Enterohemorrhagic Escherichia coli O157 : H7 produces Tir, which is translocated to the host cell membrane but is not tyrosine phosphorylated

Intimate attachment to the host cell leading to the formation of attaching and effacing (A/E) lesions is an essential feature of enterohemorrhagic Esc herichia coli (EHEC) O157:H7 pathogenesis. In a related pathogen, enteropat hogenic E. coli (EPEC), this activity is dependent upon translocation of th e intimin receptor, Tir, which becomes tyrosine phosphorylated within the h ost cell membrane, In contrast, the accumulation of tyrosine-phosphorylated proteins beneath adherent EHEC bacteria does not occur, leading to questio ns about whether EHEC uses a Tir-based mechanism for adherence and A/E lesi on formation. In this report, we demonstrate that EHEC produces a functiona l Tir that is inserted into host cell membranes, where it serves as an inti min receptor. However, unlike in EPEC, in EHEC Tir is not tyrosine phosphor ylated yet plays a key role in both bacterial adherence to epithelial cells and pedestal formation. EHEC, but not EPEC, was unable to synthesize Tir i n Luria-Bertani medium but was able to secrete Tir into M9 medium, suggesti ng that Tir synthesis and secretion may be regulated differently in these t wo pathogens. EHEC Tir and EPEC Tir both bind intimin and focus cytoskeleta l rearrangements, indicating that tyrosine phosphorylation is not needed fo r pedestal formation. EHEC and EPEC intimins are functionally interchangeab le, but EHEC Tir shows a much greater affinity for EHEC intimin than for EP EC intimin, These findings highlight some of the differences and similariti es between EHEC and EPEC virulence mechanisms, which can be exploited to fu rther define the molecular basis of pedestal formation.