Selective depolymerisation of keratan sulfate: production of radiolabelled substrates for 6-O-sulfogalactose sulfatase and beta-D-galactosidase

Analysis of disaccharides and tetrasaccharides released from glycosaminoglycans

Glycosaminoglycans (GAGs) are converted to disaccharides by various methods. This unit describes separation of individual disaccharides by paper chromatography or paper electrophoresis or high-performance liquid chromatography (HPLC). Lyase-released disaccharides can also be monitored by UV absorbance. Support protocols describe mild conditions for reduction of alkali-labile disaccharides obtained by cleavage of GAGs with lyases, scintillation counting of samples obtained from HPLC separation of radiolabeled saccharides, and calculations for the quantitation of disaccharides.

Structural characterization of the exopolysaccharide produced by Lactobacillus acidophilus LMG9433

The exopolysaccharide produced by Lactobacillus acidophilus LMG9433 in a semi-defined medium was found to be a charged heteropolymer, with a composition of D-glucose, D-galactose, D-glucuronic acid, and 2-acetamido-2-deoxy-D-glucose in molar ratios of 2:1:1:1. By means of methylation analysis, uronic acid degradation, de-N-acetylation/deamination, partial acid hydrolysis, and 1D/2D NMR studies the polysaccharide was demonstrated to consist of repeating units with the following structure: [Table: see text]

Spectroscopic characterisation of disaccharides derived from keratan sulfates

Skeletal keratan sulfates have been degraded by three independent techniques and the resultant, borohydride-reduced, disaccharides have been characterised by NMR spectroscopy. The 1H and 13C (where available) chemical shifts are reported for the following substances, where GalNAc-ol represents N-acetyl-galactosaminitol, GlcNAc-ol represents N-acetyl-glucosaminitol, GlcNAc(6S)-ol represents N-acetyl-glucosaminitol 6-O-sulfate and 2,5AnMan(6S)-ol represents 2,5-anhydro-D-mannitol 6-O-sulfate. (a) GlcNAc(6S)beta(1-3)Gal-ol, isolated after keratanase (from Pseudomonas sp.) digestion. (b) Gal beta(1-4)GlcNAc(6S)-ol and Gal(6S)beta(1-4) GlcNAc(6S)-ol, the 1H chemical shifts have been reported previously [Brown, G. M., Huckerby, T. N., Morris, H. G., Abram, B. L. & Nieduszynski, I. A. (1994) Biochemistry 33, 4836-4846; Brown, G. M., Huckerby, T. N. & Nieduszynski, I. A. (1994) Eur. J. Biochem. 224, 281-308], GlcNAc(6S)beta(1-6)GalNAc-ol, [formula: see text], [formula: see text], all isolated after keratanase II digestion. (c) Gal beta(1-4)2,5AnMan(6S)-ol and Gal(6S)beta(1-4)2,5AnMan(6S)-ol, isolated after hydrazinolysis and nitrous acid digestion. In addition, the model compounds Gal beta(1-4)GlcNAc-ol and Gal beta(1-6)GlcNAc-ol have also been examined by 1H and 13C NMR spectroscopy. The value of these data for microstructural analysis of keratan sulfate samples is discussed.

N.m.r. spectroscopic studies of fucose-containing oligosaccharides derived from keratanase digestion of articular cartilage keratan sulphates. Influence of fucose residues on keratanase cleavage

