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PLoS Pathog. 2013;9(4):e1003307. doi: 10.1371/journal.ppat.1003307. Epub 2013 Apr 25.

A refined model of the prototypical Salmonella SPI-1 T3SS basal body reveals the molecular basis for its assembly.

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Department of Biochemistry and Molecular Biology, and Centre for Blood Research, University of British Columbia, Vancouver, British Columbia, Canada.


The T3SS injectisome is a syringe-shaped macromolecular assembly found in pathogenic Gram-negative bacteria that allows for the direct delivery of virulence effectors into host cells. It is composed of a "basal body", a lock-nut structure spanning both bacterial membranes, and a "needle" that protrudes away from the bacterial surface. A hollow channel spans throughout the apparatus, permitting the translocation of effector proteins from the bacterial cytosol to the host plasma membrane. The basal body is composed largely of three membrane-embedded proteins that form oligomerized concentric rings. Here, we report the crystal structures of three domains of the prototypical Salmonella SPI-1 basal body, and use a new approach incorporating symmetric flexible backbone docking and EM data to produce a model for their oligomeric assembly. The obtained models, validated by biochemical and in vivo assays, reveal the molecular details of the interactions driving basal body assembly, and notably demonstrate a conserved oligomerization mechanism.

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