A Multiplex Assay for the Diagnosis of Mucopolysaccharidoses and Mucolipidoses

Introduction

Diagnosis of the mucopolysaccharidoses (MPSs) generally relies on an initial analysis of total glycosaminoglycan (GAG) excretion in urine. Often the dimethylmethylene blue dye-binding (DMB) assay is used, although false-negative results have been reported. We report a multiplexed diagnostic test with a high sensitivity for all MPSs and with the potential to identify patients with I-cell disease (ML II) and mucolipidosis III (ML III).

Methods

Urine samples of 100 treatment naive MPS patients were collected and analyzed by the conventional DMB assay and a multiplex assay based on enzymatic digestion of heparan sulfate (HS), dermatan sulfate (DS) and keratan sulfate (KS) followed by quantification by LC-MS/MS. Specificity was calculated by analyzing urine samples from a cohort of 39 patients suspected for an inborn error of metabolism, including MPSs.

Results

The MPS cohort consisted of 18 MPS I, 16 MPS II, 34 MPS III, 10 MPS IVA, 3 MPS IVB, 17 MPS VI and 2 MPS VII patients. All 100 patients were identified by the LC-MS/MS assay with typical patterns of elevation of HS, DS and KS, respectively (sensitivity 100%). DMB analysis of the urine was found to be in the normal range in 10 of the 100 patients (sensitivity 90%). Three out of the 39 patients were identified as false-positive, resulting in a specificity of the LS-MS/MS assay of 92%. For the DMB this was 97%. All three patients with MLII/MLIII had elevated GAGs in the LC-MS/MS assay while the DMB test was normal in 2 of them.

Conclusion

The multiplex LC-MS/MS assay provides a robust and very sensitive assay for the diagnosis of the complete spectrum of MPSs and has the potential to identify MPS related disorders such as MLII/MLIII. Its performance is superior to that of the conventional DMB assay.

Selective removal of keratan sulfate in chondroitin sulfate samples by sequential precipitation with ethanol

Keratan sulfate (KS) is present as a contaminant in chondroitin sulfate (CS) mainly extracted from shark cartilage. We report a selective removal procedure of KS in CS samples by means of sequential precipitation with ethanol. Purified shark CS containing approximately 10% to 15% KS was subjected to a precipitation procedure in the presence of increasing percentages of saturated ethanol. In contrast to other solvents, 1.0 volume of ethanol was able to selectively purify CS, with a purity of approximately 100%, from KS. The current selective and simple procedure appears to be a reliable industrial preparation of CS devoid of large amounts of the residual KS.

Soluble lumican glycoprotein purified from human amniotic membrane promotes corneal epithelial wound healing

PURPOSE

To purify and characterize the glycoprotein lumican, isolated from human amniotic membrane (AM), and to examine its efficacy in treating corneal epithelium debridement.

METHODS

An affinity-purified, anti-human lumican antibody-conjugated protein A Sepharose column was used to purify soluble lumican protein from human AM. The purified AM lumican was characterized by two-dimensional and SDS gel electrophoresis, plus Western blot analysis with anti-lumican antibody. The effects of lumican on corneal epithelial wound healing were examined in an organ culture mouse eye model.

RESULTS

Lumican was found to be abundantly present in the stroma of human AM. It was extracted from the AM by isotonic, 1 M NaCl, and 4 M guanidine HCl solutions, suggesting that it is present in both the soluble and matrix-bound states. In two-dimensional gel electrophoresis, the 50-kDa human amniotic lumican purified by antibody-conjugated affinity chromatography migrated in a smear between pH 3.0 and 6.0. After endo-beta-galactosidase digestion, it existed as a single core protein at pH 6.0, suggesting that native human amniotic lumican is a glycoprotein with short sugar moiety. Addition of purified human AM lumican to cultured medium promoted re-epithelialization and enhanced cell proliferation of wild-type mouse corneal epithelial cells in an organ culture. In lumican-knockout (lum(-/-)) mice, the effect of human lumican on promoting corneal epithelial wound healing was even more dramatic than in wild-type mice.

CONCLUSIONS

The diversified functions of lumican include modulation of epithelial cells in wound healing and serving as an extracellular matrix component. Administration of lumican may be beneficial for treating epithelial defects in the cornea and other tissues.

Interaction of lumican with aggrecan in the aging human sclera

PURPOSE

Lumican is a keratan sulfate proteoglycan originally identified in cornea, but present in a variety of connective tissues where it presumably regulates collagen fibril formation and organization. The present study was designed to describe the chemical nature of lumican core protein in the aging human sclera.

METHODS

Western blot analyses, immunohistochemistry, and immunoaffinity chromatography were used to detect and purify the lumican core protein from tissue extracts from human donors 6 to 89 years of age. Treatment of lumican with chondroitinase ABC, keratanase-I and -II, and/or endo-beta-galactosidase was used to determine the degree of glycosylation of the lumican core protein.

RESULTS

Lumican was present in the human sclera as a 70- to 80-kDa core protein with short unsulfated lactosaminoglycan side chains. In addition, on Western blots, a larger >200-kDa species was apparent that was immunologically related to lumican. This high-molecular-weight material increased in scleral extracts with increasing age. The complex was most abundant in unreduced samples, and approximately two thirds of the 70- to 80-kDa lumican core protein was released from the complex on reduction of the scleral extract. Further characterization of the >200-kDa lumican-immunopurified complex indicated that aggrecan (the cartilage proteoglycan) was covalently associated with lumican.

CONCLUSIONS

Reducible and nonreducible lumican-aggrecan interactions occur in the scleral extracellular matrix and result in the formation of high-molecular-weight complexes that increase with age. These results represent the first report demonstrating lumican-aggrecan interactions and suggest they may play a role in age-related scleral extracellular matrix changes.

Biochemical properties of a keratan sulphate/chondroitin sulphate proteoglycan expressed in primate pluripotent stem cells

We previously identified a pericellular matrix keratan sulphate/chondroitin sulphate proteoglycan present on the surface of human embryonal carcinoma stem cells, cells whose differentiation mimics early development. Antibodies reactive with various epitopes on this molecule define a cluster of differentiation markers for primate pluripotent stem cells. We describe the purification of a form of this molecule which is secreted or shed into the culture medium. Biochemical analysis of the secreted form of this molecule shows that the monomeric form, whilst containing keratan sulphate, resembles mucins in its structure and its modification with O-linked carbohydrate. Immunofluorescence and immunoblotting data show that monkey and human pluripotent stem cells react with antibodies directed against epitopes on either carbohydrate side chains or the protein core of the molecule.

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.

Organic components of crystal sheaths in bones

Crystals in bones are enveloped within organic crystal sheaths of 5-10 nm widths. In order to analyse their components, we investigated the immunolocalizations of chondroitin 4- and 6-sulphate, keratan sulphate, bone sialoprotein and osteopontin. All of these, except chondroitin 6-sulphate, were found in bone matrix. Although the localizations of chondroitin 4-sulphate and keratan sulphate tended to focus within calcified nodules, bone sialoprotein and osteopontin were widely distributed in the area, being linearly arranged along electron-dense structures corresponding to crystal sheaths. These two proteins possess the ability to affect nucleation or elongation of hydroxyapatite, positively or negatively, in vitro. Our results suggested that bone sialoprotein and osteopontin may combine to form the crystal sheaths which are thought to control crystal formation and growth, using the seemingly opposite functions of bone sialoprotein and osteopontin.

Keratan sulfates from bovine tracheal cartilage structural studies of intact polymer chains using H and 13C NMR spectroscopy

Intact keratan sulfate chains derived from bovine tracheal cartilage have been examined using both one-dimensional methods and the two-dimensional experiments COSY-45 and TOCSY for homonuclear shift correlations and a modified COLOC (correlated spectroscopy for long-range couplings) approach for 13C-1H shift correlations. Partial 1H and 13C NMR signal assignments for residues within the intact polymer chain are reported; data derived from the repeat region signals and from chain cap residues are assigned by comparison with published data derived from oligosaccharides obtained through cleavage of keratan sulfate polymer chains using keratanase and keratanase II and are discussed in detail. The one-dimensional spectra for both 1H and 13C nuclei contain highly crowded signal clusters for which data analysis is not directly possible. COSY-45 analysis allow the correlation and assignment of many proton resonances located within the 3.4-4.8 p.p.m. chemical shift region while from the C/H correlation spectrum data are assignable for some signals within the complex set of carbon resonances which fall in the region between 68 and 86 p.p.m., This work using material from tracheal cartilage has permitted the first detailed combined 1H and 13C NMR examination of the primary keratan sulfate polymer structure; this sequence forms the basis for the more complex members of the keratan sulfate family present in other tissues such as articular cartilage and cornea where further residues such as (alpha1-3)-linked fucose and (alpha2-6)-linked N-acetylneuraminic acid are also present. This nondestructive method of analysis complements the currently available degradative methods for structure determination which may then subsequently be utilized.

