title: ATP-induced FliI hexamerization facilitates bacterial flagellar protein export.
abstract: FliI ATPase forms a homo-hexamer to fully exert its ATPase activity, facilitating bacterial flagellar protein export. However, it remains unknown how FliI hexamerization is linked to protein export. Here, we analyzed the capability of ring formation by FliI and its catalytic mutant variants. Compared to ATP a non-hydrolysable ATP analog increased the probability of FliI hexamerization. In contrast, FliI(E221Q), which retained the affinity for ATP but has lost ATPase activity, efficiently formed the hexamer even in the presence of ATP. The mutations, which reduced the binding affinity for ATP, significantly abolished the ring formation. These results indicate that ATP-binding induces FliI hexamerization and that the release of ADP and Pi destabilizes the ring structure. FliI(E221Q) facilitated flagellar protein export in the absence of the FliH regulator of the export apparatus although not at the wild-type FliI level while the other did not. We propose that FliI couples ATP binding and hydrolysis to its assembly-disassembly cycle to efficiently initiate the flagellar protein export cycle.
authors: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors: Ken-Ichi
authors: K
authors: Kazetani
authors: Tohru
authors: T
authors: Minamino
authors: Tomoko
authors: T
authors: Miyata
authors: Takayuki
authors: T
authors: Kato
authors: Keiichi
authors: K
authors: Namba
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D000409:Alanine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001120:Arginine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002384:Catalysis; D006868:Hydrolysis; D008854:Microscopy, Electron; D017354:Point Mutation; D055503:Protein Multimerization; D021381:Protein Transport; D006180:Proton-Translocating ATPases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012475:Salmonella
chemical_list: D001426:Bacterial Proteins; C069251:fliI protein, bacteria; D000255:Adenosine Triphosphate; D001120:Arginine; D006180:Proton-Translocating ATPases; D000409:Alanine