaccharides (accounting for about 70% of the uronic acid contents of the starting materials) are isolated and converted into the corresponding aldono-1,4-lactones, which are separated by g.l.c. The calculated ratios of glucuronic acid/iduronic acid are reproducible within 5%. 2. Samples of heparin from pig intestinal mucosa (molar ratio of sulphate/disaccharide unit, 2.40) and heparan sulphate from human aorta (sulphate/disaccharide ratio, 0.46) were subjected to uronic acid analysis. l-Iduronic acid constituted 77% and 19% respectively of the total uronic acid contents. 3. The correlation between the contents of sulphate and iduronic acid indicated by this finding also applied to the fractionated deamination products of the two polymers. The sulphated fragments varied in size from disaccharide to octasaccharide (or larger) and showed sulphate/disaccharide molar ratios in the range of 0.05-2.0. The proportion of iduronic acid increased with increasing ester sulphate contents of the oligosaccharides. 4. Previous studies on the biosynthesis of heparin in a cell-free system have shown that l-iduronic acid residues are formed by C-5 epimerization of d-glucuronic acid units at the polymer level; the process requires concomitant sulphation of the polymer. The results obtained in the present structural study conform to these findings, and suggest further that similar mechanisms may operate in the biosynthesis of heparan sulphate. The epimerization reaction appears to be linked to the sulphation of hydroxyl groups but does not seem to require sulphation of the target uronic acid residues. The significance of sulphamino groups in relation to the formation of iduronic acid is unknown.
Animals↗
Structural diversity of N-sulfated heparan sulfate domains: distinct modes of glucuronyl C5 epimerization, iduronic acid 2-O-sulfation, and glucosamine 6-O-sulfation.
The N-sulfated regions (NS domains) represent the modified sequences of heparan sulfate chains and mediate interactions of the polysaccharide with proteins. We have investigated the relationship between the type/extent of polymer modification and the length of NS domains in heparan sulfate species from human aorta, bovine kidney, and cultured NMuMG and MDCK cells. C5 epimerization of D-glucuronic acid to L-iduronic acid was found to be extensive and essentially similar in all heparan sulfate species studied, regardless of domain size, whereas the subsequent 2-O-sulfation of the formed iduronic acid residues varies appreciably. In aorta heparan sulfate, up to 90% of the formed iduronate residues were 2-O-sulfated, whereas in kidney heparan sulfate 2-O-sulfation occurred only in </=50% of the iduronate residues. The degree of 2-O-sulfation was consistently increased with increasing NS domain length, suggesting a correlation between 2-O-sulfation efficiency and length of the polymeric substrate during heparan sulfate biosynthesis. By contrast, 6-O-sulfation of glucosamine units did not correlate to domain size. 6-O-Sulfation exceeded 2-O-sulfation in NS domains from kidney heparan sulfate, but was very low in aorta heparan sulfate. Remarkably, total O-sulfation of NS domains, i.e., the sum of 2-O- and 6-O-sulfate groups, was highly similar in all heparan sulfate samples investigated. The results reveal marked tissue-specific variation in the sulfation patterns of NS domains and indicate previously unrecognized distinctions in the coordination of the three polymer modification reactions during heparan sulfate biosynthesis.
Acetylglucosamine↗
Epimerization of D-glucuronic acid to L-iduronic acid by deamination of heparins.
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Amines↗
Diagnostic methods for the determination of iduronic acid in oligosaccharides.
