Aggregation of Cartilage Proteoglycans

Abstract A protein-hyaluronic acid complex was isolated from Sepharose 2B chromatography of a sequential chondroitinase plus trypsin digest of a proteoglycan aggregate preparation from bovine nasal cartilage. Two were subsequently isolated from this complex by Sephadex G-200 chromatography with 4 m guanidine hydrochloride as the eluent. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the two had molecular weights of about 90,000 and 45,000 and that treatment with β-mercaptoethanol did not decrease their sizes. The larger protein gave a broad, diffuse band in the gel, perhaps attributable to the 10 to 15% keratan sulfate present in this fraction. The larger protein accounted for 20%, and the smaller for 10% of the protein in the original proteoglycan aggregate preparation. Both retained their ability to bind to hyaluronic acid. Experiments with aggregate preparations reconstituted from mixtures with 3Hacetylated or unlabeled proteoglycans showed that the larger protein fraction is derived from a portion of the protein in the proteoglycan monomer molecules while the smaller is derived from one of the small molecular weight link proteins that are present in proteoglycan aggregate preparations.