title: Interactions in the TonB-dependent energy transduction complex: ExbB and ExbD form homomultimers.
abstract: The cytoplasmic membrane proteins ExbB and ExbD support TonB-dependent active transport of iron siderophores and vitamin B12 across the essentially unenergized outer membrane of Escherichia coli. In this study, in vivo formaldehyde cross-linking analysis was used to investigate the interactions of T7 epitope-tagged ExbB or ExbD proteins. ExbB and ExbD each formed two unique cross-linked complexes which were not dependent on the presence of TonB, the outer membrane receptor protein FepA, or the other Exb protein. Cross-linking analysis of ExbB- and ExbD-derived size variants demonstrated instead that these ExbB and ExbD complexes were homodimers and homotrimers and suggested that ExbB also interacted with an unidentified protein(s). Cross-linking analysis of epitope-tagged ExbB and ExbD proteins with TonB antisera afforded detection of a previously unrecognized TonB-ExbD cross-linked complex and confirmed the composition of the TonB-ExbB cross-linked complex. The implications of these findings for the mechanism of TonB-dependent energy transduction are discussed.
authors.affiliation: Departments of Microbiology, Washington State University, Pullman, Washington 99164-4233, USA.
authors.forename: P I
authors.initials: PI
authors.lastname: Higgs
authors.forename: P S
authors.initials: PS
authors.lastname: Myers
authors.forename: K
authors.initials: K
authors.lastname: Postle
mesh_terms: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000378:metabolism*; D017123:Bacteriophage T7; D002352:Carrier Proteins / Q000378:metabolism; D003432:Cross-Linking Reagents; D019281:Dimerization; D004735:Energy Transfer; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins; D005822:Genetic Vectors; D008565:Membrane Proteins / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D003432:Cross-Linking Reagents; D029968:Escherichia coli Proteins; C052874:ExbB protein, E coli; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C029489:enterobactin receptor; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli; C060790:exbD protein, E coli