Polysulfide metabolizing enzymes influence SqrR-mediated sulfide-induced transcription by impacting intracellular polysulfide dynamics

Abstract

Sulfide plays essential roles in controlling various physiological activities in almost all organisms. Although recent evidence has demonstrated that sulfide is endogenously generated and metabolized into polysulfides inside the cells, the relationship between polysulfides metabolism and polysulfides-sensing mechanisms is not well understood. To better define this interplay between polysulfide metabolism and polysulfide sensing in cells, we investigated the role of polysulfide-metabolizing enzymes such as SQR (sulfide:quinone reductase) on the temporal dynamics of cellular polysulfides speciation and on the transcriptional regulation by the persulfide-responsive transcription factor SqrR in Rhodobacter capsulatus. We show that disruption of the sqr gene resulted in the loss of SqrR repression by exogenous sulfide at longer culture times, which impacts the speciation of intracellular polysulfides of Δsqr vs. wild-type strains. Both the attenuated response of SqrR and the change in polysulfide dynamics of the Δsqr strain is fully reversed by the addition to cells of cystine-derived polysulfides, but not by glutathione disulfide (GSSG)-derived polysulfides. Furthermore, cysteine persulfide (CysSSH) yields a higher rate of oxidation of SqrR relative to glutathione persulfide (GSSH), which leads to DNA dissociation in vitro. The oxidation of SqrR was confirmed by a mass spectrometry-based kinetic profiling strategy that showed distinct polysulfide-crosslinked products obtained with CysSSH vs. GSSH. Taken together, these results establish a novel association between the metabolism of polysulfides and the mechanisms for polysulfide sensing inside the cells.

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

“…SqrR forms an intramolecular polysulfide crosslink between two cysteine residues following polysulfide exposure [ 10 , 11 ]. We, therefore, analyzed the role of TrxC in the reduction of the polysulfide crosslink in SqrR.…”

“…Furthermore, the trxC complementing strain showed similar transcriptional changes as WT. In our previous study, rhodanese (rcc01557)-deletion mutant maintained high expression levels of sqr at longer time points as well [ 10 ]. These observations are thought to be due to abnormal degradation of polysulfidation in SqrR and intracellular polysulfide.…”

“…We recently characterized the dynamics of polysulfide metabolism with regard to bacterial polysulfide-responsive transcription in Rhodobacter capsulatus [ 10 ]. SqrR (rcc01453), a bacterial polysulfide sensor isolated from R. capsulatus , exerts extensive control over sulfide-responsive genes that encode polysulfide metabolism-related proteins in R. capsulatus [ 11 ].…”

“…SqrR (rcc01453), a bacterial polysulfide sensor isolated from R. capsulatus , exerts extensive control over sulfide-responsive genes that encode polysulfide metabolism-related proteins in R. capsulatus [ 11 ]. SqrR forms an intramolecular polysulfide crosslink via two conserved Cys residues when exposed to polysulfide, resulting in a decline in repressor activity [ 10 , 11 ]. A mass spectrometry-based kinetic profiling study further defined this polysulfidation process and the chemical specificity of SqrR [ 12 ].…”

“…These data indicate that SqrR-related polysulfide signal transduction is a suitable model system for investigations of sulfide/polysulfide signaling. Our current study revealed that two SqrR-regulated polysulfide-metabolizing enzymes, sulfide:quinone reductase (SQR) (rcc00785) and rhodanese (rcc01557), affect SqrR-mediated polysulfide-induced transcription and speciation of intracellular polysulfide, which in turn modulates the polysulfide response in R. capsulatus [ 10 ]. SQR provides sustained levels of polysulfide to suppress the transcriptional repression caused by the reduction of SqrR.…”