Structural insights into bacterial flagellar hooks similarities and specificities

Abstract

Across bacteria, the protein that makes the flagellar hook, FlgE, has a high variability in amino acid residue composition and sequence length. We hereby present the structure of two fragments of FlgE protein from Campylobacter jejuni and from Caulobacter crescentus, which were obtained by X-ray crystallography, and a high-resolution model of the hook from Caulobacter. By comparing these new structures of FlgE proteins, we show that bacterial hook can be divided in two distinct parts. The first part comprises domains that are found in all FlgE proteins and that will make the basic structure of the hook that is common to all flagellated bacteria. The second part, hyper-variable both in size and structure, will be bacteria dependent. To have a better understanding of the C. jejuni hook, we show that a special strain of Salmonella enterica, which was designed to encode a gene of flgE that has the extra domains found in FlgE from C. jejuni, is fully motile. It seems that no matter the size of the hook protein, the hook will always have a structure made of 11 protofilaments.

Complete structure of the bacterial flagellar hook reveals extensive set of stabilizing interactions

“…The final combined reconstruction yielded a map at 3.5 Å resolution that was used to build the model of FlgE. We first built a model of FlgEcj of strain 81116 by structural homology with Swiss-Model21, using the X-ray structure of a 79 kDa fragment of FlgE from C. jejuni strain NCTC 11168 that was solved by X-ray crystallography22 as a template. The FlgE proteins from both strains of C. jejuni (81116 and NCTC 11168) have a sequence identity of 95%.…”

“…22). However, the relative position of these domains is different from their position in the crystal (Supplementary Fig.…”

“…Successive rings made by domains D2, D3 and D4 cover the surface with increasing radii, giving to the hook of C. jejuni its bulky helical tubular structure (Supplementary Movie 1). Although FlgEcj has two extra domains, D3 and D4, that do not exist in most other bacterial FlgE proteins, domains D0, D1 and D2 are structurally well conserved22. All of the molecular interactions in the hook involving these three domains can be generalized to most bacterial hooks.…”

Structural characterization of FlgE2 protein from Helicobacter pylori hook

“…All of them consist of 11 protofilaments, arranged with a different diameter according to the dimensions of the species-specific FlgE and its tridimensional organization [10]. Among them, hooks from Caulobacter crescentus, Salmonella typhimurium and Campylobacter jejuni are the best studied.…”

“…Among them, hooks from Caulobacter crescentus, Salmonella typhimurium and Campylobacter jejuni are the best studied. All of them consist of 11 protofilaments, arranged with a different diameter according to the dimensions of the species-specific FlgE and its tridimensional organization [10]. In the case of H. pylori, two genes, hp0870 and hp0908, encode proteins apparently corresponding to FlgE (Fig.…”