title: Ion-coupling determinants of Na+-driven and H+-driven flagellar motors.
abstract: The bacterial flagellar motor is a tiny molecular machine that uses a transmembrane flux of H(+) or Na(+) ions to drive flagellar rotation. In proton-driven motors, the membrane proteins MotA and MotB interact via their transmembrane regions to form a proton channel. The sodium-driven motors that power the polar flagellum of Vibrio species contain homologs of MotA and MotB, called PomA and PomB. They require the unique proteins MotX and MotY. In this study, we investigated how ion selectivity is determined in proton and sodium motors. We found that Escherichia coli MotA/B restore motility in DeltapomAB Vibrio alginolyticus. Most hypermotile segregants isolated from this weakly motile strain contain mutations in motB. We constructed proteins in which segments of MotB were fused to complementary portions of PomB. A chimera joining the N terminus of PomB to the periplasmic C terminus of MotB (PotB7(E)) functioned with PomA as the stator of a sodium motor, with or without MotX/Y. This stator (PomA/PotB7(E)) supported sodium-driven motility in motA or motB E.coli cells, and the swimming speed was even higher than with the original stator of E.coli MotA/B. We conclude that the cytoplasmic and transmembrane domains of PomA/B are sufficient for sodium-driven motility. However, MotA expressed with a B subunit containing the N terminus of MotB fused to the periplasmic domain of PomB (MomB7(E)) supported sodium-driven motility in a MotX/Y-dependent fashion. Thus, although the periplasmic domain of PomB is not necessary for sodium-driven motility in a PomA/B motor, it can convert a MotA/B proton motor into a sodium motor.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-Ku, Japan.
authors.forename: Yukako
authors.initials: Y
authors.lastname: Asai
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Yakushi
authors.forename: Ikuro
authors.initials: I
authors.lastname: Kawagishi
authors.forename: Michio
authors.initials: M
authors.lastname: Homma
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000502:physiology*; D005407:Flagella / Q000235:genetics / Q000502:physiology*; D006859:Hydrogen; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D020409:Molecular Motor Proteins / Q000502:physiology*; D008969:Molecular Sequence Data; D010957:Plasmids; D017386:Sequence Homology, Amino Acid; D012964:Sodium; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D014170:Transformation, Genetic; D014733:Vibrio / Q000502:physiology*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D008565:Membrane Proteins; D020409:Molecular Motor Proteins; C063010:MotA protein, Bacteria; C064779:MotB protein, Bacteria; C089633:MotX protein, bacteria; C088135:MotY protein, Vibrio; C107540:PomA protein, Vibrio; C107541:PomB protein, Vibrio; D015222:Sodium Channels; D006859:Hydrogen; D012964:Sodium