Fig. 3. Cys40 and Cys41 form an intramolecular disulfide bond in response to H₂O₂ stress.

a The positions of the Cys residues in the reduced structure of RexT. The two sulfur atoms of Cys40 and Cys41 are located ~7 Å apart in both monomeric units of RexT. The sulfur atoms of Cys40 and Cys41 are located 21.9 Å and 23.0 Å away from the sulfur atom of Cys105, the last modeled residue in the crystal structure, respectively (shown for chain B of the structure). There are two measurements shown in chain A since the Cys41 residue sidechain shows two orientations of the sidechain. b Using the FOX assay, wild-type RexT was shown to consume H₂O₂ over time. Two control reactions are also included in this panel that shows H₂O₂ is not consumed in the absence of RexT or in the presence of the protein bovine serum albumin (BSA). c The C105S RexT variant consumes H₂O₂ similarly to wild-type RexT, suggesting it is not involved in mediating the oxidative stress response. d In contrast, the C40S variant of RexT shows a decreased ability to consume H₂O₂ relative to wild-type RexT. e As observed for the C40S variant, the C41S RexT variant is also impaired in its ability to consume H₂O₂, albeit to a greater extent. In b–e, data was measured using n = 3 independent experiments and is presented with the individual measurements (open shapes) and as the mean value of these measurements ± SD (closed shapes). Source data are provided as a Source Data file.