| Description |
The bacterial flagellar motor is a complex nanomachine composed of thousands of individual protein subunits. One of these proteins, FlhE, has not been studied in depth and its function is not completely understood. The flhE gene is cotranscribed with flhB and flhA in the flhBAE flagellar operon. In Salmonella, FlhE has been found to be essential for the surface-associated motility called swarming, but not for swimming motility in liquid media. In an ongoing study, we have found that deletion of chromosomal flhE in E.coli causes a severe defect in swimming motility, completely abolishes swarming motility and results in distortion of the cell wall and membrane causing aberrant cellular morphologies. These motility and morphological defects in the ΔflhE strain were fully complemented by expressing the FlhE protein from a plasmid, but not by a truncated version lacking the N-terminal signal sequence that targets the protein to the periplasm. Normal morphology was also restored by overexpression of the regulatory protein FlgM that represses genes required for assembly of the flagellar filament. Through coprecipitation assays, it was found that FlhE interacts with the periplasmic domain of the FliF protein, which forms the basal body membraneous and supramembraneous (MS) ring. Mutations in the N-terminal region of flhE that yield defects in motility similar to the ΔflhE phenotype do not abolish this interaction, remained unidentified. Our model proposes that FlhE interacts with the MS ring around the secretion apparatus and tethers it to the peptidoglycan layer within the periplasm of the cell. Absence of FlhE might then allow the assembly of the flagellar filament in the periplasm, causing deformation of the cell wall and membrane. |
