The bacterial flagellar filament is a helical propeller rotated by the flagellar motor for bacterial locomotion. The filament is a supercoiled assembly of a single protein, flagellin, and is formed by 11 protofilaments. For bacterial taxis, the reversal of motor rotation switches the supercoil between left- and right-handed, both of which arise from combinations of two distinct conformations and packing interactions of the L-type and R-type protofilaments. Here we report an atomic model of the L-type straight filament by electron cryomicroscopy and helical image analysis. Comparison with the R-type structure shows interesting features: an orientation change of the outer core domains (D1) against the inner core domains (D0) showing almost invariant orientation and packing, a conformational switching within domain D1, and the conformational flexibility of domains D0 and D1 with their spoke-like connection for tight molecular packing.
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We thank C. Toyoshima for part of the helical image reconstruction programs, D.A. Agard and J.W. Sedat for support to S.M.-Y. and K.Y. and F. Oosawa, S. Asakura and D.L.D. Caspar for continuous support and encouragement. This work was partly supported by funds from the W.M. Keck Advanced Microscopy Laboratory at the University of California, San Francisco, to K.Y. and by Grants-in-Aid for Scientific Research (16087207) 'National Project on Protein Structural and Functional Analyses' from the Ministry of Education, Science and Culture of Japan to K.N.
The authors declare no competing financial interests.
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Maki-Yonekura, S., Yonekura, K. & Namba, K. Conformational change of flagellin for polymorphic supercoiling of the flagellar filament. Nat Struct Mol Biol 17, 417–422 (2010). https://doi.org/10.1038/nsmb.1774
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