Functional analysis of EspB from enterohaemorrhagic Escherichia coli

In enterohaemorrhagic Escherichia coli (EHEC), the type III secretion protein EspB is translocated into the host cells and plays an important role in adherence, pore formation and effector translocation during infection. The secretion domain of EspB has been mapped previously. To define the other functional determinants of EspB, several plasmids encoding different fragments of EspB were created and analysed to see which of them lost the functions of the full-length molecule. One finding was that residues 118-190 of EspB were required for both efficient translocation of EspB and interaction of EspB with EspA. Additionally, the segment consisting of residues 217-312 was necessary for bacterial adherence. Furthermore, a predicted transmembrane domain (residues 99-118) was found to be critical for EHEC to cause red blood cell haemolysis, presumably by forming pores in the cell membrane. The same segment was also important for actin accumulation induced beneath the bacterial-attachment site. Taken together, these data indicate that the EspB protein (312 residues in total) has functions associated with its different regions. These regions may interact with each other or with other components of the type III system to orchestrate the intricate actions of EHEC during infection.