Assay methods for H2S biogenesis and catabolism enzymes

The interplay of hydrogen sulfide and microRNAs in cardiovascular diseases: insights and future perspectives

Hydrogen sulfide (H2S) is recognized as the third gasotransmitter, after nitric oxide (NO) and carbon monoxide (CO). It is known for its cardioprotective properties, including the relaxation of blood vessels, promotion of angiogenesis, regulation of myocardial cell apoptosis, inhibition of vascular smooth muscle cell proliferation, and reduction of inflammation. Additionally, abnormal H2S generation has been linked to the development of cardiovascular diseases (CVD), such as pulmonary hypertension, hypertension, atherosclerosis, vascular calcification, and myocardial injury. MicroRNAs (miRNAs) are non-coding, conserved, and versatile molecules that primarily influence gene expression by repressing translation and have emerged as biomarkers for CVD diagnosis. Studies have demonstrated that H2S can ameliorate cardiac dysfunction by regulating specific miRNAs, and certain miRNAs can also regulate H2S synthesis. The crosstalk between miRNAs and H2S offers a novel perspective for investigating the pathophysiology, prevention, and treatment of CVD. The present analysis outlines the interactions between H2S and miRNAs and their influence on CVD, providing insights into their future potential and advancement.

Epigenetic regulation by hypoxia, N-acetylcysteine and hydrogen sulphide of the fetal vasculature in growth restricted offspring: A study in humans and chicken embryos

Fetal growth restriction (FGR) is a common outcome in human suboptimal gestation and is related to prenatal origins of cardiovascular dysfunction in offspring. Despite this, therapy of human translational potential has not been identified. Using human umbilical and placental vessels and the chicken embryo model, we combined cellular, molecular, and functional studies to determine whether N-acetylcysteine (NAC) and hydrogen sulphide (H2S) protect cardiovascular function in growth-restricted unborn offspring. In human umbilical and placental arteries from control or FGR pregnancy and in vessels from near-term chicken embryos incubated under normoxic or hypoxic conditions, we determined the expression of the H2S gene CTH (i.e. cystathionine γ-lyase) (via quantitative PCR), the production of H2S (enzymatic activity), the DNA methylation profile (pyrosequencing) and vasodilator reactivity (wire myography) in the presence and absence of NAC treatment. The data show that FGR and hypoxia increased CTH expression in the embryonic/fetal vasculature in both species. NAC treatment increased aortic CTH expression and H2S production and enhanced third-order femoral artery dilator responses to the H2S donor sodium hydrosulphide in chicken embryos. NAC treatment also restored impaired endothelial relaxation in human third-to-fourth order chorionic arteries from FGR pregnancies and in third-order femoral arteries from hypoxic chicken embryos. This NAC-induced protection against endothelial dysfunction in hypoxic chicken embryos was mediated via nitric oxide independent mechanisms. Both developmental hypoxia and NAC promoted vascular changes in CTH DNA and NOS3 methylation patterns in chicken embryos. Combined, therefore, the data support that the effects of NAC and H2S offer a powerful mechanism of human translational potential against fetal cardiovascular dysfunction in complicated pregnancy. KEY POINTS: Gestation complicated by chronic fetal hypoxia and fetal growth restriction (FGR) increases a prenatal origin of cardiovascular disease in offspring, increasing interest in antenatal therapy to prevent against a fetal origin of cardiovascular dysfunction. We investigated the effects between N-acetylcysteine (NAC) and hydrogen sulphide (H2S) in the vasculature in FGR human pregnancy and in chronically hypoxic chicken embryos. Combining cellular, molecular, epigenetic and functional studies, we show that the vascular expression and synthesis of H2S is enhanced in hypoxic and FGR unborn offspring in both species and this acts to protect their vasculature. Therefore, the NAC/H2S pathway offers a powerful therapeutic mechanism of human translational potential against fetal cardiovascular dysfunction in complicated pregnancy.

Structural and biochemical characterization of an encapsulin-associated rhodanese from Acinetobacter baumannii

Rhodanese-like domains (RLDs) represent a widespread protein family canonically involved in sulfur transfer reactions between diverse donor and acceptor molecules. RLDs mediate these transsulfuration reactions via a transient persulfide intermediate, created by modifying a conserved cysteine residue in their active sites. RLDs are involved in various aspects of sulfur metabolism, including sulfide oxidation in mitochondria, iron-sulfur cluster biogenesis, and thio-cofactor biosynthesis. However, due to the inherent complexity of sulfur metabolism caused by the intrinsically high nucleophilicity and redox sensitivity of thiol-containing compounds, the physiological functions of many RLDs remain to be explored. Here, we focus on a single domain Acinetobacter baumannii RLD (Ab-RLD) associated with a desulfurase encapsulin which is able to store substantial amounts of sulfur inside its protein shell. We determine the 1.6 Å x-ray crystal structure of Ab-RLD, highlighting a homodimeric structure with a number of unusual features. We show through kinetic analysis that Ab-RLD exhibits thiosulfate sulfurtransferase activity with both cyanide and glutathione acceptors. Using native mass spectrometry and in vitro assays, we provide evidence that Ab-RLD can stably carry a persulfide and thiosulfate modification and may employ a ternary catalytic mechanism. Our results will inform future studies aimed at investigating the functional link between Ab-RLD and the desulfurase encapsulin.

