Mechanosensitivity of the talin molecular clutch

Cells sense substrate mechanical properties through the integrin-talin-F-actin linkage. Talin's N-terminal head domain binds β-integrin, whereas its C-terminal domain connects to F-actin directly via two actin-binding sites (ABSs) and indirectly through cryptic vinculin-binding sites (VBSs) within rod domain bundles. Force-induced unfolding of these α-helical bundles exposes VBSs, recruiting vinculin to strengthen the talin-actin bond. This system is sensitive to the loading rate and is influenced by rates of F-actin movement and substrate stiffness. Although the components of this pathway are well studied, how talin, vinculin, and actin synergize to mechanically buffer loads and mediate cellular stiffness sensing remains incompletely understood. We developed a multiscale stochastic finite element model to simulate talin unfolding during interactions with retrograde actin flows and analyzed the contributions of ABS2, ABS3, and VBSs to talin mechanosensitivity. Vinculin attachments strengthened the force-bearing capacity in talin, stabilized the actin-talin contact, and regulated binding site activity at RD3. Lifetime of the dynamic bond formed between talin and actin decreased with an increase in actin flow velocity. Higher substrate stiffness enhanced the lifetime at low actin flow velocity but negatively impacted it at higher velocities. ABS3 primarily mediated force transfer from actin to talin at rapid actin flows, whereas vinculin and ABS2 reinforced the F-actin bond under slower flows. Stiffer substrates enhanced force transmission through VBSs. Our results show that stretch rate modulates force feedback between the unfolding of talin rod domains and VBS attachments, driving the sensitivity of talin to substrate stiffness.