Staphylococcus aureus sqr Encodes a Type II Sulfide:Quinone Oxidoreductase and Impacts Reactive Sulfur Speciation in Cells

Abstract

Recent studies implicate hydrogen sulfide (H2S) oxidation as an important aspect of bacterial antibiotic resistance and sulfide homeostasis. The cst operon of the major human pathogen Staphylococcus aureus is induced by exogenous H2S stress and encodes enzymes involved in sulfide oxidation, including a group I flavoprotein disulfide oxidoreductase sulfide:quinone oxidoreductase (SQR). In this work, we show that S. aureus SQR catalyzes the two-electron oxidation of sodium sulfide (Na2S) into sulfane sulfur (S0) when provided flavin adenine dinucleotide and a water-soluble quinone acceptor. Cyanide, sulfite, and coenzyme A (CoA) are all capable of functioning as the S0 acceptor in vitro. This activity requires a C167–C344 disulfide bond in the resting enzyme, with the intermediacy of a C344 persulfide in the catalytic cycle, verified by mass spectrometry of sulfide-reacted SQR. Incubation of purified SQR and S. aureus CstB, a known FeII persulfide dioxygenase-sulfurtransferase also encoded by the cst operon, yields thiosulfate from sulfide, in a CoA-dependent manner, thus confirming the intermediacy of CoASSH as a product and substrate of SQR and CstB, respectively. Sulfur metabolite profiling of wild-type, Δsqr, and Δsqr::pSQR strains reveals a marked and specific elevation in endogenous levels of CoASSH and inorganic tetrasulfide in the Δsqr strain. We conclude that SQR impacts the cellular speciation of these reactive sulfur species but implicates other mechanisms not dependent on SQR in the formation of low-molecular weight thiol persulfides and inorganic polysulfides during misregulation of sulfide homeostasis.

Sulfide-responsive transcriptional repressor SqrR functions as a master regulator of sulfide-dependent photosynthesis

“…3E). Our data collectively reveal that C41 and C107 form an intramolecular tetrasulfide bond upon sensing of sulfide-derived reactive sulfur species, such as glutathione persulfide, that are expected to accumulate in sulfide-treated bacterial cells (39) (Fig. 4).…”

“…The expression level of sqr, which encodes a canonical sulfide:quinone oxidoreductase (39,40), is induced by sulfide in WT cells and is elevated in the sqrR-disrupted mutant irrespective of the presence of sulfide (Fig. 3B).…”

Hydrogen Sulfide and Reactive Sulfur Species Impact Proteome S-Sulfhydration and Global Virulence Regulation in Staphylococcus aureus

“…20,24 Here, we show that these RSS levels can be affected by genetic background and growth conditions. The concentration of the major reducing LMW thiol, bacillithiol (BSH), is in the ≈3 mM range, as expected, 30 with the concentration of coenzyme A (CoASH) and cysteine (CysSH) comparable and ≈3-fold lower, respectively, relative to BSH (Table S1).…”

“…It is hypothesized that RSS are generated either by direct attack of H 2 S on low-molecule-weight (LMW) thiol disulfides or enzymatically via sulfide/quinone oxidoreductases (SQR). 19,20 RSS are maintained at micromolar levels in mammalian cells and animal tissues to allow H 2 S signaling. 5 …”

“…21–23 These regulators sense RSS directly, which can be detected and quantified in bacterial cells. 20,24 However, little is known about what role H 2 S and downstream RSS play in cellular sulfur speciation and if H 2 S signaling impacts S. aureus pathogenesis and other biological processes. Sulfur metabolism is generally important for bacterial pathophysiology, and targeting microbial sulfur assimilation is a validated approach for the development of new antimicrobial agents.…”