Keratan sulphate chains from bovine articular cartilage were fully digested with keratanase from Pseudomonas sp. and the products were reduced with alkaline borohydride. The resultant fragments were fractionated on a Nucleosil 5SB column and the earliest eluting fucose-containing oligosaccharides were isolated. Structural analysis using 1H n.m.r. spectroscopy (600 MHz) showed the two least-charged species to have the following structure: GlcNAc(6S) beta 1-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc(6S) beta 1- 3Gal beta 1-4GlcNAc(6S) beta 1-3Gal-ol and GlcNAc(6S) beta 1-3Gal beta 1- 4(Fuc alpha 1-3)GlcNAc(6S) beta 1-3Gal beta 1-4GlcNAc(6S) beta 1-6(Gal beta 1- 3)GalNAc-ol. Both galactoses adjacent to the fucosylated N-acetylglucosamine residue are unsulphated. Therefore, it can be deduced from these structures that the presence of fucose on N-acetylglucosamine residues in keratan sulphates protects both of the adjacent unsulphated galactose residues from keratanase cleavage. This result has implications for the interpretation of keratanase fingerprints, because in articular cartilage keratan sulphates the keratanase-resistant blocks are not solely those with fully sulphated galactose residues, but also include the fucosylated sequences, which have unsulphated galactoses. It is, therefore, not possible to estimate their galactose sulphation or the size of the fully sulphated disaccharide-repeat sequences from keratan sulphates that contain fucose.

Degradation of articular cartilage keratan sulphates using hydrazinolysis and nitrous acid. Environment of fucose residues

Alkaline borohydride-reduced keratan sulphate (KS) chains from bovine articular cartilage (6-8-year-old animals) were fragmented by an anhydrous hydrazine/nitrous acid procedure, previously used on KS by Hopwood & Elliott to isolate the major disaccharides from the poly-N-acetyl-lactosamine repeat sequence [Hopwood & Elliott (1983) Carbohydr. Res. 117, 263-274]. The resulting oligosaccharides were reduced with NaB3H4 or NaBH4 and subjected to ion-exchange chromatography on a Nucleosil 5SB column. In addition to the major disaccharides, two fucose-containing oligosaccharides were examined by high-field 1H n.m.r. spectroscopy, and shown to have the following structures (where AnManOH is 2,5-anhydro-D-mannitol): [formula: see text] It is evident that the presence of fucose protects the N-acetylglucosamine residue from de-N-acetylation, and therefore fragments are produced which preserve the immediate environment of the fucose residue. It may be of biosynthetic significance that these two oligosaccharides contain an unsulphated galactose on the non-reducing side of the fucose residue. The hydrazine/nitrous acid/NaB3H4 method followed by h.p.l.c. provides a sensitive fingerprinting technique for the assay of KS composition and sub-populations.

Human liver N-acetylgalactosamine 6-sulphatase. Purification and characterization

Human N-acetylgalactosamine 6-sulphatase (EC 3.1.6.14), which is involved in the lysosomal degradation of the glycosaminoglycans keratan sulphate and chondroitin 6-sulphate, was purified more than 130,000-fold in 2.8% yield from liver by an eight-step column procedure. One major form was identified with a pI of 5.7 and a native molecular mass of 62 kDa by gel filtration. When analysed by SDS/PAGE, dithioerythritol-reduced enzyme contained polypeptides of molecular masses 57 kDa, 39 kDa and 19 kDa, whereas non-reduced enzyme contained a major polypeptide of molecular mass 70 kDa. It is proposed that active enzyme contains either the 57 kDa polypeptide or disulphide-linked 39 kDa and 19 kDa polypeptides. Minor amounts of other enzyme forms separated during the chromatofocusing step and the Blue A-agarose step were not further characterized. Purified N-acetylgalactosamine 6-sulphatase was inactive towards 4-methylumbelliferyl sulphate, but was active, with pH optima of 3.5-4.0, towards 6-sulphated oligosaccharide substrates. Km values of 12.5 and 50 microM and Vmax. values of 1.5 and 0.09 mumol/min per mg were determined with oligosaccharide substrates derived from chondroitin 6-sulphate and keratan sulphate respectively. Sulphate, phosphate and chloride ions were inhibitors of enzyme activity towards both substrates, with 50 microM-Na2SO4 giving 50% inhibition towards the chondroitin 6-sulphate trisaccharide substrate.

