Force-dependent allostery of the α-catenin actin-binding domain controls adherens junction dynamics and functions.

α-catenin is a key mechanosensor that forms force-dependent interactions with F-actin, thereby coupling the cadherin-catenin complex to the actin cytoskeleton at adherens junctions (AJs). However, the molecular mechanisms by which α-catenin engages F-actin under tension remained elusive. Here we show that the α1-helix of the α-catenin actin-binding domain (αcat-ABD) is a mechanosensing motif that regulates tension-dependent F-actin binding and bundling. αcat-ABD containing an α1-helix-unfolding mutation (H1) shows enhanced binding to F-actin in vitro. Although full-length α-catenin-H1 can generate epithelial monolayers that resist mechanical disruption, it fails to support normal AJ regulation in vivo. Structural and simulation analyses suggest that α1-helix allosterically controls the actin-binding residue V796 dynamics. Crystal structures of αcat-ABD-H1 homodimer suggest that α-catenin can facilitate actin bundling while it remains bound to E-cadherin. We propose that force-dependent allosteric regulation of αcat-ABD promotes dynamic interactions with F-actin involved in actin bundling, cadherin clustering, and AJ remodeling during tissue morphogenesis.

α-Catenin homodimers are recruited to phosphoinositide-activated membranes to promote adhesion.

A unique feature of α-catenin localized outside the cadherin-catenin complex is its capacity to form homodimers, but the subcellular localization and functions of this form of α-catenin remain incompletely understood. We identified a cadherin-free form of α-catenin that is recruited to the leading edge of migrating cells in a phosphatidylinositol 3-kinase-dependent manner. Surface plasmon resonance analysis shows that α-catenin homodimers, but not monomers, selectively bind phosphatidylinositol-3,4,5-trisphosphate-containing lipid vesicles with high affinity, where three basic residues, K488, K493, and R496, contribute to binding. Chemical-induced dimerization of α-catenin containing a synthetic dimerization domain promotes its accumulation within lamellipodia and elaboration of protrusions with extended filopodia, which are attenuated in the α-cateninKKR<3A mutant. Cells restored with a full-length, natively homodimerizing form of α-cateninKKR<3A display reduced membrane recruitment, altered epithelial sheet migrations, and weaker cell-cell adhesion compared with WT α-catenin. These findings show that α-catenin homodimers are recruited to phosphoinositide-activated membranes to promote adhesion and migration, suggesting that phosphoinositide binding may be a defining feature of α-catenin function outside the cadherin-catenin complex.