Identification of chick corneal keratan sulfate proteoglycan precursor protein in whole corneas and in cultured corneal fibroblasts.

The precursor protein to the chick corneal keratan sulfate proteoglycan was identified by immunoprecipitation with antiserum to its core protein from lysates of [35S]methionine-pulsed corneas and corneal fibroblasts in cell culture. Antiserum to the keratan sulfate proteoglycan immunoprecipitated a doublet of Mr 52,000 and 50,000 and minor amounts of a Mr 40,000 protein from pulsed corneas. Pulse-chase experiments, which permitted the conversion of the precursor proteins to proteoglycans and digestion of the glycosaminoglycans on immunoprecipitated proteoglycans with keratanase or chondroitinase ABC, showed that the Mr 52,000-50,000 doublet was converted to a keratan sulfate proteoglycan and the Mr 40,000 protein was converted to a chondroitin sulfate proteoglycan. Chick corneal fibroblasts in cell culture primarily produced the smaller (Mr50,000) precursor protein, and in the presence of tunicamycin the precursor protein size was reduced to Mr35,000, which indicates that the core protein contains approximately five N-linked oligosaccharides. Pulse-chase experiments with corneal fibroblasts in culture showed that the precursor protein was processed and secreted into the medium. However, its sensitivity to endo-beta-galactosidase and resistance to keratanase indicate that the precursor protein was converted to a glycoprotein with large oligosaccharides and not to a proteoglycan. This suggests that, although the precursor protein for the proteoglycan is produced in cultured corneal fibroblasts, the sulfation enzymes for keratan sulfate may be absent.     

Biosynthesis of small proteoglycan II (decorin) by chondrocytes and evidence for a procore protein

We have studied the biosynthesis of cartilage dermatan sulfate proteoglycan II (DS-PGII) (decorin) using in vitro translation of mRNA to determine the size of the primary gene product and by radiolabeling the protein in the presence of tunicamycin to inhibit the addition of Asn-linked oligosaccharides. Pulse-chase experiments were performed to examine post-translational processing and secretion. Inhibitors of oligosaccharide processing were used to determine whether DS-PGII molecules containing partially processed oligosaccharides could become proteoglycans and be secreted. Cell-free translation of sucrose gradient-fractionated RNA and subsequent immunoprecipitation of the core protein confirmed that the functional translated mRNA is in the size range of the two mRNA species observed by hybridization of chondrocyte RNA with a bone PGII cloned probe and that the translation product is a single protein with an apparent molecular mass of 42 kDa. Digestion of the intact proteoglycan (average molecular mass = 103 kDa) with chondroitinase ABC or AC results in an approximately 48-49-kDa product. Chondrocytes treated with tunicamycin to inhibit Asn-linked oligosaccharide addition synthesize and secrete a glycosaminoglycan (GAG)-substituted proteoglycan (average molecular mass = 86 kDa), yielding a 42-kDa core protein after chondroitinase ABC digestion, showing that Asn-linked oligosaccharides are not required for the addition of GAG chains or secretion. Following a short pulse (10 min) of [3H]leucine, three glycosylated forms of the DS-PGII core protein were observed, one of which is likely to be the precursor form of PGII predicted by the implied protein sequence of both bovine and human cDNA clones. Following the apparent cleavage of the propeptide, GAG-substituted intracellular core protein is detectable. Susceptibility to endoglycosidase H indicates that approximately one-third of the secreted core protein contains exclusively complex-type Asn-linked oligosaccharides and approximately two-thirds contain high mannose as well as complex-type oligosaccharides. Secreted DS-PGII appears to be fully substituted with three Asn-linked oligosaccharide chains. Inhibitors of oligosaccharide processing, however, permitted secretion of GAG-substituted DS-PGII that was fully (three chains) or incompletely (one or two chains) substituted with partially processed Asn-linked carbohydrate chains. By comparison of chondrocyte DS-PGII with fibroblast DS-PGII, we conclude that the addition and processing of Asn-linked carbohydrate chains are directed by the amino acid sequence of the core protein. The results reported here also suggest that the addition of xylose, the initial step in GAG chain synthesis, occurs early in biosynthesis and is determined by the primary amino acid sequence of the core protein.(ABSTRACT TRUNCATED AT 400 WORDS)     

Binding of the proteoglycan decorin to collagen type VI.

