Ultracentrifugal study of polydisperse and paucidisperse biological systems using capillary microcells

The cartilage proteoglycan aggregate: assembly through combined protein-carbohydrate and protein-protein interactions

In vitro reassembled aggregates of cartilage proteoglycan (aggrecan) were studied by glycerol spraying/rotary shadowing electron microscopy and compared to the corresponding native (i.e. never dissociated) structures. In both cases a tightly packed central filament structure was observed consisting of the hyaluronate binding region (HABR) of the proteoglycan, link protein (LP) and hyaluronate (HA). This differs from earlier results where a discontinuous central filament structure was seen after spreading proteoglycan aggregates at a water/air interphase. Binding of isolated HABR to HA is random but upon addition of link protein a clustering of the HA-binding proteins is observed, indicating a cooperativity. In a fully saturated aggregate the HA is covered by a continuous protein shell consisting of HABR and LP. When added in amounts below saturation HABR and LP bind to the HA in clusters which are interrupted by free strands of HA. The proteoglycan aggregate is thus an example for a structure where a polysaccharide forms a template for a supramolecular assembly largely stabilized by protein-protein interactions.

Heterogeneity, polydispersity, and physiologic role of corneal proteoglycans

Gel chromatography, affinity chromatography, ultracentrifugation, enzymic fragmentation, and analysis of amino acids, hexosamines and neutral sugars were used to characterize a heterogeneous fraction of proteoglycans from bovine corneal stroma. The results indicate that the fraction largely consists of a mixture of the 2 main types of corneal proteoglycans described earlier, namely keratan sulfate proteoglycans and chondroitin sulfate-rich proteoglycans with covalently bound oligosaccharides. Models for the structure of proteoglycans are suggested, an it is concluded that the molecular size of corneal proteoglycans makes them appropriate as 'spacers' between the collagen fibrils, a property important for corneal transparency. Cornea is softer than cartilage because corneal proteoglycans are less underhydrated than cartilage proteoglycans.

Biomechanical and biochemical properties of dog cartilage in experimentally induced osteoarthritis

The finding of other investigators that increased water content is often associated with signs of a torn collagen network in human osteoarthritic (OA) cartilage led to this study. In the Pond-Nuki model of post-traumatic OA experimental but not control femoral condylar cartilage showed evidence of breakdown and stiffening of collagen network as assessed by measurement of swelling properties and indentation behaviour respectively. These changes in the unstable knees occurred despite lack of erosion of that surface cartilage ascertained from carbon black mapping and history. The stiffening rather than softening change was therefore attributed to cartilage oedema of the middle and deep certilagenous zones, wherein breakdown of collagen network has been postulated to occur. Because of insignificant reduction of total hexuronate in these cartilages, a proteoglycan (PG) profile of sedimentation coefficients for aggregate (PGA) and subunit species (PGS) was analysed to see if collagen network changes in the dog preceded PG alteration. Despite minimal histological changes our results confirmed previous findings in the tibial plateau cartilage in this model, that PGA was reduced in size and PGS increased in amount. Slight enzymatic breakdown of PGs, or altered synthesis due to cellular responses to either the injury directly or to synovial inflammation, seems necessary to explain such changes in the absence of cartilage erosion.

A sectorial centrifuge cell for swinging bucket rotors--application to a velocity gradient centrifugation methodology

A sectorial cell of 1.55 ml capacity, designed to be used in swinging bucket rotors, is introduced and applied to boundary sedimentation studies. The cell, made of polycarbonate by injection molding, represents an improvement over previously existing models in terms of resistance and attainable speeds. Its use has been extended to polydispersity determination by evaluation of the s value distribution function g(s) = dC/ds. The latter can be corrected to standard conditions (water at 20 degrees C), by using newly derived equations in connection with a cesium sulfate linear density and viscosity gradient which is introduced for boundary stabilization. The cell performance is illustrated with the centrifugal characterization of a polydisperse hyaluronate solution and a paucidisperse proteoglycan A1 preparation. In the latter case a distinctive distribution of aggregates into two polydisperse families of molecules, hitherto not reported in the literature but previously observed with cylindrical cells in this laboratory, has been clearly confirmed. Analysis of plateau dilution during centrifugation indicated absence of artifacts.

Cartilage proteoglycan alterations in an experimentally induced model of rabbit osteoarthritis

Size distribution of cartilage proteoglycans (PG) extracted from control and osteoarthritic rabbit knees after partial meniscectomy was analyzed. In normal control knees, about 30% of PG molecules were in aggregate form and average sedimentation constant was 60S. No aggregates were found in osteoarthritic cartilage, whether ulcer, rim about ulcer, or distant normal-appearing cartilage was examined. Weight average sedimentation constants for PG subunits were similar to controls, 15S. Up to 70% of guanidinium-extractable PG could be extracted from osteoarthritic cartilage by using 0.5M guanidine HC1 (GuHCl); sedimentation characteristics of extracted PG were similar to those using 4.0M GuHCl. Absence of aggregates is consistent with a disorder of link protein, hyaluronic acid, or PG subunit hyaluronic acid binding sites. Absence of subunit degradation was an enexpected finding. The demonstrated ability of 0.5 M GuHCl to extract large amounts of PG from osteoarthritic cartilage will allow study of cartilage proteoglycans in their native nondissociated state.

Characterization of the keratan sulphate proteoglycans from bovine corneal stroma

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

Interaction of cartilage proteoglycans with hyaluronic acid. The role of the hyaluronic acid carboxyl groups

Hyaluronic acid-derived oligomers of five to fifteen repeat dissaccharides effectively bind to bovine nasal-cartilage proteoglycan and inhibit the interaction between proteoglycans and high-molecular-weight hyaluronic acid. If, however, the hyaluronic acid oligosaccharides are modified by reaction with diazomethane to form the carboxyl methyl esters of the glucuronic acid residues, their inhibitory activity is abolished. The binding capacity can be fully restored by saponification. The amide derivative, which is formed by condensation of the oligosaccharide carboxyl groups with glycine methyl ester, is also ineffective in blocking the proteoglycan-hyaluronic acid interaction. In this case, binding activity is not restored when the amidated oligomers are subjected to saponification to yield the free carboxylate groups on the glycine residues. Thus the displacement of the carboxylate groups on the polysaccharide chain by the interposition of a glycine residue blocks the interaction between the proteoglycans and the hyaluronic acid oligomers. When the oligosaccharide methyl ester is reduced with NaBH4, the resultant glucose-containing oligomers exhibit decreased binding to proteoglycans. Thus it appears that the hyaluronic acid carboxylate anion in a specific spatial orientation is required for hyaluronic acid-proteoglycan interaction.