title: Hierarchal type III secretion of translocators and effectors from Escherichia coli O157:H7 requires the carboxy terminus of SepL that binds to Tir.
abstract: Type III secretion (T3S) from enteric bacteria is a co-ordinated process with a hierarchy of secreted proteins. In enteropathogenic and enterohaemorrhagic Escherichia coli, SepL and SepD are essential for translocator but not effector protein export, but how they function to control this differential secretion is not known. This study has focused on the different activities of SepL including membrane localization, SepD binding, EspD export and Tir secretion regulation. Analyses of SepL truncates demonstrated that the different functions associated with SepL can be separated. In particular, SepL with a deletion of 11 amino acids from the C-terminus was able to localize to the bacterial membrane, export translocon proteins but not regulate Tir or other effector protein secretion. From the repertoire of effector proteins only Tir was shown to bind directly to full-length SepL and the C-terminal 48 amino acids of SepL was sufficient to interact with Tir. By synchronizing induction of T3S, it was evident that the Tir-binding capacity of SepL is important to delay the release of effector proteins while the EspADB translocon is secreted. The interaction between Tir and SepL is therefore a critical step that controls the timing of T3S in attaching and effacing pathogens.
authors.affiliation: Immunity and Infection Division, The Roslin Institute and R(D)SVS, Chancellor's Building, University of Edinburgh, Edinburgh, EH16 4SB, UK.
authors.forename: Dai
authors.initials: D
authors.lastname: Wang
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Roe
authors.forename: Sean
authors.initials: S
authors.lastname: McAteer
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Shipston
authors.forename: David L
authors.initials: DL
authors.lastname: Gally
mesh_terms: D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000737:chemistry; D003470:Culture Media / Q000737:chemistry; D019453:Escherichia coli O157 / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011956:Receptors, Cell Surface / Q000378:metabolism*; D016415:Sequence Alignment; D017384:Sequence Deletion
chemical_list: D003470:Culture Media; D029968:Escherichia coli Proteins; C474481:EspD protein, E coli; D011956:Receptors, Cell Surface; C495684:SepD protein, E coli; C416081:SepL protein, E coli; C109287:Tir protein, E coli