Preparing well-oriented sols of straight bacterial flagellar filaments for X-ray fiber diffraction

Well-oriented sols of straight bacterial flagellar filaments have been obtained by preparing reconstituted flagellar filaments with an appropriate length distribution and choosing appropriate solvent conditions. An average filament length of 300 to 500 nm and the use of solvents with very low concentrations of salt has allowed us to prepare highly fluid sols that make flow orientation possible. X-ray fiber diffraction from these sols has shown distinct layer-line reflections to 3.5 A resolution in the meridional direction. Layer-line intensities have been collected by the angular deconvolution method up to 5 A resolution. The possibility of using a magnetic field to further improve the orientation has been explored and a solvent condition that makes flagellar sols sensitive to the magnetic field has been found. General applicability of the method to other systems is also discussed.