A role for disulphide bridges in the protein core in the interaction of proteodermatan sulphate and collagen

Bovine pericardial proteoglycan: biochemical, immunochemical and ultrastructural studies

The major proteoglycan in bovine parietal pericardium is a low molecular weight dermatan-sulfate proteoglycan. It possesses structural and immunologic characteristics similar to those of the small proteoglycan found in tendon. We demonstrate that digestion of purified pericardial proteoglycan with low levels of V8 protease results in the liberation of the glycosaminoglycan chain and of a 40 kDa resistant fragment. A similar 40 kDa fragment can be obtained by V8 protease digestion of the proteoglycan deglycosylated by chondroitinase ABC. Although the protein core size of the pericardial proteoglycan is similar to that of tendon PG II, the size of the glycosaminoglycan chain liberated from the former is smaller. The pericardial proteoglycan and its V8 protease products reacted with an anti-PG II antiserum by immunoblotting. The anti-PG-II antibody localized in the pericardial tissue by the immunoperoxidase technique. The presence of intrachain disulfide bonds in the structure of pericardial proteoglycan core protein and V8 resistant fragment was demonstrated by their decreased electrophoretic mobility after disulfide reduction. Digestion of pericardial proteoglycan with Cathepsin C resulted in a rapid liberation of the glycosaminoglycan chain from the core protein, indicating that its attachment site was very close to the amino terminus. Ultrastructural examination of pericardial tissue utilizing Cuprolinic Blue revealed a periodic association of the proteoglycan with the d/e band on the collagen fibrils. Electron microscopic immunohistochemical studies confirmed the perifibrillar association of pericardial proteoglycan. The present data demonstrate that, although the pericardial proteoglycan possesses some unique structural features, it shares structural and immunological characteristics to place it in the category of the small PG II family.

Proteoglycans of the articular disc of the bovine temporomandibular joint. II. Low molecular weight dermatan sulphate proteoglycan

The low molecular weight proteoglycan fraction extracted from articular discs with 4 M guanidinium chloride was found to consist predominantly of an iduronate-rich dermatan sulphate proteoglycan, together with chondroitin sulphate-containing material. The dermatan sulphate proteoglycan was purified by ion-exchange and gel-filtration chromatography and its core protein isolated after digestion with chondroitinase ABC. The amino acid composition and pattern of cyanogen bromide peptides obtained from this core were closely similar to those of the protein core of bovine skin proteodermatan sulphate. Four monoclonal antibodies raised against bovine skin proteodermatan sulphate also reacted with the disc protein core and its cyanogen bromide peptides. Results of digestion with glycopeptidase F demonstrated the presence of three N-linked oligosaccharides. The combined size of these oligosaccharides appeared to be somewhat less than the size of those on skin proteodermatan sulphate. The glycosaminoglycan chain released by digestion with cathepsin C had a higher molecular weight than that from skin. These differences in glycosylated structures may be responsible for the different effects on collagen fibrillogenesis in vitro; whereas skin proteodermatan sulphate only reduced the rate of fibril growth, disc dermatan sulphate proteoglycan also increased the length of the lag-phase and the final opacity.

Light scattering studies of bovine skin proteodermatan sulfate

The proteodermatan sulfate (PDS) of bovine skin is a low molecular weight proteoglycan with a molecular structure consisting of a protein chain and a sulfated polysaccharide chain covalently linked at the 4-serine of the protein. Static and dynamic laser light scattering methods have been used to determine the weight-average molecular weight, Mw, zeta-average radius of gyration, Rg zeta, and zeta-average translational diffusion coefficient, Dto, zeta, of bovine skin PDS. We have also characterized the two components of PDS, i.e., the protein core and the dermatan sulfate (DS) chain. (The latter contained an N-terminal-linked penta- or tetrapeptide.) Interpretation of the PDS data is complicated by the block copolymer nature of its structure. When appropriate corrections are made, our results indicate that Mw for PDS monomer is 62,000 when dissolved in 4M guanidine hydrochloride (GdnHCl), and increases to 610,000 in 0.15M NaCl. Mw for the core protein in 4M GdnHCl is 39,000, and this also increases substantially to 650,000 in 0.15M NaCl. In contrast, Mw for the DS chain is 24,000 in 0.15M NaCl, indicating that there is minimal self-association of DS in 0.15M NaCl. Thus we conclude that the self-association of PDS involves the protein core. Comparison of Rg zeta and Rh, the average hydrodynamic radius, suggests that trace amounts of aggregation persist for the PDS and its core protein even in 4M GdnHCl. This conclusion is supported by evaluation of the second moments of the dynamic light scattering correlation function. Comparisons of the observed Dto, zeta for PDS with predicted values using hydrodynamic theory are consistent with a "lollipop" conformation for the molecule.

