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

Activation of the Echerichia coli SoxRS-regulon by nitric oxide (NO) and it s physiological donors (S-nitrosothiol (GS-NO) and dinitrosyl iron complexe s with glutathione (DNICglu) and cysteine (DNICcys) ligands) has been studi ed. To elucidate the molecular mechanisms of signal transduction via nitros ylation of Fe-S-centers in SoxR, the ability of pure NO and NO-producing ag ents to activate the SoxRS-regulon in E. coli cells bearing a soxS:lacZ ope ron (promoter) fusion has been compared. EPR spectroscopy of whole cells ha s been used to monitor the formation of inducible protein-DNIC complexes. D NICcys, GS-NO, and pure NO appeared to be potent inducers of soxS expressio n, whereas DNICglu was considerably less efficient. Thus, lower in vitro st ability of DNICcys was in contrast with its higher biological activity Pret reatment of the cells with o-phenanthroline, a chelating agent for iron, pr evented soxS expression by GS-NO. Treatment of intact E. coli cells with DN ICcys, GS-NO, and NO at equimolar concentration 150 muM resulted in formati on of a single EPR detectable DNIC-type signal with g = 2.03. The initial s tage in the SoxR transcription activity is supposed to include two steps: f irst, DNIC primers are formed from exogenous NO and free iron, and then the se DNIC disintegrate SoxR [2Fe-2S] clusters and thus activate SoxRS-regulon transcription.