Mechanical opening of the αE-catenin M-region gates afadin condensation in cardiomyocytes.

In mechanically active tissues, cell-cell adhesions must withstand high and dynamic loads to maintain tissue integrity. The ability to detect and withstand load centers on the mechanosensitive adherens junction (AJ), which couples the actin networks of adjacent cells. The mechanosensor αE-catenin responds to force by opening its Middle (M) region, revealing cryptic binding sites for adaptor proteins such as afadin and vinculin. Here we show that the afadin coiled-coil (CC) region binds the open αE-catenin M-region with modest affinity and fast exchange, unlike the high-affinity, long-lived binding of vinculin, suggesting distinct roles. In cardiomyocytes, the afadin CC is necessary and sufficient for afadin localization at high-load AJs, where it exhibits the dynamic, hexanediol-sensitive properties of a biomolecular condensate. By contrast, the afadin CC is dispensable for recruitment at low-load epithelial AJs, suggesting that junctional load determines the basis of afadin recruitment. We propose that force-gated opening of αE-catenin seeds afadin condensate formation, a mechanism that drives reorganization of high-load AJs.