A structural model of flagellar filament switching across multiple bacterial species

Abstract

The bacterial flagellar filament has long been studied to understand how a polymer composed of a single protein can switch between different supercoiled states with high cooperativity. Here we present near-atomic resolution cryo-EM structures for flagellar filaments from both Gram-positive Bacillus subtilis and Gram-negative Pseudomonas aeruginosa. Seven mutant flagellar filaments in B. subtilis and two in P. aeruginosa capture two different states of the filament. These reliable atomic models of both states reveal conserved molecular interactions in the interior of the filament among B. subtilis, P. aeruginosa and Salmonella enterica. Using the detailed information about the molecular interactions in two filament states, we successfully predict point mutations that shift the equilibrium between those two states. Further, we observe the dimerization of P. aeruginosa outer domains without any perturbation of the conserved interior of the filament. Our results give new insights into how the flagellin sequence has been “tuned” over evolution.

The flagellotropic bacteriophage YSD1 targets Salmonella Typhi with a Chi‐like protein tail fibre

“…As the structure of the S. Typhimurium flagellar filament (PDB: http://www.rcsb.org/pdb/search/structidSearch.do?structureId=3A5X) was deposited as a single subunit, the rest of the filament was modelled based on the helical symmetry of the B. subtillis flagellar filament [PDB:5WJT, (Wang et al , )] in Chimera 1.13.1 [(Pettersen et al , ); http://www.rbvi.ucsf.edu/chimera/]. The 3A5X monomer was aligned to a subunit of the B. subtillis flagellar filament and the helical symmetry was applied to generate additional subunits.…”

“…As the structure of the S. Typhimurium flagellar filament (PDB: 3A5X) was deposited as a single subunit, the rest of the filament was modelled based on the helical symmetry of the B. subtillis flagellar filament [PDB:5WJT, (Wang et al, 2017)] in Chimera 1.13.1 [ (Pettersen et al, 2004); http://www.rbvi.ucsf. edu/chime ra/].…”

An asymmetric sheath controls flagellar supercoiling and motility in the Leptospira spirochete

“…The morphology of the inner 127 two density layers ( Fig. 2F) closely resembles that of helically assembled flagellin domains D0 128 and D1 of filaments from exoflagellated bacteria (Wang et al, 2017;Yonekura, Maki-Yonekura, & 129 Namba, 2003). This structural homology is consistent with earlier predictions that the core of the 130 spirochete filament is composed of FlaB (Li, Wolgemuth, Marko, Morgan, & Charon, 2008;Nauman, 131 Holt, & Cox, 1969), which is homologous to flagellin but lacks the D2 and D3 domains 132 ( Supplementary Fig.…”

“…2C, F, Supplementary Video 1). The 138 finding of a break in the helical symmetry in the Leptospira endoflagella sharply contrasts with 139 symmetric structures which were previously observed for exoflagella from Salmonella (Sasaki et 140 al., 2018;Wang et al, 2017;Yonekura et al, 2003), Campylobacter (Galkin et al, 2008), Pseudomonas 141 aeruginosa and Bacillus subtilis (Wang et al, 2017).…”

“…Further 167 modelling of the sheath was precluded as atomic models are not available for FlaA1 and FlaA2, 168 the only other known components of the Leptospira flagellar filament. FlaA is also presumed to 169 reside in the spirochete sheath (Li et al, 2008), and comparing the fcpBmap with the wild-type Salmonella and other exoflagellates (Wang et al, 2017). Due to a strongly preferred filament 176 orientation in the specimen ice layer ( Supplementary Fig.…”