Adiabatic compressibility of flagellin and flagellar filament of Salmonella typhimurium.

The partial specific volume and adiabatic compressibility of flagellin, its F40 fragment deprived of the disordered terminal regions, from Ala-1 to Arg-65 and from Ser-451 to Arg-494, and the flagellar filament of Salmonella typhimurium were determined from the density and the sound velocity measurements at 15 degrees C. The partial specific volumes were 0.728 cm3/g, 0.745 cm3/g, and 0.734 cm3/g, and the partial specific adiabatic compressibilities were 4.0 x 10(-12) cm2/dyn, 6.7 x 10(-12) cm2/dyn, and 4.7 x 10(-12) cm2/dyn, for flagellin, F40, and the filament, respectively. The smaller values of flagellin than those of F40 are reasonably explained by the presence of disordered terminal regions, which are supposed to be highly hydrated by water molecules. The volume increase upon polymerization of flagellin into the filament is also confirmed by depolymerization under a high pressure. The smaller volume and compressibility of the filament compared with those of F40 suggest an extensive hydration of the filament on its complex surface structure, which surpasses the effect on the volume and compressibility by a possible increase in the cavity volume at intersubunit interfaces upon polymerization.