A high-performance liquid chromatography (HPLC) method with pulsed amperometric detection (PAD) was used for the determination of the acid hydrolysis products of L-iduronic acid containing oligosaccharides isolated from biological sources. This HPLC-PAD method was compared with gas chromatographic (GLC) methods. Since acid hydrolysis of oligosaccharides can produce a number of products, several uronic acid derivatives were prepared by chemical synthesis. These well characterized standards in conjunction with mass spectrometry allowed for the identification of most of the products of methanolysis or hydrolysis of glycosamino-glycans, which included chondroitin sulfates A and B (dermatan sulfate), heparin, and hyaluronic acid. (4 M) HCl in methanol 100 degrees C for 24 h was found to be optimum for GLC and 1 M aqueous HCl for 4 h at 100 degrees C for HPLC-PAD. All of the monosaccharides, hexosamines, and uronic acids could be separately identified in a single chromatographic step using either technique. Good resolution, high sensitivity (low microgram samples) and rapid analysis makes these methods particularly useful for the determination of small amounts of glycosaminoglycans and other glycoconjugates found in samples isolated from biological sources. These two techniques are specifically designed to allow the qualitative determination of the carbohydrate content and composition of samples whose carbohydrate composition and content is completely unknown.
Chondroitin Sulfates↗
The acid lability of the glycosidic bonds of L-iduronic acid residues in glycosaminoglycans.
Heparan sulphate, heparin and dermatan sulphate were hydrolysed in 0.5M-H2SO4 at 100 degrees C. At intervals portions of the hydrolysate were removed and treated with HNO2 at pH 4.0 to cleave the glycosidic bonds of the N-unsubstituted hexosamine residues and to convert both free and combined hexosamines into anhydrohexoses. These hydrolysis/deamination mixtures were reduced with NaB3H4 and analysed by radiochromatography for alpha-L-iduronosylanhydrohexose, beta-D-glucuronosylanhydrohexose, and the free uronic acids and anhydrohexose. These data gave a kinetic profile of the cleavage of the alpha-L-iduronosyl and the beta-D-glucuronosyl bonds in these glycosaminoglycans. The beta-D-glucuronosyl bonds showed the expected resistance to acid hydrolysis, but the alpha-L-iduronosyl bonds were found to be as labile to acid as some neutral sugar glycosides. This unusual lability of alpha-D-iduronosyl-anhydromannitol and beta-D-glucuronosylanhydromannitol. The procedures used to follow the kinetics of glycosaminoglycan hydrolysis can also be sued to obtain quantitative analyses of L-iduronic acid, D-glucuronic acid and hexosamine in these polymers.
Chemical Phenomena↗
Synthesis of conformationally locked L-iduronic acid derivatives: direct evidence for a critical role of the skew-boat 2S0 conformer in the activation of antithrombin by heparin.
We have used organic synthesis to understand the role of L-iduronic acid conformational flexibility in the activation of antithrombin by heparin. Among known synthetic analogues of the genuine pentasaccharidic sequence representing the antithrombin binding site of heparin, we have selected as a reference compound the methylated anti-factor Xa pentasaccharide 1. As in the genuine original fragment, the single L-iduronic acid moiety of this molecule exists in water solution as an equilibrium between three conformers 1C4, 4C1 and 2S0. We have thus synthesized three analogues of 1, in which the L-iduronic acid unit is locked in one of these three fixed conformations. A covalent two atom bridge between carbon atoms two and five of L-iduronic acid was first introduced to lock the pseudorotational itinerary of the pyranoid ring around the 2S0 form. A key compound to achieve this connection was the D-glucose derivative 5 in which the H-5 hydrogen atom has been replaced by a vinyl group, which is a progenitor of the carboxylic acid. Selective manipulations of this molecule resulted in the 2S0-type pentasaccharide 23. Starting from the D-glucose derivative 28, a covalent two atom bridge was now built up between carbon atoms three and five to lock the L-iduronic acid moiety around the 1C4 chair form conformation, and the 1C4-type pentasaccharide 43 was synthesized. Finally the L-iduronic acid containing disaccharide 58 which, due to the presence of the methoxymethyl substituent at position five adopts a 4C1 conformation, was directly used to synthesize the 4C1-type pentasaccharide 61. The locked pentasaccharide 23 showed about the same activity as the reference compound 1 in an antithrombin-mediated anti-Xa assay, whereas the two pentasaccharides 43 and 61 displayed very low activity. These results clearly establish the critical importance of the 2S0 conformation of L-iduronic acid in the activation of antithrombin by heparin.
