Abstract
The bacterial flagellum is a motility organelle consisting of a long helical filament as a propeller and a rotary motor that drives rapid filament rotation to produce thrust. Salmonella enterica serovar Typhimurium has two genes of flagellin, fljB and fliC, for flagellar filament formation and autonomously switches their expression at a frequency of 10−3–10−4 per cell per generation. We report here differences in their structures and motility functions under high-viscosity conditions. A Salmonella strain expressing FljB showed a higher motility than one expressing FliC under high viscosity. To examine the reasons for this motility difference, we carried out structural analyses of the FljB filament by electron cryomicroscopy and found that the structure was nearly identical to that of the FliC filament except for the position and orientation of the outermost domain D3 of flagellin. The density of domain D3 was much lower in FljB than FliC, suggesting that domain D3 of FljB is more flexible and mobile than that of FliC. These differences suggest that domain D3 plays an important role not only in changing antigenicity of the filament but also in optimizing motility function of the filament as a propeller under different conditions.
Highlights
Salmonella infection is one of the four major causes of disease involving diarrheas in the world
The bacterial flagellum consists of three main parts: the basal body, which works as a rotary motor; the filament, which functions as a screw propeller; and the hook as a universal joint connecting the filament to the motor [3]
We have discussed the relationship between the structure and motility function by comparing FljB and FliC
Summary
Salmonella infection is one of the four major causes of disease involving diarrheas in the world. Salmonella has two flagellin genes, fljB and fliC, and their expression is autonomously regulated to produce either FljB or FliC for filament formation at a frequency of 10−3–10−4 per cell per generation This is called phase variation [4], and it is thought to be a mechanism to enable escape from the host immune system by changing flagellar antigenicity. A β-hairpin structure in domain D1 is considered to be important for switching the conformation of flagellin subunits between the two states to produce various types of supercoiled filaments in left- and right-handed forms for swimming and tumbling [6,8]. Domain D3 of FljB showed a higher flexibility and mobility than that of FliC These differences suggest that domain D3 plays an important role in changing antigenicity, and in optimizing motility function of the filament as a propeller under different conditions. We have discussed the relationship between the structure and motility function by comparing FljB and FliC
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