The structure of flagellin is responsible for the helical shape of the flagellar filament, which is important for its proper function. It is transported through the center of the filament to the tip where it polymerases spontaneously into a part of the filament. It is unfolded by the FliS () flagellar secretion chaperone during transport. The filament is made up of eleven smaller "protofilaments", nine of which contains flagellin in the L-type shape and the other two in the R-type shape.