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-β1 precursor (pro-TGF-β1), integrins bind to the prodomain, apply force, and release the TGF-β 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 αVβ6 binds pro-TGF-β1 in an orientation biologically relevant for force-dependent release of TGF-β 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-β orientation that defines the pathway through these macromolecules which actin-cytoskeleton-generated tensile force takes when applied through the integrin β-subunit. Simulations of force-dependent activation of TGF-β demonstrate evolutionary specializations for force application through the TGF-β prodomain and through the β- and not α-subunit of the integrin. Integrin αVβ6 binds the transforming growth factor-β1 precursor (pro-TGF-β1) in an orientation that is biologically relevant for force-dependent release of TGF-β from its latent form. Members of the transforming growth factor-β (TGF-β) family have functions in development, wound healing, immune response and tumorigenesis. They occur in a latent form, and only specific stimuli—such as binding to the receptor integrin αVβ6—release TGF-β from the embrace of its prodomain, which keeps it inactive. By solving the co-crystal structure of the integrin αVβ6 head bound to intact pro-TGF-β1, and through modelling work, Timothy Springer and colleagues describe structural features of integrin binding to latent pro-TGF-β1. One of their findings is that force-dependent molecular changes in the latent complex result in activation of TGF-β1.