600 MHz NMR studies of human articular cartilage keratan sulfates

The use of high-field two-dimensional 1H-correlation data is described for the detailed comparison of intact keratan sulfate polymer chains derived from human articular cartilage sources as a function of age. For fetal material the nonreducing chain termini are shown to be sparsely capped by sialyl groups which, if present, are exclusively (alpha2-3)-linked to an unsulfated galactose residue. The asialo capping segment has the structure: Gal-GlcNAc6S-Gal-GlcNAc6S-. Examination of keratan sulfate from 10-year-old cartilage shows that capping by sialyl groups is complete, with (alpha2-3)-linkages predominant; for both this and the 38-year-old cartilage the three capping structures: NeuAc(alpha2-3)-Gal-GlcNAc6S-Gal-GlcNAc6S-, NeuAc(alpha2-3)-Gal-GlcNAc6S-Gal6S-GlcNAc6S-, and NeuAc(alpha2-3)-Gal6S-GlcNAc6S-Gal6S-GlcNAc6S- are clearly recognizable. The level of (alpha2-6)-linked chain capping sialyl groups is significant for 38-year-old cartilage keratan sulfate. Structural information concerning the linkage region to protein and the distribution of galactose environments is readily obtained from the spectra. Signal complexities severely limit the usefulness of two-dimensional correlation spectroscopy at 600 MHz for the examination of N-acetylglucosamine residues within the poly(N-acetyllactosamine) repeat sequence and signals representing fucose placements remain undifferentiated. This nondestructive approach complements current degradative methods for the structural examination of keratan sulfates.

Isolation and characterization of proteoglycans from growing antlers of wapiti (Cervus elaphus)

Proteoglycans were extracted with 4 M guanidine-HCl from the zone of maturing chondrocytes, the site of endochondral ossification of growing antlers of wapiti (Cervus elaphus). Proteoglycans were isolated by DEAE-Sephacel chromatography and separated by Sepharose CL-4B chromatography into three fractions. Fraction I contained a high molecular mass (> 1000 kDa) chondroitin sulfate proteoglycan capable of interacting with hyaluronic acid. Its amino acid composition resembled that of the cartilage proteoglycan, aggrecan. Fraction II contained proteoglycans with intermediate molecular weight which were recognized by monoclonal antibodies specific to chondroitin sulfate and keratan sulfate. Fraction III contained a low molecular mass (< 160 kDa) proteoglycan, decorin, with a glucuronate-rich glycosaminoglycan chain.

Isolation, characterization and localization of glycosaminoglycans in growing antlers of wapiti (Cervus elaphus)

Glycosaminoglycans were isolated from the four sections (tip, upper, middle and base) of the main beam of growing antlers of wapiti (Cervus elaphus) by papain digestion and DEAE-Sephacel chromatography. Chondroitin sulfate was the major glycosaminoglycan in each section of antler accounting for, on average, 88% of the total uronic acid. The yield of chondroitin sulfate liberated from the tissue was approximately 6-fold greater in the cartilaginous (tip and upper) sections than in the bony (middle and base) sections. This was consistent with the higher intensity of glycosaminoglycan staining with either Alcian Blue or Safranin-O. The majority (average 88%) of chondroitin sulfate was precipitated with 40 and 50% ethanol. The average molecular size of chondroitin sulfate determined by gel chromatography on Sephacryl S-300 tended to be greater in the 40% ethanol than in the 50% ethanol fraction. In either fraction, the molecular size of chondroitin sulfate was smaller in cartilaginous tissues than in osseous tissues of growing antler. In addition to chondroitin sulfate, the antler contained small amounts of hyaluronic acid, dermatan sulfate and keratan sulfate. The immunohistochemical study showed wide distribution of chondroitin sulfate, decorin, and keratan sulfate throughout the antler. On the other hand, keratan sulfate was more prominent in the cartilaginous sections than in the bony sections where the anti-keratan sulfate monoclonal antibody staining was seen in the osteoid tissue only.

Structure of keratan sulfate from bonefish (Albula sp.) larvae deduced from NMR spectroscopy of keratanase-derived oligosaccharides

Structural details of keratan sulfate (KS) glycosaminoglycan, isolated from early-metamorphosing larvae (leptocephali) of bonefish (Albula sp.), are described. Bonefish KS was analyzed by first hydrolyzing the purified compound with KS endo-beta-galactosidase (keratanase) from Pseudomonas spp., and then examining the resulting oligosaccharides with reversed-phase high-performance liquid chromatography (HPLC) and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy at 400 MHz. Spectral analyses were performed by COSY and HMQC. The results showed that a single oligosaccharide was produced whose structure is consistent with that of a tetrasaccharide containing two, beta-linked, N-acetyllactosamine units. Enzymic evidence indicated that the internal galactose of the tetrasaccharide was O-sulfated at C-6, and that the reducing-end galactose was unsulfated. Spectral data for C-1 of the two galactose residues were consistent with the proposed sulfation pattern. In addition, spectral evidence confirmed that a C-6 on one of the sugars was sulfated: this sulfate was tentatively assigned to the internal galactose. Chemical studies have shown that an additional sulfate group is present, but its assignment could not be confirmed, owing to the complexity of the spectral data. The known specificities of keratanase, and the production of a single tetrasaccharide, however, require that the additional sulfate reside on C-6 of either of the two available N-acetylglucosamine (GlcNAc) moieties, and that it cannot alternate between the two. The inability of beta-N-acetylglucosaminidase from beef kidney to liberate GlcNAc from the tetrasaccharide provided preliminary support for the view that this sulfate is located on the nonreducing-end GlcNAc. We conclude that the native, high molecular weight (M(r) = 55,000) KS polymer from bonefish larvae consists of a disulfated disaccharide alternating with an unsulfated disaccharide in the adjacent N-acetyllactosamine unit, with this pattern repeating itself in a regular fashion along most, or all, of the chain. This structure could provide an explanation for the ability of bonefish KS chains to self-associate into dimers. Although the N-acetyllactosamine repeat is characteristics of KS in general, the sulfation pattern is different from that postulated for the well-characterized KS chains of lower molecular weight obtained from mammalian cornea and cartilage. An additional difference was the inability to demonstrate sialic acid in bonefish KS.

Bone matrix proteins: isolation and characterization of a novel cell-binding keratan sulfate proteoglycan (osteoadherin) from bovine bone

A small cell-binding proteoglycan for which we propose the name osteoadherin was extracted from bovine bone with guanidine hydrochloride-containing EDTA. It was purified to homogeneity using a combination of ion-exchange chromatography, hydroxyapatite chromatography, and gel filtration. The Mof the proteoglycan was 85, 000 as determined by SDS-PAGE. The protein is rich in aspartic acid, glutamic acid, and leucine. Two internal octapeptides from the proteoglycan contained the sequences Glu-Ile-Asn-Leu-Ser-His-Asn-Lys and Arg-Asp-Leu-Tyr-Phe-Asn-Lys-Ile. These sequences are not previously described, and support the notion that osteoadherin belongs to the family of leucine-rich repeat proteins. A monospecific antiserum was raised in rabbits. An enzyme-linked immunosorbent assay was developed, and showed the osteoadherin content of bone extracts to be 0.4 mg/g of tissue wet weight, whereas none was found in extracts of various other bovine tissues. Metabolic labeling of primary bovine osteoblasts followed by immunoprecipitation showed the cells to synthesize and secrete the proteoglycan. Digesting the immunoprecipitated osteoadherin with N-glycosidase reduced its apparent size to 47 kD, thus showing the presence of several N-linked oligosaccharides. Digestion with keratanase indicated some of the oligosaccharides to be extended to keratan sulfate chains. In immunohistochemical studies of the bovine fetal rib growth plate, osteoadherin was exclusively identified in the primary bone spongiosa. Osteoadherin binds to hydroxyapatite. A potential function of this proteoglycan is to bind cells, since we showed it to be as efficient as fibronectin in promoting osteoblast attachment in vitro. The binding appears to be mediated by the integrin alphavbeta3, since this was the only integrin isolated by osteoadherin affinity chromatography of surface-iodinated osteoblast extracts.

