RECRUITMENT OF VINCULIN DURING TALIN STRETCHING

Abstract

Talin is a critical focal adhesion adaptor protein that connects actin and integrin directly. Talin dimer has up to 22 cryptic vinculin binding sites (VBS) that are exposed by stretching. A method was developed to dynamically measure both the length of talin and the binding of vinculin at a superresolution level in live cells. Unlike many models of the talin dimer, talin N-termini(integrin-binding domain) are sperated by about 180nm, whereas the C-terminal dimerization domains colocalize. The rapid stretching and relaxation cycles of the talin dimers occurs majority in peripheral cell regions, with a direction that agrees with actin flow. This is consistent with a stick-slip model for transient binding to flowing actin. By tagging a vinculin-dihydrofaolate reductase(DHFR) chimera with a covalent fluorophore(TMP-atto655). Vinculin binding to talin was monitored in parallel with talin length. A peak of binding was found at the length of 180nm for both full-length vinculin and vinculin head domain, but controls didn’t bind. Surprisingly, multiple vinculins bound within a single second in narrowly localized regions of the talin rod during stretching. Thus we suggest that talin stretching activates vinculin binding in a cooperative manner, consistent with vinculin dynamics in vivo.