Flagella are critical for bacterial motility and pathogenesis. The flagellar capping protein (FliD) regulates filament assembly by chaperoning and sorting flagellin (FliC) proteins after they traverse the hollow filament and exit the growing flagellum tip. In the absence of FliD, flagella are not formed resulting in impaired motility and infectivity. Here, we report the 2.2 Å resolution X-ray crystal structure of FliD from Pseudomonas aeruginosa, the first high-resolution structure of any FliD protein from any bacterium. In combination with a multitude of biophysical and functional analyses, we find that Pseudomonas FliD exhibits unexpected structural similarity to other flagellar proteins at the domain level, adopts a unique hexameric oligomeric state, and depends on flexible determinants for oligomerization. Considering that the flagellin filaments on which FliD oligomers are affixed vary between bacteria in protofilament number, our results suggest that FliD oligomer stoichiometries vary across bacteria to complement their filament assemblies.
- Dorothy Beckett
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Richard M Berry, University of Oxford, United Kingdom
© 2016, Postel et al.
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