Abstact

Motility promotes the complex life cycle and infectious capabilities of Vibrio cholerae and is driven by rotation of a single polar flagellum. The flagellar filament comprises four flagellin proteins (FlaA-D) and is covered by a membranous sheath continuous with the outer membrane. Here we combine in situ cryo-electron microscopy single-particle analysis, fluorescence microscopy and molecular genetics to determine 2.92-3.43 Å structures of the sheathed flagellar filament from intact bacteria. Our data reveal the spatial arrangement of FlaA-D, showing that FlaA localizes at the cell pole and functions as a template for filament assembly involving multiple flagellins. Unlike unsheathed flagellar filaments, the sheathed filament from V. cholerae possesses a highly conserved core but a smooth, hydrophilic surface adjacent to the membranous sheath. A tiny conformational change at the single flagellin level results in a supercoiled filament and curved membranous sheath, supporting a model wherein the filament rotates separately from the sheath, enabling the distinct motility of V. cholerae.