We have examined the interactions between the small dermatan sulfate proteoglycan decorin and collagen types I-VI using solid phase binding assays. The results of these studies showed that 125I-decorin bound most efficiently to collagen type VI in a time- and concentration-dependent manner. Furthermore, this interaction was specific and of moderately high affinity (Kd approximately 3 x 10(-7) M). Binding of decorin to collagen type VI appears to involve the decorin core protein rather than the glycosaminoglycan side chains, since the isolated core protein as well as a recombinant fusion protein containing a major segment (65%) of the human decorin core protein inhibited binding of 125I-decorin to collagen type VI. Other related proteoglycans and their respective core proteins also inhibited the binding of 125I-decorin to collagen type VI, whereas unrelated proteins and isolated glycosaminoglycan chains were without effect. In addition to decorin, collagen type II was also shown to bind to immobilized collagen type VI. Both interactions were effectively inhibited by preincubation of the immobilized collagen VI with decorin or collagen type II. These results suggested that the collagen type VI molecule has binding sites for collagen type II and decorin which are located in close proximity on the collagen type VI molecule. Possible functional roles of these interactions are discussed.     

Extraction and purification of decorin from corneal stroma retain structure and biological activity

We developed a method to purify decorin core protein from tissue with the goal of preserving its native structure and biological function. Currently, most procedures rely on the use of denaturing reagents potentially altering the biological activity. Decorin was purified from corneal stromas without the use of detergents or chaotropic reagents. Proteoglycans isolated using anion exchange chromatography on Q-Sepharose were treated with chondroitinase ABC. Decorin was isolated by a second Q-Sepharose chromatography with affinity chromatographies on heparin-Sepharose and concanavalin A-Sepharose. SDS-PAGE revealed a 98.4% pure 44kDa protein identified as decorin with a yield of 35mg per 100 bovine corneas. Identification was confirmed by NanoESI and MALDI qTOF. The novel inclusion of 20% propylene glycol in extraction and column buffers resulted in recoveries of proteoglycans comparable with those observed with detergents and urea. Purified decorin did alter the rate of fibrillogenesis of type I collagen and inhibited the lateral fusion of collagen fibrils. It also bound to [125I]TGF-beta1 with an apparent K(d) of 40nM. Circular dichroism spectroscopy of decorin displayed the spectra of alpha-helices and beta-pleated sheets consistent with those obtained from recombinant decorin. Urea-induced unfolding was cooperative and reversible while thermal denaturation caused irreversible unfolding. Native decorin can be purified from tissue in quantity and quality for biophysical, biochemical, and biological assays.     

Proteoglycans of Wharton's jelly

Wharton's jelly (WJ) is a myxomatous substance surrounding the blood vessels of the umbilical cord. Proteoglycans (PGs) of Wharton's jelly have not been studied to date therefore it was decided to explore proteoglycan composition of this tissue. Proteoglycans were subjected to dissociative extraction with 4M guanidine hydrochloride containing Triton X-100 and protease inhibitors, purified by Q-Sepharose anion-exchange chromatography and lyophilised. They were analysed by gel filtration and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) before and after treatment with chondroitinase ABC. It was found that 1g of Wharton's jelly contains 2.43+/-0.63mg (n=10) of sulphated glycosaminoglycans (GAGs), reflecting the presence of proteoglycans. The proteoglycans were mainly substituted with chondroitin/dermatan sulphate (DS) chains. The predominant proteoglycan fraction included small proteoglycans with core proteins of 45 and 47kD, immunologically related to decorin (45 and 47kD) and biglycan (45kD). The expression of decorin core proteins was much higher than that of biglycan. Larger proteoglycans (core proteins of 90, 110, 220 and 260kD) were found in lower amounts. The most abundant of them (core protein of 260kD) was immunologically related to versican. Perlecan was not identified in Wharton's jelly. The study shows that Wharton's jelly contains mainly small chondroitin/dermatan sulphate proteoglycans, with decorin strongly predominating over biglycan. We suggest that an intensive expression of decorin is associated with very high content of its ligand, collagen.     

