Studies of a monoclonal antibody to skeletal keratan sulphate. Importance of antibody valency.

A mouse monoclonal antibody (AN9P1) to keratan sulphate is described. In a competitive-inhibition solution-phase radioimmunoassay employing 125I-labelled intact proteoglycan, it reacts preferentially with keratan sulphate bound to the core protein of adult human articular-cartilage proteoglycan and to a much lesser degree with keratan sulphate purified from this proteoglycan. Proteolytic cleavage of the proteoglycan by pepsin and trypsin has little effect on antibody binding, but treatment with papain decreases binding considerably and more than does treatment with keratanase. An even greater decrease in binding is observed after treatment with alkaline borohydride. A comparison of binding of antibody AN9P1 with that of another previously described monoclonal antibody, 1/20/5-D-4, to keratan sulphate [Caterson, Christner & Baker (1983) J. Biol. Chem. 258, 8848-8854] revealed similar binding characteristics, both showing much diminished binding after papain digestion of proteoglycan and even less with purified skeletal keratan sulphate. Removal of the Fc piece of antibody AN9P1 had no significant effect on the differential binding of divalent F(ab')2 fragment to proteoglycan, to papain-digested proteoglycan and to keratan sulphate, although there was a small decrease in binding to papain-digested proteoglycan. Conversion of the antibody into univalent Fab fragment with removal of the Fc piece resulted in diminished binding to proteoglycan, compared with that observed with IgG, and in enhanced binding to free keratan sulphate and to papain-digested proteoglycan. These results suggest that close proximity of keratan sulphate chains on the core protein of proteoglycans favours preferential reactivity of bivalent antibody with these species through cross-bridging of chains by antibody. Conversely, much decreased binding to keratan sulphate on proteoglycan core-protein fragments and to free keratan sulphate results from a lack of close proximity of keratan sulphate. By using univalent Fab fragment in these assays these differences in binding are minimized by preventing cross-bridging and thereby enhancing detection of smaller fragments without sacrificing too much sensitivity of detection of larger proteoglycan species. The persistent preferential binding of Fab fragment to proteoglycan is probably in part the result of the increased epitope density in the intact molecule compared with keratan sulphate in a more disperse form.     

Identification of specific binding sites for keratan sulphate proteoglycans and chondroitin-dermatan sulphate proteoglycans on collagen fibrils in cornea by the use of cupromeronic blue in ''critical-electrolyte-concentration'' techniques.

Proteoglycans (PGs) in bovine corneal stroma were stained with Cupromeronic Blue in 'critical-electrolyte-concentration' (CEC) methods for electron microscopy, and were located vis-à-vis collagen fibril a-e banding patterns. Keratanase and chondroitin ABC lyase digestion showed that a + c-band- and d + e-band-associated PGs were keratan sulphate-rich and chondroitin (dermatan) sulphate-rich respectively. The CEC pattern proved that the keratan sulphate PGs at the a and c bands differed. Comparison of their CECs with their behaviour on anion-exchange chromatography confirmed previous (indirect) attempts at identification [Scott & Haigh (1985) Biosci. Rep. 5, 765-774]. Similar arguments were applied to the dermatan sulphate PGs at the d and e bands. These results strongly support the one-PG-one-binding-site hypothesis [e.g. Scott (1988) Biochem. J. 252, 313-323]. Remarkable inter-species variations in the keratan sulphate PG patterns contrast with the relatively constant picture of dermatan sulphate PG-collagen fibril interactions.     

The structure and composition of cartilage keratan sulphate

Keratan sulphate was isolated from bovine intervertebral disc and bovine nasal septum after hydrolysis with proteinases and treatment with dilute alkali. Each preparation was found to contain, per keratan sulphate chain: (a) 1 residue of mannose; (b) 3 residues of N-acetylneuraminic acid (2 residues after alkali treatment); (c) 1 residue of N-acetylgalactosamine (lost after alkali treatment); (d) 1 residue or less of fucose. N-Acetyl-neuraminic acid residues were at non-reducing termini and were bonded to keratan sulphate through galactose residues. Evidence is presented for two different types of linkage between skeletal keratan sulphate and protein. Consideration of molecular parameters and compositions leads to a proposed structure for keratan sulphate-protein as found in skeletal proteoglycans.     

