Insight into the flagella type III export revealed by the complex structure of the type III ATPase and its regulator

Abstract

FliI and FliJ form the FliI 6 FliJ ATPase complex of the bacterial flagellar export apparatus, a member of the type III secretion system. The FliI 6 FliJ complex is structurally similar to the α 3 β 3 γ complex of F 1 -ATPase. The FliH homodimer binds to FliI to connect the ATPase complex to the flagellar base, but the details are unknown. Here we report the structure of the homodimer of a C-terminal fragment of FliH (FliH C2 ) in complex with FliI. FliH C2 shows an unusually asymmetric homodimeric structure that markedly resembles the peripheral stalk of the A/V-type ATPases. The FliH C2 -FliI hexamer model reveals that the C-terminal domains of the FliI ATPase face the cell membrane in a way similar to the F/A/V-type ATPases. We discuss the mechanism of flagellar ATPase complex formation and a common origin shared by the type III secretion system and the F/A/V-type ATPases.bacterial flagellum | type III protein export | crystal structure | F/A/V-type ATPase

High-Resolution pH Imaging of Living Bacterial Cells To Detect Local pH Differences

“…Because depletion of neither the ΔpH component nor D 2 O affects the rate of protein export by wild-type cells (34), the rate of proton influx through the gate would be high enough to obscure the effect of ΔpH depletion and D 2 O in the presence of FliH and FliI. The FliH 12 FliI 6 FliJ ring complex is structurally very similar to the extra membrane part of F- and V-type ATPases (16), which hydrolyze ATP to induce an outward-directed proton pumping. Therefore, we propose that the FliH 12 FliI 6 FliJ complex and the export gate together act as an H + /protein antiporter to couple an inward-directed H + flow through the gate with an outward-directed type III protein export and that ATP hydrolysis by FliI probably contributes to efficient inward-directed proton translocation through the gate.…”

“…The FliI ATPase forms the FliH 2 FliI complex with the FliH 2 homodimer in the cytoplasm (15, 16). Since FliI-yellow fluorescent protein (YFP) shows rapid exchanges between the flagellar basal body (FBB) and the cytoplasmic pool in an ATP-independent manner, the FliH 2 FliI complex is proposed to act as a dynamic carrier to deliver export substrates and chaperone-substrate complexes to the export gate (17).…”

“…1A). The FliH 12 FliI 6 FliJ complex is structurally similar to F- and V-type rotary ATPases, which couple ATP synthesis or hydrolysis with H + translocation (16, 20, 24). …”

In Situ Molecular Architecture of the Salmonella Type III Secretion Machine

“…InvA C (the carboxy-terminal domain of InvA: PDB-2×4a) (Worrall et al, 2010) was used to build the nonameric ring based on the homologous structure from Shigella flexneri MxiA C (PDB-4A5P) (Abrusci et al, 2013). Structures of the flagellar ATPase complex FliI–FliH (PDB-5B0O) (Imada et al, 2016) and FliJ (PDB-3AJW) (Ibuki et al, 2011) were used to build the model of the InvC–InvI–OrgB complex.…”

Molecular Models for the Core Components of the Flagellar Type-III Secretion Complex

“…Most work has centered upon the cytoplasmic regions, with structures of flagellar C-ring [14–16] and ATPase complex proteins [17, 18] obtained by X-ray crystallography and located in situ by electron cryo-microscopy methods [10, 19–21]. Considerably less is known about the structures of the transmembrane proteins, due partly to the intrinsic challenges these proteins pose to crystallograpic and electron cryo-microscopic methods.…”