Vinculin targeting by Shigella IpaA promotes stable cell adhesion independent of mechanotransduction

Shigella, the causative agent of bacillary dysentery, invades epithelial cells by injecting type III effectors that locally reorganize the actin cytoskeleton1. The type III effector IpaA targets the focal adhesion protein vinculin to induce bacterial adhesion associated with the recruitment of mature focal adhesion markers, despite the inability of bacteria to exert significant counter-forces2, 3. Here, we show that three vinculin-binding sites (VBSs) exposed at the IpaA C-terminus act in a cooperative manner to trigger a yet unreported mode of vinculin activation through specific interactions with sites in the vinculin head sub-domain D2. Structural modeling based on the mass spectrometry identification of interacting residues by cross-linking indicated that upon IpaA binding to vinculin D2, vinculin head sub-domains undergo major conformational changes leading to higher order heterocomplexes and vinculin homo-trimers. IpaA-mediated vinculin activation induces the formation of large and stable focal adhesions resisting the action of actin relaxing drugs. This property enables IpaA to rapidly elicit strong cell adhesion to fibronectin-coated substrates. While Shigella IpaA promotes strong adhesion in the absence of mechanotransduction, its mode of vinculin activation likely reflects a key step during maturation of cell adhesions driven by acto-myosin contractility.