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In situ structure of the complete Treponema primitia flagellar motor

Abstract

The bacterial flagellar motor is an amazing nanomachine: built from approximately 25 different proteins, it uses an electrochemical ion gradient to drive rotation at speeds of up to 300 Hz (refs 1, 2). The flagellar motor consists of a fixed, membrane-embedded, torque-generating stator and a typically bidirectional, spinning rotor that changes direction in response to chemotactic signals. Most structural analyses so far have targeted the purified rotor3,4, and hence little is known about the stator and its interactions. Here we show, using electron cryotomography of whole cells, the in situ structure of the complete flagellar motor from the spirochaete Treponema primitia at 7 nm resolution. Twenty individual motor particles were computationally extracted from the reconstructions, aligned and then averaged. The stator assembly, revealed for the first time, possessed 16-fold symmetry and was connected directly to the rotor, C ring and a novel P-ring-like structure. The unusually large size of the motor suggested mechanisms for increasing torque and supported models wherein critical interactions occur atop the C ring, where our data suggest that both the carboxy-terminal and middle domains of FliG are found.

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Acknowledgements

We thank E. Matson for growing the T. primitia cultures. This work was supported, in part, by NIH grants to G.J.J., a DOE grant to G.J.J., a Searle Scholar Award to G.J.J., an NSF grant to J.R.L., an NIH graduate fellowship to G.E.M., and gifts to Caltech from the Ralph M. Parsons Foundation, the Agouron Institute, and the Gordon and Betty Moore Foundation. Author Contributions G.E.M. collected and analysed the data, and drafted the text and figures; J.R.L. provided cells and discourse; and G.J.J. guided the research and manuscript editing throughout.

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Correspondence to Grant J. Jensen.

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The averaged and symmetrized structure has been deposited in the EM Data Bank (http://www.ebi.ac.uk/msd/index.html) with the accession code EMD-1235. Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Supplementary information

Supplementary Notes

Supplementary Figures and Legends 1-5; Supplementary Video Legend; Supplementary Methods; Supplementary Notes. (PDF 620 kb)

Supplementary Video

The movie shows the reconstruction of a single intact T. primitia cell and its periplasmic flagella in three-dimensions, plus the average flagellar motor structure and its presumed rotation. (MOV 77676 kb)

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Further reading

Figure 1: Electron cryotomography of T. primitia and its periplasmic flagellar motor.
Figure 2: Isosurface of the symmetrized average flagellar motor.
Figure 3: The Treponema motor and its comparison with the Salmonella basal body.

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