NON-HELICAL PERTURBATIONS OF THE FLAGELLAR FILAMENT - SALMONELLA-TYPHIMURIUM SJW117 AT 9.6-ANGSTROM RESOLUTION

Using a liquid-helium-cooled superconducting electron cryo-microscope, we obtained low-dose images of negatively stained preparations at 4 K and collected structural data to 1/9.6 Angstrom(-1) for flagellar fil aments from the strain SJW117 of Salmonella typhimurium (serotype gt). The subunits of this left-handed, straight filament are non-helically perturbed in a pairwise manner. The perturbation corresponds to an al ternating conformation in every other row of subunits. These are the 5 -start rows and, necessarily, the resulting structure has a seam. The perturbation is not confined to the outside but extends into the struc ture. We separated the non-symmetric and symmetric parts of the struct ural data and generated a three-dimensional reconstruction from the la tter. The resulting density map is a structure similar in domain organ ization to the left-handed filament of S. typhimurium SJW1660. Filtere d images generated from the non-symmetric component show an ordered an d polar structure. The nature of the perturbation was analyzed by mode l building using a sphere to represent the subunit at low resolution. A lateral shift of similar to 10 degrees mimics the perturbation. (C) 1997 Academic Press Limited.