Widespread S-persulfidation in activated macrophages as a protective mechanism against oxidative-inflammatory stress

Acute inflammatory responses often involve the production of reactive oxygen and nitrogen species by innate immune cells, particularly macrophages. How activated macrophages protect themselves in the face of oxidative-inflammatory stress remains a long-standing question. Recent evidence implicates reactive sulfur species (RSS) in inflammatory responses; however, how endogenous RSS affect macrophage function and response to oxidative and inflammatory insults remains poorly understood. In this study, we investigated the endogenous pathways of RSS biogenesis and clearance in macrophages, with a particular focus on exploring how hydrogen sulfide (H2S)-mediated S-persulfidation influences macrophage responses to oxidative-inflammatory stress. We show that classical activation of mouse or human macrophages using lipopolysaccharide and interferon-γ (LPS/IFN-γ) triggers substantial production of H2S/RSS, leading to widespread protein persulfidation. Biochemical and proteomic analyses revealed that this surge in cellular S-persulfidation engaged ∼2% of total thiols and modified over 800 functionally diverse proteins. S-persulfidation was found to be largely dependent on the cystine importer xCT and the H2S-generating enzyme cystathionine γ-lyase and was independent of changes in the global proteome. We further investigated the role of the sulfide-oxidizing enzyme sulfide quinone oxidoreductase (SQOR), and found that it acts as a negative regulator of S-persulfidation. Elevated S-persulfidation following LPS/IFN-γ stimulation or SQOR inhibition was associated with increased resistance to oxidative stress. Upregulation of persulfides also inhibited the activation of the macrophage NLRP3 inflammasome and provided protection against inflammatory cell death. Collectively, our findings shed light on the metabolism and effects of RSS in macrophages and highlight the crucial role of persulfides in enabling macrophages to withstand and alleviate oxidative-inflammatory stress.

Catalytic specificity and crystal structure of cystathionine γ-lyase from Pseudomonas aeruginosa

The escalating drug resistance among microorganisms underscores the urgent need for innovative therapeutic strategies and a comprehensive understanding of bacteria's defense mechanisms against oxidative stress and antibiotics. Among the recently discovered barriers, the endogenous production of hydrogen sulfide (H2S) via the reverse transsulfuration pathway, emerges as a noteworthy factor. In this study, we have explored the catalytic capabilities and crystal structure of cystathionine γ-lyase from Pseudomonas aeruginosa (PaCGL), a multidrug-opportunistic pathogen chiefly responsible for nosocomial infections. In addition to a canonical L-cystathionine hydrolysis, PaCGL efficiently catalyzes the production of H2S using L-cysteine and/or L-homocysteine as alternative substrates. Comparative analysis with the human enzyme and counterparts from other pathogens revealed distinct structural features within the primary enzyme cavities. Specifically, a distinctly folded entrance loop could potentially modulate the access of substrates and/or inhibitors to the catalytic site. Our findings offer significant insights into the structural evolution of CGL enzymes across different pathogens and provide novel opportunities for developing specific inhibitors targeting PaCGL.

Structural and biochemical characterization of an encapsulin-associated rhodanese from Acinetobacter baumannii

Rhodanese-like domains (RLDs) represent a widespread protein family canonically involved in sulfur transfer reactions between diverse donor and acceptor molecules. RLDs mediate these transsulfuration reactions via a transient persulfide intermediate, created by modifying a conserved cysteine residue in their active sites. RLDs are involved in various aspects of sulfur metabolism, including sulfide oxidation in mitochondria, iron-sulfur cluster biogenesis, and thio-cofactor biosynthesis. However, due to the inherent complexity of sulfur metabolism caused by the intrinsically high nucleophilicity and redox sensitivity of thiol-containing compounds, the physiological functions of many RLDs remain to be explored. Here, we focus on a single domain Acinetobacter baumannii RLD (Ab-RLD) associated with a desulfurase encapsulin which is able to store substantial amounts of sulfur inside its protein shell. We determine the 1.6 Å x-ray crystal structure of Ab-RLD, highlighting a homodimeric structure with a number of unusual features. We show through kinetic analysis that Ab-RLD exhibits thiosulfate sulfurtransferase activity with both cyanide and glutathione acceptors. Using native mass spectrometry and in vitro assays, we provide evidence that Ab-RLD can stably carry a persulfide and thiosulfate modification and may employ a ternary catalytic mechanism. Our results will inform future studies aimed at investigating the functional link between Ab-RLD and the desulfurase encapsulin.

