Oligomerization of the Bacterial Flagellar ATPase FliI is Controlled by its Extreme N-terminal Region

Structural similarity between the flagellar type III ATPase FliI and F 1 -ATPase subunits

“…In contrast, FliI still retains the ATPase activity to some extent even in an apparently monomeric state (13). The corresponding arginine Arg-374 of FliI is also conserved among different bacterial species.…”

“…FliI is a member of the Walker-type ATPase family (10), and it is thought to form a ring-shaped hexamer for protein export (11)(12)(13)(14). FliI has significant similarity in its primary sequence to the ␣ and ␤ subunits of F 0 F 1 -ATPsynthase (14,15).…”

“…FliI has significant similarity in its primary sequence to the ␣ and ␤ subunits of F 0 F 1 -ATPsynthase (14,15). Although F 1 -ATPase requires both the ␣ and ␤ subunits to form the ␣ 3 ␤ 3 hexameric ring to exert its ATPase activity (16), FliI can self-assemble into a hexameric ring in solution, and it shows a cooperative increase in ATPase activity in the presence of ATP and phospholipids (11,13). Therefore, it is thought that FliI also forms a hexameric ring when it docks to the FlhA-FlhB platform of the flagellar export apparatus (13).…”

Distinct roles of the FliI ATPase and proton motive force in bacterial flagellar protein export

“…Unlike F 1 -ATPase, however, which forms the a 3 b 3 hexameric ring, FliI self-assembles into a homohexamer 9,10 . When FliI oligomerization is suppressed by a small deletion in its amino-terminal region, flagellar protein export does not occur efficiently, suggesting that FliI hexamerizes on docking to the export gate made of the six integral membrane components, for which the cytoplasmic domains of FlhA and FlhB are thought to form the docking platform 11 . FliI binds to FlgN (chaperone) and to a FlgN-FlgK (HAP1) complex 12 , suggesting that FliI has a critical role in substrate recognition as well.…”

“…2 Dynamic NanoMachine Project, ICORP, JST, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan. FliH and FliI interact not only with FlhA and FlhB but also with flagellar chaperones such as FliJ and export substrates, leading to the proposal that the FliH-FliI complex is responsible for delivery of the substrates to the export gate 4,11,12,14 . To test this, gain-offunction mutants were isolated from the fliH fliI double null mutant by streaking an overnight culture out on soft agar plates, incubating at 30 uC for 2 days and looking for motility haloes emerging from the streak.…”