Structural basis for vinculin activation at sites of cell adhesion

Vinculin is a highly conserved intracellular protein with a crucial role in the maintenance and regulation of cell adhesion and migration(1-3). In the cytosol, vinculin adopts a default autoinhibited conformation(4,5). On recruitment to cell - cell and cell - matrix adherens-type junctions, vinculin becomes activated and mediates various protein - protein interactions that regulate the links between F-actin and the cadherin and integrin families of cell-adhesion molecules. Here we describe the crystal structure of the full-length vinculin molecule ( 1,066 amino acids), which shows a five-domain autoinhibited conformation in which the carboxyterminal tail domain is held pincer-like by the vinculin head, and ligand binding is regulated both sterically and allosterically. We show that conformational changes in the head, tail and proline-rich domains are linked structurally and thermodynamically, and propose a combinatorial pathway to activation that ensures that vinculin is activated only at sites of cell adhesion when two or more of its binding partners are brought into apposition.