The core molecule from type H proteoglycan. Release of mannose-containing oligosaccharides by digestion with N-oligosaccharide glycopeptidase.

Chick-embryo cartilage contains a unique set of proteoglycans. Type H proteoglycan (PG-H) is the most abundant, constituting over 90% of the total cartilage hexuronate. We previously showed that treatment of PG-H with chondroitinase ACII and keratanase yields a protein-enriched core molecule [PG(-CS,KS)] with enzymically modified linkage oligosaccharides of the chondroitin sulphate and keratan sulphate chains. We report here that further treatment of PG(-CS,KS) with pepsin and N-oligosaccharide glycopeptidase (almond glycopeptidase) released four distinct types of mannose-containing oligosaccharide. Two of them were shown to be: (Formula: see text). Of the mannose-containing glycopeptides formed by pepsin digestion, about 40% (as mannose) were resistant to N-oligosaccharide glycopeptidase. Since the resistant fraction was enriched in keratan sulphate remnants, it is suggest that the mannose-containing oligosaccharides in this fraction represent those located in a keratan sulphate-enriched region of PG-H.     

Human colon adenocarcinoma is associated with specific post-translational modifications of versican and decorin

In this study, the amounts and the fine structural characteristics of versican and decorin present in human colon adenocarcinomas (HCC) were investigated and compared with those in human normal colon (HNC). HCC is characterized by significant increase in the amounts of versican and decorin (13- and 8-fold in terms of protein, respectively). These two proteoglycans (PGs) were the predominant in HCC (86% of total uronic acid). In HNC, versican and decorin contained both chondroitin sulfate/dermatan sulfate chains (CS/DS), with DS to be the predominant one (90-93%). The molecular sizes (M(r)s) estimated for DS and CS chains were 25-28 and 21-28 kDa, respectively. In CS/DS chains isolated from both versican and decorin, 4-sulfated disaccharides accounted for 79-86% of total disaccharide units, respectively, whereas lower amounts of 6- and non-sulfated units were also recorded. In contrast, the tumor-associated versican and decorin were of smaller hydrodynamic size with lower glycosaminoglycan (GAG) content per PG molecule as compared with those found in HNC. In HCC, both PGs contained mainly CS chains (up to 86%) and the M(r)s of CS and DS chains were also found to be of smaller size (12 and 16 kDa, respectively). The sulfation patterns of CS/DS chains from both PGs were also significantly different. They were composed mainly of 6-sulfated disaccharides (63-70%), whereas 4-sulfated units accounted for 23-31%. A significant increase in the proportion of non-sulfated disaccharides was also recorded. These findings indicate that the colon adenocarcinoma is characterized by a remarkable increase in the concentration of versican and decorin. Furthermore, these PGs are significantly modified at the post-translational level, i.e. the type, length and the sulfation pattern of their GAG chains. These specific structural alterations of versican and decorin may influence the biology of cancer cells in HCC.     

