Structural Analysis of Collagen Type I Interactions with Human Fibronectin Reveals a Cooperative Binding Mode

Despite its biological importance, the interaction between fibronectin (FN) and collagen, two abundant and crucial tissue components, has not been well characterized on a structural level. Here, we analyzed the four interactions formed between epitopes of collagen type I and the collagen-binding fragment (gelatin-binding domain (GBD)) of human FN using solution NMR, fluorescence, and small angle x-ray scattering methods. Collagen association with FN modules 8–9 FnI occurs through a conserved structural mechanism but exhibits a 400-fold disparity in affinity between collagen sites. This disparity is reduced in the full-length GBD, as 6 FnI 1–2 FnII 7 FnI binds a specific collagen epitope next to the weakest 8–9 FnI-binding site. The cooperative engagement of all GBD modules with collagen results in four broadly equipotent FN-collagen interaction sites. Collagen association stabilizes a distinct monomeric GBD conformation in solution, giving further evidence to the view that FN fragments form well defined functional and structural units. Background: The fibronectin (FN)-collagen interaction is important for cell adhesion and migration. Results: FN modules 8–9 FnI interact with two distinct sites in both chains of collagen I. All six collagen-binding FN modules interact cooperatively with a single collagen site. Conclusion: Collagen I possesses four equipotent sites for FN. Significance: We have mapped FN binding to collagen I and demonstrated the first cooperative interaction.