Impact of Reactive Sulfur Species on Entamoeba histolytica: Modulating Viability, Motility, and Biofilm Degradation Capacity

Reactive sulfur species (RSS) like hydrogen sulfide (H2S) and cysteine persulfide (Cys-SSH) emerged as key signaling molecules with diverse physiological roles in the body, depending on their concentration and the cellular environment. While it is known that H2S and Cys-SSH are produced by both colonocytes and by the gut microbiota through sulfur metabolism, it remains unknown how these RSS affect amebiasis caused by Entamoeba histolytica, a parasitic protozoan that can be present in the human gastrointestinal tract. This study investigates H2S and Cys-SSH's impact on E. histolytica physiology and explores potential therapeutic implications. Exposing trophozoites to the H2S donor, sodium sulfide (Na2S), or to Cys-SSH led to rapid cytotoxicity. A proteomic analysis of Cys-SSH-challenged trophozoites resulted in the identification of >500 S-sulfurated proteins, which are involved in diverse cellular processes. Functional assessments revealed inhibited protein synthesis, altered cytoskeletal dynamics, and reduced motility in trophozoites treated with Cys-SSH. Notably, cysteine proteases (CPs) were significantly inhibited by S-sulfuration, affecting their bacterial biofilm degradation capacity. Immunofluorescence microscopy confirmed alterations in actin dynamics, corroborating the proteomic findings. Thus, our study reveals how RSS perturbs critical cellular functions in E. histolytica, potentially influencing its pathogenicity and interactions within the gut microbiota. Understanding these molecular mechanisms offers novel insights into amebiasis pathogenesis and unveils potential therapeutic avenues targeting RSS-mediated modifications in parasitic infections.

Regulatory effects of hydrogen sulfide on the female reproductive system

Hydrogen sulfide (H2S), a colorless exhaust gas, has been traditionally considered an air pollutant. However, recent studies have revealed that H2S functions as a novel gas signaling molecule, exerting diverse biological effects on various systems, including the cardiovascular, digestive, and nervous systems. Thus, H2S is involved in various pathophysiological processes. As H2S affects reproductive function, it has potential therapeutic implications in reproductive system diseases. This review examined the role of H2S in various female reproductive organs, including the ovary, fallopian tube, vagina, uterus, and placenta. Additionally, the regulatory function of H2S in the female reproductive system has been discussed to provide useful insights for developing clinical therapeutic strategies for reproductive diseases.

Sulfur signaling pathway in cardiovascular disease

Hydrogen sulfide (H2S) and sulfur dioxide (SO2), recognized as endogenous sulfur-containing gas signaling molecules, were the third and fourth molecules to be identified subsequent to nitric oxide and carbon monoxide (CO), and exerted diverse biological effects on the cardiovascular system. However, the exact mechanisms underlying the actions of H2S and SO2 have remained elusive until now. Recently, novel post-translational modifications known as S-sulfhydration and S-sulfenylation, induced by H2S and SO2 respectively, have been proposed. These modifications involve the chemical alteration of specific cysteine residues in target proteins through S-sulfhydration and S-sulfenylation, respectively. H2S induced S-sulfhydrylation can have a significant impact on various cellular processes such as cell survival, apoptosis, cell proliferation, metabolism, mitochondrial function, endoplasmic reticulum stress, vasodilation, anti-inflammatory response and oxidative stress in the cardiovascular system. Alternatively, S-sulfenylation caused by SO2 serves primarily to maintain vascular homeostasis. Additional research is warranted to explore the physiological function of proteins with specific cysteine sites, despite the considerable advancements in comprehending the role of H2S-induced S-sulfhydration and SO2-induced S-sulfenylation in the cardiovascular system. The primary objective of this review is to present a comprehensive examination of the function and potential mechanism of S-sulfhydration and S-sulfenylation in the cardiovascular system. Proteins that undergo S-sulfhydration and S-sulfenylation may serve as promising targets for therapeutic intervention and drug development in the cardiovascular system. This could potentially expedite the future development and utilization of drugs related to H2S and SO2.

Biosynthesis of meso-lanthionine in Fusobacterium nucleatum

The opportunistic oral pathogen, Fusobacterium nucleatum contains meso-lanthionine as the diaminodicarboxylic acid in the pentapeptide crosslink of the peptidoglycan layer. The diastereomer, l,l-lanthionine is formed by lanthionine synthase, a PLP-dependent enzyme that catalyzes the β-replacement of l-cysteine with a second equivalent of l-cysteine. In this study, we explored possible enzymatic mechanisms for the formation of meso-lanthionine. Our inhibition studies with lanthionine synthase, described herein, revealed that meso-diaminopimelate, a bioisostere of meso-lanthionine, is a more potent inhibitor of lanthionine synthase compared to the diastereomer, l,l-diaminopimelate. These results suggested that lanthionine synthase could also form meso-lanthionine by the β-replacement of l-cysteine with d-cysteine. Through steady-state and pre-steady state kinetic analysis, we confirm that d-cysteine reacts with the ⍺-aminoacylate intermediate with a k_on that was 2-3-fold faster and K_d value that was 2-3fold lower compared to l-cysteine. However, given that intracellular levels of d-cysteine levels are assumed to be significantly lower than that of l-cysteine, we also determined if the gene product, FN1732, with low sequence identity to diaminopimelate epimerase could convert l,l-lanthionine to meso-lanthionine. Using diaminopimelate dehydrogenase in a coupled spectrophotometric assay, we show that FN1732 can convert l,l-lanthionine to meso-lanthionine with a k_cat of 0.07 ± 0.001 s^-1 and a K_M of 1.9 ± 0.1 mM. In summary, our results provide two possible enzymatic mechanisms for the biosynthesis of meso-lanthionine in F. nucleatum.

