Activation of the Escherichia coli SoxRS-regulon by nitric oxide and its physiological donors.

Activation of the Escherichia coli SoxRS-regulon by nitric oxide (NO) and its physiological donors (S-nitrosothiol (GS-NO) and dinitrosyl iron complexes with glutathione (DNIC(glu)) and cysteine (DNIC(cys)) ligands) has been studied. To elucidate the molecular mechanisms of signal transduction via nitrosylation of Fe-S-centers in SoxR, the ability of pure NO and NO-producing agents to activate the SoxRS-regulon in E. coli cells bearing a soxS::lacZ operon (promoter) fusion has been compared. EPR spectroscopy of whole cells has been used to monitor the formation of inducible protein-DNIC complexes. DNIC(cys), GS-NO, and pure NO appeared to be potent inducers of soxS expression, whereas DNIC(glu) was considerably less efficient. Thus, lower in vitro stability of DNIC(cys) was in contrast with its higher biological activity. Pretreatment of the cells with o-phenanthroline, a chelating agent for iron, prevented soxS expression by GS-NO. Treatment of intact E. coli cells with DNIC, GS-NO, and NO at equimolar concentration 150 microM resulted in formation of a single EPR-detectable DNIC-type signal with g = 2.03. The initial stage in the SoxR transcription activity is supposed to include two steps: first, DNIC primers are formed from exogenous NO and free iron, and then these DNIC disintegrate SoxR [2Fe-2S] clusters and thus activate SoxRS-regulon transcription.