Antithrombins↗
Structure of a highly acidic O-specific polysaccharide of lipopolysaccharide of Pseudoalteromonas haloplanktis KMM 223 (44-1) containing L-iduronic acid and D-QuiNHb4NHb.
An acidic O-specific polysaccharide was obtained by mild acid degradation of the lipopolysaccharide isolated by phenol-water extraction of Pseudoalteromonas haloplanktis strain KMM 223 (44-1). L-Iduronic acid (IdoA) was found to be a component of the polysaccharide and identified by NMR spectroscopy and after carboxyl-reduction followed by acid hydrolysis and acetylation, by GLC-MS as 2,3,4-tri-O-acetyl-1,6-anhydroidose. On the basis of 1H and 13C NMR spectroscopic studies, including 1D NOE, 2D NOESY, HSQC and HMBC experiments, the following structure of the branched pentasaccharide repeating unit of the polysaccharide was established: -->4)-beta-D-GlcpAI-(1-->4)-beta-D-GlcpAII-(1-->3)-beta-D-++ +QuipNHb4NHbII- (1-->2)-alpha-L-IdopA-(-->4 increases 1 alpha-D-QuipNAc4NAcI where QuiNAc4NAc and QuiNHb4NHb are 2,4-diacetamido-2,4,6-trideoxyglucose and 2,4,6-tri-deoxy-2,4- di[(S)-3-hydroxybutyramido]glucose, respectively. This is the first report of L-iduronic acid in a lipopolysaccharide and of D-QuiNHb4NHb in nature.
Carbohydrate Sequence↗
Distribution of glucuronic and iduronic acid units in heparin chains.
The distribution of glucuronic and iduronic acid within the chains of anticoagulantly active and inactive beef lung heparin was investigated. A fraction with an average molecular weight of 19,500 was isolated from the heterodisperse mixture and then separated into active and inactive components by affinity chromatography. Each sample was linked through its reducing terminus to tyramine, reduced with sodium borotritide, and bound covalently to Sepharose via an azo bridge. The bound reduced heparin was treated with a limited amount of HNO2 and the degraded fragments were removed. The sections of the chain contiguous with the original reducing terminus were then detached from the insoluble matrix by reaction with sodium dithionite. The recovered polysaccharide was fractionated according to size on Sephadex G-200 and the amount of each uronic acid in the individual fractions was determined. Inactive heparin showed a constant percentage of glucuronic acid in all fragments, i.e. about 8.9% of the total uronic acid. With active heparin the percentage of glucuronic acid increased with the distance from the reducing terminus of the polysaccharide chain, ranging from 9.5 to 20% of the uronic acids. These results suggest that the biosynthesis of active heparin involves unique reactions or specific processing of the macromolecule.
Animals↗
Synthesis of iduronic acid building blocks for the modular assembly of glycosaminoglycans.
The modular synthesis of glycosaminoglycans requires straightforward methods for the production of large quantities of protected uronic acid building blocks. In particular, the preparation of fully differentiated iduronic acids has proven particularly challenging. An efficient route to methyl 3-O-benzyl-1,2-O-isopropylidene-alpha-l-idopyranosiduronate 6 from diacetone glucose in nine steps and 36% overall yield is described. Idopyranosiduronate 6 is useful as a glycosyl acceptor and as an intermediate that may be further elaborated into iduronic acid trichloroacetimidate glycosyl donors for the assembly of glycosaminoglycan structures as illustrated here.
Combinatorial Chemistry Techniques↗
The co-polymeric structure of pig skin dermatan sulphate. Distribution of L-iduronic acid sulphate residues in co-polymeric chains.
