Interaction of tropocollagen with protein-polysaccharide complexes. An analysis of the ionic groups responsible for interaction

Proteoglycans in human burn hypertrophic scar from a patient with Ehlers-Danlos syndrome

Proteoglycans (PGs) from human burn hypertrophic scar of a patient with Ehlers-Danlos syndrome were extracted with 4M guanidinium chloride and purified by DEAE-cellulose chromatography. Differential ethanol precipitation of the PG fraction obtained after ion-exchange chromatography yielded two low mol.-wt. PGs, on rich in glucuronic acid (PGGLCA; Mr 66 kDa) and the other rich in iduronic acid (PGIDOA; Mr 48 kDa). In PGGLCA, 84% of the glycosaminoglycan chains are composed of GlcA----GalNAc(SO4) units, whereas in PGIDOA, the chains contain 95% IdoA----GalNAc(SO4) disaccharide units. Upon treatment with testicular hyaluronidase, the PGs gave different-sized oligosaccharides. Chondroitinase ABC digestion of PGGLCA or PGIDOA gave a single protein core (Mr approximately 20 kDa). The presence of glucosamine and sialic acid in PGGLCA and PGIDOA suggests that both contain N-linked oligosaccharides.

Two species of dermatan sulfate proteoglycans with different molecular sizes from newborn calf skin

Two species of dermatan sulfate-proteoglycans (DS-PGs) were isolated from calf skin. The first species, PDS-H (high-molecular-weight proteodermatan sulfate), contains the core protein with a molecular weight of either about 55,000 or 53,000. Both the core proteins are capable of binding to concanavalin A (Con A). The second species, PGs-L (low-molecular-weight proteoglycan containing dermatan sulfate and/or chondroitin sulfate), contains a core protein of Mr = 20,000 that did not bind to Con A. Tryptic peptide mappings revealed that Mr = 55,000 core protein and Mr = 53,000 core protein were of the same origin. However, the tryptic peptides and the amino acid composition of PGs-L core protein were completely different from those of PDS-H core proteins. The polyclonal antibodies against Mr = 55,000 core protein reacted with both the core proteins of Mr = 55,000 and Mr = 53,000 but not with the core protein from PGs-L. The DS was found to be the only glycosaminoglycan component of PDS-H. That is, the glycosaminoglycan from PDS-H was composed of 46% iduronosylhexosamine units and 54% glucuronosylhexosamine units, while the glycosaminoglycan of PGs-L was composed of 30% iduronosylhexosamine units and 70% glucuronosylhexosamine units.

Salicylate-induced depletion of endogenous inorganic sulfate. Potential role in the suppression of sulfated glycosaminoglycan synthesis in murine articular cartilage

Sodium salicylate has been shown to suppress glycosaminoglycan (GAG) synthesis by articular hyaline cartilage in vitro. We investigated the in vivo effect of sodium salicylate on murine patellar cartilage, using incorporation of intraperitoneally administered 35S-sulfate as a measure of sulfated GAG synthesis. Our results indicated that a single dose of sodium salicylate (200 mg/kg) inhibited in vivo sulfated GAG synthesis by 56%, compared with controls, and had no effect on sulfated GAG breakdown. A striking finding was that sodium sulfate treatment reduced the serum concentration of inorganic sulfate from 1.1 mM to approximately 0.3 mM, and that this serum reduction was associated with a twofold increase in urinary excretion of sulfate. Using anatomically intact patellar cartilage, in vitro studies clearly showed that, in concentrations reached in vivo (greater than or equal to 1 mM), salicylate suppressed murine chondrocyte GAG synthesis. However, in the presence of serum, the effects of 1 mM salicylate were abolished. We also found that sulfated GAG synthesis was clearly inhibited at low concentrations of sulfate (less than 0.5 mM). Our data indicate that sodium salicylate can suppress articular chondrocyte sulfated GAG synthesis in vivo, and that this effect may particularly be due to a drug-induced reduction of endogenous sulfate.

Elastin-proteoglycans association revealed by cytochemical methods

By using various cytochemical stains, proteoglycans are shown to be present inside elastic fibers in aortas of beta-aminopropionitrile-induced lathyritic chicks. Depending on the characteristics of the dyes, the shape, size and distribution of the proteoglycan-revealing precipitates are described. The monocationic dye toluidine blue O and the tetracationic dye Alcian blue in the presence of 0.3 M MgCl2 give the most detailed results. With these stains the proteoglycans inside lathyritic elastin appear to be lateral branches of matrix proteoglycans, lying on the external surface of the elastic fibers. A possible general biological significance of elastin-proteoglycan association is briefly discussed.

