The effects of nitroxyl (HNO) on soluble guanylate cyclase activity: interactions at ferrous heme and cysteine thiols

It has been previously proposed that nitric oxide (NO) is the only biologically relevant nitrogen oxide capable of activating the enzyme soluble guanylate cyclase (sGC). However, recent reports implicate HNO as another possible activator of sGC. Herein, we examine the affect of HNO donors on the activity of purified bovine lung sGC and find that, indeed, HNO is capable of activating this enzyme. Like NO, HNO activation appears to occur via interaction with the regulatory ferrous heme on sGC. Somewhat unexpectedly, HNO does not activate the ferric form of the enzyme. Finally, HNO-mediated cysteine thiol modification appears to also affect enzyme activity leading to inhibition. Thus, sGC activity can be regulated by HNO via interactions at both the regulatory heme and cysteine thiols

Biological hydropersulfides and related polysulfides – a new concept and perspective in redox biology

The chemical biology of thiols (RSH, e.g., cysteine and cysteine‐containing proteins/peptides) has been a topic of extreme interest for many decades due to their reported roles in protein structure/folding, redox signaling, metal ligation, cellular protection, and enzymology. While many of the studies on thiol/sulfur biochemistry have focused on thiols, relatively ignored have been hydropersulfides (RSSH) and higher order polysulfur species (RSSnH, RSSnR, n > 1). Recent and provocative work has alluded to the prevalence and likely physiological importance of RSSH and related RSSnH. RSSH of cysteine (Cys‐SSH) has been found to be prevalent in mammalian systems along with Cys‐SSH‐containing proteins. The RSSH functionality has not been examined to the extent of other biologically relevant sulfur derivatives (e.g., sulfenic acids, disulfides, etc.), whose roles in cell signaling are strongly indicated. The recent finding of Cys‐SSH biosynthesis and translational incorporation into proteins is an unequivocal indication of its fundamental importance and necessitates a more profound look into the physiology of RSSH. In this Review, we discuss the currently reported chemical biology of RSSH (and related species) as a prelude to discussing their possible physiological roles

Cysteinyl-tRNA synthetase governs cysteine polysulfidation and mitochondrial bioenergetics

Cysteine hydropersulfide (CysSSH) occurs in abundant quantities in various organisms, yet little is known about its biosynthesis and physiological functions. Extensive persulfide formation is apparent in cysteine-containing proteins in Escherichia coli and mammalian cells and is believed to result from post-translational processes involving hydrogen sulfide-related chemistry. Here we demonstrate effective CysSSH synthesis from the substrate l-cysteine, a reaction catalyzed by prokaryotic and mammalian cysteinyl-tRNA synthetases (CARSs). Targeted disruption of the genes encoding mitochondrial CARSs in mice and human cells shows that CARSs have a crucial role in endogenous CysSSH production and suggests that these enzymes serve as the principal cysteine persulfide synthases in vivo. CARSs also catalyze co-translational cysteine polysulfidation and are involved in the regulation of mitochondrial biogenesis and bioenergetics. Investigating CARS-dependent persulfide production may thus clarify aberrant redox signaling in physiological and pathophysiological conditions, and suggest therapeutic targets based on oxidative stress and mitochondrial dysfunction

The reactive species interactome: evolutionary emergence, biological significance, and opportunities for redox metabolomics and personalized medicine

SIGNIFICANCE: Oxidative stress is thought to account for aberrant redox homeostasis and contribute to aging and disease. However, more often than not administration of antioxidants is ineffective, suggesting our current understanding of the underlying regulatory processes is incomplete. Recent Advances. Similar to reactive oxygen and nitrogen species (ROS, RNS), reactive sulfur species (RSS) are now emerging as important signaling molecules, targeting regulatory cysteine redox switches in proteins, affecting gene regulation, ion transport, intermediary metabolism and mitochondrial function. To rationalize the complexity of chemical interactions of reactive species with themselves and their targets and help define their role in systemic metabolic control, we here introduce a novel integrative concept coined the reactive species interactome (RSI). The RSI is a primeval multi-level redox-regulatory system whose architecture, together with the physicochemical characteristics of its constituents, allows efficient sensing and rapid adaptation to environmental changes and various other stresses to enhance fitness and resilience at the local and whole-organism level. CRITICAL ISSUES: To better characterise the RSI-related processes that determine fluxes through specific pathways and enable integration, it is necessary to disentangle the chemical biology and activity of reactive species (including precursors and reaction products), their targets, communication systems and effects on cellular, organ and whole-organism bioenergetics using systems-level/network analyses. FUTURE DIRECTIONS: Understanding the mechanisms through which the RSI operates will enable a better appreciation of the possibilities to modulate the entire biological system; moreover, unveiling molecular signatures that characterize specific environmental challenges or other stresses will provide new prevention/intervention opportunities for personalized medicine

