Distinct characteristics of OxyR 2, a new OxyR ‐type regulator, ensuring expression of P eroxiredoxin 2 detoxifying low levels of hydrogen peroxide in V ibrio vulnificus

Summary Two peroxiredoxins, Prx 1 and Prx 2, were previously identified in V ibrio vulnificus . Besides OxyR 1, a homologue of E scherichia coli   OxyR ( Ec OxyR ), OxyR 2 that shares low homology with Ec OxyR was first identified in V . vulnificus . OxyR 2 activated prx 2 during aerobic growth, while OxyR 1 activated prx 1 only when exposed to exogenous H 2 O 2 . OxyR 2 was oxidized to form a reversible C 206 to C 215 disulphide bond by sensing low levels of H 2 O 2 , which were insufficient to oxidize OxyR 1, and only the oxidized OxyR 2 activated prx 2. OxyR 2 5 CA , in which all cysteine residues except for C 206 and C 215 were replaced with alanines, and its mutants, OxyR 2 5 CA ‐ C 206 S and OxyR 2 5 CA ‐ C 215 S , were constructed. OxyR 2 5 CA and OxyR 2 5 CA ‐ C 215 S directly bound to a specific binding sequence centred at −56.5 from the prx 2 transcription start site, albeit with different binding affinities. The binding sequence consisted of four ATCGnt elements spaced by a helical turn and aligned in the twofold dyad symmetry, suggesting that OxyR 2 binds DNA as a tetramer. OxyR 2 5 CA ‐ C 206 S also directly bound to DNA comprising more extended sequences, indicating that oxidized and reduced OxyR 2 adopt different conformational states, leading to altered DNA contacts. The oxyR 2 mutation reduced cytotoxicity and growth during infection, indicating that OxyR 2 is essential for the pathogenesis of V . vulnificus .