Molecular basis of actin reorganization promoted by binding of enterohaemorrhagic Escherichia coli EspB to α-catenin

EspB is a multifunctional protein associated with the type III secretion system of enterohaemorrhagic Escherichia coli, and interacts with various biomolecules including α-catenin in the host cell. The binding of EspB to α-catenin is thought be involved in actin reorganization during bacterial infection, although the precise mechanism of this phenomenon is still unclear. Recent research shows that dimerization of α-catenin dissociates it from E-cadherin/β-catenin/α-catenin complexes, and that the dimer suppresses Arp2/3-mediated actin branching or polymerization. These results inspired us to evaluate the effect of EspB on the functions of α-catenin. Based on a series of in vitro biochemical approaches, including pull-down, co-sedimentation and pyrene–actin polymerization assays combined with transmission electron microscopy, we conclude that EspB promotes all the functions of dimeric α-catenin described above. These results clarified the molecular basis of reorganization of actin filaments during infection with enterohaemorrhagic Escherichia coli.