title: Insight into the assembly mechanism in the supramolecular rings of the sodium-driven Vibrio flagellar motor from the structure of FlgT.
abstract: Flagellar motility is a key factor for bacterial survival and growth in fluctuating environments. The polar flagellum of a marine bacterium, Vibrio alginolyticus, is driven by sodium ion influx and rotates approximately six times faster than the proton-driven motor of Escherichia coli. The basal body of the sodium motor has two unique ring structures, the T ring and the H ring. These structures are essential for proper assembly of the stator unit into the basal body and to stabilize the motor. FlgT, which is a flagellar protein specific for Vibrio sp., is required to form and stabilize both ring structures. Here, we report the crystal structure of FlgT at 2.0-Å resolution. FlgT is composed of three domains, the N-terminal domain (FlgT-N), the middle domain (FlgT-M), and the C-terminal domain (FlgT-C). FlgT-M is similar to the N-terminal domain of TolB, and FlgT-C resembles the N-terminal domain of FliI and the α/β subunits of F1-ATPase. To elucidate the role of each domain, we prepared domain deletion mutants of FlgT and analyzed their effects on the basal-body ring formation. The results suggest that FlgT-N contributes to the construction of the H-ring structure, and FlgT-M mediates the T-ring association on the LP ring. FlgT-C is not essential but stabilizes the H-ring structure. On the basis of these results, we propose an assembly mechanism for the basal-body rings and the stator units of the sodium-driven flagellar motor.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-Ku, Nagoya 464-8602, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Terashima
authors.forename: Na
authors.initials: N
authors.lastname: Li
authors.forename: Mayuko
authors.initials: M
authors.lastname: Sakuma
authors.forename: Masafumi
authors.initials: M
authors.lastname: Koike
authors.forename: Seiji
authors.initials: S
authors.lastname: Kojima
authors.forename: Michio
authors.initials: M
authors.lastname: Homma
authors.forename: Katsumi
authors.initials: K
authors.lastname: Imada
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D018360:Crystallography, X-Ray; D004926:Escherichia coli; D029968:Escherichia coli Proteins / Q000737:chemistry; D005407:Flagella / Q000737:chemistry / Q000502:physiology*; D006859:Hydrogen / Q000737:chemistry; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000737:chemistry*; D009154:Mutation; D010457:Peptidoglycan / Q000737:chemistry; D033903:Periplasmic Proteins / Q000737:chemistry; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012964:Sodium / Q000737:chemistry*; D044149:Vibrio alginolyticus / Q000502:physiology*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D020409:Molecular Motor Proteins; D010457:Peptidoglycan; D033903:Periplasmic Proteins; C062094:tolB protein, E coli; D006859:Hydrogen; D012964:Sodium