Distinct Binding Interactions of αβ-Integrin and Proteoglycans with Fibronectin.

Dynamic single-molecule force spectroscopy was performed to monitor the unbinding of fibronectin with the proteoglycans syndecan-4 (SDC4) and decorin and to compare this with the unbinding characteristics of αβ-integrin. A single energy barrier was sufficient to describe the unbinding of both SDC4 and decorin from fibronectin, whereas two barriers were observed for the dissociation of αβ-integrin from fibronectin. The outer (high-affinity) barriers in the interactions of fibronectin with αβ-integrin and SDC4 are characterized by larger barrier heights and widths and slower dissociation rates than those of the inner (low-affinity) barriers in the interactions of fibronectin with αβ-integrin and decorin. These results indicate that SDC4 and (ultimately) αβ-integrin have the ability to withstand deformation in their interactions with fibronectin, whereas the decorin-fibronectin interaction is considerably more brittle.