Self-association of scleral proteodermatan sulfate. Evidence for interaction via the dermatan sulfate side chains

Previous studies on scleral proteoglycans (proteodermatan sulfate) using light scattering and ultracentrifugation techniques have shown that the molecules form aggregates in 0.15 M NaCl (Cöster, L., Fransson, L.-A., Sheehan, J. K., Nieduszynski, I. A., and Phelps, C. F. (1981) Biochem. J., 197, 483-490). Aggregation was not promoted by hyaluronate but addition of free scleral dermatan sulfate chains enhanced multimerization. To investigate the possibility that scleral proteoglycans interact via their dermatan sulfate side chains, we have adopted an affinity chromatography procedure where binding of proteoglycans to various dermatan sulfate-agaroses may be studied. The evidence for an interaction between the side chains of the macromolecules and the immobilized dermatan sulfates are as follows: (a) the dermatan sulfate chains released from the proteoglycan by proteolysis display affinity for dermatan sulfate-agarose, (b) a significant proportion of the [3H]acetylated proteoglycans that were bound to the dermatan sulfate gel can be displaced by eluting with a solution of dermatan sulfate chains, (c) selective periodate oxidation of L-iduronate in the dermatan sulfate chains of the proteoglycans abolishes the affinity, (d) the core protein prepared by chondroitinase ABC digestion of the proteoglycan does not bind to dermatan sulfate-agarose, and (e) binding is retained after reduction-alkylation of the protein core. Furthermore, free [3H]dermatan sulfate chains co-elute with the proteoglycan upon gel filtration in 0.2 M NaCl.