Hydrogen Sulfide Sensing through Reactive Sulfur Species (RSS) and Nitroxyl (HNO) in Enterococcus faecalis

Abstract

Recent studies of hydrogen sulfide (HS) signaling implicate low molecular weight (LMW) thiol persulfides and other reactive sulfur species (RSS) as signaling effectors. Here, we show that a CstR protein from the human pathogen Enterococcus faecalis ( E. faecalis), previously identified in Staphylococcus aureus ( S. aureus), is an RSS-sensing repressor that transcriptionally regulates a cst-like operon in response to both exogenous sulfide stress and Angeli's salt, a precursor of nitroxyl (HNO). E. faecalis CstR reacts with coenzyme A persulfide (CoASSH) to form interprotomer disulfide and trisulfide bridges between C32 and C61', which negatively regulate DNA binding to a consensus CstR DNA operator. A Δ cstR strain exhibits deficiency in catheter colonization in a catheter-associated urinary tract infection (CAUTI) mouse model, suggesting sulfide regulation and homeostasis is critical for pathogenicity. Cellular polysulfide metabolite profiling of sodium sulfide-stressed E. faecalis confirms an increase in both inorganic polysulfides and LMW thiols and persulfides sensed by CstR. The cst-like operon encodes two authentic thiosulfate sulfurtransferases and an enzyme we characterize here as an NADH and FAD-dependent coenzyme A (CoA) persulfide reductase (CoAPR) that harbors an N-terminal CoA disulfide reductase (CDR) domain and a C-terminal rhodanese homology domain (RHD). Both cysteines in the CDR (C42) and RHD (C508) domains are required for CoAPR activity and complementation of a sulfide-induced growth phenotype of a S. aureus strain lacking cstB, encoding a nonheme Fe persulfide dioxygenase. We propose that S. aureus CstB and E. faecalis CoAPR employ orthogonal chemistries to lower CoASSH that accumulates under conditions of cellular sulfide toxicity and signaling.

H2S and reactive sulfur signaling at the host-bacterial pathogen interface

“…It was not until 2014 that RSS were shown to function as antioxidants in mammalian cells (47), which may partly explain H 2 S-enhanced bacterial resistance to antibiotics (21). RSS have been detected in a number of bacterial pathogens (17,20,53,96) and are the subject of ongoing work to better understand the role of RSS in the bacterial response to the host immune system.…”

“…1A, top) (11)(12)(13)(14). In an analogous fashion, bacteria encode specialized transcriptional regulators that sense oxidized or "reactive" sulfur species (RSS), derived from hydrogen sulfide (H 2 S) (15)(16)(17)(18)(19)(20). As cellular concentrations of RSS rise, RSS sensors turn on the expression of genes that encode enzymes that reduce cellular loads of H 2 S/RSS to avoid H 2 S toxicity and overpersulfidation of the metabolome and proteome (Fig.…”

“…1B, bottom) (27). Analogous to a metallosensor, known RSS sensors specifically surveil the cytoplasm for a particular feature of the RSS pool, in this case sulfane sulfur (15)(16)(17)(18)(19)(20).…”

“…These dual sensors collaboratively control metal bioavailability in a concentration range that is compatible with cellular physiology (gray box). H 2 S/RSS homeostasis (bottom) is achieved by a single RSS sensor that transcriptionally regulates the expression of enzymes involved in the biogenesis, clearance, transport, and assimilation of H 2 S/RSS (16)(17)(18)(19)(20). The transcriptional response of an RSS sensor detects a concentration range (gray box) that prevents cellular toxicity, while maintaining access to H 2 S/RSS that is physiologically beneficial at lower concentrations.…”

Thioredoxin Profiling of Multiple Thioredoxin-Like Proteins in Staphylococcus aureus

“…Since protein persulfides can be considered hydrodisulfides, an analogous Trx-like catalytic mechanism may well be operative, in the reduction of protein persulfides except that formation of the initial mixed disulfide intermediate gives rise to the release of H 2 S ( Figure 1B ). The ultimate cellular fate of this H 2 S is not known but may well be assimilated by low molecular weight (LMW) thiols via a number of enzymatic and non-enzymatic processes ( Peng et al, 2017a ; Shen et al, 2018 ) or used directly in Fe-S cofactor biogenesis.…”