Elastin fiber-associated glycosaminoglycans in beta-aminopropionitrile-induced lathyrism

Ruthenium red and toluidine blue O precipitates were described associated with lathyritic elastic fibers in aortas of chickens treated with beta-aminopropionitrile fumarate (I. Pasquali-Ronchetti, C. Fornieri, I. Castellani, G. M. Bressan, and D. Volpin (1981). Alterations of the connective tissue components induced by beta-aminopropionitrile. Exp. Mol. Pathol. 35, 42-56). In this report evidence is given that these precipitates reveal the presence of proteoglycans, as they are completely removed by 5 M guanidine-HCl incubation and by specific enzymatic digestions. In particular, proteoglycans associated with the poorly cross-linked lathyritic elastin can be removed by testicular hyaluronidase, chondroitinase ABC, heparitinase, and nitrous acid treatments, whereas they are rather resistant to streptococcal hyaluronidase and chondroitinase AC. On the contrary, proteoglycans of the matrix or associated with collagen fibers are particularly sensitive to these latter enzymatic treatments. The conclusion is reached that glycosaminoglycans associated with beta-aminopropionitrile-induced lathyritic elastin (i) are different from those of the matrix or associated with collagen, and (ii) include mainly dermatan and heparan sulfates.

Mechanical properties of reconstituted collagen fibrils. Influence of a glycosaminoglycan: dermatan sulfate

The mechanical properties of membranes composed of fibrils reconstituted from solubilized and purified rat skin collagen were investigated following the addition of various concentrations of dermatan sulfate. Dermatan sulfate was added to collagen 48 hrs before and immediately after aggregation into fibrils and was added to membranes prematured for various time periods. Dermatan sulfate reduced the mechanical strength developed below the levels observed for control membranes during maturation. The stiffness was analyzed as a function of strain and for each increment of per cent strain was expressed in relation to the maximum stiffness of the membrane under consideration. When dermatan sulfate was added to the membranes in concentrations that were the same or higher than those in skin (about 1%) an increase in the relative stiffness was observed during the first part of the deformation. The length of time that the membranes were matured before the addition of dermatan sulfate did not correlate with any of the effects of dermatan sulfate.

Design of an artificial skin. II. Control of chemical composition

Detailed methodology is described for the reproducible preparation of collagen--glycosaminoglycan (GAG) membranes with known chemical composition. These membranes have been used to cover satisfactorily large experimental full-thickness skin wounds in guinea pigs over the past few years. Such membranes have effectively protected these wounds from infection and fluid loss for over 25 days without rejection and without requiring change or other invasive manipulation. When appropriately designed for the purpose, the membranes have also strongly retarded wound contraction and have become replaced by newly synthesized, stable connective tissue. In our work, purified, fully native collagen from two mammalian sources is precipitated from acid dispersion by addition of chondroitin 6-sulfate. The relative amount of GAG in the coprecipitate varies with the amount of GAG added and with the pH. Since coprecipitated GAG is generally eluted from collagen fibers by physiological fluids, control of the chemical composition of membranes is arrived at by crosslinking the collagen--GAG ionic complex with glutaraldehyde, or, alternately, by use of high-temperature vacuum dehydration. Appropriate use of the crosslinking treatment allows separate study of changes in membrane composition due to elution of GAG by extracellular fluid in animal studies from changes in composition due to enzymatic degradation of the grafted or implanted membrane in these studies. Exhaustive in vitro elution studies extending up to 20 days showed that these crosslinking treatments insolubilize in an apparently permanent manner a fraction of the ionically complexed GAG, although it could not be directly confirmed that glutaraldehyde treatment covalently crosslinks GAG to collagen. By contrast, the available evidence suggests strongly that high-temperature vacuum dehydration leads to formation of chemical bonds between collagen and GAG. Procedures are described for control of insolubilized and "free" GAG in these membranes as well as for control of the molecular weight between crosslinks (Mc). The insolubilized GAG can be controlled in the range 0.5--10 wt. % while "free" GAG can be independently controlled up to at least 25 wt. %; Mc can be controlled in the range 2500--40,000. Studies by infrared spectroscopy have shown that treatment of collagen--GAG membranes by glutaraldehyde or under high-temperature vacuum does not alter the configuration of the collagen triple helix in the membranes. Neither do these treatments modify the native banding pattern of collagen as viewed by electron microscopy. Collagen--GAG membranes appear to be useful as chemically well-characterized, solid macromolecular probes of biomaterial--tissue interactions.