13C-NMR spectroscopy of keratan sulphates--assignments for five sialylated pentasaccharides derived from the non-reducing chain termini of bovine articular cartilage keratan sulphate by keratanase II digestion

Skeletal keratan sulphate has been fragmented using the enzyme keratanase II, and 13C chemical-shift data are reported for five reduced sialylated pentasaccharides that derived from the non-reducing chain terminal region. They have the structures: NeuAc(alpha2-6)Gal(beta1-4)GlcNAc6S(beta1-3)Gal(beta1-4)GlcNAc6 S-ol, NeuAc(alpha2-3)Gal(beta1-4)GlcNAc6S(beta1-3)Gal(beta1-4)GlcNAc6 S-ol, NeuAc(alpha2-6)Gal(beta1-4)GlcNAc6S(beta1-3)Gal6S(beta1-4)++ +GlcNAc6S-ol, NeuAc(alpha2-3)Gal(beta1-4)GlcNAc6S(beta1-3)Gal(6S)(beta1-4)Glc NAc6S-ol, and NeuAc(alpha2-3)Gal(6S)(beta1-4)GlcNAc6S(beta1-3)Gal(6S)(beta1-4)++ +GlcNAc6S-ol, where GlcNAc6S-ol represents N-acetyl-glucosaminitol 6-O-sulphate and NeuAc represents N-acetylneuraminic acid. The use of these 13C-NMR spectroscopy data for the recognition of specific chain-capping structures within native keratan sulphates is discussed. In addition, examination of the data derived from the NeuAc(alpha2-6) capping structures strongly suggests that sulphation three residues away from the neuraminic acid cap has a profound effect upon the conformation of the capping region.

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

Fibromodulin has been isolated from bovine and equine articular cartilage and the attached keratan sulphate chains subjected to digestion by keratanase II. The oligosaccharides generated have been reduced and subsequently isolated by strong anion-exchange chromatography. Their structures have been determined by high-field 1H-NMR spectroscopy and high-pH anion-exchange chromatography. Both alpha(2-6)- and alpha(2-3)-linked N-acetylneuraminic acid have been found in the capping oligosaccharides, and, fucose which is alpha(1-3)-linked to N-acetylglucosamine has been found as a branch in both repeat region and capping oligosaccharides. These data demonstrate that there are fundamental differences between the structures present in the N-linked keratan sulphate chains attached to fibromodulin from articular cartilage and those from tracheal cartilage, which lack both alpha(2-6)-linked N-acetylneuraminic acid and alpha(1-3)-linked fucose. It has been confirmed that the keratan sulphate chains are short, being only eight or nine disaccharides in length. Very significant differences in the levels of galactose sulphation have been identified at the non-reducing end of the chain. The galactose residue adjacent to the non-reducing cap is sulphated in only 1-3% of chains, compared with a sulphation level of over 40% closer to the reducing end. This highlights the difference between the chain termini and the repeat region in terms of structure and points to the potential for functional importance. The repeat region and capping fragments of the N-linked keratan sulphates from bovine and equine articular cartilage fibromodulin have been found to have the following general structure: NeuAc-(alpha 2-3/6)Gal[6SO3-](beta 1-4)GlcNAc6SO3-(beta 1-3)Gal[6SO3-] (beta 1-4)¿[Fuc(alpha 1-3)]0-1GlcNAc6SO3-(beta 1-3)Gal-[6SO3-](beta 1-4)¿ 6-7GlcNAc6SO3-.

Evidence for the presence of a large keratan sulphate proteoglycan in the human uterine cervix

Profound changes occur in the uterine cervix during pregnancy. In particular, the extracellular matrix of the connective tissue is remodelled extensively. To elucidate the mechanisms involved in this process, we have analysed the proteoglycan pattern in the human cervix from pregnant and non-pregnant women. Proteoglycans of the cervix tissue specimen were extracted with 4 M guanidine hydrochloride and precipitated with 80% ethanol. Purification of proteoglycans was performed by several chromatographic steps. Characterization of proteoglycans was done by SDS/PAGE before and after digestion with glycosaminoglycan-specific enzymes. Proteoglycans were detected by combined Alcian Blue/silver staining or, after blotting of biotin-labelled proteoglycans on to poly(vinylidene difluoride) membrane, with peroxidase-conjugated avidin or by the use of keratan sulphate- or decorin-specific monoclonal antibodies. In contrast with previous reports, where only chondroitin/dermatan sulphate proteoglycans have been found in the uterine cervix, we have shown in the present study the existence of a large keratan sulphate proteoglycan with an M(r) > 220,000 in cervix samples from non-pregnant and pregnant women. This proteoglycan showed a strong reaction with the keratan sulphate-specific monoclonal antibody 5D4 and could be degraded by keratanases. The size of the core protein of this keratan sulphate proteoglycan was estimated to be about M(r) 220,000.

A novel keratan sulphate domain preferentially expressed on the large aggregating proteoglycan from human articular cartilage is recognized by the monoclonal antibody 3D12/H7

Monoclonal antibodies (mAbs) were prepared against aggrecan which has been isolated from human articular cartilage and purified by several chromatographic steps. One of these mAbs, the aggrecan-specific mAb 3D12/H7, was selected for further characterization. The data presented indicate that this mAb recognizes a novel domain of keratan sulphate chains from aggrecan: (1) immunochemical staining of aggrecan is abolished by treatment with keratanase/keratanase II, but not with keratanase or chondroitin sulphate lyase AC/ABC; (2) after chemical deglycosylation of aggrecan no staining of the core-protein was observed; (3) different immunochemical reactivity was observed against keratan sulphates from articular cartilage, intervertebral disc and cornea for the mAbs 3D12/H7 and 5D4. For further characterization of the epitope, reduced and 3H-labelled keratan sulphate chains were prepared. In an IEF-gel-shift assay it was shown that the 3H-labelled oligosaccharides obtained after keratanase digestion of reduced and 3H-labelled keratan sulphate chains were recognized by the mAb 3D12/H7. Thus it can be concluded that the mAb 3D12/H7 recognizes an epitope in the linkage region present in, at least some, keratan sulphate chains of the large aggregating proteoglycan from human articular cartilage. Moreover, this domain seems to be expressed preferentially on those keratan sulphate chains which occur in the chondroitin sulphate-rich region of aggrecan, since the antibody does not recognize the keratan sulphate-rich region obtained after combined chondroitinase AC/ABC and trypsin digestion of aggrecan.

Up-regulation of a keratan sulfate proteoglycan following cortical injury in neonatal rats

The up-regulation of the keratan sulfate proteoglycan (ABAKAN) was examined using indirect immunohistochemical methods. Previous studies indicate that the keratan sulfate proteoglycan is associated with astrocytes in the optic nerve and in the developing rat brain. In model culture systems, this proteoglycan is capable of inhibiting the growth of neurites over laminin. To determine whether the proteoglycan is up-regulated specifically during reactive gliosis, stab wounds were made in the cerebral cortex of early postnatal rats, and the up-regulation of the proteoglycan was related to the developmentally regulated gliotic response to injury. Following a stab wound in the cortex of the late postnatal rat, reactive gliosis was consistently observed along with an up-regulation of ABAKAN. When the cortex was injured on postnatal day 2, there was a variable gliotic response and considerable variation in the regulation of proteoglycan expression. Biochemical analysis revealed that ABAKAN is a large proteoglycan with multiple keratan sulfate side-chains, at least one chondroitin sulfate side-chain and at least one additional carbohydrate chain with a terminal 3-sulfoglucuronic acid. Taken together, these data demonstrate that the boundary proteoglycan ABAKAN is also associated with reactive gliosis during early postnatal development.

