Recently mechanical force has been recognized as a ubiquitous physiological factor that plays critical roles in diverse crucial biological processes.Vinculin binding to focal adhesion protein talin and cell-cell junction protein α-catenin plays important roles in regulation of the cell-ECM and cell-cell adhesions, which have been proposed to be dependent on actomyosin contractile force.We have investigated vinculin binding to talin and α-catenin under force using magnetic tweezers.We find that force in physiological range can expose the vinculin binding sites in talin rod and α-catenin core domains, which activates subsequent binding of the vinculin head domain.Binding of vinculin head then irreversibly locks talin rod and α-catenin core in unfolded conformations after force is released.These results indicate that both vinculin-talin and vinclulin-α-catenin interactions are biphasic with force and optimized over a physiological force range.