Glycosaminoglycans: structure and interaction

In the last few years, there has been considerable progress in the studies on glycosaminoglycans, a group of acidic polysaccharides present in the intercellular matrix of connective tissue. X-ray diffraction studies have indicated that these polymers can exist in the condensed phase in some helical form. Chiroptical and hydrodynamic measurements have provided significant information regarding the molecular conformation in solution and other physicochemical properties of the polymers. Studies related to the interaction properties of glycosaminoglycans with polypeptides, metal ions, and other molecules are numerous. This review covers mainly the results and their interpretations of both published and as yet unpublished material of the 1970s, but certain previous data are also included. A present-day concept regarding the structure and interaction properties of these molecules on the basis of various physicochemical measurements is presented. The biosynthesis and metabolism of glycosaminoglycans, and the structure of proteoglycans and glycoproteins, are not discussed.

Quantitation of collagen - proteoglycan interaction in tissue sections

Since the dye Sirius Red reacts with the basic groups of collagen, and it is possible to hydrolyze the proteoglycans bound to collagen by enzymatic digestion, a method was developed to quantitate the collagen-proteoglycan interaction in tissue sections. The method consists of measuring, with a spectrophotometer, the amount of dye bound to control and papain-digested tissue sections. The difference observed between the results obtained in control and digested sections is considered to be due to the unmasking of basic groups of collagen originally bound to proteoglycans. The initial results show a variability of this interaction in different tissues. They also suggest a reduction of collagen-proteoglycan interaction in atherosclerotic lesions.

Structural glycoprotein from the media of pig aorta. Aggregation of the S-carboxamidomethyl subunits

Media of pig aorta was extracted with 1 M NaCl and 2 M MgCl2 to remove most of the soluble collagen, proteoglycans and glycoproteins. The glycoproteins remaining in the residue were extracted with 6 M urea-0.1 M mercaptoethanol. The urea soluble proteins were precipitated by dialysis, redissolved in 4 M guanidine-0.05 M DTT and were S-carboxamidomethylated (CM-guanidine extract). This extract was further fractionated by a variety of methods in order to separate a glycoprotein from collagen and proteoglycans. Caesium chloride density-gradient ultracentrifugation of the CM-guanidine extract separated a minor proteoglycan peak from a major glycoprotein fraction still containing some hydroxyproline. This major glycoprotein fraction was excluded as a single peak from Sephadex G 100 and G 200 in 4 M guanidinium chloride or in 6 M urea-0.2 per cent SDS. Sodium dodecylsulphate gel electrophoresis separated this high molecular weight Sephadex fraction into a major low molecular weight (approximately 35000 daltons) component and a minor high molecular weight component. This glycoprotein fraction could also be separated from a collagenous fraction and from proteoglycans by ion exchange chromatography on DEAE cellulose or by gelfiltration on Sepharose 4 B in 6 M urea-0.02 M EDTA-0.2 per cent SDS at pH 7.0. The isolated glycoprotein fraction is rich in dicarboxylic amino acids, contains galactose, mannose, (glucose), N-acetylglucosamine and sialic acid. The S-carboxamidomethyl glycoprotein preparation interacts with acid soluble calf skin collagen on isoelectric focusing in sucrose gradient in urea. This interaction is in favour of the biological role claimed for structural glycoproteins during fibrogenesis and differentiation.

Connective tissue metabolism in culture fibroblasts of a patient with Ehlers-Danlos syndrome type I

Study on connective tissue metabolism was conducted with a patient with Ehlers-Danlos syndrome (E-D) of Type I who visited our institute. The conversion of procollagen into tropocollagen in the medium of cultured fibroblasts was assayed by the chase technique using 3H-proline. The conversion was inhibited in the cultured fibroblasts of the patient. The components of glycosaminoglycans in cultured medium and fibroblasts from E-D were within normal ranges, however, the ratio of glycoprotein to glycosaminoglycans of intra- and extra-cellular fractions of E-D fibroblasts was higher than the normal one. These findings suggest that the insufficient maturation of collagen fiber may be considered fundamental disorders of E-D.

Elastin--proteoglycan interaction. Conformational changes of alpha-elastin induced by the interaction

The interaction between alpha-elastin and a connective tissue proteoglycan was followed by optical density measurements and circular dichroism spectroscopy. It was found that interaction takes place at pH values below the isoelectric point of elastin with the formation of a complex coacervate. CD spectra demonstrated conformational changes of alpha-elastin caused by the interaction and resulting in an increase in the content of helical structure. This finding suggests the possibility of the involvement of proteoglycans in the molecular organization of elastin.