Lipid-directed vinculin dimerization.

Vinculin localizes to cellular adhesions where it regulates motility, migration, development, wound healing, and response to force. Importantly, vinculin loss results in cancer phenotypes, cardiovascular disease, and embryonic lethality. At the plasma cell membrane, the most abundant phosphoinositide, phosphatidylinositol 4,5-bisphosphate (PIP2), binds the vinculin tail domain, Vt, and triggers homotypic and heterotypic interactions that amplify binding of vinculin to the actin network. Binding of PIP2 to Vt is necessary for maintaining optimal focal adhesions, for organizing stress fibers, for cell migration and spreading, and for the control of vinculin dynamics and turnover of focal adhesions. While the recently determined Vt/PIP2 crystal structure revealed the conformational changes occurring upon lipid binding and oligomerization, characterization of PIP2-induced vinculin oligomerization has been challenging in the adhesion biology field. Here, via a series of novel biochemical assays not performed in previous studies that relied on chemical cross-linking, we characterize the PIP2-induced vinculin oligomerization. Our results show that Vt/PIP2 forms a tight dimer with Vt or with the muscle-specific vinculin isoform, metavinculin, at sites of adhesion at the cell membrane. Insight into how PIP2 regulates clustering and into mechanisms that regulate cell adhesion allows the development for a more definite sensor for PIP2, and our developed techniques can be applied generally and thus open the door for the characterization of many other protein/PIP2 complexes under physiological conditions.