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Sci Rep. 2013 Nov 28;3:3369. doi: 10.1038/srep03369.

Common and distinct structural features of Salmonella injectisome and flagellar basal body.

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1] Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan [2] Riken Quantitative Biology Center, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.


Bacterial pathogens use an injectisome to deliver virulence proteins into eukaryotic host cells. The bacterial flagellum and injectisome export their component proteins for self-assembly. These two systems show high structural similarities and are classified as the type III secretion system, but it remains elusive how similar they are in situ because the structures of these complexes isolated from cells and visualized by electron cryomicroscopy have shown only the export channel and housing for the export apparatus. Here we report in situ structures of Salmonella injectisome and flagellum by electron cryotomography. The injectisome lacks the flagellar basal body C-ring, but a wing-like disc and a globular density corresponding to the export gate platform and ATPase hexamer ring, respectively, are stably attached through thin connectors, revealing yet unidentified common architectures of the two systems. The ATPase ring is far from the disc, suggesting that both apparatuses are observed in an export-off state.

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