title: Structure of the flagellar motor protein complex PomAB: implications for the torque-generating conformation.
abstract: The bacterial flagellar motor is driven by an ion flux through a channel called MotAB in Escherichia coli or Salmonella and PomAB in Vibrio alginolyticus. PomAB is composed of two transmembrane (TM) components, PomA and PomB, and converts a sodium ion flux to rotation of the flagellum. Its homolog, MotAB, utilizes protons instead of sodium ions. PomB/MotB has a peptidoglycan (PG)-binding motif in the periplasmic domain, allowing it to function as the stator by being anchored to the PG layer. To generate torque, PomAB/MotAB is thought to undergo a conformational change triggered by the ion flux and to interact directly with FliG, a component of the rotor. Here, we present the first three-dimensional structure of this torque-generating stator unit analyzed by electron microscopy. The structure of PomAB revealed two arm domains, which contain the PG-binding site, connected to a large base made of the TM and cytoplasmic domains. The arms lean downward to the membrane surface, likely representing a "plugged" conformation, which would prevent ions leaking through the channel. We propose a model for how PomAB units are placed around the flagellar basal body to function as torque generators.
authors.affiliation: Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, Harima Institute, Sayo, Hyogo 679-5148, Japan. yone@spring8.or.jp
authors.forename: Koji
authors.initials: K
authors.lastname: Yonekura
authors.forename: Saori
authors.initials: S
authors.lastname: Maki-Yonekura
authors.forename: Michio
authors.initials: M
authors.lastname: Homma
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D001696:Biomechanical Phenomena; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005407:Flagella / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D019415:Torque; D044149:Vibrio alginolyticus / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; C103352:PomA protein, bacteria; C103353:PomB protein, bacteria