Dental findings in mucopolysaccharidosis type IV A (Morquio's disease type A)

Dental examinations on nine patients with mucopolysaccharidosis type IV A (MPS IV A, Morquio's disease type A) were carried out. Detailed medical, radiologic, and biochemical studies of each case were also performed independently. Dental changes were present in all cases, although the severity varied. The severity of the dental changes did not correlate with the clinical or biochemical findings in all cases. These dental changes are seen only in MPS IV A (N-acetylgalactosamine-6-sulphate sulphatase deficiency) and are not found in MPS IV B (beta-galactosidase deficiency) or the recently delineated MPS IV C (enzyme defect unknown). The dental changes can aid in the diagnosis of patients affected by MPS IV A and are especially useful in mild atypical cases.

Types of oligosaccharide sulphation, depending on mucus glycoprotein source, corpus or antral, in rat stomach

Radiolabelled mucus glycoprotein was obtained from tissue and a culture medium each of the corpus and antrum of rat stomach incubated with [35S]sulphate in vitro. Gel-filtration analysis of oligosaccharides liberated by alkaline-borohydride treatment from glycoproteins indicated that 35S-labelled oligosaccharides from the corpus vary considerably with respect to chain length whereas those from antral mucus glycoprotein are composed of small oligosaccharides. Examination of the reduced radiolabelled products obtained by HNO2 cleavage of the hydrazine-treated oligosaccharides indicated sulphate esters of N-acetylglucosamine to be present at three locations on a carbohydrate unit: [35S]sulphated monosaccharide (2,5-anhydromannitol 6-sulphate), [35S]sulphated disaccharide [galactosyl(beta 1-4)-2,5-anhydromannitol 6-sulphate] and [35S]sulphated trisaccharide [fucosyl(alpha 1-2)-galactosyl(beta 1-4)-2,5-anhydromannitol 6-sulphate]. Sulphated disaccharide and trisaccharide, possibly originating from the N-acetyl-lactosamine and fucosyl-N-acetyl-lactosamine sequences respectively, were detected in the corpus, especially as large oligosaccharides, but were present in the antrum in only very small amounts. The sulphated monosaccharide, however, most probably originating from 6-sulphated N-acetylglucosamine residues at non-reducing termini, was present in all oligosaccharide fractions in both the corpus and antrum.

Clinical findings in 12 patients with MPS IV A (Morquio's disease). Further evidence for heterogeneity. Part I: Clinical and biochemical findings

Clinical heterogeneity in MPS IV A (Mucopolysaccharidosis IV A, Morquio Disease Type A)has become more clearly identified in recent years. The clinical findings in 12 cases of MPS IV A are described. Clinical presentation was variable, and some cases were only mildly affected. All showed deficiency of N-acetylgalactosamine-6-sulphate sulphatase in fibroblasts, but the patient with the mildest clinical presentation showed a high residual enzyme activity. The urinary glycosaminoglycans (GAGs) were examined on all patients by a two-dimensional electrophoresis technique which proved to be highly reliable and efficient. In particular, no false negative results were obtained, a problem often encountered with routine screening methods. These cases support the division of MPS IV A into three subgroups: the severe "classical" type, an intermediate type and a mild type, all caused by N-acetylgalactosamine-6-sulphate sulphatase deficiency. Residual enzyme activity may be an important prognostic indicator.

Developmental changes in glycosaminoglycan sulfotransferase activities in animal sera

Glycosaminoglycan sulfotransferase activities in sera during the prenatal and postnatal development of the ox, rat, and chicken were systematically measured with chemically desulfated cartilage chondroitin 4-sulfate, cornea keratan sulfate, and kidney heparan sulfate as exogenous sulfate acceptors and with [35S]sulfate-labeled 3'-phosphoadenosine 5'-phosphosulfate as a sulfate donor. The results of specificity studies and product analyses indicated that these enzymes introduce sulfates at position 6 of the internal N-acetylgalactosamine units of chondroitin, position 6 of the galactose units of keratan sulfate, and position 2 (an amino group) of the glucosamine units of heparan sulfate, respectively. The results of the enzyme assays indicated that (1) the three activities change in a development-associated manner in each animal species, (2) generally, the activities of the former two enzymes decrease with embryonic development and aging after birth, although in chicken serum they increase transiently at the late prenatal stage and decrease thereafter, and (3) the pattern of the changes in heparan sulfate sulfotransferase activity is species-dependent: the activity increases in the rat, decreases in the ox, and does not significantly change in the chicken during prenatal or postnatal development. These alterations may reflect development-associated biosynthesis of the corresponding glycosaminoglycans or maturation of the proteoglycans in some tissues.

