Activation of the Escherichia coli SoxRS-Regulon by Nitric Oxide and Its Physiological Donors

S. V. Vasil'eva¹, M. V. Stupakova¹, I. I. Lobysheva², V. D. Mikoyan^2*, and A. F. Vanin²

¹Institute of Biochemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 117977 Russia; fax: (095) 137-4101; E-mail: chembio@sky.chph.ras.ru

²Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119991 Russia; fax: (095) 238-2156; E-mail: mikoyan@center.chph.ras.ru

^* To whom correspondence should be addressed.

Received January 23, 2001; Revision received May 14, 2001

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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 µM 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.

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KEY WORDS: nitric oxide, SoxRS-regulon, S-nitrosothiols, dinitrosyl iron complexes, Escherichia coli

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