Thioredoxin-2 Regulates SqrR-Mediated Polysulfide-Responsive Transcription via Reduction of a Polysulfide Link in SqrR

Polysulfide plays an essential role in controlling various physiological activities in almost all organisms. We recently investigated the impact of polysulfide metabolic enzymes on the temporal dynamics of cellular polysulfide speciation and transcriptional regulation by the polysulfide-responsive transcription factor SqrR in Rhodobacter capsulatus. However, how the polysulfidation of thiol groups in SqrR is reduced remains unclear. In the present study, we examined the reduction of polysulfidated thiol residues by the thioredoxin system. TrxC interacted with SqrR in vitro and reduced the polysulfide crosslink between two cysteine residues in SqrR. Furthermore, we found that exogenous sulfide-induced SqrR de-repression during longer culture times is maintained upon disruption of the trxC gene. These results establish a novel signaling pathway in SqrR-mediated polysulfide-induced transcription, by which thioredoxin-2 restores SqrR to a transcriptionally repressed state via the reduction of polysulfidated thiol residues.