Immunological studies of sheep brain keratan sulphate proteoglycans

Recently, we reported the isolation and partial characterization of keratan sulphate (KS) from sheep brain. In this study, a panel of monoclonal antibodies (Mab) recognizing epitopes within KS chains and core proteins of KS-containing proteoglycans were used to detect, by immunoblotting, antigenically related molecules extracted from cerebrum, cerebellum and brainstem, respectively. Although the intensity of labelling varied with each of the antibodies, the brain KSPGs were recognized by all the monoclonals used, confirming the presence of KS side chains, which react with the Mabs: 5-D-4, EFG-11, EFG-4, I22, as also the presence of KSPGs related to phosphacan-KS (3H1 proteoglycan). Extracts of all the three brain areas could bind both anti-KS and anti-core protein Mabs, as also anti-HNK-1 monoclonal antibody. Binding was sensitive to keratanases degradation in the cerebrum and brainstem except cerebellum where the presence of a large molecular size hybrid CS/KSPG bearing KS chains partially resistant to keratanases was identified. This population reacts only with 5-D-4, EFG-11 and EFG-4 antibodies. Furthermore, the presence of HNK-1 epitope in CSPGs was detected in the cerebellum and brainstem. In contrast, in the cerebrum the coexistence of HNK-1 epitope and KS in KSPGs was identified. These data suggest that the KSs of sheep brain are part of proteoglycans containing protein and KS antigenic sites related to those of corneal and cartilage KSPG, as also of the brain proteoglycan phosphacan-KS.     

Proteoglycan biosynthesis by human corneas from patients with types 1 and 2 macular corneal dystrophy

Corneal buttons were obtained from patients with types 1 and 2 macular corneal dystrophy (MCD) and from control patients with Fuchs' dystrophy or keratoconus. Buttons were incubated for 20 h in the presence of [3H]glucosamine or [2-3H]mannose. Radiolabeled proteoglycans and lactosaminoglycan-glycoproteins (L-GPs) were purified using chromatography on Q-Sepharose, Superose 6, and octyl-Sepharose. They were identified using chondroitinase ABC, keratanase or endo-beta-galactosidase digestion, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis or Superose 6 chromatography. This study confirms previous reports that type 1 MCD corneas synthesize a normal dermatan sulfate-proteoglycan (DS-PG) and an abnormal keratan sulfate-proteoglycan (KS-PG). The data indicate that typ 1 MCD corneas synthesize L-GP instead of KS-PG. This L-GP has a core protein of similar hydrophobicity (elution from octyl-Sepharose) and nearly similar mass (42 kDa) as the core protein of the KS-PG. It has identical glycoconjugates as those of the KS-PG except that they lack sulfate. Thus, type 1 MCD fails to synthesize keratan sulfate as a result of a defect in a sulfotransferase specific for sulfating lactosaminoglycans. Further, proteoglycans synthesized by a cornea from a patient with type 2 MCD were studied. This cornea synthesized a normal ratio of KS-PG to DS-PG although net synthesis of proteoglycans was approximately 30% below normal. The KS-PG appeared normal whereas the DS-PG had dermatan sulfate chains that were approximately 40% shorter than normal.     

Characterization of chondroitin sulfate and dermatan sulfate proteoglycans of extracellular matrices of human umbilical cord blood vessels and Wharton's jelly

The chondroitin sulfate/dermatan sulfate proteoglycans (CS/DSPGs) of the human umbilical cord vein, arteries and Wharton's jelly matrices were characterized and localized by immunohistochemical analysis. The CS/DSPGs were found to be decorins and biglycans with 43-48 kDa core proteins and are distributed throughout the umbilical cord. A truncated form of decorin having only the approximately 14 kDa NH(2)-terminal portion of the core protein was found exclusively in the vein. The proteoglycans, regardless of their locations, have two types of CS/DS chains, one with approximately 90% CS and approximately 10% DS and the other with approximately 65% CS and approximately 35% DS. The glycosaminoglycan (GAG) chains of the truncated decorin consist of approximately 53% CS and approximately 47% DS. Both decorin and biglycan including the truncated form of decorin could efficiently bind collagen I and fibronectin. The decorin and biglycan with approximately 10% DS and approximately 90% CS were loosely bound in the extracellular matrices, whereas those with approximately 35% DS bound strongly. Together, these data demonstrate that, the GAG chains with 35-47% DS but not those with 10% DS, interact strongly with the matrix. Our data also show that the GAG chain composition is a significant factor in binding of the decorin and biglycan to matrix proteins. The expression of decorin and biglycan with distinctively different CS/DS proportions implies specific biological functions for these PGs in the umbilical cord. The occurrence of the truncated form of decorin exclusively in the umbilical vein suggests a specific functional role.     

