Nano-mechanical characterization of tension-sensitive helix bundles in talin rod

Tension-induced exposure of a cryptic signaling binding site is one of the most fundamental mechanisms in molecular mechanotransduction. Helix bundles in rod domains of talin, a tension-sensing protein at focal adhesions, unfurl under tension to expose cryptic vinculin binding sites. Although the difference in their mechanical stabilities would determine which helix bundle is tension-sensitive, their respective mechanical behaviors under tension have not been characterized. In this study, we evaluated the mechanical behaviors of residues 486–654 and 754–889 of talin, which form helix bundles with low and high tension-sensitivity, by employing AFM nano-tensile testing. As a result, residues 754–889 exhibited lower unfolding energy for complete unfolding than residues 486–654. In addition, we found that residues 754–889 transition into intermediate conformations under lower tension than residues 486–654. Furthermore, residues 754–889 showed shorter persistence length in the intermediate conformation than residues 486–654, suggesting that residues 754–889 under tension exhibit separated α-helices, while residues 486–654 assume a compact conformation with inter-helix interactions. Therefore, we suggest that residues 754–889 of talin work as a tension-sensitive domain to recruit vinculin at the early stage of focal adhesion development, while residues 486–654 contribute to rather robust tension-sensitivity by recruiting vinculin under high tension. [Display omitted] •Nano-mechanical behaviors of tension-sensitive helix bundles in talin were tested.•Residues 754–889 formed less stable helix bundle than that of residues 486–654.•Residues 754–889 transited intermediate conformations under low tension.•Residues 754–889 showed smaller tensile stiffness than that of residues 486–654.