Human liver N-acetylglucosamine-6-sulphate sulphatase. Catalytic properties

Kinetic parameters (Km and kcat.) of the two major forms (A and B) and a minor form (C) of human liver N-acetylglucosamine-6-sulphate sulphatase [Freeman, Clements & Hopwood (1987) Biochem. J. 246, 347-354] were determined with a variety of substrates matching structural aspects of the physiological substrates in vivo, namely heparin, heparan sulphate and keratan sulphate. Enzyme activity is highly specific towards glucosamine 6-sulphate or glucose 6-sulphate residues. More structurally complex substrates, in which several aspects of the aglycone structure of the natural substrate were maintained, are hydrolysed with catalytic efficiencies up to 3900 times above that observed for the monosaccharide substrate N-acetylglucosamine 6-sulphate. Forms A and B both desulphate substrates derived from keratan sulphate and heparin. Aglycone structures that influence substrate binding and/or enzyme activity were penultimate-residue 6-carboxy and 2-sulphate ester groups for heparin-derived substrates and penultimate-residue 6-sulphate ester groups for keratan sulphate-derived substrates. The 4-hydroxy group of the N-acetylglucosamine 6-sulphate or the 2-sulphaminoglucosamine 6-sulphate under enzymic attack is involved in the catalytic mechanism. The presence of a 2-amino group in place of a 2-acetamido or a 2-sulphoamino group considerably decreases the catalytic efficiency of the sulphatase, particularly in the absence of a penultimate-aglycone-residue 6-carboxy group. Both forms A and B are exo-enzymes, since activity towards internal sulphate ester bonds was not observed. The effect of incubation pH on enzyme activity towards the variety of substrates evaluated was complex and dependent on substrate aglycone structure. The presence of aglycone 2-sulphate ester, 6-carboxy group and 6-sulphate ester groups on the glucosamine 6-sulphate residue under attack considerably affects the pH response. Sulphate and phosphate ions are potent inhibitors of enzyme activity.

The histological and ultrastructural features of the epiphyseal plate in Morquio type A syndrome (mucopolysaccharidosis type IVA)

Tissue from the epiphyseal plate of a patient with Morquio type A syndrome (mucopolysaccharidosis type IVA) was studied by undecalcified histological and electron microscopical techniques. Cartilage cells in the plate were vacuolated to a variable degree. The orderly proliferating structure of the epiphyseal plate was absent and calcification was markedly reduced. The related bone tissue was morphologically normal although reduced in quantity.

The disaccharides formed by deaminative cleavage of N-deacetylated glycosaminoglycans