Characterization of the keratan sulphate proteoglycans from bovine corneal stroma.

The keratan sulphate proteoglycans that can be prepared from bovine corneal stroma [Axelsson & Heineg?rd (1975) Biochem. J. 145, 491-500] were characterized by gel chromatography, gel electrophoresis and analytical ultracentrifugation in associative (0.6 M-NaCl) and dissociative (6M-guanidinum chloride) solvents. The proteoglycans aggreagated at low salt concentrations and pH. The weight-average molecular weight of the monomer proteoglycans was established. Keratan sulphate peptides and oligosaccharide peptides were isolated after proteolysis. Their composition indicated that both are linked to protein via asparagine residues. A tentative model for corneal keratan sulphate proteoglycans is suggested.     

Absence of keratan sulphate from skeletal tissues of mouse and rat.

The absence of keratan sulphate synthesis from skeletal tissues of young and mature mice and rats has been confirmed by (1) analysis of specific enzyme degradation products of newly synthesized glycosaminoglycans, and (2) immunohistochemistry and radioimmunoassay using a monoclonal antibody directed against keratan sulphate. Approx. 98% of the [35S]glycosaminoglycans synthesized in vivo by mouse and rat costal cartilage, and all of those of lumbar disc, are chondroitin sulphate. The remainder in costal cartilage were identified as heparan sulphate in mature rats. In contrast, [35S]glycosaminoglycans synthesized by cornea of both species comprised both chondroitin sulphate and keratan sulphate. In mice keratan sulphate accounted for 12-25% and in rats 40-50% of the total [35S]glycosaminoglycans, depending on the age of the animal. Experiments in vitro with organ culture of cartilage and cornea confirm these results. Absence of keratan sulphate from mouse costal cartilage and lumbar disc D1-proteoglycans was corroborated by inhibition radioimmunoassay with the monoclonal antibody MZ15 and by lack of staining for keratan sulphate in indirect immunofluorescence studies using the same antibody.     

Keratan sulphate in the interglobular domain has a microstructure that is distinct from keratan sulphate elsewhere on pig aggrecan

The microstructure of keratan sulphate purified from the interglobular domain, the keratan sulphate-rich region and total aggrecan was compared using fluorophore-assisted-carbohydrate-electrophoresis. Keratan sulphate in the interglobular domain was substantially less sulphated than keratan sulphate elsewhere on aggrecan, based on the ratio of unsulphated: monosulphated disaccharides generated by endo-β-galactosidase digestion, and the ratio of monosulphated: disulphated disaccharides generated by keratanase II digestion. The ratio of unsulphated: monosulphated: disulphated disaccharides was 1:4:5 for keratan sulphate from total aggrecan and the keratan sulphate-rich region, but only 1:0.9:0.8 for the interglobular domain. These results show that keratan sulphate in the interglobular domain of pig aggrecan has a microstructure that is distinct from keratan sulphate in the keratan sulphate-rich region.     

Two linkage-region fragments isolated from skeletal keratan sulphate contain a sulphated N-acetylglucosamine residue.