Membrane-associated chondroitin sulfate proteoglycans of human lung fibroblasts

Cultured human fetal lung fibroblasts produce some chondroitin sulfate proteoglycans that are extracted as an aggregate in chaotropic buffers containing 4 M guanidinium chloride. The aggregated proteoglycans are excluded from Sepharose CL4B and 2B, but become included, eluting with a Kav value of 0.53 from Sepharose CL4B, when Triton X-100 is included in the buffer. Conversely, some of the detergent-extractable chondroitin sulfate proteoglycans can be incorporated into liposomes, suggesting the existence of a hydrophobic membrane-intercalated chondroitin sulfate proteoglycan fraction. Purified preparations of hydrophobic chondroitin sulfate proteoglycans contain two major core protein forms of 90 and 52 kD. A monoclonal antibody (F58-7D8) obtained from the fusion of myeloma cells with spleen cells of BALB/c mice that were immunized with hydrophobic proteoglycans recognized the 90- but not the 52-kD core protein. The epitope that is recognized by the antibody is exposed at the surface of cultured human lung fibroblasts and at the surface of several stromal cells in vivo, but also at the surface of Kupffer cells and of epidermal cells. The core proteins of these small membrane-associated chondroitin sulfate proteoglycans are probably distinct from those previously identified in human fibroblasts by biochemical, immunological, and molecular biological approaches.

The small dermatan sulphate proteoglycans synthesized by fibroblasts derived from skin, synovium and gingiva show tissue-related heterogeneity

Dermatan sulphate proteoglycans (DSPGs) synthesized in the presence of 35SO4 were characterized in culture media of fibroblast lines obtained from skin, synovium, and gingiva. The molecular mass of DSPG varied from 95-130 kDa as estimated by SDS/polyacrylamide-gel electrophoresis. Gingival fibroblasts constantly produced larger DSPGs than skin fibroblasts. This was due to the larger dermatan sulphate (DS) chains, which also showed tissue-related heterogeneity in the distribution of 4- and 6-sulphated disaccharide units. The N-glycosylated cores (44 and 47 kDa) obtained following chondroitinase ABC treatment were of identical size in all tissues. The cores from the different tissues were also of the same size (38 kDa) when addition of the N-linked oligosaccharides was inhibited by tunicamycin or when they were removed by N-glycanase treatment. No evidence for low-molecular-mass sulphated oligosaccharides was found. All tissues contained two mRNA species (1.6 and 1.9 kb) for the DSPG core protein. These data suggest that the pattern of transferase activities involved in the construction of DS chains differs from one tissue to another. This variation may modulate the functions of DSPG in the extracellular matrix.

Isolation and partial characterization of dermatan sulfate proteoglycans from human post-burn scar tissues

Dermatan sulfate (DS) proteoglycans (PGs) were extracted from human post-burn scar (Sc) tissues with 4M guanidinium chloride and isolated from the extracts by DEAE-cellulose chromatography and by differential ethanol precipitation. The DS.PGs were further purified by Sepharose CL-6B column chromatography. The average molecular weight (Mr) of hypertrophic scar (HSc) tissue DS.PGs was 39,000 based on sedimentation equilibrium measurements. Alkaline borohydride treatment of DS.PGs liberated glycosaminoglycan (GAG) chains and the presence of xylitol indicated that these chains were attached to protein core by xylosyl residues. The average Mr of the DS.GAG chain from HSc and normal scar (NSc) samples were 23,500 and 20,000 respectively. After digestion of the HSc and NSc, DS.PGs with chondroitinase ABC in the presence of proteinase inhibitors, two peptide components with Mr values of 21,500 and 17,000 were detected by SDS-polyacrylamide gel electrophoresis using reducing conditions. Analysis of the protein core fractions derived from NSc and HSc DS.PGs by Sepharose CL-6B column chromatography showed the presence of a single NH2-terminal amino acid (aspartic acid) and also that the fractions with different KAV values had an identical NH2-terminal sequence (A1-A5). The A1-A23 sequence of NSc DS.PG (major fraction, C): NH2Asp-Glu-Ala-O-Gly-Ile-Gly-Pro-Glu-Val-Pro-Asp-Asp-Arg-Asp-Phe-G lu-Pro- Ser-Leu-Gly-Pro-Val was the same as reported for a DS.PG isolated from human fetal membrane (HFM) tissue (Brennan et al., 1984). ELISA inhibition assay using monoclonal antibodies raised in rabbit against the NH2-terminal peptide (containing 15 amino acids) of human fetal membrane tissue were found to cross-react with HSc and NSc DS.PGs. Monoclonal antibodies to bovine skin DS.PGs protein core (Pearson et al., 1983) did not show any cross-reactivity with scar DS.PGs. These results show that the scar DS.PGs described here are different from normal bovine skin DS.PGs in the size and type of the protein core, and that in all the samples, the peptide components have the same NH2-terminal amino acid sequence.

