The effects of Cys to Ser substitutions in OxyR on the response of E. coli to stress induced by copper (II) sulfate, diamide, hydrochloric acid, hydrogen peroxide, kanamycin, and methyl viologen dichloride

OxyR is a redox-sensitive transcriptional regulator that activates the expression of defense genes responsible for an oxidative stress response in Escherichia coli. The transcription factor is activated by the modification of thiols. Six cysteine residues are in the amino acid sequence of OxyR; two are evolutionarily conserved at positions 199 and 208. Cys-199 is critical for protein activity and Cys-208 is essential for protein activity. An oxyR knock out line, TA4112, was complemented with plasmids containing oxyR with altered cysteines. Cysteine to serine point mutations allowed for further investigation into the role of cysteines in OxyR. The resulting bacteria were grown on agar plates containing different chemical stressors. Using the Carestream Molecular Imaging camera / software system, the total colony number and the mean of the area of the colonies were recorded. Stressors producing reactive oxygen species were shown to impart cysteine-dependent effects. However, the results from each reactive oxygen species did not produce similar data. Stressors that did not produce reactive oxygen species resulted in no significant data. The differences in distribution observed on the untreated E.coli plates appeared to go away in the presence of a stressor. The plating assay demonstrated that cell lines expressing C208S produced differences in the number and area of colonies. H2O2 analysis in liquid culture produced alterations in growth for cell lines with Cys-199 when controls are corrected for. Diamide does not result in significant changes in growth in the critical Cys-199 or the important Cys-208. This work sheds light on E. coli response to stress and that OxyR response is altered by Cys to Ser substitutions.M.S.Includes bibliographical referencesby Salvador Gome