A conformational change in α-catenin's actin-binding domain governs adherens junction maturation.

The formation and maintenance of epithelia is critical for animal development and survival. Central to epithelial integrity are cadherin-based complexes called adherens junctions (AJs), which form physically robust but inherently dynamic cell-cell adhesions. How AJs function at the molecular level remains incompletely understood because techniques to study the central AJ proteins within the dynamic adhesion structure are scarce. Using a conformation sensitive probe that is amenable to fluorescence lifetime and anisotropy imaging, we demonstrate that the maturation of AJs is accompanied by a conformational change in the actin-binding domain of α-catenin. The structural transition depends on the degree of junctional maturation and requires actin polymerisation, but it is insensitive to vinculin binding to α-catenin. These different conformational states correlate with distinct α-catenin mobilities, with α-catenin unexpectedly showing an overall increased protein turnover in mature AJs. Collectively, the data reveal that α-catenin undergoes a previously proposed C-terminal conformational transition during epidermal differentiation to form mechanically stable yet dynamic cell-cell adhesions.