Bacteria closely control gene expression to ensure optimal physiological responses to their environment. Such careful gene expression can minimize the fitness cost associated with antibiotic resistance. We previously described a novel regulatory logic in Bacillus subtilis enabling the cell to directly monitor its need for detoxification. This cost‐effective strategy is achieved via a two‐component regulatory system (BceRS) working in a sensory complex with an ABC‐transporter (BceAB), together acting as a flux‐sensor where signaling is proportional to transport activity. How this is realized at the molecular level has remained unknown. Using experimentation and computation we here show that the histidine kinase is activated by piston‐like displacements in the membrane, which are converted to helical rotations in the catalytic core via an intervening HAMP‐like domain. Intriguingly, the transporter was not only required for kinase activation, but also to actively maintain the kinase in its inactive state in the absence of antibiotics. Such coupling of kinase activity to that of the transporter ensures the complete control required for transport flux‐dependent signaling. Moreover, we show that the transporter likely conserves energy by signaling with sub‐maximal sensitivity. These results provide the first mechanistic insights into transport flux‐dependent signaling, a unique strategy for energy‐efficient decision making.
Bibliographical noteFunding Information:
The authors thank Roger Draheim for helpful advice in establishing the cysteine crosslinking assays. We also thank our undergraduate research students Jessica Lancaster and Adam McCartan for constructing plasmids pJL705 and pAM703, respectively. We thank Jean van den Elsen and Laurence Hurst for critical reading of and feedback on the manuscript. Work in SG's lab was supported by the Biotechnology and Biological Sciences Research Council (BBSRC; BB/M029255/1). MWK is a BBSRC David Phillips Fellow (BB/M026280/1).
© 2020 The Authors. Molecular Microbiology published by John Wiley & Sons Ltd