The bacterial flagellar hook connects the helical flagellar filament to the rotary motor at its
base. Bending flexibility of the hook allows the helical filaments to form a bundle behind the
cell body to produce thrust for bacterial motility. The hook protein FlgE shows considerable
sequence and structural similarities to the distal rod protein FlgG; however, the hook is
supercoiled and flexible as a universal joint whereas the rod is straight and rigid as a drive
shaft. A short FlgG specific sequence (GSS) has been postulated to confer the rigidity on the …