The role of decorin and biglycan dermatan sulfate chain(s) in fibrosis-affected fascia

Organ fibrosis is associated with excessive deposition of dermatan sulfate (DS) in the extracellular matrix (ECM) of the affected tissue. However, the significance of DS in fibrosis process is poorly known. Thus, we have analyzed both in vitro and in vivo the binding potential toward fibroblast growth factor-2, platelet-derived growth factor BB and fibronectin (FN) of DS representing glycosaminoglycan (GAG) chains of two proteoglycans decorin and biglycan derived from fascia undergoing fibrosis due to Dupuytren's disease. Moreover, to investigate the relation between DS structure and its binding properties to above ligands, we have also studied the interactions of the GAG chains from normal porcine skin decorin and biglycan. The examined interactions, especially those engaging extractable pool of both human and porcine decorin DS, are characterized by very high affinity and low capacity. Moreover, the presence of iduronate residues is not essential for the DS binding to all studied ligands and the interactions more strongly depend on the GAG sulfation pattern. All investigated interactions have biological relevance as judged from the coexistence of decorin (and biglycan) DS, both growth factors and FN in supra-molecular complexes localized in ECM of both fibrous and normal human fascia. Moreover, these complexes also include collagen type III. It seems that fascia fibrosis process when compared with physiological circumstances is associated with the preservation of at least some functions of decorin and biglycan DSs such as the regulation of growth factor bioavailability and most probably influence FN fibrillogenesis as well as coupling of various fibrilar matrix element assembly.     

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

Two discrete peptido-keratan sulphate fragments were isolatedvia 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 by¹³C-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.Abbreviations KS keratan sulphate - A1 proteoglycan aggregate - T diphenyl carbamyl chloride (DPCC)-trypsintreated - CB chondroitinase ABC-treated - C chymotrypsin-treated - P papain-treated - R alkaline borohydride-reduced - TSP sodium 3-trimethylsilylpropionate     

Cell-surface heparan sulfate and heparan-sulfate/chondroitin-sulfate hybrid proteoglycans of mouse mammary epithelial cells

The hydrophobic cell-surface proteoglycans of mouse mammary epithelial cells were purified by gel filtration, ion-exchange chromatography, and liposome incorporation. The size of the proteoglycans appeared to be directly proportional to the size of their heparan-sulfate chains, larger proteoglycans yielding larger chains. The chondroitin sulfate chains, in contrast, showed no size heterogeneity. Digestion of 125I-labeled proteoglycans with heparitin-sulfate lyase and chondroitin ABC lyase yielded core proteins of approximately 93 kDa, approximately 85 kDa and approximately 38 kDa. Comparison with single enzyme digestions identified the 93-kDa and 85-kDa cores as components of hybrid proteoglycans that carried both heparan-sulfate and chondroitin-sulfate chains. Immunoblotting indicated that the 93-kDa and 85-kDa cores shared the epitope defined by monoclonal antibody 281-2. The 38-kDa core, in contrast, carried only heparan-sulfate chains and lacked the 281-2 epitope. Preparations enriched in heparan sulfate or in heparan-sulfate/chondroitin-sulfate hybrid proteoglycans were obtained by N-desulfation and ion-exchange chromatography. Hybrid proteoglycans accounting for the bulk of the chondroitin-sulfate and nearly half of the heparan-sulfate residues of the proteoglycans showed a similar polydispersity of heparan-sulfate chain sizes as found in proteoglycans that carried only, or predominantly, heparan-sulfate chains. These hybrids contained heparan-sulfate and chondroitin-sulfate chains in similar molar amounts. Analysis of 125I-labeled proteoglycans suggested that typical hybrid proteoglycans were composed of a 85-kDa core protein that carries a single chondroitin-sulfate chain and a single heparan-sulfate chain of variable length. A minority of hybrids seemed characterized by the variant, but possibly structurally related, 93-kDa core protein. The other half of the hydrophobic proteoglycans were composed of the 38-kDa core and carried only heparan-sulfate chains. The significance of the co-existence of hybrid and heparan-sulfate proteoglycans at the cell surface and possible relationships between the proteoglycans need to be further clarified.     

