Insight into the assembly mechanism in the supramolecular rings of the sodium-driven Vibrio flagellar motor from the structure of FlgT

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 15; pp. 6133 - 6138
• Main Authors: Terashima, Hiroyuki, Li, Na, Sakuma, Mayuko, Koike, Masafumi, Kojima, Seiji, Homma, Michio, Imada, Katsumi
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 09-04-2013; National Acad Sciences
• Subjects: Bacterial Outer Membrane Proteins - chemistry; Bacterial proteins; Bacterial Proteins - chemistry; Bacterial Proteins - physiology; Biological Sciences; Cell Membrane - physiology; Crystal structure; Crystallography; Crystallography, X-Ray; Crystals; E coli; Escherichia coli; Escherichia coli Proteins - chemistry; Flagella; Flagella - chemistry; Flagella - physiology; Gram-negative bacteria; Hydrogen - chemistry; Models, Molecular; Molecular biology; Molecular Motor Proteins - chemistry; Motors; Mutation; Peptidoglycan - chemistry; Periplasmic Proteins - chemistry; Plasmids; Protein Structure, Secondary; Protein Structure, Tertiary; Proteins; Sodium; Sodium - chemistry; Stators; Vibrio; Vibrio alginolyticus; Vibrio alginolyticus - physiology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1222655110

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 F ₁-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.