Chondroitin 4-sulphate, chondroitin 6-sulphate, dermatan sulphate and keratan sulphate were N-deacetylated by treatment with hydrazine and then cleaved with HNO2 at pH 4.0, and the resulting products were reduced with NaB3H4. This reaction sequence cleaved the glycosaminoglycans at their N-acetyl-D-glucosamine or N-acetyl-D-galactosamine residues, which were converted into 3H-labelled 2,5-anhydro-D-mannitol (AManR) or 2,5-anhydro-D-talitol (ATalR) residues respectively. The end-labelled disaccharides, composed of D-glucuronic acid (GlcA), L-iduronic acid (IdoA) or D-galactose (Gal) and one of the anhydrohexitols, were identified as follows: both chondroitin 4-sulphate and chondroitin 6-sulphate gave GlcA----ATalR(4-SO4), GlcA----ATalR(6-SO4), IdoA----ATalR (4-SO4) and GlcA(2-SO4)----ATalR(6-SO4); dermatan sulphate gave IdoA----ATalR(4-SO4), GlcA----ATalR(4-SO4), GlcA----ATalR(6-SO4)----IdoA(2-SO4)ATalR(4-SO4) and IdoA----ATalR (4,6-diSO4); keratan sulphate gave Gal(6-SO4)----AManR(6-SO4), Gal----AManR(6-SO4), Gal(6-SO4)----AManR and Gal----AManR. Several additional disaccharides were generated by treatment of the uronic acid-containing disaccharides with hydrazine to epimerize their uronic acid residues at C-5. A number of these disaccharides were found to be substrates for lysosomal sulphatases and glycuronidases. Methods were developed for the separation of all of the disaccharide products by h.p.l.c. The rate of N-deacetylation of chondroitin 4-sulphate by hydrazinolysis was significantly lower than the rate of N-deacetylation of chondroitin 6-sulphate or chondroitin. Dermatan sulphate was N-deacetylated at an intermediate rate. The relative amounts of disaccharides obtained from chondroitin 4-sulphate, chondroitin 6-sulphate and dermatan sulphate under optimum hydrazinolysis/deamination conditions were comparable with the amounts of the corresponding products released from the polymers by chondroitinase treatment.

Human alpha-L-iduronidase. 2. Catalytic properties

The kinetic parameters of human liver alpha-L-iduronidase were determined with three disaccharide substrates: alpha-L-iduronosyl(1----4)2,5-anhydro-D-[1-3H]mannitol 6-sulphate, alpha-L-iduronosyl(1----4)2,5-anhydro-D-[1-3H]mannitol and alpha-L-iduronosyl(1----3)2,5-anhydro-D-[1-3H]talitol 4-sulphate, derived from the natural substrates heparin and dermatan sulphate and one synthetic, fluorogenic substrate, 4-methylumbelliferyl alpha-L-iduronide. The enzyme activity with all four substrates was optimal at about pH 4.5. The Km values derived using the disaccharide substrates were elevated up to 10-fold with up to a 6.5-fold increase in ionic strength whereas that for the synthetic substrate was only increased by 1.7-fold. The V values for all substrates were unaffected. The inhibitory effect of NaCl, Na2SO4, NaH2PO4 or CuCl2 on enzyme activity was more pronounced with the disaccharide substrates than with the synthetic substrate. The moiety which is most important in binding is the idopyranosyl residue. While the aglycone residue adds to the net affinity for the enzyme, it is the substituent groups of both residues which appear to control catalysis. Specifically the carboxyl moiety of the alpha-L-iduronic acid residue is essential for catalysis while the presence of sulphate on the C4 or C6 position of the aglycone residue has a major influence on catalysis rather than binding. alpha-L-Idosyl(1----4)2,5-anhydro-D-[1-3H]mannitol 6-sulphate did not undergo catalysis and was a potent inhibitor of enzyme activity, whereas beta-glucuronosyl(1----4)2,5-anhydro-D-[1-3H]mannitol 6-sulphate, alpha-L-iduronosyl-2-sulphate(1----4)2,5-anhydro-D-[1-3H]-mannitol 6-sulphate and 4-methylumbelliferyl alpha-L-idoside did not undergo catalysis and were not inhibitory. A model of the catalytic requirements of alpha-L-iduronidase is proposed.

Structural elucidation of glycosaminoglycans through characterization of disaccharides obtained after fragmentation by hydrazine-nitrous acid treatment

