Force interacts with macromolecular structure in activation of TGF-β

Integrins are adhesion receptors that transmit force across the plasma membrane between extracellular ligands and the actin cytoskeleton. In activation of the transforming growth factor-beta 1 precursor (pro-TGF-beta 1), integrins bind to the prodomain, apply force, and release the TGF-beta growth factor. However, we know little about how integrins bind macromolecular ligands in the extracellular matrix or transmit force to them. Here we show how integrin alpha(V)beta(6) binds pro-TGF-beta 1 in an orientation biologically relevant for force-dependent release of TGF-beta from latency. The conformation of the prodomain integrin-binding motif differs in the presence and absence of integrin binding; differences extend well outside the interface and illustrate how integrins can remodel extracellular matrix. Remodelled residues outside the interface stabilize the integrin-bound conformation, adopt a conformation similar to earlier-evolving family members, and show how macromolecular components outside the binding motif contribute to integrin recognition. Regions in and outside the highly interdigitated interface stabilize a specific integrin/pro-TGF-beta orientation that defines the pathway through these macromolecules which actin-cytoskeleton-generated tensile force takes when applied through the integrin beta-subunit. Simulations of force-dependent activation of TGF-beta demonstrate evolutionary specializations for force application through the TGF-beta prodomain and through the beta- and not alpha-subunit of the integrin.