Transport of UDP-galactose into the Golgi lumen regulates the biosynthesis of proteoglycans

The lumen of the Golgi apparatus is the subcellular site where galactose is transferred, from UDP-galactose, to the oligosaccharide chains of glycoproteins, glycolipids, and proteoglycans. The nucleotide sugar, which is synthesized in the cytosol, must first be transported into the Golgi lumen by a specific UDP-galactose transporter. Previously, a mutant polarized epithelial cell (MDCKII-RCAr) with a 2% residual rate of transport of UDP-galactose into the lumen of Golgi vesicles was described (Brandli, A. W., Hansson, G. C., Rodriguez-Boulan, E., and Simons, K. (1988) J. Biol. Chem. 263, 16283-16290). The mutant has an enrichment in glucosyl ceramide and cell surface glycoconjugates bearing terminal N-acetylglucosamine, as well as a 75% reduction in sialylation of cell surface glycoproteins and glycosphingolipids. We have now studied the biosynthesis of galactose containing proteoglycans in this mutant and the corresponding parental cell line. Wild-type Madin-Darby canine kidney cells synthesize significant amounts of chondroitin sulfate, heparan sulfate, and keratan sulfate, while the above mutant synthesizes chondroitin sulfate and heparan sulfate but not keratan sulfate, the only proteoglycan containing galactose in its glycosaminoglycan polymer. The mutant also synthesizes chondroitin 6-sulfate rather than only chondroitin 4-sulfate as wild-type cells. Together, the above results demonstrate that the Golgi membrane UDP-galactose transporter is rate-limiting in the supply of UDP-galactose into the Golgi lumen; this in turn results in selective galactosylation of macromolecules. Apparently, the Km for galactosyltransferases involved in the synthesis of linkage regions of heparan sulfate and chondroitin sulfate are significantly lower than those participating in the synthesis of keratan sulfate polymer, glycoproteins, and glycolipids. The results also suggest that the 6-O-sulfotransferases, in the absence of their natural substrates (keratan sulfate) may catalyze the sulfation of chondroitin 4-sulfate as alternative substrate.

The structure of the keratan sulphate chains attached to fibromodulin isolated from bovine tracheal cartilage: oligosaccharides generated by keratanase II digestion

The repeat region and chain caps of the N-linked keratan sulphates attached to bovine tracheal cartilage fibromodulin were fragmented by digestion with keratanase II, and the oligosaccharides generated were isolated by strong anion-exchange chromatography. Each of these oligosaccharides has been examined by both HPAE chromatography and high field 1H-NMR spectroscopy. All of the capping oligosaccharides isolated terminated with alpha(2-6)-linked N-acetyl-neuraminic acid chain terminators, nor fucose alpha(1-3)-linked to N-acetylglucosamine were found. The keratan sulphate chains were short, with average lengths of five to seven disaccharides, and the level of galactose sulphation varied along the length of the chain. The repeat region and chain cap were confirmed as having the following general structure: [formula: see text]. This study has identified a novel structure in fibromodulin, namely a cap containing a sulphated galactose adjacent to a non-reducing terminal N-acetyl-neuraminic acid. We have also confirmed that the general structure of the repeat units and chain caps of N-linked keratan sulphate attached to fibromodulin isolated from bovine tracheal cartilage, is similar to that of O-linked keratan sulphate chains attached to aggrecan from non-articular cartilage. However, there are important differences in chain lengths and sulphation patterns.

N- and O-linked keratan sulfate on the hyaluronan binding region of aggrecan from mature and immature bovine cartilage

In the hyaluronan binding region (HABR) peptide of aggrecan, there is a marked increase in the level of keratan sulfate (KS) during aging. To determine the sites of KS attachment, KS-containing peptides were prepared from HABRs from immature and mature bovine articular cartilage by digestion with trypsin or papain followed by carbohydrate analysis and peptide sequencing. KS is attached to Thr42 within loop A in mature, but not in immature, HABR. Within loop B KS is N-linked to Asn220 in both HABRs, but in the immature HABR the chains are shorter. Asn314 in loop B' of mature HABR is substituted either with a KS chain or with an oligosaccharide of the complex type. In immature HABR this site does not carry KS. In the interglobular domain, 2 threonine residues within the sequence TIQTVT are substituted in both calf and steer, and in steer further substitution occurs within the sequence NITEGEA, which contains a major catabolic cleavage site (Sandy, J., Neame, P.J., Boynton, R., and Flannery, C.R. (1991) J. Biol. Chem. 266, 8683-8685). The extreme polydispersity of mature HABR was investigated by preparing four subfractions of increasing molecular size which had essentially the same protein core, i.e. Val1-Arg367 or Val1-Arg375. The smaller species lacked the KS chains attached to loop A. These results show that KS substitution occurs within each of the disulfide-bonded loops of the HABR, that the KS may be either N- or O-linked, and that variations in the addition of KS are responsible for the polydispersity of mature HABR.

Oligosaccharides derived by keratanase II digestion of bovine articular cartilage keratan sulphates

Alkaline borohydride-reduced keratan sulphate chains from bovine articular cartilage (6-8-year-old animals) were subjected to a limit digest with the enzyme keratanase II. Using 1H-NMR spectroscopy, 25 reduced oligosaccharides deriving from keratan sulphate were shown to have the following structures [GlcNAc(6S)-ol represents N-acetylglucosaminitol 6-O-sulphate]: Gal beta 1-4-GlcNAc(6S)-ol, Gal beta 1-4GlcNAc(6S)beta 1-3Gal beta 1-4GlcNAc(6S)-ol, Gal(6S)beta 1-4GlcNAc(6S)-ol, Gal-(6S)beta 1-4GlcNAc(6S) beta 1-3Gal beta 1-4GlcNAc(6S)-ol, Gal beta 1-4GlcNAc(6S)beta 1-3Gal(6S)beta 1-4GlcNAc(6S)-ol, Gal(6S)beta 1-4GlcNAc(6S)beta 1-3Gal(6S)1-4GlcNAc(6S)-ol, Gal beta 1-4(Fuc alpha 1-3)GlcNAc(6S)-ol, Gal beta 1-4-(Fuc alpha 1-3)GlcNAc(6S)beta1-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc(6S)-ol, Gal beta 1-4GlcNAc(6S)beta 1-3Gal beta 1-4(Fuc alpha 1-3)-GlcNAc(6S)-ol, Gal beta 1-4(Fuc alpha 1-3)GlcNAc(6S)beta 1-3Gal beta 1-4GlcNAc(6S)-ol, Gal(6S) beta 1-4GlcNAc-(6S)beta 1-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc(6S)-ol, Gal beta 1-4(Fuc alpha 1-3)GlcNAc(6S)beta 1-3Gal(6S)1-4GlcNAc(6S)-ol, Gal beta 1-4GlcNAc(6S)beta 1-6(Gal beta 1-3)GalNAc-ol, Gal beta 1-4GlcNAc(6S) beta1-6(NeuAc2-3Gal beta 1-3)Gal-NAc-ol, Gal beta 1-4GlcNAc(6S)beta 1-3Gal beta 1-4GlcNAc(6S)beta 1-6(Gal beta 1-3) GalNAc-ol, Gal(6S)beta 1-4GlcNAc-(6S)beta 1-6(Gal beta 1-3)GalNAc-ol, Gal beta 1-4GlcNAc(6S)beta 1-3Gal beta 1-4GlcNAc(6S)beta 1-6(NeuAc2-3Gal beta 1-3)-GalNAc-ol, Gal(6S)beta 1-4GlcNAc(6S)beta 1-6(NeuAc alpha 2-3Gal beta 1-3)GalNAc-ol, Gal(6S) beta 1-4GlcNAc-(6S)beta 1-3Gal beta 1-4GlcNAc(6S)beta 1-6(Gal beta 1-3)GalNAc- ol, Gal(6S)beta 1-4GlcNAc(6S)beta 1-3Gal beta 1-4GlcNAc-(6S)beta 1-6(NeuAc alpha 2-3Gal beta 1-3)GalNAc-ol, NeuAc alpha 2-6Gal beta 1-4GlcNAc(6S)beta 1-3Gal beta 1-4GlcNAc(6S)-ol, NeuAc alpha 2-3Gal beta 1-4GlcNAc(6S)beta 1-3Gal beta 1-4GlcNAc(6S)-ol, NeuAc alpha 2-6Gal beta 1-4GlcNAc(6S)beta 1-3Gal-(6S)beta 1-4GlcNAc(6S)-ol, NeuAc alpha 2-3Gal beta 1-4GlcNAc(6S)beta 1-3Gal(6S)beta 1-4GlcNAc(6S)-ol and Neu-Ac alpha 2-3Gal(6S)beta 1-4GlcNAc(6S)beta 1-3Gal(6S beta)1-4GlcNAc(6S)-ol. Proton chemical shifts for these oligosaccharides were assigned using one- and two-dimensional NMR spectroscopic methods. These results confirm the findings of Nakazawa et al. [Nakazawa, K., Ito, M., Yamagata, T. and Suzuki, S. (1989) in Keratan sulphate: chemistry, biology and chemical pathology (Greiling, H. and Scott, J.E., eds) pp. 99-110, The Biochemical Society, London], namely that keratanase II cleaves the O-glycosidic bond of a beta(1-3)-linked 6-O-sulphated N-acetylglucosamine.(ABSTRACT TRUNCATED AT 400 WORDS)

Production and characterization of monoclonal antibodies to shark cartilage proteoglycan

1. Two proteoglycans, PG1 and PG2, have been isolated from shark cartilage. Both are highly polydisperse and large (molecular mass: 1-10 x 10(6) Daltons) and contain chondroitin sulfate and keratan sulfate side chains, but PG2 is somewhat smaller than PG1 and contains less keratan sulfate. 2. Monoclonal antibodies were raised against PG1. Many antibodies were obtained and one of them, MST1, was subcloned and further characterized. This monoclonal antibody reacts with PG1 and PG2 from shark cartilage and also with aggrecan from bovine trachea cartilage. Chondroitinase AC-treated proteoglycans react with MST1, indicating that the antibody does not recognize chondroitin sulfate. MST1 also recognizes aggrecan from human cartilage and a proteoglycan from bovine brain (neurocan) but it does not recognize proteoglycans from rat Walker tumor, fetal calf muscle and decorin from human myoma. 3. Using MST1 we were able to demonstrate that both PG1 and PG2 aggregate with hyaluronic acid.

