Direct observation of a coil-to-helix contraction triggered by vinculin binding to talin

Abstract

Vinculin binds unfolded talin domains in focal adhesions, which recruits actin filaments to reinforce the mechanical coupling of this organelle. However, it remains unknown how this interaction is regulated and its impact on the force transmission properties of this mechanotransduction pathway. Here, we use magnetic tweezers to measure the interaction between vinculin head and the talin R3 domain under physiological forces. For the first time, we resolve individual binding events as a short contraction of the unfolded talin polypeptide caused by the reformation of the vinculin-binding site helices, which dictates a biphasic mechanism that regulates this interaction. Force favors vinculin binding by unfolding talin and exposing the vinculin-binding sites; however, the coil-to-helix contraction introduces an energy penalty that increases with force, defining an optimal binding regime. This mechanism implies that the talin-vinculin-actin association could operate as a negative feedback mechanism to stabilize force on focal adhesions.

Talin Folding as the Tuning Fork of Cellular Mechanotransduction

“…The talin R3 domain is the weakest of all 13-rod domains, thought to be the precursor of talin-based adhesions, given its low unfolding force and the presence of two vinculin-binding sites [16,21,24,25]. This low mechanical stability is due to the four-residue threonine belt on its hydrophobic core; the substitution of these residues in the mutant R3 IVVI increases its stability significantly [16,21]. Due to these different mechanical properties, we explore both the R3 WT and R3 IVVI domains perturbed by complex mechanical signals, which will allow us to compare and relate their responses with their mechanics.…”

“…Talin is a mechanosensing hub protein in focal adhesions, which crosslinks transmembrane integrins with the active F-actin filaments and recruits several binding proteins to control the function and fate of this organelle [16][17][18]. For example, vinculin binds to cryptic helices in mechanically unfolded talin domains, subsequently recruiting actin filaments that reinforce the cellular junction [13,[19][20][21]. Hence, talin transduces mechanical forces through its folding dynamics.…”

Different Vinculin Binding Sites Use the Same Mechanism to Regulate Directional Force Transduction

“…We found that mechanical strength in this geometry is modulated by complex synergies of hydrophobic and polar contacts, which vary between VBSs. A recent study has shown that these interactions stabilize the helical conformation of the VBS so strongly that vinculin binding can trigger a coil-to-helix transition in mechanically overstretched talin ( 47 ). Interestingly, we can partially observe this process in our simulations when we see refolding of the VBS in the binding groove under load ( Fig.…”

Mechanical Unfolding of Proteins—A Comparative Nonequilibrium Molecular Dynamics Study

“…This suggests that binding of vinculin to talin requires the folded conformation of α -helices, and at large forces, the α -helical secondary structure becomes unstable, leading to dissociation of vinculin. A recent study suggests that vinculin binding can contribute to talin helix refolding ( 41 ). All-atom SMD suggests an unfolding mechanism in which the α -helical secondary structure permanently breaks during subdomain unfolding ( Fig.…”