Chaperone-mediated coupling of subunit availability to activation of flagellar Type III secretion.

Change log
Bryant, Owain J 
Chung, Betty Y-W 

Bacterial flagellar subunits are exported across the cell membrane by the flagellar Type III Secretion System (fT3SS), powered by the proton motive force (pmf) and a specialized ATPase that enables the flagellar export gate to utilize the pmf electric potential (ΔΨ). Export gate activation is mediated by the ATPase stalk, FliJ, but how this process is regulated to prevent wasteful dissipation of pmf in the absence of subunit cargo is not known. Here, we show that FliJ activation of the export gate is regulated by flagellar export chaperones. FliJ binds unladen chaperones and, by using novel chaperone variants specifically defective for FliJ binding, we show that disruption of this interaction attenuates motility and cognate subunit export. We demonstrate in vitro that chaperones and the FlhA export gate component compete for binding to FliJ, and show in vivo that unladen chaperones, which would be present in the cell when subunit levels are low, sequester FliJ to prevent activation of the export gate and attenuate subunit export. Our data indicate a mechanism whereby chaperones couple availability of subunit cargo to pmf-driven export by the fT3SS.

Type III secretion system, bacterial flagella biogenesis, protein export, proton motive force, Adenosine Triphosphatases, Bacterial Proteins, Cell Membrane, Enzyme Activation, Flagella, Membrane Proteins, Molecular Chaperones, Protein Transport, Proton-Motive Force, Salmonella typhimurium, Type III Secretion Systems
Journal Title
Mol Microbiol
Conference Name
Journal ISSN
Volume Title
All rights reserved
Biotechnology and Biological Sciences Research Council (BB/M007197/1)
Medical Research Council (MR/R021821/1)
Isaac Newton Trust (19.07(h))