Abstract
The Hha and TomB proteins from Escherichia coli form an oxygen-dependent toxin–antitoxin (TA) system. Here we show that YmoB, the Yersinia orthologue of TomB, and its single cysteine variant [C117S]YmoB can replace TomB as antitoxins in E. coli. In contrast to other TA systems, [C117S]YmoB transiently interacts with Hha (rather than forming a stable complex) and enhances the spontaneous oxidation of the Hha conserved cysteine residue to a -SOxH-containing species (sulfenic, sulfinic or sulfonic acid), which destabilizes the toxin. The nuclear magnetic resonance structure of [C117S]YmoB and the homology model of TomB show that the two proteins form a four-helix bundle with a conserved buried cysteine connected to the exterior by a channel with a diameter comparable to that of an oxygen molecule. The Hha interaction site is located on the opposite side of the helix bundle.
Highlights
The Hha and TomB proteins from Escherichia coli form an oxygen-dependent toxin–antitoxin (TA) system
We tested the hypothesis that the Hha-TomB pair was an oxygen-dependent TA system by measuring E. coli growth at increasing agitation rates (Fig. 1)
A significant antitoxin effect of TomB was observed after B4 h, and after 6 h, cultures overexpressing both Hha and TomB reached the same cell densities as the controls
Summary
The Hha and TomB proteins from Escherichia coli form an oxygen-dependent toxin–antitoxin (TA) system. We hypothesized that the oxygen-dependent antitoxin activity of TomB and [C117S]YmoB towards Hha could be related to the oxidation of this conserved cysteine residue.
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