Biglycan and decorin bind close to the n-terminal region of the collagen VI triple helix

The binding of native biglycan and decorin to pepsin-extracted collagen VI from human placenta was examined by solid phase assay and by measurement of surface plasmon resonance in the BIAcore(TM)2000 system. Both proteoglycans exhibited a strong affinity for collagen VI with dissociation constants (K(D)) of approximately 30 nm. Removal of the glycosaminoglycan chains by chondroitinase ABC digestion did not significantly affect binding. In coprecipitation experiments, biglycan and decorin bound to collagen VI and equally competed with the other, suggesting that biglycan and decorin bind to the same binding site on collagen VI. This was confirmed by electron microscopy after negative staining of complexes between gold-labeled proteoglycans and collagen VI, demonstrating that both biglycan and decorin bound exclusively to a domain close to the interface between the N terminus of the triple helical region and the following globular domain. In solid phase assay using recombinant collagen VI fragments, it was shown that the alpha2(VI) chain probably plays a role in the interaction.     

Proteoglycans of human umbilical cord arteries

Proteoglycans (PGs) were dissociatively extracted from human umbilical cord arteries (UCAs) with 4 M guanidine hydrochloride containing Triton X-100 and protease inhibitors, purified by Q-Sepharose anion exchange chromatography and lyophilized. They were analysed by gel filtration, SDS/PAGE and agarose gel electrophoresis before and after treatment with chondroitinase ABC. It was found that the PG preparation was especially enriched in chondroitin/dermatan sulphate PGs. The predominant PG fraction included small PGs that emerged from Sepharose CL-2B with Kav = 0.74. Their molecular mass, estimated by SDS/PAGE, was 160-200 kDa and 90-150 kDa, i.e. it was typical for biglycan and decorin, respectively. Treatment with chondroitinase ABC yielded the core proteins of 45 and 47 kDa, characteristic for both small PGs. Remarkable amounts of the 45 kDa protein were detected in non-treated PG samples, suggesting the presence of free core proteins of biglycan and decorin. Large PGs were present in lower amounts. In intact form they were eluted from Sepharose CL-2B with Kav = 0.17 and 0.43. Digestion with chondroitinase ABC yielded the core proteins with a molecular mass within the range of 180-360 kDa but predominant were the bands of 200, 250 and 360 kDa. The large PGs probably represent various forms of versican or perlecan bearing chondroitin sulphate chains.     

Purification and characterization of decorin from the culture media of MRC-5 cells

Myofibroblasts play an important role in fibrogenesis. Myofibroblasts secrete several components of the extracellular matrix, including decorin. To clarify the properties of decorin synthesized by myofibroblasts, we have purified and characterized decorin secreted into culture medium by the myofibroblast cell line MRC-5. Decorin was purified by successive chromatography steps using Hitrap Q and Superdex 200. Purified decorin showed a broad band on SDS-polyacrylamide gel electrophoresis, which was resolved into two smaller molecular weight bands after digestion with chondroitinase ABC. Further digestion with N-glycanase resolved these two bands into a single band, indicating that the N-glycation pattern of decorin is heterogeneous. The N-terminal amino acid sequence analysis of the purified protein and its reactivity towards an antibody raised against a C-terminal peptide of decorin indicate that MRC-5 cells secrete full-length decorin into the culture medium. To characterize the glycosaminoglycan chains attached to decorin, glycosaminoglycans from the purified protein were treated with chondroitinase ACI, chondroitinase ACII, chondroitinase ABC and chondroitinase B. The resulting disaccharides were analyzed by chromatography, which indicated that decorin secreted by MRC-5 cells is a dermatan sulfate proteoglycan. In conclusion, the decorin secreted by MRC-5 cells has similar characteristics to the decorin expressed in several tissues. Thus, culturing MRC-5 cells may be highly useful for studying the role of decorin and myofibroblasts in fibrosis.     

