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Three-Dimensional Model of Salmonella’s Needle Complex at Subnanometer Resolution
03/04/2011
Solving the 3D-structure of the NC. Top row: Average images of NC inner ring (left) and outer ring (right) substructures obtained by selective disassembly of wild type NC. The top views allow for a direct counting of the inner and outer ring subunits and reveal a 24- and 15-fold symmetry, respectively. Bottom row: (left) Surface views of a 3D-reconstruction of the NC. With α-helical densities visible, (right) atomic structures could be placed unambiguously into the NC.
Type III secretion systems (T3SSs) are essential pathogenic factors used by many Gram-negative bacteria like EHEC, Salmonella, Shigella or Cholera to inject proteins that make eukaryotic host cells accessible to invasion. In this study we were able to generate a cryo electron microscopy density map of the core structure of the T3SS, the needle complex (NC), a ~3.5 megadalton-sized, membrane-embedded injection machine with subnanomter resolution. Showing secondary structural elements like α-helices this highly resolved density map allowed for confident docking of atomic structures. The resulting atomic model revealed insights into the NC’s overall organization and into the structural requirements during assembly. We thereby provide a framework that will strongly promote further structural and functional studies of the T3SS and hopefully will also assist in generating new antibacterial strategies.