Roles of Fe-C amendment on sulfate-containing pharmaceutical wastewater anaerobic treatment: Microbial community and sulfur metabolism

The effects of multiple two-phase anaerobic treatment involving acidification coupling Fe-C on sulfate-containing chemical synthesis-based pharmaceutical wastewater treatment were investigated. Fe-C was added as a filler with 25% vol. to acidogenic reactors for semi-continuous operation. The results suggested that Fe-C amendment promoted sulfate removal efficiency by 47.5% and shortened the reaction time by 50% in the acidogenic phase. With mitigation of sulfate inhibition, SCOD removal efficiency and methane production were further increased by 24.6% and 398% compared to direct raw wastewater anaerobic digestion, respectively, in methanogenic phase. The results of sulfate removal kinetics confirmed a 150% increase of removal rate in acidogenic phase. However, the apparent kinetic microbial sulfate removal constant without Fe-C amendment was maintained at approximately 0.06 h^-1. The Fe-C amendment not only increased the relative abundance of Methanothrix and Desulfovibrio for sulfate reduction but also enriched unclassified_p__Chloroflexi and unclassified_c__Deltaproteobacteria for acidification. Metagenomic results indicated that Fe-C enhanced dissimilatory sulfate reduction and PAPS synthesis of assimilatory step. The hydrogen sulfide production through the 3-mercaptopyruvate to pyruvate pathways was also enhanced. Butyrate-oxidizing genes were increased synchronously to convert butyrate to acetate.

Oxidative Post-Translational Modifications: A Focus on Cysteine S-Sulfhydration and the Regulation of Endothelial Fitness

Significance: Changes in the oxidative balance can affect cellular physiology and adaptation through redox signaling. The endothelial cells that line blood vessels are particularly sensitive to reactive oxygen species, which can alter cell function by a number of mechanisms, including the oxidative post-translational modification (oxPTM) of proteins on critical cysteine thiols. Such modifications can act as redox-switches to alter the function of targeted proteins. Recent Advances: Mapping the cysteine oxPTM proteome and characterizing the effects of individual oxPTMs to gain insight into consequences for cellular responses has proven challenging. A recent addition to the list of reversible oxPTMs that contributes to cellular redox homeostasis is persulfidation or S-sulfhydration. Critical Issues: It has been estimated that up to 25% of proteins are S-sulfhydrated, making this modification almost as abundant as phosphorylation. In the endothelium, persulfides are generated by the trans-sulfuration pathway that catabolizes cysteine and cystathionine to generate hydrogen sulfide (H₂S) and H₂S-related sulfane sulfur compounds (H₂S_n). This pathway is of particular importance for the vascular system, as the enzyme cystathionine γ lyase (CSE) in endothelial cells accounts for a significant portion of total vascular H₂S/H₂S_n production. Future Directions: Impaired CSE activity in endothelial dysfunction has been linked with marked changes in the endothelial cell S-sulfhydrome and can contribute to the development of atherosclerosis and hypertension. It will be interesting to determine how changes in the S-sulfhydration of specific networks of proteins contribute to endothelial cell physiology and pathophysiology. Antioxid. Redox Signal. 35, 1494-1514.

The hepatic compensatory response to elevated systemic sulfide promotes diabetes

Impaired hepatic glucose and lipid metabolism are hallmarks of type 2 diabetes. Increased sulfide production or sulfide donor compounds may beneficially regulate hepatic metabolism. Disposal of sulfide through the sulfide oxidation pathway (SOP) is critical for maintaining sulfide within a safe physiological range. We show that mice lacking the liver- enriched mitochondrial SOP enzyme thiosulfate sulfurtransferase (Tst-/- mice) exhibit high circulating sulfide, increased gluconeogenesis, hypertriglyceridemia, and fatty liver. Unexpectedly, hepatic sulfide levels are normal in Tst-/- mice because of exaggerated induction of sulfide disposal, with associated suppression of global protein persulfidation and nuclear respiratory factor 2 target protein levels. Hepatic proteomic and persulfidomic profiles converge on gluconeogenesis and lipid metabolism, revealing a selective deficit in medium-chain fatty acid oxidation in Tst-/- mice. We reveal a critical role of TST in hepatic metabolism that has implications for sulfide donor strategies in the context of metabolic disease.

Biosynthesis, Quantification and Genetic Diseases of the Smallest Signaling Thiol Metabolite: Hydrogen Sulfide

Hydrogen sulfide (H2S) is a gasotransmitter and the smallest signaling thiol metabolite with important roles in human health. The turnover of H2S in humans is mainly governed by enzymes of sulfur amino acid metabolism and also by the microbiome. As is the case with other small signaling molecules, disease-promoting effects of H2S largely depend on its concentration and compartmentalization. Genetic defects that impair the biogenesis and catabolism of H2S have been described; however, a gap in knowledge remains concerning physiological steady-state concentrations of H2S and their direct clinical implications. The small size and considerable reactivity of H2S renders its quantification in biological samples an experimental challenge. A compilation of methods currently employed to quantify H2S in biological specimens is provided in this review. Substantial discrepancy exists in the concentrations of H2S determined by different techniques. Available methodologies permit end-point measurement of H2S concentration, yet no definitive protocol exists for the continuous, real-time measurement of H2S produced by its enzymatic sources. We present a summary of available animal models, monogenic diseases that impair H2S metabolism in humans including structure-function relationships of pathogenic mutations, and discuss possible approaches to overcome current limitations of study.