1. Pig skin dermatan sulphate was degraded by periodate oxidation followed by alkaline elimination or by chondroitinase-ABC to quantify irregular repeating units, i.e. those containing D-GlcUA (D-glucuronic acid) and L-IdUA-SO4 (sulphated iduronic acid). 2. Previous results of periodate oxidation (Fransson, 1974) indicated repeating sequences in pig skin dermatan sulphate containing, on average, 3D-GlcUA, 9 L-IdUA-SO4 or 28 L-IdUA units in addition to N-acetylgalactosamine sulphate. However, complete digestion with chondroitinase-ABC yielded, at the most, 3-4 disulphated disaccharides/chain. Consequently, more than one-half of the L-IdUA-SO4 residues were present in monosulphated periods, i.e. IdUA-(SO4)-GalNAc. 3. To determine the location of L-IdUA-SO4 residues along the copolymeric chain dermatan sulphate was digested with testicular hyaluronidase. (This enzyme cleaves GalNAc-GlcUA bonds within block regions containing D-GlcUA.) By NaB3H4 reduction GalNAc residues located in the reducing end of the fragments were converted into [3H]GalNAcOH (N-acetylgalactosaminitol). Finally, the radioactive product was fragmented by periodate oxidation followed by alkaline elimination. The bulk of the radioactivity was associated with periodate-resistant oligosaccharides indicating that clusters of GlcUA-GalNAc-SO4 periods are often adjacent to a varying number of (n = 1-4) of L-IdUA-SO4-containing periods. 4. To study the distribution of L-IdUA-SO4-containing periods in relation to blocks of IdUA-GalNAc-SO4 periods different fractions of hyaluronidase-degraded dermatan sulphate were degraded separately. In all types of fragments (mol. wts. 1,500-10,000) L-IdUA-SO4-containing periods were demonstrated. In short fragments reducing terminal GalNAc-6-SO4 (6-sulphated N-acetylgalactosamine) was found confirming that these sequences were joined to relatively long D-GlcUA-containing block sequences via GalNAc-6-SO4. Moreover, low-molecular-weight oligosaccharides composed of alternating sequences were encountered. An octasaccharide derived from the carbohydrate sequence -GalNAc---GlcUA-GalNAc-IdUA-GalNAc-GlcUA-GalNAc-IdUA-GalNAc---GlcUA-GalNAc (--- indicates the position of cleavage by hyaluronidase) was identified.
Animals↗
Determination of iduronic acid and glucuronic acid in glycosaminoglycans after stoichiometric reduction and depolymerization using high-performance liquid chromatography and ultraviolet detection.
The reduction of uronic acids in glycosaminoglycans (GAGs) prior to depolymerization reactions is one way in which the uronic acid content of polysaccharides can be studied without major losses. The obtained monosaccharides can be recovered from the subsequent depolymerization with a yield better than 95%. Following reduction, depolymerization, and lyophilization, D-glucuronic acid is converted to D-Glc and L-iduronic acid to 1,6-anhydro-idose. Per-O-benzoyl derivatives of these monosaccharides can be separated and detected in nanogram amounts using reversed phase HPLC. A linear detector response was obtained for injections up to 22 nmol (4 micrograms) of Glc and 1,6-anhydro-idose and the detection limit was 5 and 7 pmol, respectively. Reduction, depolymerization, and derivatization with subsequent chromatography of various GAGs can be readily performed in the 1- to 30-micrograms range.
Chromatography, High Pressure Liquid↗
Chondroitin sulfate/dermatan sulfate hybrid chains from embryonic pig brain, which contain a higher proportion of L-iduronic acid than those from adult pig brain, exhibit neuritogenic and growth factor binding activities.
