Endogenous S-nitrosylation of proteins, a principal mechanism of cellular signaling in eukaryotes, has not been observed in microbes. We report that protein S-nitrosylation is an obligate concomitant of anaerobic respiration on nitrate in E. coli. Endogenous S-nitrosylation during anaerobic respiration is controlled by the transcription factor OxyR, previously thought to operate only under aerobic conditions. Deletion of OxyR resulted in large increases in protein S-nitrosylation, and S-nitrosylation of OxyR induced transcription from a regulon that is distinct from the regulon induced by OxyR oxidation. Furthermore, products unique to the anaerobic regulon protected against S-nitrosothiols, and anaerobic growth of E.coli lacking OxyR was impaired on nitrate. Thus, OxyR serves as a master regulator of S-nitrosylation, and alternative posttranslational modifications of OxyR control distinct transcriptional responses.
Figure MS/MS spectra of the cysteine-containing peptides in SNO-OxyR identified after SNO-RAC enrichment and LC-MS/MS analysis. Shown are representative annotated MS/MS fragmentation spectra for the Cys199-containing peptide with ascorbate. Cys199-containing peptide was not observed in the absence of ascorbate. Peptide sequence is shown at the top of each spectrum, with the annotation of the identified matched amino terminus-containing ions (b ions) in black and the carboxyl terminus-containing ions (y ions) in red. For clarity, only major identified peaks are labeled.
Results from: Seth D, Hausladen A, Wang YJ, Stamler JS. Science. 336(6080):470-473,2012. PMID: 22539721