A Fold Type II PLP-Dependent Enzyme from Fusobacterium nucleatum Functions as a Serine Synthase and Cysteine Synthase

Serine synthase (SS) from Fusobacterium nucleatum is a fold type II pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes the β-replacement of l-cysteine with water to form l-serine and H₂S. Herein, we show that SS can also function as a cysteine synthase, catalyzing the β-replacement of l-serine with bisulfide to produce l-cysteine and H₂O. The forward (serine synthase) and reverse (cysteine synthase) reactions occur with comparable turnover numbers and catalytic efficiencies for the amino acid substrate. Reaction of SS with l-cysteine leads to transient formation of a quinonoid species, suggesting that deprotonation of the Cα and β-elimination of the thiolate group from l-cysteine occur via a stepwise mechanism. In contrast, the quinonoid species was not detected in the formation of the α-aminoacrylate intermediate following reaction of SS with l-serine. A key active site residue, D232, was shown to stabilize the more chemically reactive ketoenamine PLP tautomer and also function as an acid/base catalyst in the forward and reverse reactions. Fluorescence resonance energy transfer between PLP and W99, the enzyme's only tryptophan residue, supports ligand-induced closure of the active site, which shields the PLP cofactor from the solvent and increases the basicity of D232. These results provide new insight into amino acid metabolism in F. nucleatum and highlight the multiple catalytic roles of D232 in a new member of the fold type II family of PLP-dependent enzymes.

Hydrogen sulfide and vascular regulation - An update

BACKGROUND

Hydrogen sulfide (H₂S) is considered to be the third gasotransmitter after carbon monoxide (CO) and nitric oxide (NO). It plays an important role in the regulation of vascular homeostasis. Vascular remodeling have has proved to be related to the impaired H₂S generation.

AIM OF REVIEW

This study aimed to summarize and discuss current data about the function of H₂S in vascular physiology and pathophysiology as well as the underlying mechanisms.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Endogenous hydrogen sulfide (H₂S) as a third gasotransmitter is primarily generated by the enzymatic pathways and regulated by several metabolic pathways. H₂S as a physiologic vascular regulator, inhibits proliferation, regulates its apoptosis and autophagy of vascular cells and controls the vascular tone. Accumulating evidence shows that the downregulation of H₂S pathway is involved in the pathogenesis of a variety of vascular diseases, such as hypertension, atherosclerosis and pulmonary hypertension. Alternatively, H₂S supplementation may greatly help to prevent the progression of the vascular diseases by regulating vascular tone, inhibiting vascular inflammation, protecting against oxidative stress and proliferation, and modulating vascular cell apoptosis, which has been verified in animal and cell experiments and even in the clinical investigation. Besides, H₂S system and angiotensin-converting enzyme (ACE) inhibitors play a vital role in alleviating ischemic heart disease and left ventricular dysfunction. Notably, sulfhydryl-containing ACEI inhibitor zofenopril is superior to other ACE inhibitors due to its capability of H₂S releasing, in addition to ACE inhibition. The design and application of novel H₂S donors have significant clinical implications in the treatment of vascular-related diseases. However, further research regarding the role of H₂S in vascular physiology and pathophysiology is required.

Roles of Hydrogen Sulfide Donors in Common Kidney Diseases

Hydrogen sulfide (H2S) plays a key role in the regulation of physiological processes in mammals. The decline in H2S level has been reported in numerous renal disorders. In animal models of renal disorders, treatment with H2S donors could restore H2S levels and improve renal functions. H2S donors suppress renal dysfunction by regulating autophagy, apoptosis, oxidative stress, and inflammation through multiple signaling pathways, such as TRL4/NLRP3, AMP-activated protein kinase/mammalian target of rapamycin, transforming growth factor-β1/Smad3, extracellular signal-regulated protein kinases 1/2, mitogen-activated protein kinase, and nuclear factor kappa B. In this review, we summarize recent developments in the effects of H2S donors on the treatment of common renal diseases, including acute/chronic kidney disease, renal fibrosis, unilateral ureteral obstruction, glomerulosclerosis, diabetic nephropathy, hyperhomocysteinemia, drug-induced nephrotoxicity, metal-induced nephrotoxicity, and urolithiasis. Novel H2S donors can be designed and applied in the treatment of common renal diseases.

S224 Presents a Catalytic Trade-off in PLP-Dependent l-Lanthionine Synthase from Fusobacterium nucleatum

Lanthionine synthase from the oral bacterium Fusobacterium nucleatum is a fold type II pyridoxal-5'-phosphate (PLP)-dependent enzyme that catalyzes the β-replacement of l-cysteine by a second molecule of l-cysteine to form H₂S and l-lanthionine. The meso-isomer of the latter product is incorporated into the F. nucleatum peptidoglycan layer. Herein, we investigated the catalytic role of S224, which engages in hydrogen-bond contact with the terminal carboxylate of l-lanthionine in the closed conformation of the enzyme. Unexpectedly, the S224A variant elicited a 7-fold increase in the turnover rate for H₂S and lanthionine formation and a 70-fold faster rate constant for the formation of the α-aminoacrylate intermediate compared to the wild-type enzyme. Presteady state kinetic analysis further showed that the reaction between S224A and l-cysteine leads to the formation of the more reactive ketoenamine tautomer of the α-aminoacrylate. The α-aminoacrylate with the protonated Schiff base is not an observable intermediate in the analogous reaction with the wild type, which may account for its attenuated kinetic properties. However, the S224A substitution is detrimental to other aspects of the catalytic cycle; it facilitates the α,β-elimination of l-lanthionine, and it weakens the enzyme's catalytic preference for the formation of l-lanthionine over that of l-cystathionine.

