New Models for Regulation of Vinculin by Actin and Phospholipids

Abstract

Vinculin is an essential cytoskeletal protein that is a prominent component of focal adhesions and adherens junctions. It exists in an autoinhibited conformation that masks interactions of ligands with the head (Vh) and tail (Vt) domain. Upon activation, vinculin functions as a scaffold to regulate cellular events resulting in cell migration, cell survival and embryogenesis. Vinculin null cells display tumorigenic properties and mutation or loss of vinculin is associated with cardiac disease. The interaction between vinculin and actin plays a pivotal role in linking transmembrane receptors to the cytoskeleton, which, in turn, is important for controlling cellular cell morphology, force transmission and motility. Binding of F-actin to Vt causes a conformational change that induces formation of a cryptic dimer necessary for actin filament bundling, however, the conformational change that occurs and dimer that is formed is unknown. It is also unclear how vinculin recognizes PIP2, inserts into membranes and is regulated by this interaction. We have now obtained a sub-nanometer resolution reconstruction of the Vt/actin complex which sheds light on actin-induced conformational changes necessary for vinculin dimerization and actin filament bundling, and have integrated computational and experimental approaches to generate and test models for the actin-induced vinculin dimer and vinculin/PIP2 membrane interaction and assess their significance in vinculin function both in vitro and in cells.