Peptido-keratan sulphate fragments were isolated from the nucleus pulposus of bovine intervertebral discs (6-year-old animals) after chondroitin ABC lyase digestion followed by digestion of A1D1 proteoglycans by diphenylcarbamoyl chloride-treated trypsin and gel-permeation chromatography on Sepharose CL-6B. Treatment of these peptido-keratan sulphate fragments with alkaline NaB3H4 yielded keratan sulphate chains with [3H]galactosaminitol end-labels, and these chains were further purified by gel-permeation chromatography on Sephadex G-50 and ion-exchange chromatography on a Pharmacia Mono-Q column in order to exclude any contamination with O-linked oligosaccharides. The chains were then treated with keratanase, and the digest was chromatographed on a Bio-Gel P-4 column followed by anion-exchange chromatography on a Nucleosil 5 SB column. Two oligosaccharides, each representing 18% of the recovered radiolabel, were examined by 500 MHz 1H-n.m.r. spectroscopy, and shown to have the following structures: [formula: see text] The structure of oligosaccharide (I) confirms the N-acetylneuraminylgalactose substitution at position 3 of N-acetylgalactosamine in the keratan sulphate-protein linkage region found by Hopwood & Robinson [(1974) Biochem. J. 141, 57-69] but additionally shows the presence of a 6-sulphated N-acetylglucosamine. Electron micro-probe analysis specifically confirmed the presence of sulphur in this sample. This sulphate ester group differentiates the keratan sulphate linkage region from similar structures derived from O-linked oligosaccharides [Lohmander, De Luca, Nilsson, Hascall, Caputo, Kimura & Heinegård (1980) J. Biol. Chem. 255, 6084-6091].     

Sequential distribution of keratan sulphate and chondroitin sulphate epitopes during ameloblast differentiation

Proteoglycans are complex macromolecules containing one or more glycosaminoglycan chains and exhibiting a variety of biological functions in connective tissues. The aim of the present study was to immunolocalize the distribution of keratan sulphate and chondroitin sulphate epitopes during initial enamel formation in order to study temporo-spatial expression patterns of these macromolecules. Third molars of four-months-old pigs were used for immunolocalization of keratan sulphate and chondroitin sulphate epitopes in the developing enamel layer. Tooth organs were prepared for paraffin sections in order to perform indirect immunohistochemistry. The results demonstrated a mutually exclusive positioning between these two epitopes. Keratan sulphate epitopes were observed in pre-secretory pre-ameloblasts and adjacent stratum intermedium while chondroitin sulphate epitopes were demonstrated in secretory ameloblasts and adjacent stratum intermedium. Our findings suggest that proteoglycans containing glycosaminoglycan chains may play a regulatory role during enamel mineralization.     

Sulphate groups are involved in the antigenicity of keratan sulphate and mask i antigen expression on their poly-N-acetyllactosamine backbones. An immunochemical and chromatographic study of keratan sulphate oligosaccharides after desulphation or nitrosation

Conditions were established for desulphation of hexa-, octa-, deca- and larger oligosaccharides derived from corneal keratan sulphate after treatment with endo-beta-galactosidase. The antigenicities of the desulphated oligosaccharides were compared with those of the native oligosaccharides in chromatogram binding, plastic-plate binding or inhibition of binding assays using a novel microimmunochemical approach with oligosaccharide-lipid conjugates (neoglycolipids). The results clearly show that sulphate residues are essential components of the antigenic determinant(s) recognised by three monoclonal antibodies to keratan sulphate, 5-D-4, 1-B-4 and MZ15, but they mask the i antigen activity of the linear poly-(N-acetyllactosamine) backbones of this glycosaminoglycan. Immunochemical assays, before and after beta-N-acetylglucosaminidase treatment of desulphated linear hexa-, octa- and decasaccharides derived from keratan sulphate, indicate that for reaction with one anti-i antibody, Den, there is an absolute requirement for the non-reducing beta-galactosyl residue of the i antigen structure to be in the terminal position, but with a second anti-i antibody, Tho, there is in addition some reactivity with the i antigen structure having an N-acetylglucosamine residue at the non-reducing end. The chromatographic properties after desulphation or nitrosation of a minor keratan sulphate oligosaccharide (a dodecasaccharide), which reacts especially well with antibody 5-D-4, have provided the first evidence for the presence of glucosamine residues that may be N-sulphated in corneal keratan sulphate.     

Degradation of keratan sulphate by beta-N-acetylhexosaminidases A and B.

