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


ABSTRACT: 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.

SUBMITTER: Kuhlen L 

PROVIDER: S-EPMC7064499 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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

Kuhlen Lucas L   Johnson Steven S   Zeitler Andreas A   Bäurle Sandra S   Deme Justin C JC   Caesar Joseph J E JJE   Debo Rebecca R   Fisher Joseph J   Wagner Samuel S   Lea Susan M SM  

Nature communications 20200310 1


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 pr  ...[more]

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