We have shown that over-sulfated chondroitin sulfate/dermatan sulfate (CS/DS) chains from various marine organisms exhibit growth factor binding activities and neurite outgrowth-promoting activities in embryonic mouse hippocampal neurons in vitro. In this study we demonstrated that CS/DS hybrid chains purified from embryonic pig brain displayed marked neuritogenic activity and growth factor binding activities toward fibroblast growth factor 2 (FGF2), FGF10, FGF18, pleiotrophin, and midkine, all of which exhibit neuroregulatory activities in the brain. In contrast, the CS/DS preparation from adult pig brain showed considerably less activity to bind these growth factors and no neuritogenic activity. Structural analysis indicated that the average size of the CS/DS chains was similar (40 kDa) between these two preparations, but the disaccharide compositions differed considerably, with a significant proportion of l-iduronic acid (IdoUA)-containing disaccharides (8 approximately 9%) in the CS/DS chains from embryos but not in those from adults (<1%). Interestingly, both neurite outgrowth-promoting activity and growth factor binding activities of the CS/DS chains from embryos were abolished by digestion not only with chondroitinase ABC but also with chondroitinase B, suggesting that the IdoUA-containing motifs are essential for these activities. These findings imply that the temporal expression of CS/DS hybrid structures containing both GlcUA and IdoUA and binding activities toward various growth factors play important roles in neurogenesis in the early stages of the development of the brain.
Amino Acid Motifs↗
The copolymeric structure of dermatan sulphate produced by cultured human fibroblasts. Different distribution of iduronic acid and glucuronic acid-containing units in soluble and cell-associated glycans.
The structure of dermatan [35S]sulphate-chondroitin [35S]sulphate copolymers synthesized and secreted by fibroblasts in culture was studied. 35S-labelled glycosaminoglycans were isolated from the medium, a trypsin digest of the cells and the cell residue after 72h of 35SO42-incorporation. The galactosaminoglycan component (dermatan sulphatechondroitin sulphate copolymers) was isolated and subjected to various degradation procedures including digestion with testicular hyaluronidase, chondroitinase-AC and-ABC and periodate oxidation followed by alkaline elimination. The galactosaminoglycans from the various sources displayed significant structural differences with regard to the distribution of various repeating units, i.e. IdUA-GalNAc-SO4 (L-iduronic acid-N-acetyl-galactosamine sulphate), GlcUA-GalNAc-SO4 (D-glucuronic acid-N-acetylgalactosamine-sulphate) and IdUA(-SO4)-GalNAc (L-iduronosulphate-N-acetylgalactosamine). The galactosaminoglycans of the cell residue contained larger amounts of IdUA-GalNAc-SO4 than did those isolated from the medium or those released by trypsin. In contrast, the glycans from the latter 2 sources contained large proportions of periodate-resistant repeat periods [GlcUA-GalNAc-SO4 and IdUA(-SO4)-GalNAc]. Periods containing L-iduronic acid sulphate were particularly prominent in copolymers found in the medium. Kinetic studies indicated that the 35S-labelled glycosaminoglycan of the cell residue accumulated radioactivity more slowly than did the glycans of other fractions, indicating that the material remaining with the cells was not exclusively a precursor of the secreted polymers. The presence of copolymers rich in glucuronic acid or iduronic acid sulphate residues in the soluble fractions may be the result of selective secretion from the cells. Alternatively, extracellular, polymer-level modifications such as C-5 inversion of L-iduronic acid to D-glucuronic acid, or sulphate rearrangements, would yield similar results.
Cells, Cultured↗
Conformer populations of L-iduronic acid residues in glycosaminoglycan sequences.
The 1H-n.m.r. 3J values for the L-iduronic acid (IdoA) residues for solutions in D2O of natural and synthetic oligosaccharides that represent the biologically important sequences of dermatan sulfate, heparan sulfate, and heparin have been rationalized by force-field calculations. The relative proportions of the low-energy conformers 1C4, 2S0, and 4C1 vary widely as a function of sequence and of pattern of sulfation. When IdoA or IdoA-2-sulfate units are present inside saccharide sequences, only 1C4 and 2S0 conformations contribute significantly to the equilibrium. This equilibrium is displaced towards the 2S0 form when IdoA-2-sulfate is preceded by a 3-O-sulfated amino sugar residue, and towards the 1C4 form when it is a non-reducing terminal. For terminal non-sulfated IdoA, the 4C1 form also contributes to the equilibrium. N.O.e. data confirm these conclusions. Possible biological implications of the conformational flexibility and the counter-ion induced changes in conformer populations are discussed.
Carbohydrate Conformation↗