A novel molecular switch controls assembly of bacterial focal adhesions

Abstract Cell motility is universally driven by focal adhesion complexes (FAs) assembled in the cell envelope to connect the underlying substrate to cytoskeletal motors, generating traction forces in a highly regulated manner. In bacteria, focal adhesion complexes (bFAs) assembly is mediated by the Agl-Glt motility machinery, however how this machinery is connected to the cytoskeleton via cytoplasmic platform proteins, MglA and AglZ, remains unknown. Here, combining in vitro and single cell approaches, we show that the cytoplasmic region of the transmembrane GltJ protein contains two cytosolic motifs that independently recruit MglA-GTP (Linker) and AglZ (GYF), thus driving bFA assembly. Remarkably, binding of MglA-GTP causes a switch in the conformation of an adjacent Zinc finger domain (ZnR) that becomes available to recruit MglB, a MglA GTPase-Activating Protein. This binding activates GTP hydrolysis, which dissociates MglA from GltJ and is important to regulate bFA stability in vivo . These findings thus unravel the molecular mechanism of bFA assembly and regulation. Remarkably, the large number of other bacterial receptor proteins containing adjacent GYF and ZnR domains suggests conservation of this novel type of molecular switches.