Enzymic cleavage of beta-N-acetylglucosamine residues of keratan sulphate was studied in vitro by using substrate a [3H]glucosamine-labelled desulphated keratan sulphate with N-acetylglucosamine residues at the non-reducing end. Both lysosomal beta-N-acetylhexosaminidases A and B are proposed to participate in the degradation of keratan sulphate on the basis of the following observations. Homogenates of fibroblasts from patients with Sandhoff disease, but not those from patients with Tay--Sachs disease, were unable to release significant amounts of N-acetyl[3H]glucosamine. On isoelectric focusing of beta-N-acetylhexosaminidase from human liver the peaks of keratan sulphate-degrading activity coincided with the activity towards p-nitrophenyl beta-N-acetylglucosaminide. A monospecific antibody against the human enzyme reacted with both enzyme forms and precipitated the keratan sulphate-degrading activity. Both isoenzymes had the same apparent Km of 4mM, but the B form was approximately twice as active as the A form when compared with the activity towards a chromogenic substrate. Differences were noted in the pH--activity profiles of both isoenzymes. Thermal inactivation of isoenzyme B was less pronounced towards the polymeric substrate than towards the p-nitrophenyl derivative.     

The alkali-labile linkage between keratan sulphate and protein

Keratan sulphate was isolated from adult intervertebral disc in 90% yield by sequential digestion of the whole tissue with papain, Pronase and Proteus vulgaris chondroitin sulphate lyase. Treatment of this preparation with alkali cleaved a glycosidic bond between N-acetylgalactosamine and threonine and produced, by an alkali-catalysed ;peeling' reaction, an unsaturated derivative of N-acetylgalactosamine which reacted as a chromogen in the Morgan-Elson reaction, but remained covalently bonded to the keratan sulphate chain. This derivative was reduced and labelled by alkaline NaB(3)H(4). The substituent at position 3 of N-acetylgalactosamine in the keratan sulphate-protein linkage was identified as a disaccharide, N-acetylneuraminylgalactose, which was isolated from the reaction mixture after alkali treatment.     

The effect of benzyl beta-D-xyloside on keratan sulphate synthesis in ox articular cartilage

Cartilage from adult bovine hock joints was incubated with [3H]galactose or [35S]sulphate in the presence of benzyl beta-D-xyloside. Radioisotope incorporation into proteoglycan was inhibited by the xyloside; the magnitude of this inhibition depended on the concentration of xyloside used. With 0.2mM xyloside radioisotope incorporation into keratan sulphate was not altered but inhibition was observed at xyloside concentrations of 1.0mM or higher. The decrease in radioisotope incorporation into keratan sulphate in the presence of 1.0mM benzyl beta-xyloside was directly related to a reduction in the average length of the keratan sulphate chains. This effect of beta-xyloside on keratan sulphate biosynthesis was markedly different from its effect on chondroitin sulphate biosynthesis.     

Conformation of keratan sulphate

X-ray diffraction patterns from stretched films of keratan sulphate, isolated from bovine cornea, indicate that the molecules are twofold helices with an axial rise per disaccharide residue of 0.945 nm. These helices are oriented with their twofold screw axes parallel and about equally spaced, but are not further organized into regular crystalline arrays. Computer methods were used to construct a molecular model with the observed symmetry and axial rise per disaccharide residue, with standard bond lengths, bond angles and pyranose ring conformations and with a hydrogen bond of length 0.270 nm between O(3) of N-acetylglucosamine and O(5) of galactose. This model has no unacceptably short non-bonded interatomic distances. The intensity distribution of the diffraction pattern calculated from the co-ordinates of the model is in reasonable agreement with the observed intensity distribution. This keratan sulphate model is an extended polysaccharide chain fringed with charged sulphate side groups, and is similar to those that have already been reported for chondroitin sulphates and dermatan sulphate, paralleling the similarities in covalent structure and biological occurrence among these substances.     

