Aggregation of Cartilage Proteoglycans

Abstract

Abstract Viscosimetric and centrifugal analyses of nasal and tracheal proteoglycan preparations indicate that: a, the proteoglycan molecules from both cartilages have very similar physical properties (limiting viscosity numbers of 140 and 145 ml per g and s0 values of 25 and 20 S, respectively); b, about 80% of the proteoglycan molecules in each preparation can form aggregates; and c, the aggregates are much larger in nasal than in tracheal preparations (s0 values of 93 and 43 S, respectively). Hyaluronic acid is present at a concentration of 0.4 to 0.8% (w/w) in nasal proteoglycan aggregate preparations. Evidence is presented which suggests that the hyaluronic acid-proteoglycan interactions described by Hardingham and Muir ((1972) Biochim. Biophys. Acta 279, 401) are involved in aggregate formation and that the relative sizes of the aggregates are probably determined by the relative sizes of the hyaluronic acid molecules. Mild proteolysis of proteoglycan aggregates with papain removes the chondroitin sulfate and keratan sulfate from the aggregates while leaving about 25% of the total protein still bound to hyaluronic acid. This bound protein fraction was separated from the hyaluronic acid by chromatography on Sephadex G-200 with 4 m guanidine hydrochloride as the solvent. Polyacrylamide gel electrophoresis indicated that this fraction contains two proteins (molecular weights approximately 40,000 and 65,000) both of which are reduced to smaller peptide fragments when treated with β-mercaptoethanol. The two proteins retain their ability to bind to hyaluronic acid. The interactions between the proteins and the hyaluronic acid in the intact aggregates partially protect the hyaluronic acid from digestion with bacterial chondroitinase.