Pathogenic variants in SQOR encoding sulfide:quinone oxidoreductase are a potentially treatable cause of Leigh disease

Hydrogen sulfide, a signaling molecule formed mainly from cysteine, is catabolized by sulfide:quinone oxidoreductase (gene SQOR). Toxic hydrogen sulfide exposure inhibits complex IV. We describe children of two families with pathogenic variants in SQOR. Exome sequencing identified variants; SQOR enzyme activity was measured spectrophotometrically, protein levels evaluated by western blotting, and mitochondrial function was assayed. In family A, following a brief illness, a 4-year-old girl presented comatose with lactic acidosis and multiorgan failure. After stabilization, she remained comatose, hypotonic, had neurostorming episodes, elevated lactate, and Leigh-like lesions on brain imaging. She died shortly after. Her 8-year-old sister presented with a rapidly fatal episode of coma with lactic acidosis, and lesions in the basal ganglia and left cortex. Muscle and liver tissue had isolated decreased complex IV activity, but normal complex IV protein levels and complex formation. Both patients were homozygous for c.637G > A, which we identified as a founder mutation in the Lehrerleut Hutterite with a carrier frequency of 1 in 13. The resulting p.Glu213Lys change disrupts hydrogen bonding with neighboring residues, resulting in severely reduced SQOR protein and enzyme activity, whereas sulfide generating enzyme levels were unchanged. In family B, a boy had episodes of encephalopathy and basal ganglia lesions. He was homozygous for c.446delT and had severely reduced fibroblast SQOR enzyme activity and protein levels. SQOR dysfunction can result in hydrogen sulfide accumulation, which, consistent with its known toxicity, inhibits complex IV resulting in energy failure. In conclusion, SQOR deficiency represents a new, potentially treatable, cause of Leigh disease.

Hydrogen Sulfide and Endoplasmic Reticulum Stress: A Potential Therapeutic Target for Central Nervous System Degeneration Diseases

There are three members of the endogenous gas transmitter family. The first two are nitric oxide and carbon monoxide, and the third newly added member is hydrogen sulfide (H₂S). They all have similar functions: relaxing blood vessels, smoothing muscles, and getting involved in the regulation of neuronal excitation, learning, and memory. The cystathionine β-synthase (CBS), 3-mercaptopyruvate sulfur transferase acts together with cysteine aminotransferase (3-MST/CAT), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfur transferase with D-amino acid oxidase (3-MST/DAO) pathways are involved in the enzymatic production of H₂S. More and more researches focus on the role of H₂S in the central nervous system (CNS), and H₂S plays a significant function in neuroprotection processes, regulating the function of the nervous system as a signaling molecule in the CNS. Endoplasmic reticulum stress (ERS) and protein misfolding in its mechanism are related to neurodegenerative diseases. H₂S exhibits a wide variety of cytoprotective and physiological functions in the CNS degenerative diseases by regulating ERS. This review summarized on the neuroprotective effect of H₂S for ERS played in several CNS diseases including Alzheimer’s disease, Parkinson’s disease, and depression disorder, and discussed the corresponding possible signaling pathways or mechanisms as well.

Folic Acid Protects Rat Cerebellum Against Oxidative Damage Caused by Homocysteine: the Expression of Bcl-2, Bax, and Caspase-3 Apoptotic Genes

There is evidence that oxidative stress involves in homocysteine-induced pathogenesis. Considering the antioxidative properties of folic acid and its involvement as a cofactor for methionine synthase (MS) in the homocysteine-methionine cycle, the aim of this study was to evaluate the mechanism associated with homocysteine-induced toxicity and its prevention with folic acid supplementation. Male rat pups were divided into four groups including control, homocysteine (Hcy), Hcy + folic acid and folic acid groups. The Hcy group received Hcy 0.3-0.6 μmol/g body weight, while Hcy + folic acid group received folic acid orally as 0.011 μmol/g body weight along with Hcy on a postnatal day (PD) 4 until 25. The reduced and oxidized glutathione (GSH and GSSG) levels, GSH/GSSG ratio, protein carbonyl content, cystathionine β synthase (CBS), and MS activities in the cerebellum were measured 25 days after birth. Levels of malondialdehyde (MDA), marker of lipid peroxidation were measured. Also, Bcl2, Bax, and caspase-3 expression levels were measured by real-time quantitative PCR. Furthermore, caspase-3 protein level assay was performed by the ELISA test. Results indicated that Hcy administration could promote both lipid and protein oxidation, which was associated with increased amounts of caspase-3 mRNA and protein levels and Bax mRNA expression level in this group. Cerebellar MS, CBS enzyme activity, GSH, GSSG, and GSH/GSH ratio did not change following Hcy administration. Folic acid significantly reduced MDA level, protein carbonyl content, Bax, the caspase-3 mRNA, and protein expression levels in the cerebellum of Hcy-treated group. Moreover, cerebellar MS, CBS enzyme activity, GSH, and GSH/GSH ratio increased following folic acid treatment. We conclude that Hcy might cause apoptosis in the cerebellum. We suggest that folic acid, in addition of having antioxidant properties, can protect cerebellum against homocysteine-mediated neurotoxicity via modulating the expression of proteins that are contributed in regulation of apoptosis in the rat's cerebellum.

