A Sensory Complex Consisting of an ATP-Binding-Cassette Transporter and a Two-Component Regulatory System Controls Bacitracin Resistance in Bacillus subtilis [Microbiology]

August 12th, 2014 by Dintner, S., Heermann, R., Fang, C., Jung, K., Gebhard, S.

Resistance against antimicrobial peptides (AMPs) in many Firmicutes bacteria is mediated by detoxification systems that are comprised of a two-component regulatory system (TCS) and an ATP-binding-cassette (ABC) transporter. The histidine kinases of these systems depend entirely on the transporter for sensing of AMPs, suggesting a novel mode of signal transduction where the transporter constitutes the actual sensor. The aim of the present study was to investigate the molecular mechanisms of this unusual signaling pathway in more detail, using the bacitracin resistance system BceRS-BceAB of Bacillus subtilis as an example. To analyze the proposed communication between TCS and ABC transporter, we characterized their interactions by bacterial two-hybrid analyses and could show that the permease BceB and the histidine kinase BceS interact directly. In vitro pull-down assays confirmed this interaction, which was found to be independent of bacitracin. Because it was unknown if BceAB-type transporters could detect their substrate peptides directly or instead recognized the peptide:target complex in the cell envelope, we next analyzed substrate binding by the transport permease, BceB. Direct and specific binding of bacitracin by BceB was demonstrated by surface plasmon resonance spectroscopy. Finally, in vitro signal transduction assays indicated that complex formation with the transporter influenced the autophosphorylation activity of the histidine kinase. Taken together, our findings clearly show the existence of a sensory complex comprised of TCS and ABC transporter, and provide first functional insights into the mechanisms of stimulus perception, signal transduction and antimicrobial resistance employed by Bce-like detoxification systems.
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