# IpaA reveals distinct modes of vinculin activation during Shigella invasion and cell-matrix adhesion

## TL;DR

The study shows that Shigella's IpaA protein activates vinculin in a way that strengthens cell-matrix adhesion rather than directly aiding bacterial invasion.

## Contribution

The paper reveals distinct roles of vinculin conformers in Shigella invasion and adhesion, challenging prior assumptions about IpaA's function.

## Key findings

- Mutations targeting the closed D1D2 conformer reduced Shigella invasion but not focal adhesion formation.
- IpaA-induced vinculin activation primarily strengthens cell-matrix adhesion rather than promoting bacterial entry.
- Shear stress experiments confirmed the role of IpaA in accelerating adhesion.

## Abstract

Mutational analysis supports a role for IpaA-mediated vinculin head domain oligomerization in the maturation of focal adhesions during Shigella invasion of epithelial cells.

Vinculin is a cytoskeletal linker strengthening cell adhesion. The Shigella IpaA invasion effector binds to vinculin to promote vinculin supra-activation associated with head-domain–mediated oligomerization. Our study investigates the impact of mutations of vinculin D1D2 subdomains’ residues predicted to interact with IpaA VBS3. These mutations affected the rate of D1D2 trimer formation with distinct effects on monomer disappearance, consistent with structural modeling of a closed and open D1D2 conformer induced by IpaA. Notably, mutations targeting the closed D1D2 conformer significantly reduced Shigella invasion of host cells as opposed to mutations targeting the open D1D2 conformer and later stages of vinculin head-domain oligomerization. In contrast, all mutations affected the formation of focal adhesions (FAs), supporting the involvement of vinculin supra-activation in this process. Our findings suggest that IpaA-induced vinculin supra-activation primarily reinforces matrix adhesion in infected cells, rather than promoting bacterial invasion. Consistently, shear stress studies pointed to a key role for IpaA-induced vinculin supra-activation in accelerating and strengthening cell-matrix adhesion.