Force-dependent conformational switch of α -catenin controls vinculin binding

Force sensing at cadherin-mediated adhesions is critical for their proper function. α-Catenin, which links cadherins to actomyosin, has a crucial role in this mechanosensing process. It has been hypothesized that force promotes vinculin binding, although this has never been demonstrated. X-ray structure further suggests that α-Catenin adopts a stable auto-inhibitory conformation that makes the vinculin-binding site inaccessible. Here, by stretching single acatenin molecules using magnetic tweezers, we show that the subdomains M_I vinculinbinding domain (VBD) to M_III unfold in three characteristic steps: a reversible step at B5pN and two non-equilibrium steps at 10-15 pN. 5 pN unfolding forces trigger vinculin binding to the MI domain in a 1:1 ratio with nanomolar affinity, preventing MI domain refolding after force is released. Our findings demonstrate that physiologically relevant forces reversibly unfurl acatenin, activating vinculin binding, which then stabilizes α-Catenin in its open conformation, transforming force into a sustainable biochemical signal.