Proteoglycan-fibrillar collagen interactions

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A study of the interaction in vitro between type I collagen and a small dermatan sulphate proteoglycan

The interaction between a small dermatan sulphate proteoglycan isolated from human uterine cervix and collagen type I from human and rat skin was investigated by collagen-fibrillogenesis experiments. Collagen fibrillogenesis was initiated by elevation of temperature and pH after addition of proteoglycan, chondroitinase-digested proteoglycan or isolated side chains, and monitored by turbidimetry. Collagen-associated and unbound proteoglycan was determined by enzyme-linked immunosorbent assay after aggregation was complete. (1) The binding of proteoglycan to collagen could be explained by the presence of two mutually non-interacting binding sites, with Ka1 = 1.3 x 10(8) M-1 and Ka2 = 1.3 x 10(6) M-1. The number of binding sites per tropocollagen molecule was n1 = 0.11 and n2 = 1.1. The 0.1 high-affinity binding site per tropocollagen molecule indicates that the strong interaction between proteoglycan and collagen results from a concerted action of tropocollagen molecules in fibrils. Digestion of the proteoglycan with chondroitinase ABC did not affect these binding characteristics. (2) Proteoglycan did not affect the rate of fibrillogenesis, but increased the steady-state A400 by up to 90%. This increase was directly proportional to the saturation of the high-affinity type of binding sites. Neither isolated core protein nor isolated side chains induced a similar high increase in steady-state A400. (3) Electron micrographs showed that the fibril diameter was affected only to a minor extent, if at all, by the proteoglycan, whereas bundles of laterally aligned fibrils were common in the presence of proteoglycan. (4) Results obtained with human and rat collagen were similar.

Comparative structural studies of reconstituted and native type I and type II collagen fibrils by low-angle X-ray diffraction

Acid-soluble and pepsin-soluble type I collagen from calf skin and pepsin-soluble type II collagen from bovine articular cartilage were precipitated in fibrillar form by various methods. Reconstituted native-like fibrils were analysed by low-angle X-ray diffraction, and the patterns were compared with those obtained with native type I (rat tail tendon) and type II fibrils (bovine articular cartilage). For both orientated and disorientated forms of these samples, we measured the ratio of the first/third-order intensities of the meridional diffraction peaks which are associated with the gap-filling. The values obtained with the reconstituted native-like fibrils (types I and II) were double and 20-times the values, respectively, measured for rat tail tendon and bovine articular cartilage. These differences reflect the extent of specific interactions of other components (proteoglycans) at the gap level along the collagen fibrils in the two tissues.

Isolation and characterization of a collagen fibril-associated dermatan sulphate proteoglycan from bovine lung

Dermatan sulphate proteoglycans have been extracted from bovine lung with 2.0 M CaCl2 and isolated using CsCl density gradient centrifugation, DEAE ion-exchange chromatography, gel chromatography and preparative sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Ultrastructurally these proteoglycans are specifically associated with collagen fibrils. Dermatan sulphate (Mr 15.10(3)-35.10(3), with a strong prevalence for the higher Mr) is link via an O-glycosidic bond to a protein core, which is rich in Asx, Glx and Leu. Of the total uronic acid, 91% is iduronic acid. A part of the glucuronic acid residues is located near the protein core and a large cluster of disaccharides is devoid of glucuronic acid residues. An inhibition enzyme immunoassay has been developed to quantitate the proteoglycan. A model for the interaction between dermatan sulphate proteoglycans and collagen fibrils is proposed.

Characterization and interactions of a fragment of the core protein of the small proteoglycan (PGII) from bovine tendon

Sequence analysis showed that Staphylococcus aureus V8 protease cleaved the core protein of the small dermatan sulfate proteoglycan of bovine tendon (PGII) on the carboxy side of a glutamic acid residue located 17 amino acids from the N-terminus of the intact molecule. The remaining 40 kDa core protein fragment inhibited collagen fibrillogenesis in an in vitro assay. V8 protease readily generated this fragment in tendon tissue, but it was not released from the tissue during treatment. These results indicate that neither the 17-amino acid N-terminal peptide nor the glycosaminoglycan chain attached to this peptide is required for maintaining the interaction of this proteoglycan with a collagen matrix.

The effect of proteoglycans on the morphology of collagen fibrils formed in vitro

The morphology of collagen fibrils at various times during formation in vitro was quantitatively examined by negative staining and by scanning electron microscopy. The presence of a small dermatan sulfate proteoglycan from bovine tendon (5 micrograms proteoglycan/100 micrograms collagen) resulted in collagen fibrils that were significantly thinner in width at all times by both methodologies. The rate of fibril diameter increase was also retarded by the small proteoglycans, suggesting that they inhibited the lateral aggregation of forming collagen fibrils. Large proteoglycans from cartilage did not produce this effect.