A comparative study of the binding of cartilage link protein and the hyaluronate-binding region of the cartilage proteoglycan to hyaluronate-substituted Sepharose gel

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Abstract
Hyaluronate-binding proteins from bovine nasal cartilage, i.e., the hyaluronate-binding region of the proteoglycan and the link protein, were labeled with 125I and separated from each other by gel chromatography. The proteins were characterized by MW determinations and their purity was established by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and immunodiffusion. The binding properties of the 2 proteins to hyaluronate-substituted Sepharose gel were compared. Both proteins behaved similarly. They bound with the same efficiency to the gel, they showed the same time course of binding, had slightly different pH optima for binding and had a decreasing affinity for the gel with increasing ionic strength. The binding to the gel could be inhibited by soluble hyaluronate and the minimum size of a hyaluronate oligosaccharide required for inhibition was in both cases a decasaccharide (only even-numbered oligosaccharides were tested). The proteins did not show any co-operative binding in the system tested, which could be explained by the large number of binding sites in the hyaluronate-substituted gel. Binding constants for the protein-hyaluronate interaction were estimated. A value of 1.3 .times. 107 M-1 was obtained for the hyaluronate-binding region of the proteoglycan in agreement with literature data. The corresponding value for the link protein was 0.7 .times. 107 M-1.