Comment on “Evidence that the ProPerDP method is inadequate for protein persulfidation detection due to lack of specificity”

The recent report by Fan et al. alleged that the ProPerDP method is inadequate for the detection of protein persulfidation. Upon careful evaluation of their work, we conclude that the claim made by Fan et al. is not supported by their data, rather founded in methodological shortcomings. It is understood that the ProPerDP method generates a mixture of cysteine-containing and non–cysteine-containing peptides. Instead, Fan et al. suggested that the detection of non–cysteine-containing peptides indicates nonspecific alkylation at noncysteine residues. However, if true, then such peptides would not be released by reduction and therefore not appear as products in the reported workflow. Moreover, the authors’ biological assessment of ProPerDP using Escherichia coli mutants was based on assumptions that have not been confirmed by other methods. We conclude that Fan et al. did not rigorously assess the method and that ProPerDP remains a reliable approach for analyses of protein per/polysulfidation

Carbon disulfide. Just toxic or also bioregulatory and/or therapeutic?

The overview presented here has the goal of examining whether carbon disulfide (CS2) may play a role as an endogenously generated bioregulator and/or has therapeutic value. The neuro- and reproductive system toxicity of CS2 has been documented from its long-term use in the viscose rayon industry. CS2 is also used in the production of dithiocarbamates (DTCs), which are potent fungicides and pesticides, thus raising concern that CS2 may be an environmental toxin. However, DTCs also have recognized medicinal use in the treatment of heavy metal poisonings as well as having potency for reducing inflammation. Three known small molecule bioregulators (SMBs) nitric oxide, carbon monoxide, and hydrogen sulfide were initially viewed as environmental toxins. Yet each is now recognized as having intricate, though not fully elucidated, biological functions at concentration regimes far lower than the toxic doses. The literature also implies that the mammalian chemical biology of CS2 has broader implications from inflammatory states to the gut microbiome. On these bases, we suggest that the very nature of CS2 poisoning may be related to interrupting or overwhelming relevant regulatory or signaling process(es), much like other SMBs

Induction of a feed forward pro-apoptotic mechanistic loop by nitric oxide in a human breast cancer model.

We have previously demonstrated that relatively high concentrations of NO [Nitric Oxide] as produced by activated macrophages induced apoptosis in the human breast cancer cell line, MDA-MB-468. More recently, we also demonstrated the importance of endogenous H2O2 in the regulation of growth in human breast cancer cells. In the present study we assessed the interplay between exogenously administered NO and the endogenously produced reactive oxygen species [ROS] in human breast cancer cells and evaluated the mechanism[s] in the induction of apoptosis. To this end we identified a novel mechanism by which NO down regulated endogenous hydrogen peroxide [H2O2] formation via the down-regulation of superoxide [O2 (.-)] and the activation of catalase. We further demonstrated the existence of a feed forward mechanistic loop involving protein phosphatase 2A [PP2A] and its downstream substrate FOXO1 in the induction of apoptosis and the synthesis of catalase. We utilized gene silencing of PP2A, FOXO1 and catalase to assess their relative importance and key roles in NO mediated apoptosis. This study provides the potential for a therapeutic approach in treating breast cancer by targeted delivery of NO where NO donors and activators of downstream players could initiate a self sustaining apoptotic cascade in breast cancer cells

Induction of a feed forward pro-apoptotic mechanistic loop by nitric oxide in a human breast cancer model.

We have previously demonstrated that relatively high concentrations of NO [Nitric Oxide] as produced by activated macrophages induced apoptosis in the human breast cancer cell line, MDA-MB-468. More recently, we also demonstrated the importance of endogenous H2O2 in the regulation of growth in human breast cancer cells. In the present study we assessed the interplay between exogenously administered NO and the endogenously produced reactive oxygen species [ROS] in human breast cancer cells and evaluated the mechanism[s] in the induction of apoptosis. To this end we identified a novel mechanism by which NO down regulated endogenous hydrogen peroxide [H2O2] formation via the down-regulation of superoxide [O2 (.-)] and the activation of catalase. We further demonstrated the existence of a feed forward mechanistic loop involving protein phosphatase 2A [PP2A] and its downstream substrate FOXO1 in the induction of apoptosis and the synthesis of catalase. We utilized gene silencing of PP2A, FOXO1 and catalase to assess their relative importance and key roles in NO mediated apoptosis. This study provides the potential for a therapeutic approach in treating breast cancer by targeted delivery of NO where NO donors and activators of downstream players could initiate a self sustaining apoptotic cascade in breast cancer cells