Distinct intramolecular interactions regulate autoinhibition of vinculin binding in αT-catenin and αE-catenin

alpha-Catenin binds directly to beta-catenin and connects the cadherin-catenin complex to the actin cytoskeleton. Tension regulates alpha-catenin conformation. Actomyosin-generated force stretches the middle (M)-region to relieve autoinhibition and reveal a binding site for the actin-binding protein vinculin. It is not known whether the intramolecular interactions that regulate epithelial (alpha E)-catenin binding are conserved across the alpha-catenin family. Here, we describe the biochemical properties of testes (alpha T)-catenin, an alpha-catenin isoform critical for cardiac function and how intramolecular interactions regulate vinculin-binding autoinhibition. Isothermal titration calorimetry showed that alpha T-catenin binds the beta-catenin-N-cadherin complex with a similar low nanomolar affinity to that of alpha E-catenin. Limited proteolysis revealed that the alpha T-catenin M-region adopts a more open conformation than alpha E-catenin. The alpha T-catenin M-region binds the vinculin N-terminus with low nanomolar affinity, indicating that the isolated alpha T-catenin Mregion is not autoinhibited and thereby distinct from alpha E-catenin. However, the alpha T-catenin head (N- and M-regions) binds vinculin 1000-fold more weakly (low micromolar affinity), indicating that the N-terminus regulates the M-region binding to vinculin. In cells, alpha 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 show that the alpha T-catenin N-terminus is required to maintain M-region autoinhibition and modulate vinculin binding. We postulate that the unique molecular properties of alpha T-catenin allow it to function as a scaffold for building specific adhesion complexes.

Automated summary

The study reveals that alpha T-catenin has similar binding characteristics to alpha E-catenin but with differences in affinity and conformation when binding to vinculin. The N-terminus of alpha T-catenin is crucial in maintaining M-region autoinhibition and recruiting vinculin to cell-cell contacts.