Hyaluronic acid in cartilage and proteoglycan aggregation

Abstract

1. Dissociation of purified proteoglycan aggregates was shown to release an interacting component of buoyant density higher than that of the glycoprotein-link fraction of Hascall & Sajdera (1969). 2. This component, which produced an increase in hydrodynamic size of proteoglycans on gel chromatography, was isolated by ECTEOLA-cellulose ion-exchange chromatography and identified as hyaluronic acid. 3. The effect of pH of extraction showed that the proportion of proteoglycan aggregates isolated from cartilage was greatest at pH4.5. 4. The proportion of proteoglycans able to interact with hyaluronic acid decreased when extracted above or below pH4.5, whereas the amount of hyaluronic acid extracted appeared constant from pH3.0 to 8.5. 5. Sequential extraction of cartilage with 0.15m-NaCl at neutral pH followed by 4m-guanidinium chloride at pH4.5 was shown to yield predominantly non-aggregated and aggregated proteoglycans respectively. 6. Most of the hyaluronic acid in cartilage, representing about 0.7% of the total uronic acid, was associated with proteoglycan aggregates. 7. The non-aggregated proteoglycans were unable to interact with hyaluronic acid and were of smaller size, lower protein content and lower keratan sulphate content than the disaggregated proteoglycans. Together with differences in amino acid composition this suggested that each type of proteoglycan contained different protein cores.

Degradation of cartilage proteoglycan by human leukocyte granule neutral proteases--a model of joint injury. II. Degradation of isolated bovine nasal cartilage proteoglycan.

“…G, CT, and E each degrade the larger of the two link proteins without affecting the smaller and without altering the immunological reactivity of the GPL fraction in which they are isolated. Although they serve to stabilize the proteoglycan aggregate under certain conditions in vitro (7,8,21), the link proteins are not necessary for aggregate formation (6). The link proteins appear to share antigenic determinants with PGS and it has been suggested that they may, in fact, be derived from PGS (21a); this suggestion is supported by the finding described here that prolonged digestion of PGS with E produces a link protein-like precipitin line (24).…”

“…The main structural features of bovine nasal cartilage proteoglycan, as established by recent biochemical, physicochgmical, immunological, and electron-microscopic studies (2)(3)(4)(5)(6)(7)(8)(9)(10)(11), are illustrated in Fig. 1.…”

The proteoglycans of the human intervertebral disc

“…The two components observed by ultracentrifugation of such extracts were shown to be a proteoglycan subunit and glycoprotein link, which aggregated to form a protein-polysaccharide complex. Subsequently the aggregation has been shown to require the interaction of hyaluronate and a protein-rich fraction (Gregory, 1973;Hardingham & Muir, 1974;Hascall & Heinegard, 1974a,b;Heinegard & Hascall, 1974).…”

Study of hyaluronic acid flexibility by electric birefringence

“…It is present in very small quantities (< 1% of the total glycosaminoglycan composition) in connective tissue, where it plays an important role in the hierarchy of the tissue matrix. It is known to bind extensively to proteoglycan (Hardingham & Muir, 1974), thereby forming a hydrophilic aggregate that causes the inflation of the cartilage matrix. These extended aggregates are constrained within a network of collagen fibres.…”