Insight Into Distinct Functional Roles of the Flagellar ATPase Complex for Flagellar Assembly in Salmonella

Tohru Minamino; Miki Kinoshita; Keiichi Namba

doi:10.3389/fmicb.2022.864178

Insight Into Distinct Functional Roles of the Flagellar ATPase Complex for Flagellar Assembly in Salmonella

Front Microbiol. 2022 May 4:13:864178. doi: 10.3389/fmicb.2022.864178. eCollection 2022.

Authors

Tohru Minamino¹, Miki Kinoshita¹, Keiichi Namba^{1

2

3}

Affiliations

¹ Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan.
² RIKEN SPring-8 Center and Center for Biosystems Dynamics Research, Osaka, Japan.
³ JEOL YOKOGUSHI Research Alliance Laboratories, Osaka University, Osaka, Japan.

Abstract

Most motile bacteria utilize the flagellar type III secretion system (fT3SS) to construct the flagellum, which is a supramolecular motility machine consisting of basal body rings and an axial structure. Each axial protein is translocated via the fT3SS across the cytoplasmic membrane, diffuses down the central channel of the growing flagellar structure and assembles at the distal end. The fT3SS consists of a transmembrane export complex and a cytoplasmic ATPase ring complex with a stoichiometry of 12 FliH, 6 FliI and 1 FliJ. This complex is structurally similar to the cytoplasmic part of the F_OF₁ ATP synthase. The export complex requires the FliH₁₂-FliI₆-FliJ₁ ring complex to serve as an active protein transporter. The FliI₆ ring has six catalytic sites and hydrolyzes ATP at an interface between FliI subunits. FliJ binds to the center of the FliI₆ ring and acts as the central stalk to activate the export complex. The FliH dimer binds to the N-terminal domain of each of the six FliI subunits and anchors the FliI₆-FliJ₁ ring to the base of the flagellum. In addition, FliI exists as a hetero-trimer with the FliH dimer in the cytoplasm. The rapid association-dissociation cycle of this hetero-trimer with the docking platform of the export complex promotes sequential transfer of export substrates from the cytoplasm to the export gate for high-speed protein transport. In this article, we review our current understanding of multiple roles played by the flagellar cytoplasmic ATPase complex during efficient flagellar assembly.

Keywords: ATPase; F0F1 ATP synthase; bacterial flagella; flagellar assembly; protein translocation; proton motive force (pmf); type III secretion system (T3SS).

Publication types

Review