TABLE OF CONTENTS 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.
Keywords: bacterial flagellum, polymorphic supercoiling, mechanical switching, self-assembly.
The bacterial flagellum, an organelle of locomotion for bacterial cells (Fig. 1), is a large macromolecular assembly consisting of over 20 kinds of proteins as shown in Fig. 2 (Namba and Vonderviszt, 1997). Most of them are represented by a few to several tens of molecules, while flagellin, which makes up the long helical filament, is present in a few tens of thousands copies. These proteins combine to form a long thin helical propeller in the cell exterior and a rotary motor at its base. The...
