title: The TolQ-TolR proteins energize TolA and share homologies with the flagellar motor proteins MotA-MotB.
abstract: The Tol-Pal system of Escherichia coli is required for the maintenance of outer membrane stability. Recently, proton motive force (pmf) has been found to be necessary for the co-precipitation of the outer membrane lipoprotein Pal with the inner membrane TolA protein, indicating that the Tol-Pal system forms a transmembrane link in which TolA is energized. In this study, we show that both TolQ and TolR proteins are essential for the TolA-Pal interaction. A point mutation within the third transmembrane (TM) segment of TolQ was found to affect the TolA-Pal interaction strongly, whereas suppressor mutations within the TM segment of TolR restored this interaction. Modifying the Asp residue within the TM region of TolR indicated that an acidic residue was important for the pmf-dependent interaction of TolA with Pal and outer membrane stabilization. Analysis of sequence alignments of TolQ and TolR homologues from numerous Gram-negative bacterial genomes, together with analyses of the different tolQ-tolR mutants, revealed that the TM domains of TolQ and TolR present structural and functional homologies not only to ExbB and ExbD of the TonB system but also with MotA and MotB of the flagellar motor. The function of these three systems, as ion potential-driven molecular motors, is discussed
authors.affiliation: Laboratoire d'Ingénierie de Systèmes Macromoléculaires, Institut de Biologie Structurale et Microbiologie, CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
authors.forename: E
authors.initials: E
authors.lastname: Cascales
authors.forename: R
authors.initials: R
authors.lastname: Lloubès
authors.forename: J N
authors.initials: JN
authors.lastname: Sturgis
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D016384:Consensus Sequence; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D017136:Ion Transport; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D010457:Peptidoglycan / Q000235:genetics / Q000378:metabolism; D011509:Proteoglycans; D017386:Sequence Homology, Amino Acid
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C031163:ExcC protein, E coli; D008074:Lipoproteins; D008565:Membrane Proteins; C063010:MotA protein, Bacteria; C064779:MotB protein, Bacteria; D010457:Peptidoglycan; D011509:Proteoglycans; C062093:tolA protein, E coli; C060792:tolQ protein, E coli; C060794:tolR protein, E coli; C069988:PplA protein, Legionella pneumophila