Characterization and biosynthesis of proteoglycans of corneal stroma from rhesus monkey.

The proteoglycans of the Rhesus monkey corneal stroma were characterized by analyzing both radiolabeled proteoglycans synthesized by corneas in organ culture and native corneal proteoglycans obtained by large scale preparations. The analyses indicate that the proteoglycans synthesized in organ culture were similar to, if not identical with, their counterparts in the stroma although they are synthesized in different prportions in vitro than they acumulate in vivo. The corneal stroma contains two proteoglycans. The chondroitin-dermatan sulfate proteoglycan consists of approximately 70% protein and has a Mr = approximately 100,000 to 150,000. It contains one chondroitin-dermatan sulfate side chain of Mr = approximately 55,000. The keratan sulfate proteoglycan consists of approximately 74% protein and has a Mr = approximately -40,000 to 70,000. It contains one or two keratan sulfate side chains with a Mr = approximately 7,000 each. Radiolabeling indicates that both proteoglycans contain glycoprotein-type oligosaccharides as part of their structure.     

Isolation and characterization of bovine gingival proteoglycans versican and decorin.

1. We have isolated, chemically and immunologically characterized versican and decorin from bovine gingiva. 2. Versican was of large molecular weight and the molecular size of the core protein was estimated to be greater than 200 kDa. 3. The glycosaminoglycan chains were susceptible to chondroitinase ABC and N-linked oligosaccharides were present on the protein core of the molecule. 4. Immunological studies provided evidence that a hyaluronic acid binding region was present in the core protein of versican. 5. The overall structure was similar to that of versican isolated from bovine sclera. 6. Decorin had a molecular weight of 102 kDa and its glycosaminoglycan chain was completely digested by specific glycosidases. 7. The partially deglycosylated core protein had a molecular weight of 55 kDa and N-linked oligosaccharides were present on the molecule.     

Molecular interactions of biglycan and decorin with elastic fiber components: biglycan forms a ternary complex with tropoelastin and microfibril-associated glycoprotein 1.

The interactions of the dermatan sulfate proteoglycans biglycan and decorin have been investigated with the elastic fiber components, tropoelastin, fibrillin-containing microfibrils, and microfibril-associated glycoproteins (MAGP) 1 and 2. Both proteoglycans were found to bind tropoelastin and fibrillin-containing microfibrils but not MAGPs 1 and 2 in solid phase binding assays. The specificity of the binding of biglycan and decorin to tropoelastin was confirmed by co-immunoprecipitation experiments and by the blocking of the interactions with elastin-derived peptides. Isolated core proteins from biglycan and decorin bound to tropoelastin more strongly than the intact proteoglycans, and there were no differences in the tropoelastin binding characteristics of distinct glucuronate-rich and iduronate-rich glycoforms of biglycan. These findings indicated that the binding sites were contained in the protein cores of the proteoglycans rather than the glycosaminoglycan side chains. Scatchard analysis showed that biglycan bound more avidly than decorin to tropoelastin with K(d) values estimated as 1.95 x 10(-7) m and 5.3 x 10(-7) m, respectively. In blocking experiments each proteoglycan showed extensive inhibition of binding of the other to tropoelastin but was most effective at blocking its own binding. This result suggested that biglycan and decorin had closely spaced but distinct binding sites on tropoelastin. Addition of the elastin-binding protein MAGP-1 to the assays enhanced the binding of biglycan to tropoelastin but had no effect on the decorin-tropoelastin interaction. Co-immunoprecipitation experiments showed that MAGP-1 interacted with biglycan but not decorin in the solution phase. The results indicated that biglycan specifically formed a ternary complex with tropoelastin and MAGP-1. Overall the study supports the concept that biglycan may have a specific role in the elastinogenic phase of elastic fiber formation.     

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)