A conformational switch in vinculin drives formation and dynamics of a talin-vinculin complex at focal adhesions

Dynamic interactions between the cytoskeleton and integrins control cell adhesion, but regulatory mechanisms remain largely undefined. Here, we tested the extent to which the autoinhibitory head-tail interaction (HTI) in vinculin regulates formation and lifetime of the talin-vinculin complex, a proposed mediator of integrin-cytoskeleton bonds. In an ectopic recruitment assay, mutational reduction of HTI drove assembly of talin-vinculin complexes, whereas ectopic complexes did not form between talin and wild-type vinculin. Moreover, reduction of HTI altered the dynamic assembly of vinculin and talin in focal adhesions. Using fluorescence recovery after photo-bleaching, we show that the focal adhesion residency time of vinculin was enhanced up to 3-fold by HTI mutations. The slow dynamics of vinculin correlated with exposure of its cryptic talin-binding site, and a talin-binding site mutation rescued the dynamics of activated vinculin. Significantly, HTI-deficient vinculin inhibited the focal adhesion dynamics of talin, but not paxillin or α-actinin. These data show that talin conformation in cells permits vinculin binding, whereas the auto-inhibited conformation of vinculin constitutes the barrier to complex formation. Down-regulation of HTI in vinculin to K_d ∼ 10 ^-7 is sufficient to induce talin binding, and HTI is essential to the dynamics of vinculin and talin at focal adhesions. We therefore conclude that vinculin conformation, as modulated by the strength of HTI, directly regulates the formation and lifetime of talin-vinculin complexes in cells.