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

Force sensing at cadherin-mediated adhesions is critical for their proper function. alpha-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 alpha-catenin adopts a stable auto-inhibitory conformation that makes the vinculin-binding site inaccessible. Here, by stretching single alpha-catenin molecules using magnetic tweezers, we show that the subdomains M-I vinculin-binding domain (VBD) to M-III unfold in three characteristic steps: a reversible step at similar to 5pN and two non-equilibrium steps at 10-15 pN. 5 pN unfolding forces trigger vinculin binding to the M-I domain in a 1: 1 ratio with nanomolar affinity, preventing M-I domain refolding after force is released. Our findings demonstrate that physiologically relevant forces reversibly unfurl alpha-catenin, activating vinculin binding, which then stabilizes alpha-catenin in its open conformation, transforming force into a sustainable biochemical signal.