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Mol Microbiol. 2019 Nov;112(5):1519-1530. doi: 10.1111/mmi.14377. Epub 2019 Sep 13.

Role of flagellar hydrogen bonding in Salmonella motility and flagellar polymorphic transition.

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Department of Structural Infection Biology, Center for Structural Systems Biology (CSSB), Helmholtz-Center for Infection Research (HZI), Notkestrasse 85, Hamburg, 22607, Germany.
Structural Systems Biology Group, Max Planck Institute for Infection Biology, Berlin, Germany.
Department of Structural Cell Biology of Viruses, Subunit Quantitative Virology, Heinrich Pette Institute, Leibniz Institute for Experimental Virology, Hamburg.
Advanced Light and Fluorescence Microscopy (ALFM) Facility, Centre for Structural Systems Biology (CSSB), University of Hamburg, Notkestrasse 85, Hamburg, 22607, Germany.
MIN-Faculty University Hamburg, Hamburg, Germany.


Bacterial flagellar filaments are assembled by tens of thousands flagellin subunits, forming 11 helically arranged protofilaments. Each protofilament can take either of the two bistable forms L-type or R-type, having slightly different conformations and inter-protofilaments interactions. By mixing different ratios of L-type and R-type protofilaments, flagella adopt multiple filament polymorphs and promote bacterial motility. In this study, we investigated the hydrogen bonding networks at the flagellin crystal packing interface in Salmonella enterica serovar typhimurium (S. typhimurium) by site-directed mutagenesis of each hydrogen bonded residue. We identified three flagellin mutants D108A, N133A and D152A that were non-motile despite their fully assembled flagella. Mutants D108A and D152A trapped their flagellar filament into inflexible right-handed polymorphs, which resemble the previously predicted 3L/8R and 4L/7R helical forms in Calladine's model but have never been reported in vivo. Mutant N133A produces floppy flagella that transform flagellar polymorphs in a disordered manner, preventing the formation of flagellar bundles. Further, we found that the hydrogen bonding interactions around these residues are conserved and coupled to flagellin L/R transition. Therefore, we demonstrate that the hydrogen bonding networks formed around flagellin residues D108, N133 and D152 greatly contribute to flagellar bending, flexibility, polymorphisms and bacterial motility.


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