Hydrazinolysis of glycosaminoglycans to bring about N-deacetylation followed by nitrous acid treatment to effect deaminative cleavage at alternating hexosamine residues has been used to make possible identification and quantitation of disaccharide sequences and position of O-sulfate substitution in nanogram amounts of these polymers. After radiolabeling by NaB3H4 reduction the hydrazine-nitrous acid products were fractionated on Dowex 1 and further resolved by thin-layer chromatography into disaccharides terminating in either sulfated or unsulfated anhydromannitol or anhydrotalitol. Fragmentation of hyaluronic acid, keratan sulfate, chondroitin 4-sulfate, chondroitin 6-sulfate, dermatan sulfate, and heparin yielded a total of 14 disaccharides comprising the major sequences (greater than 1 mol%) occurring in mammalian glycosaminoglycans. Disaccharides representing the predominant variants of the chondroitin sulfates [GlcUA beta 1----3anhydrotalitol(4-SO4) and GlcUA beta 1----3anhydrotalitol(6-SO4)] as well as of dermatan sulfate chains [IdUA alpha 1----3anhydrotalitol(4-SO4) and GlcUA beta 1----3anhydrotalitol(4-SO4)] chains could readily be quantitated by this approach. In the case of heparin a comparison of the disaccharides produced by direct nitrous acid and hydrazine-nitrous acid treatments moreover provided an assessment of the distribution of N-sulfate groups. The characterization of the various disaccharides by Smith periodic acid degradation and glycosidase digestions was facilitated by the preparation and thin-layer chromatographic resolution of the complete series of monosulfated derivatives of anhydromannitol and anhydrotalitol; the sulfate esters were shown to be stable to both the hydrazine and nitrous acid treatments. The high sensitivity of the hydrazine-nitrous acid fragmentation procedure should prove useful in the structural elucidation of cell surface and basement membrane proteoglycans as well as other sulfated glycoconjugates which are present in small amounts.

Selective depolymerisation of dermatan sulfate: production of radiolabelled substrates for alpha-L-iduronidase, sulfoiduronate sulfatase, and beta-D-glucuronidase

Radiolabelled disaccharide substrates for alpha-L-iduronidase, beta-D-glucuronidase, and sulfoiduronate sulfatase have been prepared from dermatan sulfate by application in sequence of N-deacetylation, deaminative cleavage, and reduction with NaBT4. The yield of disaccharides was approximately 87% of the total oligosaccharide fraction. Five disaccharides were isolated and tentatively identified. The major disaccharide, O-(alpha-L-idopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-[1-3H]talitol 4-sulfate (IdoA-anT4S), represented approximately 75% of the total disaccharide fraction. The other disaccharides were O-(alpha-L-idopyranosyluronic acid 2-sulfate)-(1 leads to 3)-2,5-anhydro-D-[1-3H]talitol 4-sulfate (IdoA2S-anT4S), O-(beta-D-glucopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-[1-3H]talitol 4-sulfate (GlcA-anT4S), O-(beta-D-glucopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-[1-3H]talitol 6-sulfate (GlcA-anT6S), and O-(alpha-L-idopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-[1-3H]talitol (IdoA-anT), which represented approximately 4.5, 11.2, 1.0, and 1.8%, respectively, of the total disaccharide fraction. When incubated with cultured skin-fibroblasts from normal controls, IdoA-anT4S was shown to be a sensitive substrate for alpha-L-iduronidase to produce 2,5-anhydro-D-talitol 4-sulfate (anT4S). Activity toward IdoA-anT4S was not observed with fibroblast homogenates from alpha-L-iduronidase-deficient patients (Mucopolysaccharidosis Type I). Similarly, normal-fibroblast homogenates degraded GlcA-anT6S to anT6S, and GlcA-anT4S to anT4S, at a rate 6 to 8 times greater than found for fibroblasts from beta-D-glucuronidase-deficient patients (Mucopolysaccharidosis Type VII). IdoA-anT4S was hydrolysed by alpha-L-iduronidase at a rate 365 times greater than that for IdoA-anT. Sulfation of the anhydro-D-[1-3H]talitol residues is an important structural determinant in the mechanism of action of alpha-L-iduronidase on disaccharide substrates. IdoA2S-anT4S was degraded to IdoA-anT4S and then to anT4S by normal-fibroblast homogenates, whereas fibroblasts from alpha-L-iduronidase-deficient and sulfoiduronate sulfatase-deficient (Mucopolysaccharidosis Type II) patients produced considerably decreased levels of anT4s and IdoA-anT4S (and anT4S), respectively.