Modification of di- and tetrasaccharides from shark cartilage keratan sulphate by refined anhydromethanolic hydrochloric acid-treatments and evaluation of their specific desulphation

Highly sulphated keratan di- and tetrasaccharides were prepared from keratan sulphate (KS) of shark cartilage by enzymatic digestion with keratanase II and subsequent chromatography. The tetrasaccharide fraction carrying four sulphate groups was completely desulphated by 100 mM anhydromethanolic hydrochloric acid (MeOH-HCl) treatment at room temperature for 16 h. The conditions for the desulphation reaction by MeOH-HCl treatment were examined using sulphated keratan di- and tetrasaccharides as substrates by means of reversed phase high performance liquid chromatography (HPLC) and/or capillary electrophoresis, followed by the preparation of partially desulphated keratan oligosaccharides. Sulphate substitution patterns of monosulphated keratan disaccharide and trisulphated keratan tetrasaccharide were evaluated by methylation analysis. The results suggested that 6-O-sulphate groups of Gal moieties are cleaved faster than those of GlcNAc moieties under the present conditions adopted for the MeOH-HCl treatment of KS-derived oligosaccharides.     

The structure of the keratan sulphate chains attached to fibromodulin from human articular cartilage

The small keratan sulphate proteoglycan, fibromodulin, has been isolated from pooled human articular cartilage. The main chain repeat region and the chain caps from the attached N-linked keratan sulphate chains have been fragmented by keratanase II digestion, and the oligosaccharides generated have been reduced and isolated. Their structures and abundance have been determined by high pH anion-exchange chromatography. These regions of the keratan sulphate from human articular cartilage fibromodulin have been found to have the following general structure: Significantly, both α(2-6)- and α(2-3)-linked N-acetyl-neuraminic acid have been found in the capping oligosaccharides. Fucose, which is α(1-3)-linked as a branch to N-acetylglucosamine, has also been found along the length of the repeat region and in the capping region. The chains, which have been found to be very highly sulphated, are short; the length of the repeat region and chain caps is ca. nine disaccharides. These data demonstrate that the structure of the N-linked keratan sulphate chains of human articular cartilage fibromodulin is similar, in general, to articular cartilage derived O-linked keratan sulphate chains. Further, the general structure of the keratan sulphate chains attached to human articular cartilage fibromodulin has been found to be generally similar to that of both bovine and equine articular cartilage fibromodulin. Abbreviations: KS, keratan sulphate; IEC, ion-exchange chromatography; ELISA, enzyme linked immunosorbent assay; Gal, β-D-galactose; Fuc, α-L-Fucose; GlcNAc, N-acetylglucosamine (2-acetamido-β-D-glucose); GlcNAc-ol, N-acetylglucosaminitol (2-acetamido-D-glucitol); NeuAc, N-acetyl-neuraminic acid; 6S/(6S), O-ester sulphate group on C6 present/sometimes present; NMR -nuclear magnetic resonance; HPAE, high pH anion-exchange; PED, pulsed electrochemical detection; HPLC, high performance liquid chromatography This revised version was published online in November 2006 with corrections to the Cover Date.     

Keratan sulphate in cerebrum, cerebellum and brainstem of sheep brain.

Keratan sulphate was identified in sheep brain. We describe here the isolation and partial characterization of keratan sulphate from cerebrum, cerebellum and brainstem of young sheep brains. The galactosaminoglycan was isolated by using ion-exchange chromatography and gel filtration after exhaustive digestion with papain of the delipidated tissues, followed by alkaline borohydride degradation and chondroitinase ABC and heparinases I, II and III treatment. The material isolated by ion-exchange chromatography from each tissue was eluted as single but polydispersed peak from Sephadex G-75, with average molecular masses 8.4, 7.9 and 8.8 kDa for cerebrum, cerebellum and brainstem, respectively. Keratanase I and II totally degraded keratan sulphate from cerebrum and brainstem, but only partially that from cerebellum. The content of keratan sulphate was found to be about 215, 173 and 144 microg/g dry delipidated tissue for cerebrum, brainstem and cerebellum, respectively.     