Molecular polymorphism of lumican during corneal development

PURPOSE

To evaluate the expression of lumican and decorin, the major proteoglycans of the adult corneal stroma, during the acquisition of corneal transparency in developing chick embryos.

METHODS

mRNA levels of decorin and lumican were measured in total RNA extracted from corneas of days 9 to 18 of development by Northern blot analysis using a 32P-labeled cDNA clone to each proteoglycan. The synthesis lumican and decorin precursor proteins were determined by biosynthetically radiolabeling corneas from day 7 to 18 chick embryos with 35S-methionine, and then using antibodies specific for lumican and decorin core proteins to precipitate the radiolabeled precursor proteins. The accumulation of lumican and decorin was determined by fractionating extracts of day 7 to 18 embryonic corneas by DEAE chromatography into glycoprotein and proteoglycan fractions, and then analyzing each fraction by Western blot using antibodies to lumican and decorin.

RESULTS

Lumican and decorin mRNA increased from day 9 to day 18, with respect to beta-actin. The rate of decorin precursor protein synthesis remained relatively low and constant throughout development, but lumican precursor protein synthesis increased dramatically between days 7 and 9 of embryonic development, to a value 80-fold higher than that of decorin, and then decreased exponentially through day 18. Lumican with polylactosamine (nonsulfated keratan sulfate) side chains was detected in extracts of corneas as early as day 7 of embryonic development, and continued to accumulate within the cornea through day 18. Decorin and lumican with sulfated glycosaminoglycan side chains (ie, proteoglycans), however, were not detected in corneal extracts until day 15, when transparency starts to increase, and then accumulated considerably within the cornea by day 18.

CONCLUSIONS

The results of these studies suggest that decorin and lumican expression are independently regulated during the period of acquisition of corneal transparency. The switch in production of the polylactosamine form of lumican to the proteoglycan form of lumican at the onset of increasing corneal transparency suggests that the sulfation of lumican may be important for the development of corneal transparency.

Immunoglobulin G and serum albumin isolated from the articular cartilage of patients with rheumatoid arthritis or osteoarthritis contain covalent heteropolymers with proteoglycans

The present study was undertaken to identify the cartilage matrix molecules that are bound with intermolecular disulfide bonds to IgG and serum albumin molecules recovered from the articular cartilage of patients with rheumatoid arthritis (RA) or osteoarthritis (OA). The cartilage specimens were extracted sequentially with three changes of neutral buffer, three changes of 6 M guanidine hydrochloride and then partially degraded with bacterial collagenase. The extracted IgG and albumin, along with matrix molecules bound to these proteins, were isolated with affinity chromatography using antibodies to IgG or human serum albumin conjugated to agarose beads. The isolated materials were characterized with sodium dodecyl sulfate polyacrylamide gel electrophoresis and transfer blotting, using specific antibodies to IgG, albumin, and proteoglycans. In the isolated materials, heteropolymers with IgG or albumin were identified. These polymers contained keratan sulfate and less frequently chondroitin-4-sulfate and chondroitin-6-sulfate. These findings identified the keratan sulfate rich proteoglycans, prevalent at the surface of joint cartilage, as the most common cartilage matrix molecules that are covalently bound to IgG or to serum albumin by disulfide bonds in the articular cartilage of patients with RA or OA.

Regulation of corneal collagen fibrillogenesis in vitro by corneal proteoglycan (lumican and decorin) core proteins

Corneal transparency is dependent on the size and arrangement of collagen fibrils within the corneal stroma. The corneal stroma is composed primarily of collagen type 1 fibrils and two proteoglycans: one with chondroitin/dermatan sulfate side-chains (decorin) and one with keratan sulfate side-chains (lumican). We investigated the effects of the corneal proteoglycans on corneal collagen fibrillogenesis, utilizing an in vitro assay for fibril formation. Collagen was extracted from bovine corneal stromas with 0.1 M acetic acid and monomers purified by NaCl precipitation. Decorin and lumican were extracted from bovine corneal stroma with either 0.7 M NaCl or 4 M guanidine HCl and purified by DEAE and Sepharose CL-4B chromatography. Decorin and lumican from both extracts inhibited the rate of collagen fibrillogenesis and the development of turbidity in fibrillogenesis samples. Furthermore, the core proteins of decorin and lumican were shown to be as effective as the intact proteoglycans in inhibiting fibrillogenesis. The decorin core protein isolated from the 0.7 M NaCl extract was determined to be a 20 kDa fragment which lacks the C-terminal half of the core protein. This fragment was approximately 1/36 as effective in inhibiting fibrillogenesis as intact decorin isolated from guanidine extracts. This suggests that the C-terminal half of the decorin core plays an important role in the interaction of this proteoglycan with collagen. Lumican extracted with 0.7 M NaCl was slightly smaller and was only one-sixth as effective in inhibiting collagen fibril formation as 4 M guanidine extracted lumican. Furthermore reduction and alkylation of lumican core protein abolished the inhibitory activity of the core protein on collagen fibrillogenesis. Electron microscopic examination indicated that fibrils formed in the presence of lumican and lumican core protein were significantly thinner than fibrils formed in the absence of proteoglycans. The results of these studies indicate that in addition to decorin, lumican retards corneal collagen fibrillogenesis and results in the formation of collagen fibrils which are significantly thinner than those formed in the absence of any proteoglycan. The inhibitory activity of lumican or decorin on collagen fibrillogenesis resides in he core proteins of these proteoglycans, not the glycosaminoglycan side chains, and that interaction of the lumican core protein with collagen appears to be dependent on the presence of disulfide bridges within the protein core.

Isolation and partial characterization of lumican and decorin from adult chicken corneas. A keratan sulfate-containing isoform of decorin is developmentally regulated

The proteoglycans extracted from adult chicken were initially purified by DEAE-chromatography. Digestion of these proteoglycans with chondroitinase ABC generated a single 40-kDa core protein while digestion with keratanase generated a single 52-kDa core protein. Digestion with both enzymes combined, however, increased the amount of 40-kDa core protein produced. This suggested that the 40-kDa core protein exists with chondroitin/dermatan sulfate (C/DS) side chains alone and with both C/DS and keratan sulfate (KS) side chains. The proteoglycan fraction was initially digested with chondroitinase ABC, and the M(r) = 40,000 core protein derived from proteoglycans containing C/DS side chains alone was isolated. Amino-terminal sequencing showed it to be the chick cognate of decorin. The remaining proteoglycans were then digested with keratanase, and both the 40-kDa core protein and the 52-kDa core proteins derived from KS-containing proteoglycans were purified. The M(r) = 40,000 core protein derived from proteoglycans containing both C/DS and KS side chains had the same amino-terminal sequence as decorin and cross-reacted with antibodies to decorin. Sequence from the 52-kDa core protein derived from KS-containing proteoglycans showed it to be lumican. The results of this study suggest that adult chick corneas contain two isoforms of decorin: one containing C/DS side chains and the other, a hybrid, containing both C/DS and KS side chains. Embryonic corneas did not contain the hybrid isoform of decorin. These results suggest that different post-translational modifications occur to the decorin gene product during corneal development and maturation.

