Distinct autoinhibitory mechanisms regulate vinculin binding by alpha-T-catenin and alpha-E-catenin
-catenin binds directly to {beta}-catenin and connects the cadherin-catenin complex to the actin cytoskeleton. Tension regulates -catenin conformation: actomyosin-generated force stretches the middle(M)-region to relieve autoinhibition and reveal a binding site for the actin-binding protein vinculin. Here we describe the biochemical properties of T(testes)-catenin, an -catenin isoform critical for cardiac function, and how intramolecular interactions regulate vinculin binding autoinhibition. Isothermal titration calorimetry (ITC) showed that T-catenin binds the {beta}-catenin/N-cadherin complex with a similar low nanomolar affinity to that of E-catenin. Limited proteolysis revealed that the T-catenin M-region adopts a more open conformation than E-catenin. The T-catenin M-region binds the vinculin N-terminus with low nanomolar affinity, indicating that the isolated T-catenin M-region is not autoinhibited and thereby distinct from E-catenin. However, the T-catenin head (N- and M-regions) binds vinculin 1000-fold more weakly (low micromolar affinity), indicating that the N-terminus regulates M-region binding to vinculin. In cells, T-catenin recruitment of vinculin to cell-cell contacts requires the actin-binding domain and actomyosin-generated tension, indicating that force regulates vinculin binding. Together, our results indicate that the T-catenin N-terminus is required to maintain M-region autoinhibition and modulate vinculin binding. We postulate that the unique molecular properties of T-catenin allow it to function as a scaffold for building specific adhesion complexes.