A second fibronectin-binding region is present in collagen α chains

The interactions of plasma fibronectin with α chains or cyanogen bromide fragments of collagen types I and II have been studied using a variety of techniques. Affinity chromatography of cyanogen bromide-cleaved type II collagen on immobilized fibronectin revealed the binding of cyanogen bromide fragment CB12 in addition to the previously characterized CB10. Using fluorescence polarization, we analyzed the interaction between the collagen peptides and fluorescein isothiocyanate-labeled 42-kDa gelatin-binding fragment of fibronectin in solution. Dissociation constants for the binding of CB10 and CB12 to the fibronectin fragment were calculated as 0.38 and 0.94 μM, respectively, indicating a lower affinity for the uncharacterized site. However, as with CB10, CB12 was able to compete effectively with the intact α chain for binding to fibronectin. Additionally, both CB10 and CB12 absorbed to tissue culture surfaces were each able to support fibronectin-dependent cell adhesion. Finally, the regions of α2(I) homologous to CB12 and CB10 were found to be active in fibronectin binding, demonstrating the presence of two fibronectin-binding regions in this collagen chain.