A novel keratan sulphate proteoglycan from a human embryonal carcinoma cell line

We describe here the purification and partial characterization of a 200 kDa keratan sulphate proteoglycan found in the pericellular matrix of human embryonal carcinoma cells. Previously we have shown that this molecule is recognized by a monoclonal antibody (GCTM-2). The antigen was isolated using ion-exchange chromatography and gel filtration, purification being monitored by e.l.i.s.a. using GCTM-2. Metabolic labelling of GCT 27 C-4 embryonal carcinoma cells with sodium [35S]sulphate resulted in the incorporation of [35S]sulphate into the purified molecule. Throughout the purification procedure, the peaks of 35S radioactivity were coincident with the peaks of immunoreactivity, and this label was released both by digestion with keratanase and chondroitinase, confirming the proteoglycan nature of the antigen. The intact molecule ran as a single broad band of 200 kDa, which has been identified by silver staining and immunoblotting following gel electrophoresis. Amino acid analysis of the purified antigen indicated a high content of serine, glycine and aspartic acid/asparagine residues. Visualization by rotary-shadowing electron microscopy suggests that the purified material forms large aggregates, even under denaturing conditions. Deglycosylation of this preparation with trifluoromethanesulphonic acid yielded a major band of 55 kDa and a minor band of 48 kDa. The biochemical nature of the molecule described here, along with tissue distribution studies using GCTM-2, indicates that the antigen is not related to previously described keratan sulphate proteoglycans.

A sub-population of keratan sulphates derived from bovine articular cartilage is capped with alpha(2-6)-linked N-acetylneuraminic acid residues. Affinity chromatography using immobilized Sambucus nigra lectin and characterization using 1H n.m.r. spectroscopy

Alkaline borohydride-reduced keratan sulphate (KS) chains derived from bovine femoral head cartilage were fractionated by lectin affinity chromatography with Sambucus nigra agglutinin (SNA) into binding and non-binding populations. Analysis of the SNA-binding and non-binding KS chains using 600 MHz 1H n.m.r. spectroscopy showed that the former population contained alpha(2-6)-N-acetylneuraminic acid residues and the latter contained primarily alpha(2-3)-N-acetylneuraminic acid residues as chain terminators. Both populations contained a similar proportion of alpha(2-3)-N-acetylneuraminic acid residues within their protein-linkage regions, and similar sulphation and fucosylation levels. Analysis of these two fractions by gel-permeation chromatography (g.p.c.) on a TSK-30 XL column showed them to have the same size distributions. It was concluded from the n.m.r. spectra and g.p.c. data that the populations differed primarily in the mode of linkage of the chain-terminating sialic acids.

Heterogeneity of keratan sulfate substituted on human chondrocytic large proteoglycans

Newly synthesized 35S-labeled chondrocytic keratan sulfate chains were generated by chondrocytes of human chondrosarcoma cell line 105KC and were analyzed for heterogeneity of regional substitution, hydrodynamic size, and charge density. After isolation of the high density large chondrocytic proteoglycans and sequential digestions with chondroitinase ABC, L-1-tosylamido-2-phenylethyl chloromethyl ketone-treated trypsin, and alpha-chymotrypsin, followed by Superose 6 chromatography, two populations of keratan sulfate-containing proteoglycan fragments were identified and pooled separately. Keratan sulfate chains from each of the regions were compared after release by Pronase digestion, and differences in substitution patterns were observed; keratan sulfate chains of greater polydispersity, as well as a population of larger hydrodynamic size, were present in only one of the two regions. Alkaline/borohydride treatment confirmed both the existence of a population of uniquely large keratan sulfate chains and its restriction to a single region of proteoglycan fragments. In addition to heterogeneity of hydrodynamic size, the keratan sulfate chains exhibited regional heterogeneity of charge density and hence, of sulfation patterns. Analysis by Mono Q chromatography identified distinct groups of keratan sulfate that segregated by charge density and whose proportionate composition differed between the proteoglycan regions. Furthermore, the most highly charged species were unique to a single region and encompassed the chains of larger hydrodynamic size. This suggests that there may be regional heterogeneity of keratan sulfate chains substituted along a single class of proteoglycans and identifies a novel population of large, highly sulfated chondrocytic keratan sulfate chains.

Skeletal keratan sulphate chains isolated from bovine intervertebral disc may terminate in alpha(2----6)-linked N-acetylneuraminic acid

Peptido-keratan sulphate fragments were isolated from the nucleus pulposus of bovine intervertebral discs (2-year-old animals) after digestion with chondroitin ABC lyase followed by digestion with diphenylcarbamoyl chloride-treated trypsin of A1D1 proteoglycans and gel-permeation chromatography on Sepharose CL-6B. The peptido-keratan sulphate fragments were subjected to alkaline borohydride reduction. The reduced chains were treated with keratanase in the presence of the sialidase inhibitor 2,3-dehydro-2-deoxy-N-acetylneuraminic acid, and the digest was subjected to alkaline borohydride reduction. This produced oligosaccharides with galactitol at their reducing ends. This reduced digest was chromatographed on a Nucleosil 5 SB anion-exchange column and individual oligosaccharides were isolated. One of these was shown by 600 MHz 1H-n.m.r. spectroscopy to have the following structure: NeuAc alpha 2-6Gal beta 1-4GlcNAc(6-SO4)beta 1-3Gal-ol The structure of this oligosaccharide shows that keratan sulphate chains from bovine intervertebral disc have non-reducing termini with N-acetylneuraminic acid linked alpha(2----6) as well as alpha(2----3) to an unsulphated galactose.

Arterial lumican. Properties of a corneal-type keratan sulfate proteoglycan from bovine aorta

A glycoprotein reactive with antibodies against corneal keratan sulfate proteoglycan (KSPG) was purified 300-fold from extracts of bovine aorta using DEAE ion-exchange, gel-filtration, hydrophobic interaction, and reverse-phase chromatographic separations. The intact glycoprotein was 70-80 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Deglycosylation with endo-beta-galactosidase and N-glycanase reduced the size to 48 and 37 kDa, respectively, similar to the large isoforms of corneal KSPG. N-terminal amino acid sequence of the arterial KSPG was identical with lumican, the 37B isoform of corneal KSPG, and the arterial KSPG reacted with an antibody to synthetic peptide duplicating this sequence. Arterial KSPG and corneal lumican displayed identical tryptic maps. Arterial lumican contains fucose and mannose in amounts similar to corneal KSPG, but galactose, glucosamine, and sulfate were reduced compared to KSPG from cornea. Treatment of arterial lumican with endo-beta-galactosidase released 8-9 mol of glucosamine and galactose per mol of protein as oligosaccharides. These eluted as neutral, nonsulfated oligosaccharides on high pH anion-exchange chromatography. The size of arterial lumican was not altered by glycosidases having specificity for sulfated keratan sulfate, nor was the charge of the lumican molecule altered by digestion with endo-beta-galactosidase. These data show arterial lumican to be a glycoprotein containing unsulfated lactosaminoglycan chains. Abundance of low sulfate lumican in many tissues indicates that this protein occurs predominantly as a glycoprotein rather than as the more widely studied, highly sulfated proteoglycan present in the cornea.

Isolation and characterization of developmentally regulated chondroitin sulfate and chondroitin/keratan sulfate proteoglycans of brain identified with monoclonal antibodies

A panel of monoclonal antibodies prepared to the chondroitin sulfate proteoglycans of rat brain was used for their immunocytochemical localization and isolation of individual proteoglycan species by immunoaffinity chromatography. One of these proteoglycans (designated 1D1) consists of a major component with an average molecular size of 300 kDa in 7-day brain, containing a 245-kDa core glycoprotein and an average of three 22-kDa chondroitin sulfate chains. A 1D1 proteoglycan of approximately 180 kDa with a 150-kDa core glycoprotein is also present at 7 days, and by 2-3 weeks postnatal this becomes the major species, containing a single 32-kDa chondroitin 4-sulfate chain. The concentration of 1D1 decreases during development, from 20% of the total chondroitin sulfate proteoglycan protein (0.1 mg/g brain) at 7 days postnatal to 6% in adult brain. A 45-kDa protein which is recognized by the 8A4 monoclonal antibody to rat chondrosarcoma link protein copurifies with the 1D1 proteoglycan, which aggregates to a significant extent with hyaluronic acid. A chondroitin/keratan sulfate proteoglycan (designated 3H1) with a size of approximately 500 kDa was isolated from rat brain using monoclonal antibodies to the keratan sulfate chains. The core glycoprotein obtained after treatment of the 3H1 proteoglycan with chondroitinase ABC and endo-beta-galactosidase decreases in size from approximately 360 kDa at 7 days to approximately 280 kDa in adult brain. In 7-day brain, the proteoglycan contains three to five 25-kDa chondroitin 4-sulfate chains and three to six 8.4-kDa keratan sulfate chains, whereas the adult brain proteoglycan contains two to four chondroitin 4-sulfate chains and eight to nine keratan sulfate chains, with an average size of 10 kDa. The concentration of 3H1 increases during development from 3% of the total soluble proteoglycan protein at 7 days to 11% in adult brain, and there is a developmental decrease in the branching and/or sulfation of the keratan sulfate chains. A third monoclonal antibody (3F8) was used to isolate a approximately 500-kDa chondroitin sulfate proteoglycan comprising a 400-kDa core glycoprotein and an average of four 28-kDa chondroitin sulfate chains. In the 1D1 and 3F8 proteoglycans of 7-day brain, 20 and 33%, respectively, of the chondroitin sulfate is 6-sulfated, whereas chondroitin 4-sulfate accounts for greater than 96% of the glycosaminoglycan chains in the adult brain proteoglycans.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell-free translation and characterization of corneal keratan sulfate proteoglycan core proteins