Regulated expression of keratan sulphate and peanut agglutinin binding sites during organogenesis in the developing chick

 Keratan sulphate proteoglycans are potentially important during development and are possible binding molecules for the lectin, peanut agglutinin, a marker for areas that are inhibitory for axonal growth in early embryos. The present study describes the spatiotemporal distributions of keratan sulphate epitopes and peanut agglutinin binding sites during organogenesis in the developing chick from E5 to hatching. The widespread distributions of these molecules did not often overlap but clearly delimited different carbohydrate compartments demonstrating that peanut agglutinin does not necessarily bind to keratan sulphate proteoglycans. These markers were mostly extracellular but keratan sulphate, in particular, was found within certain specific cells in cartilage, gonad, heart and pancreas, at certain ages. The presence of keratan sulphate in putative germ cells during their migrations and in the gonads may be of particular importance. Their distributions generally evoke modulation of adhesion allowing cell migrations or morphogenetic movements related to epitheliomesenchymal interactions, but may also suggest an involvement in axonal guidance in skin, cartilage, gut and possibly heart. Furthermore, in the kidney, peanut agglutinin binding sites seem to be related to the functional differentiation of the nephrons. Accepted: 23 February 1998     

Studies on the in vitro incubation procedure for [35]sulphate labelling of articular cartilage glycosaminoglycans

Articular cartilage from cow and calf femoral condyles was incubated in Tyrodes solution containing [³⁵S]sulphate for different periods up to 80 min. Glycosaminoglycans from the cartilage tissue and incubation medium were fractionated on Cetylpyridinium chloride and ECTEOLA cellulose microcolumns.The incorporation of [³⁵S]sulphate into all individual fractions of chondroitin sulphate and keratan sulphate was found to be linear from 20 to 80 min incubation time. As a rule the total specific activities of keratan sulphate and chondroitin sulphate were similar for both calves and cows.The proteoglycan material recovered from the medium amounted to about 1% of the tissue dry weight and was found to have a higher chondroitin sulphate: keratan sulphate ratio than the corresponding cartilage tissue for both calf and cow.The solubility profiles for the newly synthesised glycosaminoglycans, obtained from determination of the radioactivity in the individual fractions, were compared with those of glycosaminoglycans already present. These curves indicated that newly synthesised chondroitin sulphate had a higher average molecular size than that present in the tissue whereas the newly synthesised keratan sulphate had a smaller average molecular size. These newly synthesised components were also detected in the proteoglycans recovered from the incubation medium.     

Skeletal keratan sulphate structural analysis using keratanase II digestion followed by high-performance anion-exchange chromatography

A semi-quantitative fingerprinting method has been developedfor the structural analysis of skeletal keratan sulphates. Thisinvolves the digestion of the parent keratan sulphate chainswith the enzyme keratanase II (Bacillus sp.), followed by reductionof the resulting oligosaccharides with sodium borohydride andchromatography on a Dionex AS4A-SC column. This column has beencalibrated for the elution positions of 26 previously characterizedoligosaccharides (Brown et al., Biochemistry, 33, 4836–4846,1994; Brown et al., Eur. J. Biochem., 224, 281–308, 1994).The technique permits sample analysis with pulsed electrochemicaldetection (sensitive to     

Studies on the in vitro incubation procedure for [35S]sulphate labelling of articular cartilage glycosaminoglycans

Articular cartilage from cow and calf femoral condyles was incubated in Tyrodes solution containing [35S]sulphate for different periods up to 80 min. Glycosaminoglycans from the cartilage tissue and incubation medium were fractionated on Cetylpyridinium chloride and ECTEOLA cellulose microcolumns. The incorporation of [35S]sulphate into all individual fractions of chondroitin sulphate and keratan sulphate was found to be linear from 20 to 80 min incubation time. As a rule the total specific activities of keratan sulphate and chondroitin sulphate were similar for both calves and cows. The proteoglycan material recovered from the medium amounted to about 1% of the tissue dry weight and was found to have a higher chondroitin sulphate: keratan sulphate ratio than the corresponding cartilage tissue for both calf and cow. The solubility profiles for the newly synthesised glycosaminoglycans, obtained from determination of the radioactivity in the individual fractions, were compared with those of glycosaminoglycans already present. These curves indicated that newly synthesised chondroitin sulphate had a higher average molecular size than that present in the tissue whereas the newly synthesised keratan sulphate had a smaller average molecular size. These newly synthesised components were also detected in the proteoglycans recovered from the incubation medium.