A study on the mechanism of polymerisation of Bacillus brevis flagellin

Optical properties of intact flagellin and of modified-on-tyrosine flagellin incapable of self-assembly have been studied by the circular dichroism (CD) method. The CD spectra of both flagellins do not change and virtually coincide within the pH range from 2.9 to 10.0. In the presence of polyethylene glycol (PEG) and ammonium sulfate which accelerate flagellin polymerization, the character of the CD spectra changes and depends on pH. The increase in the PEG content to 20% and that in the ammonium sulfate content to 1 M over the pH range from 4.3 to 10.0 results in a significant rise of the molar ellipticity at 222 nm ([theta]222) of both flagellins. However, [theta]222 does not reach values typical for bacterial flagella. The results obtained are discussed with respect to conformational changes in the flagellin molecule during polymerization.