DYNAMIC ASPECTS OF THE BACTERIAL FLAGELLUM

The bacterial flagellum is a dynamic molecular system made of a rotary motor, a universal joint, and a long helical propeller, by means of which bacteria swim. The helical propeller, for example, is made of a single protein flagellin, and yet its curved and twisted tubular structure can switch between left- and right-handed helical forms in response to the twisting force produced by quick reversal of the motor rotation, allowing bacteria to alternate their swimming pattern between run and tumble. Other parts also exert mechanical functions by their dynamic behaviors, and all these structures are constructed by a self-assembly process. Some of these dynamic aspects have been revealed by structural studies.