Bovine corneal keratan sulfate proteoglycan (KSPG) contains two core proteins, 37 and 25 kDa, if fully deglycosylated, but 47 and 35 kDa, respectively, after endo-beta-galactosidase (Funderburgh, J. L., and Conrad, G. W. (1990) J. Biol Chem. 265, 8297-8303). Chicken corneal KSPG released a single core protein of 47 kDa after endo-beta-galactosidase, and of 35 and 36 kDa, if deglycosylated with N-glycanase or trifluoromethanesulfonic acid. Affinity purified rabbit antibodies against each KSPG recognized only the intact proteoglycan or its core proteins in immunoblots of unfractionated guanidine-HCl extracts of whole cornea after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Affinity purified antibody to a synthetic peptide duplicating the NH2-terminal sequence of the 37-kDa bovine core protein showed little reactivity with untreated corneal extract but reacted with the 47-kDa bovine protein in endo-beta-galactosidase-treated extracts. RNA was isolated from bovine and chick corneal stromas and used for in vitro translation. Antibody against bovine KSPG immunoprecipitated two proteins of 56-53 kDa and a protein of 41 kDa after translation of bovine RNA. Translation of chick RNA produced a double band of 38-39 kDa and a single band of 25 kDa precipitating with antibody against chicken KSPG. Homologous unlabeled KSPG competed for binding of antibodies to these translation products. These data suggest that in vertebrate corneas, the multiple KSPG core protein isoforms may arise as products of separate mRNAs, rather than from proteolytic processing of a large polypeptide precursor.

Isoforms of corneal keratan sulfate proteoglycan

Bovine corneal keratan sulfate proteoglycan was found to contain three major protein components. Two proteins (37 and 25 kDa) were released from the proteoglycan by endo-beta-galactosidase, N-glycanase, or chemical deglycosylation. A smaller protein (20 kDa), not covalently linked to keratan sulfate, co-purified with the proteoglycan by conventional and high performance ion exchange chromatography, by ethanol precipitation, and by affinity purification on columns of monoclonal antibody to keratan sulfate, but could be separated from the proteoglycan by gel filtration chromatography in dissociative agents. The three proteins produced different fragmentation patterns on sodium dodecyl sulfate-polyacrylamide gel electrophoresis after digestion with V8 protease, and each had unique two-dimensional tryptic peptide maps. The N-terminal amino acid sequence of the core proteins differed. In addition, the proteoglycans containing these proteins differed in molecular size, suggesting different levels of glycosylation of the two core proteins. Similarity of the core proteins was suggested by similar amino acid composition, similarities in tryptic maps, and antigenic cross-reactivity. Corneal keratan sulfate proteoglycan, therefore, seems to occur in two different, but related, forms whose core proteins may represent members of a homologous family.

Synthesis of small proteoglycans substituted with keratan sulfate by rabbit articular chondrocytes

35S-Labeled proteoglycans produced by chondrocytes from immature and mature rabbits were fractionated on associative CsCl gradients. In all cultures, greater than 85% of the incorporated radioactivity was present in the A1 fraction (rho 1.60) as chondroitin sulfate/keratin sulfate-substituted aggregating proteoglycan monomer; the remainder was present in small proteoglycans in the A2, A3, and A4 fractions of low buoyant densities (rho 1.53, 1.45, 1.37, respectively). Detailed glycosaminoglycan analysis of the A2, A3, and A4 fractions showed dermatan sulfate-rich species were present throughout. However, in both immature and mature cultures, 30-45% of the glycosaminoglycans in the A3/A4 combined fractions were present as keratan sulfate, as shown by insensitivity to digestion with chondroitinase ABC, specific digestion with endo-beta-galactosidase, and reactivity with antibody 5D4. Immature and mature chondrocytes synthesized very similar amounts of the low buoyant density keratan sulfate proteoglycan on a per cell basis. Moreover, 51 and 37% of the total keratan sulfate produced by immature and mature chondrocytes, respectively, were present in the low buoyant density proteoglycan. Pulse-chase experiments indicated that the low buoyant density keratan sulfate was not derived from the large aggregating proteoglycan by proteolysis in the extracellular space. The small keratan sulfate proteoglycans appear to be present as a species distinct from the small dermatan sulfate proteoglycans in these cultures in that they can be separated on Q-Sepharose chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The apparent size (40-60 kDa), composition, and heterogeneity of the keratan sulfate proteoglycans suggest that they may be related to the small keratan sulfate proteoglycans of cornea.

Structural and immunological studies of keratan sulphates from mature bovine articular cartilage

Two populations of alkaline-borohydride-reduced keratan sulphate (KS) chains were prepared from the two peptido-keratan sulphate trypsin fragments of proteoglycan aggregates isolated from bovine femoral head cartilage (6-year-old animals). Each population was separated by high-performance ion-exchange chromatography on a Pharmacia Mono-Q column into eight pools, Q1-Q8. These were analysed by gel permeation chromatography, radioimmunoassay with the monoclonal antibody MZ15, and 500 MHz 1H n.m.r. spectroscopy. Upon chromatography on Sephadex G-75 the Mono-Q fractions were shown to increase in hydrodynamic size progressively from Q1 to Q8 for both KS populations. For each population the strongest antigenic response with the anti-KS monoclonal antibody MZ15 was expressed by the two fractions of greatest size and charge density, Q7 and Q8. Proton n.m.r. spectroscopic studies on the two series of fractions demonstrated: (i) a progressive increase in the level of galactose sulphation from Q1 to Q8, (ii) the presence of approximately one alpha(1-3)-linked fucose residue per chain in every sample, and (iii) the presence of N-acetylneuraminic acids in three discrete environments, two alpha(2-3)- and one alpha(2-6)-linked in every sample. The results are discussed in terms of a possible heterogeneity in the carbohydrate-protein linkage region of keratan sulphates from bovine articular cartilage.

Structural studies of two populations of keratan sulphate chains from mature bovine articular cartilage

Two discrete peptido-keratan sulphate fragments were isolated via chondroitinase ABC and trypsin digestion of a proteoglycan aggregate fraction prepared from bovine femoral head cartilage (six year old animals). The larger fragments (K(av) = 0.07, CL-6B) contained peptides substituted with several keratan sulphate (KS) chains from the KS-rich region of the proteoglycan and the smaller fragments (K(av) = 0.5, CL-6B) contained peptides with, perhaps, only one KS chain and the stubs of post-chondroitinase-treated chondroitin sulphate chains. The two peptido-KS samples and the KS chains derived from these by alkaline borohydride reduction were characterised by 13C-NMR spectroscopy. The two populations of KS chains were also examined by chromatography (Sephadex G-75), and keratanase digestion followed by chromatography on Bio-Gel P-10. From the results it was concluded that the KS chains from the two major trypsin-derived peptido-KS fragments had similar sulphation levels, distributions of hydrodynamic sizes and susceptibilities to keratanase.

