αE-catenin actin-binding domain alters actin filament conformation and regulates binding of nucleation and disassembly factors

The actin-binding protein alpha E-catenin may contribute to transitions between cell migration and cell-cell adhesion that depend on remodeling the actin cytoskeleton, but the underlying mechanisms are unknown. We show that the alpha E-catenin actin-binding domain (ABD) binds cooperatively to individual actin filaments and that binding is accompanied by a conformational change in the actin protomer that affects filament structure. alpha E-catenin ABD binding limits barbed-end growth, especially in actin filament bundles. alpha E-catenin ABD inhibits actin filament branching by the Arp2/3 complex and severing by cofilin, both of which contact regions of the actin protomer that are structurally altered by alpha E-catenin ABD binding. In epithelial cells, there is little correlation between the distribution of alpha E-catenin and the Arp2/3 complex at developing cell-cell contacts. Our results indicate that alpha E-catenin binding to filamentous actin favors assembly of unbranched filament bundles that are protected from severing over more dynamic, branched filament arrays.