The self-association of biglycan from bovine articular cartilage

Biglycan is a small dermatan sulfate proteoglycan present in the extracellular matrix of a variety of connective tissues. Sedimentation velocity and equilibrium studies were carried out to determine the monomer molecular weight of biglycan in denaturing solvents and to define the oligomeric states of biglycan in physiologic solvents in the presence and absence of Zn2+. In 6 M guanidine chloride, biglycan is a monomer with s0(20,w) = 2.9 S and Mz = 93,100 (where Mz is z-average molecular weight). In 0.15 M NaCl, 50 mM Tris, pH 7.5, in the absence of divalent metal ions, and at concentrations above 1 mg/ml, biglycan is predominantly dimer (s0(20,w) = 4.8 S). Under these same conditions in solvent containing 5 mM Zn2+, biglycan exists predominantly as a hexamer, with s0(20,w) = 9.4 S and Mz approximately 600,000. In either case, the oligomers dissociate reversibly. In order to determine whether the glycosaminoglycan chains or the core protein was responsible for self-association, sedimentation velocity and sedimentation equilibrium studies were conducted on the isolated components. Dermatan sulfate chains prepared from biglycan, examined in both denaturing and physiologic solvents, show no significant difference in molecular weight (Mz approximately 22,000), whether or not the solvents contain Zn2+. However, biglycan core protein strongly self-associated in physiologic solvents. Thus, the self-association of biglycan appears to be mediated by the core protein and not by its glycosaminoglycan chains.