In rod-shaped bacteria, type IV pili (Tfp) promote twitching motility by assembling and retracting at the cell pole. In Myxococcus xanthus, a bacterium that moves in highly coordinated cell groups, Tfp are activated by a polar activator protein, SgmX. However, while it is known that the Ras-like protein MglA is required for unipolar targeting, how SgmX accesses the cell pole to activate Tfp is unknown. Here, we demonstrate that a polar beacon protein, FrzS, recruits SgmX at the cell pole. We identified two main functional domains, including a Tfp-activating domain and a polarbinding domain. Within the latter, we show that the direct binding of MglA-GTP unveils a hidden motif that binds directly to the FrzS N-terminal response regulator (CheY). Structural analyses reveal that this binding occurs through a novel binding interface for response regulator domains. In conclusion, the findings unveil the protein interaction network leading to the spatial activation of Tfp at the cell pole. This tripartite system is at the root of complex collective behaviours in this predatory bacterium.
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.