Cell adhesion promoted by a unique Shigella IpaA vinculin- and talin-binding site

During Shigella cell invasion, the IpaA effector targets the focal adhesion protein vinculin through three vinculin-binding sites (VBSs). Here, we report that IpaA VBS3 also binds to talin. The 2.5 [A] resolution crystal structure indicates that IpaA VBS3 forms a tightly folded -helical bundle with talin H1-H4, contrasting with bundle unraveling upon vinculin interaction. High-affinity binding of Ipa VBS3 to talin H1-H4 requires a core of hydrophobic residues conserved in vinculin binding and a pair of electrostatic interactions accounting for talin binding specificity. IpaA VBS3 does not bind to talin H1-H5 suggesting the targeting of partially activated stretched talin but not inactive talin. Consistently, IpaA VBS3 labeled filopodial and nascent adhesions and regulated their formation through talin binding. In addition, talin-binding by IpaA VBS3 was required for bacterial capture by filopodia during Shigella invasion and for the stabilization of focal adhesions in infected cells. These findings point to the functional diversity of VBSs and a critical role for talin-binding by Shigella IpaA VBS3 and possibly talin VBSs in the regulation of adhesion structures.