Bryant Owain J, Chung Betty Y-W, Fraser Gillian M
Department of Pathology, University of Cambridge, Cambridge, UK.
Mol Microbiol. 2021 Aug;116(2):538-549. doi: 10.1111/mmi.14731. Epub 2021 Jun 23.
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.
细菌鞭毛亚基通过鞭毛III型分泌系统（fT3SS）穿过细胞膜，该过程由质子动力（pmf）和一种特殊的ATP酶驱动，这种ATP酶使鞭毛输出门能够利用pmf电势（ΔΨ）。输出门的激活由ATP酶柄FliJ介导，但在没有亚基货物的情况下，该过程如何被调节以防止pmf的浪费性耗散尚不清楚。在这里，我们表明鞭毛输出伴侣调节输出门的FliJ激活。FliJ与空载伴侣结合，通过使用对FliJ结合有特异性缺陷的新型伴侣变体，我们表明这种相互作用的破坏会减弱运动性和同源亚基输出。我们在体外证明伴侣和FlhA输出门组件竞争与FliJ的结合，并在体内表明当亚基水平较低时细胞中存在的空载伴侣会隔离FliJ以防止输出门激活并减弱亚基输出。我们的数据表明了一种机制，通过该机制伴侣将亚基货物的可用性与fT3SS的pmf驱动输出联系起来。
