Chung, B. Y.-W. | Search bioRxiv

bioRxiv2024

Activity of Salmonella SPI-1 inhibits the TLR4-dependent transcriptional but not translational response during macrophage infection

Changes in gene expression during bacterial infection are the combined result of altered transcription and translation, with the latter comparatively understudied. Gram-negative bacteria rapidly trigger cytokine gene transcription in macrophages through the activation of pathogen associated molecular pattern receptors, for example detection of Salmonella lipopolysaccharide (LPS) from the bacterial cell envelope by Toll-like receptor 4 (TLR4). Here, through time-resolved parallel translatomic and transcriptomic profiling, we now show temporal TLR4-specific translational upregulation of cell signalling proteins in macrophages induced by Salmonella. While transcriptional upregulation of these genes is dampened through the activity of the Salmonella SPI-1 type three secretion system, a robust translational response remains. These data reveal an important host-pathogen translational regulatory network that modifies the innate immune response of macrophages to infection.

molecular biology↗

bioRxiv2020

Chaperone mediated coupling of subunit availability to activation of proton motive force-driven flagellar Type III Secretion

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 utilise the pmf electric potential ({Delta}{Psi}). 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, 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.

microbiology↗