Proteoglycans from bovine proximal humeral articular cartilage. Structural basis for the polydispersity of proteoglycan subunit.

Polydisperse proteoglycan subunit from bovine proximal humeral articular cartilage has been separated into a series of relatively monodisperse fractions which have been chemically and physically characterized. The proteoglycan subunit species of the lowest molecular weight contains the least chondroitin sulfate and had an amino acid composition relatively low in serine and glycine and relatively high in cysteine, methionine, and aspartic acid, almost identical to that of the hyaluronic acid-binding region of proteoglycan subunit isolated by Heinegard and Hascall (Heinegard, D., and Hascall, V.C. (1974) J. Biol. Chem. 249, 4250-4256). The molecular weight of proteoglycan subunit increases in proportion to its chondroitin sulfate content. As the molecular weight and chondroitin sulfate content of proteoglycan subunit increase, there is a parallel increase in the serine and glycine contents, and a decrease in the cysteine, methionine, and aspartic acid contents of proteoglycan subunit core protein. The pattern of polydispersity observed strongly supports the concept that proteoglycan subunit core protein contains a hyaluronic acid-binding region of constant size and composition and a polysaccharide attachment region of variable length and composition, composed of repeating peptide sequences containing serine and glycine in equimolar amounts.