Isolation and characterization of proteoglycans and glycosaminoglycans from human chondrosarcoma

The proteoglycans and glycosaminoglycans of four human chondrosarcomas with different degrees of malignancy (I-III) have been studied. The hydrodynamic size of proteoglycan subunits and the tissue concentration of total glycosaminoglycans decreased with increasing grade of malignancy. The glycosaminoglycan distribution pattern of all chondrosarcomas showed a similar ratio of chondroitin-4-sulfate:chondroitin-6-sulfate but an increasing portion of keratan sulfate from grade I (6.5%) to grade III (19.2%). Determinations of the molecular weight (Mr values) of glycosaminoglycans were made after 3H labeling by alkaline reduction of proteoglycans in the presence of NaB3H4. The Mr of [3H]chondroitin sulfate isomers decreased markedly from grade I (35,500) to grade III (15,100) while the chain length of [3H]keratan sulfate showed minor variations (Mr 5600-6200). The previously reported decrease in the molecular weight of keratan sulfate with increasing degree of malignancy (S. Pal, W. Strider, R. Margolis, G. Gallo, S. Lee-Huang, and L. Rosenberg, 1978, J. Biol. Chem. 253, 1279-1289) was not observed.

Isolation and partial characterization of keratan sulphate from human brain

A sulphated glycoconjugate was isolated from adult human brain from a glycosaminoglycan fraction which was not precipitated with 1% cetylpyridinium chloride or ethanol below 50% concentration. It appeared heterogeneous on gel filtration, exhibiting a molecular weight range from about 7000 to over 10 000. Its main covalent structure was shown to contain sulphated, repeating disaccharide units of (beta-D-galactose-(1----4)-N-acetyl-D-glucosamine-(1----3)). In addition, it was susceptible to degradation by keratan sulphate endo-beta-galactosidase and thus was assumed to be keratan sulphate.

Influence of constituents of proteoglycans on type II collagen fibrillogenesis

Turbimetry was used to study the influence of glycosaminoglycans of cartilage proteoglycans on type II collagen fibrillogenesis. The monosaccharides, D-glucuronate, N-acetyl-D-galactosamine, N-acetyl-D-glucosamine and D-galactose, all decreased the rate of the fibril formation. D-glucuronate had the strongest effect. The influence of chondroitin sulphate on type II collagen fibrillogenesis depended on the pH of the final solution, the length of the chondroitin sulphate chains and the concentration of chondroitin sulphate. At pH = 7.3 all chondroitin sulphate preparations decreased the rate of fibrillogenesis, while at pH = 6.9 and lower fibrillogenesis was stimulated by chondroitin sulphate (whale/shark), chondroitin 4-sulphate (whale) and chondroitin 6-sulphate (shark). The chain length of these three appeared to be longer than the chain length of chondroitin sulphate (human) and chondroitin sulphate oligosaccharides (whale/shark). At high concentrations (more than 3 mg/ml) fibril formation was less strongly retarded by keratan sulphate (human) than by chondroitin sulphate. At low concentrations a slight stimulation was observed in the presence of keratan sulphate. Glycosaminoglycans did not bind to collagen fibrils. At 0.5 mg/ml chondroitin 4-sulphate had a large solubilizing effect on fibrils compared to chondroitin 6-sulphate. Fibrillogenesis of type II collagen is in many aspects not comparable with fibrillogenesis of type I collagen.

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.

Isolation and characterization of an asparagine-linked keratan sulfate from the skin of a marine teleost, Scomber japonicus

Keratan sulfate was isolated from the skin of Pacific mackerel (Scomber japonicus) after exhaustive digestion with pronase followed by ethanol precipitation and fractionation on a cellulose column with 0.3% recovery of dried material. The keratan sulfate preparation was separated into four major fractions by Dowex-1 column chromatography. The chemical and infrared spectrum analyses of the four fractions showed a high degree of heterogeneity in sulfation. Since the carbohydrate-peptide linkage in the teleost skin keratan sulfate was found to be stable in alkali, and asparagine was the predominant amino acid, the asparagine residue in the peptide backbone was most likely to be involved in the N-glycosyl linkage with the carbohydrate moiety. Besides the type of carbohydrate-peptide linkage, the teleost skin keratan sulfate is very similar to corneal keratan sulfate (keratan sulfate I) in two respects: (1) The teleost skin and bovine corneal keratan sulfates were hydrolyzed much faster by endo-beta-galactosidase than the whale nasal cartilage keratan sulfate (keratan sulfate II). (2) Although the teleost skin keratan sulfate showed considerable polydispersity, the molecular weight was in the same range as the corneal keratan sulfate, and it was relatively higher than that of the cartilage keratan sulfate.

Fractionation and isolation of heparan sulfates using poly-L-lysine-Sepharose

A simple procedure for the isolation of heparan sulfates from pig lung using a poly-L-lysine-Sepharose column is described. Glycosaminoglycans are absorbed on poly-L-lysine-Sepharose at pH 7.5 and eluted with an NaCl linear gradient in the following order: hyaluronic acid (0.32 M NaCl), chondroitin (0.36 M NaCl), keratan sulfate (0.80 M NaCl), chondroitin 4-sulfate (0.86 M NaCl), chondroitin 6-sulfate (0.95 M NaCl), dermatan sulfate (0.91 M NaCl), heparan sulfate (1.2 M NaCl), and heparin (1.35 M NaCl). Based on these observations, isolation of heparan sulfate from pig lung crude heparan sulfate fractions which contain chondroitin sulfates and dermatan sulfate was attempted, using this chromatographic technique.

Structure of oligosaccharides and the linkage region between keratan sulfate and the core protein on proteoglycans from monkey cornea

Structural analyses were performed on the intact glycopeptides and on the linkage region oligosaccharide-peptides derived from the keratan sulfate proteoglycan from monkey cornea (Nakazawa, K., Newsome, D.A., Nilsson, B., Hascall, V.C., and Hassell, J.R. (1983) J. Biol. Chem. 258, 6051-6055) using trifluoroacetolysis, Smith degradation, chromium trioxide oxidation, and gas-liquid chromatography-mass spectrometry. The following structure was found for the linkage region (formula; see text) The following structures were found for the intact oligosaccharide peptides (formula; see text) and (formula; see text) The structure of the linkage region for keratan sulfate on corneal proteoglycans is clearly derived from a complex type of N-linked glycoprotein oligosaccharide precursor, indicating that only the oligosaccharides that have been processed to the complex type are used as primers for synthesizing keratan sulfate chains. The high mannose oligosaccharide in Formula 3 is an intermediate in the normal pathway for biosynthesis of complex type oligosaccharides. The structure in Formula 2, in which a single Man alpha 1-2 is retained on the Man alpha 1-3 branch while the Man alpha 1-6 branch is unsubstituted, can be an intermediate for an alternate, presumably minor pathway for complex oligosaccharide formation (Kornfeld, S., Gregory, W., and Chapman, A. (1979) J. Biol. Chem. 254, 11649-11654) in certain cases. This structure has not previously been shown to be present on normal glycoproteins.

Purification of keratan sulfate proteoglycan from monkey cornea

An explant culture of 15 cynomolgus monkey corneas was incubated with [35S]sulfate and [2-3H]mannose as labeling precursors. A 4 M guanidine HCl extract of the corneal stromas was prepared and combined with a 4 M guanidine HCl extract of stromas from 300 unlabeled corneas. The keratan sulfate proteoglycans in the combined extracts were purified by a combination of DEAE-cellulose chromatography, chondroitinase ABC digestion to remove chondroitin-dermatan sulfate proteoglycans, and elution from immobilized concanavalin A. The purified keratan sulfate proteoglycan was digested with papain and the digest was eluted on DEAE-Sephacel. The unbound fraction contained 59% of the 3H activity and consisted of intact oligosaccharide-peptides. The bound fraction, consisting of keratan sulfate chains linked to peptides, eluted during a linear 0-0.75 M NaCl gradient as a peak centered at approximately 0.6 M NaCl and contained 41% of the 3H and all of the 35S activity in the original proteoglycan. The chains were digested with endo-beta-galactosidase, and the digest was eluted on DEAE-Sephacel with a linear 0-0.75 M NaCl gradient. Most of the sulfated digestion fragments from the chains eluted as several distinct peaks during the gradient. All the 3H activity eluted in the unbound volume along with a small proportion of 35S activity. This unbound fraction was eluted on Bio-Gel P-10 to give a 3H peak (Kav = 0.46) well resolved from the remaining 35S activity which eluted near the total volume. This 3H peak contained the oligosaccharide-peptides derived from the linkage region between the keratan sulfate chains and the core protein. Structural analyses of the linkage region oligosaccharides and the intact oligosaccharides (Nilsson, B., Nakazawa, K., Hassell, J.R., Newsome, D.A., and Hascall, V.C. (1983) J. Biol. Chem. 258, 6056-6063) in combination with the 3H-labeling data suggest that the intact keratan sulfate proteoglycans contain an average of about one intact oligosaccharide per keratan sulfate linkage site.