Mitochondria Inspire a Lifestyle

Tucked inside our cells, we animals (and plants, and fungi) carry mitochondria, minuscule descendants of bacteria that invaded our common ancestor 2 billion years ago. This unplanned breakthrough endowed our ancestors with a convenient, portable source of energy, enabling them to progress towards more ambitious forms of life. Mitochondria still manufacture most of our energy; we have evolved to invest it to grow and produce offspring, and to last long enough to make it all happen. Yet because the continuous generation of energy is inevitably linked to that of toxic free radicals, mitochondria give us life and give us death. Stripping away clutter and minutiae, here we present a big-picture perspective of how mitochondria work, how they are passed on virtually only by mothers, and how they shape the lifestyles of species and individuals. We discuss why restricting food prolongs lifespan, why reproducing shortens it, and why moving about protects us from free radicals despite increasing their production. We show that our immune cells use special mitochondria to keep control over our gut microbes. And we lay out how the fabrication of energy and free radicals sets the internal clocks that command our everyday rhythms-waking, eating, sleeping. Mitochondria run the show.

Thiosulfate sulfurtransferase-like domain-containing 1 protein interacts with thioredoxin

Rhodanese domains are structural modules present in the sulfurtransferase superfamily. These domains can exist as single units, in tandem repeats, or fused to domains with other activities. Despite their prevalence across species, the specific physiological roles of most sulfurtransferases are not known. Mammalian rhodanese and mercaptopyruvate sulfurtransferase are perhaps the best-studied members of this protein superfamily and are involved in hydrogen sulfide metabolism. The relatively unstudied human thiosulfate sulfurtransferase-like domain-containing 1 (TSTD1) protein, a single-domain cytoplasmic sulfurtransferase, was also postulated to play a role in the sulfide oxidation pathway using thiosulfate to form glutathione persulfide, for subsequent processing in the mitochondrial matrix. Prior kinetic analysis of TSTD1 was performed at pH 9.2, raising questions about relevance and the proposed model for TSTD1 function. In this study, we report a 1.04 Å resolution crystal structure of human TSTD1, which displays an exposed active site that is distinct from that of rhodanese and mercaptopyruvate sulfurtransferase. Kinetic studies with a combination of sulfur donors and acceptors reveal that TSTD1 exhibits a low Km for thioredoxin as a sulfane sulfur acceptor and that it utilizes thiosulfate inefficiently as a sulfur donor. The active site exposure and its interaction with thioredoxin suggest that TSTD1 might play a role in sulfide-based signaling. The apical localization of TSTD1 in human colonic crypts, which interfaces with sulfide-releasing microbes, and the overexpression of TSTD1 in colon cancer provide potentially intriguing clues as to its role in sulfide metabolism.

BigR is a sulfide sensor that regulates a sulfur transferase/dioxygenase required for aerobic respiration of plant bacteria under sulfide stress

To cope with toxic levels of H2S, the plant pathogens Xylella fastidiosa and Agrobacterium tumefaciens employ the bigR operon to oxidize H2S into sulfite. The bigR operon is regulated by the transcriptional repressor BigR and it encodes a bifunctional sulfur transferase (ST) and sulfur dioxygenase (SDO) enzyme, Blh, required for H2S oxidation and bacterial growth under hypoxia. However, how Blh operates to enhance bacterial survival under hypoxia and how BigR is deactivated to derepress operon transcription is unknown. Here, we show that the ST and SDO activities of Blh are in vitro coupled and necessary to oxidize sulfide into sulfite, and that Blh is critical to maintain the oxygen flux during A. tumefaciens respiration when oxygen becomes limited to cells. We also show that H2S and polysulfides inactivate BigR leading to operon transcription. Moreover, we show that sulfite, which is produced by Blh in the ST and SDO reactions, is toxic to Citrus sinensis and that X. fastidiosa-infected plants accumulate sulfite and higher transcript levels of sulfite detoxification enzymes, suggesting that they are under sulfite stress. These results indicate that BigR acts as a sulfide sensor in the H2S oxidation mechanism that allows pathogens to colonize plant tissues where oxygen is a limiting factor.

Hydrogen sulfide attenuates homocysteine-induced cognitive deficits and neurochemical alterations by improving endogenous hydrogen sulfide levels

Hyperomocysteinemia (HHcy) has been associated with mild cognitive impairment and dementia. Hydrogen sulfide (H₂ S) has been suggested to be an endogenous modulator of neuronal functions. However, the effect and mechanisms involved in beneficial effect of H₂ S has not been investigated in homocysteine (Hcy)-induced cognitive deficits. This study has been designed to evaluate the effect of exogenous H₂ S on behavioral deficits and neurochemical alterations in HHcy animals. Hcy levels were significantly elevated in plasma, cortex, and hippocampus of Hcy administered animals. A progressive decline in memory functions and increased anxiolytic behavior was observed in HHcy animals. This was accompanied by decrease in endogenous H₂ S levels along with decreased activity of cystathionase (CSE) and cystathionine β-synthase (CBS). However, a significant increase in CSE and CBS mRNAs was observed. In addition, the catecholamine and serotonin levels were reduced and the activity of monoamine oxidase A and B were increased in brain regions of HHcy animals. Haematoxylin and eosin staining revealed higher number of pyknotic cells in brain regions of HHcy animals. H₂ S administration was found to lower elevated plasma and brain Hcy levels. The activities of CBS, CSE, and levels of H₂ S were restored in HHcy animals administered H₂ S. Exogenous H₂ S also ameliorated behavioral deficits accompanied by significant increase in catecholamines. Histological analysis revealed normal cell morphology in Hcy-treated animals supplemented with H₂ S. These results clearly demonstrate that the protective effect of H₂ S on Hcy-induced cognitive deficits is mediated through increased catecholamine and H₂ S levels thereby suggesting its beneficial role in preventing HHcy-induced neurodegeneration. © 2016 BioFactors, 43(3):434-450, 2017.

