Aggregation of Cartilage Proteoglycans

Abstract

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 [3H]acetylated 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.