title: Comparison of Tir from enterohemorrahgic and enteropathogenic Escherichia coli strains: two homologues with distinct intracellular properties.
abstract: Tir of enteropathogenic Escherichia coli (EPEC) or enterohemorrahgic E. coil (EHEC) is translocated by a type III secretion system to the host cell membranes where it serves as a receptor for the binding of a second bacterial membrane protein. In response to the binding, EPEC Tir is phosphorylated at Tyr474, and this phosphorylation is necessary for the signaling of pedestal formation. Tir of EHEC has no equivalent phosphorylation site but it is similarly needed for cytoskeleton rearrangement. How these two Tir molecules achieve their function by apparently different mechanisms is not completely clear. To examine their intrinsic differences, the two Tirs were expressed in HeLa cells and compared. Actin in complexes could be pelleted down from the lysate of cells expressing EHEC Tir but not EPEC Tir. By immunostaining, neither Tir molecule was found in phosphorylated state. In the cytoplasm, EHEC Tir was frequently found in fibrous structures whereas EPEC Tir was observed completely in a diffusive form. The determinant critical for the EHEC Tir fibrous formation was mapped to the C-terminal region of the molecule that deviates from the EPEC counterpart. This region may play a role in taking an alternative route different from Tyr474 phosphorylation to transduce signals.
authors.affiliation: Institute of Microbiology and Immunology, National Yang-Ming University, 155 Sec. 2, Li-Noong St., Beitou, Taipei, 112, Taiwan.
authors.forename: Chen-Hua
authors.initials: CH
authors.lastname: Chuang
authors.forename: Hao-Jie
authors.initials: HJ
authors.lastname: Chiu
authors.forename: Sheng-Chieh
authors.initials: SC
authors.lastname: Hsu
authors.forename: Jin-Yuan
authors.initials: JY
authors.lastname: Ho
authors.forename: Wan-Jr
authors.initials: WJ
authors.lastname: Syu
mesh_terms: D000595:Amino Acid Sequence; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism / Q000472:pathogenicity; D019453:Escherichia coli O157 / Q000737:chemistry / Q000378:metabolism / Q000472:pathogenicity; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D029968:Escherichia coli Proteins; D020033:Protein Isoforms; D011956:Receptors, Cell Surface; C109287:Tir protein, E coli