Structures of chaperone-substrate complexes docked onto the export gate in a type III secretion system

Xing, Qiong; Shi, Ke; Portaliou, Athina G; Rossi, Paolo; Economou, Anastassios

doi:10.1038/s41467-018-04137-4

Cited by 74 publications

(120 citation statements)

References 60 publications

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“…5b). Such forces could initiate in the cytoplasmic domain of FlhA, which binds to substrate-chaperone complexes and has been demonstrated to exist in multiple conformations 25,26 marking it as the only component of the EA observed in multiple conformational states to date. Interestingly, this network of charged residues in FlhB includes D208.…”

Section: Discussionmentioning

confidence: 99%

The substrate specificity switch FlhB assembles onto the export gate to regulate type three secretion

et al. 2020

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Protein secretion through type-three secretion systems (T3SS) is critical for motility and virulence of many bacteria. Proteins are transported through an export gate containing three proteins (FliPQR in flagella, SctRST in virulence systems). A fourth essential T3SS protein (FlhB/SctU) functions to "switch" secretion substrate specificity once the growing hook/ needle reach their determined length. Here, we present the cryo-electron microscopy structure of an export gate containing the switch protein from a Vibrio flagellar system at 3.2 Å resolution. The structure reveals that FlhB/SctU extends the helical export gate with its four predicted transmembrane helices wrapped around FliPQR/SctRST. The unusual topology of the FlhB/SctU helices creates a loop wrapped around the bottom of the closed export gate. Structure-informed mutagenesis suggests that this loop is critical in gating secretion and we propose that a series of conformational changes in the T3SS trigger opening of the gate through interactions between FlhB/SctU and FliPQR/SctRST.

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Section: Discussionmentioning

confidence: 99%

The substrate specificity switch FlhB assembles onto the export gate to regulate type three secretion

et al. 2020

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“…Our structure of the intact cap complex, supported by mutagenesis studies, suggests that the FliD C-terminal domain interaction with the opposite pentamer in the decametric complex mimics that of the FliD interaction with the filament. We hypothesize that exposed hydrophobic residues, both on the D0 domain of flagellin molecules and in the C-terminus of FliD, act as a chaperonin-like environment to promote the folding and insertion of new flagellins 28,29 .…”

Section: Discussionmentioning

confidence: 99%

The cryo-EM structure of the bacterial flagellum cap complex suggests a molecular mechanism for filament elongation

Al-Otaibi

Taylor

Farrell

et al. 2019

Preprint

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The bacterial flagellum is a remarkable molecular motor, present at the surface of many bacteria, whose primary function is to allow motility through the rotation of a long filament protruding from the bacterial cell. A cap complex, consisting of an oligomeric assembly of the protein FliD, is localized at the tip of the flagellum, and is essential for filament assembly, as well as adherence to surfaces in some bacteria. However, the structure of the intact cap complex, and the molecular basis for its interaction with the filament, remains elusive. Here we report the cryo-EM structure of the Campylobacter jejuni cap complex. This structure reveals that FliD is pentameric, with the N-terminal region of the protomer forming an unexpected extensive set of contacts across several subunits, that contribute to FliD oligomerization. We also demonstrate that the native C. jejuni flagellum filament is 11-stranded and propose a molecular model for the filament-cap interaction.

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“…1) 11 . FlhAC forms a homo-nonamer ring 12,13 and provides binding-sites for flagellar export chaperons (FlgN, FliS and FliT) in complex with their cognate filament-type substrates [14][15][16][17] .…”

Section: Introductionmentioning

confidence: 99%

The FlhA linker mediates flagellar protein export switching during flagellar assembly

Inoue

Kida

Kinoshita

et al. 2020

Preprint

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The flagellar protein export apparatus switches export specificity from hook-type to filament-type upon completion of hook assembly, thereby initiating filament assembly at the hook tip. The C-terminal cytoplasmic domain of FlhA (FlhAC) forms a homo-nonameric ring structure that serves as a docking platform for flagellar export chaperones in complex with their cognate filament-type substrates. Interactions of the flexible linker of FlhA (FlhAL) with its nearest FlhAC subunit in the ring allow the chaperones to bind to FlhAC to facilitate filament-type protein export, but it remains unclear how it occurs. Here, we report that FlhAL acts as a switch that brings the order to flagellar assembly. The crystal structure of FlhAC(E351A/D356A) showed that Trp-354 in FlhAL bound to the chaperone-binding site of its neighboring subunit. We propose that FlhAL binds to the chaperon-binding site of FlhAC to suppress the interaction between FlhAC and the chaperones until hook assembly is completed.

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Structures of chaperone-substrate complexes docked onto the export gate in a type III secretion system

Cited by 74 publications

References 60 publications

The substrate specificity switch FlhB assembles onto the export gate to regulate type three secretion

The substrate specificity switch FlhB assembles onto the export gate to regulate type three secretion

The cryo-EM structure of the bacterial flagellum cap complex suggests a molecular mechanism for filament elongation

The FlhA linker mediates flagellar protein export switching during flagellar assembly

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