BINDING OF THE NG2 PROTEOGLYCAN TO TYPE-VI COLLAGEN AND OTHER EXTRACELLULAR-MATRIX MOLECULES

Previous studies have suggested that the NG2 proteoglycan interacts wi th type VI collagen. We have further characterized this interaction us ing a solid phase binding assay in which purified NG2 was shown to bin d to pepsin-solubilized type VI collagen. In addition, NG2 bound a rec ombinant alpha 2 (VI) collagen chain but did not appreciably bind to t he recombinant alpha 1 (VI) chain or the N-terminal domain of alpha 3 (VI) (N9-N2), Binding of NG2 to type VI collagen was shown to be conce ntration-dependent and saturable and to depend mainly on the NC2 core protein, since chondroitinase-treated NG2 bound the collagen as web as undigested samples. In addition, the binding studies revealed several other possible ligands for NG2, including type II collagen, type V co llagen, tenascin, and laminin. Binding of the proteoglycan to these mo lecules was also shown to be mediated by domains contained within the NG2 core protein. The ability of NG2 to bind to these extracellular ma trix molecules was compared with that of the chondroitin sulfate prote oglycan decorin, revealing an almost identical binding pattern of the two proteoglycans to the different collagen types. In addition, decori n was found to effectively inhibit the ability of NG2 to bind to colla gen, thus suggesting that the two proteoglycans may bind to some of th e same regions on the collagen substrates. In contrast, decorin did no t bind tenascin and was ineffective in inhibiting the binding of NG2 t o tenascin or laminin, indicating that NG2 may bind these two molecule s using a separate domain that is distinct from its collagen binding r egion.