Molecular Cloning and Characterization of a (Lys)6-Tagged Sulfide-Reactive Hemoglobin I from Lucina pectinata

A poly-Lys tag was fused to the Lucina pectinata hemoglobin I (HbI) coding sequence and purified using an efficient and fast process. HbI is a hemeprotein that binds hydrogen sulfide (H2S) with high affinity and it has been used to understand physiologically relevant reactions of this signaling molecule. The (Lys)6-tagged rHbI construct was expressed in E. coli and purified by immobilization on a cation exchange matrix, followed by size-exclusion chromatography. The identity, structure, and function of the (Lys)6-tagged rHbI were assessed by mass spectrometry, small and wide X-ray scattering, optical spectroscopy, and kinetic analysis. The scattering and spectroscopic results showed that the (Lys)6-tagged rHbI is structurally and functionally analogous to the native protein as well as to the (His)6-tagged rHbI. Kinetics studies with H2S indicated that the association (k on) and dissociation (k off) rate constants were 1.4 × 10(5)/M/s and 0.1 × 10(-3)/s, respectively. This results confirmed that the (Lys)6-tagged rHbI binds H2S with the same high affinity as its homologue.

Emerging role of hydrogen sulfide-microRNA crosstalk in cardiovascular diseases

Despite an obnoxious smell and toxicity at a high dose, hydrogen sulfide (H2S) is emerging as a cardioprotective gasotransmitter. H2S mitigates pathological cardiac remodeling by regulating several cellular processes including fibrosis, hypertrophy, apoptosis, and inflammation. These encouraging findings in rodents led to initiation of a clinical trial using a H2S donor in heart failure patients. However, the underlying molecular mechanisms by which H2S mitigates cardiac remodeling are not completely understood. Empirical evidence suggest that H2S may regulate signaling pathways either by directly influencing a gene in the cascade or interacting with nitric oxide (another cardioprotective gasotransmitter) or both. Recent studies revealed that H2S may ameliorate cardiac dysfunction by up- or downregulating specific microRNAs. MicroRNAs are noncoding, conserved, regulatory RNAs that modulate gene expression mostly by translational inhibition and are emerging as a therapeutic target for cardiovascular disease (CVD). Few microRNAs also regulate H2S biosynthesis. The inter-regulation of microRNAs and H2S opens a new avenue for exploring the H2S-microRNA crosstalk in CVD. This review embodies regulatory mechanisms that maintain the physiological level of H2S, exogenous H2S donors used for increasing the tissue levels of H2S, H2S-mediated regulation of CVD, H2S-microRNAs crosstalk in relation to the pathophysiology of heart disease, clinical trials on H2S, and future perspectives for H2S as a therapeutic agent for heart failure.

Transient Kinetic Analysis of Hydrogen Sulfide Oxidation Catalyzed by Human Sulfide Quinone Oxidoreductase

The first step in the mitochondrial sulfide oxidation pathway is catalyzed by sulfide quinone oxidoreductase (SQR), which belongs to the family of flavoprotein disulfide oxidoreductases. During the catalytic cycle, the flavin cofactor is intermittently reduced by sulfide and oxidized by ubiquinone, linking H2S oxidation to the electron transfer chain and to energy metabolism. Human SQR can use multiple thiophilic acceptors, including sulfide, sulfite, and glutathione, to form as products, hydrodisulfide, thiosulfate, and glutathione persulfide, respectively. In this study, we have used transient kinetics to examine the mechanism of the flavin reductive half-reaction and have determined the redox potential of the bound flavin to be -123 ± 7 mV. We observe formation of an unusually intense charge-transfer (CT) complex when the enzyme is exposed to sulfide and unexpectedly, when it is exposed to sulfite. In the canonical reaction, sulfide serves as the sulfur donor and sulfite serves as the acceptor, forming thiosulfate. We show that thiosulfate is also formed when sulfide is added to the sulfite-induced CT intermediate, representing a new mechanism for thiosulfate formation. The CT complex is formed at a kinetically competent rate by reaction with sulfide but not with sulfite. Our study indicates that sulfide addition to the active site disulfide is preferred under normal turnover conditions. However, under pathological conditions when sulfite concentrations are high, sulfite could compete with sulfide for addition to the active site disulfide, leading to attenuation of SQR activity and to an alternate route for thiosulfate formation.

Polymorphic Variants of Human Rhodanese Exhibit Differences in Thermal Stability and Sulfur Transfer Kinetics

Rhodanese is a component of the mitochondrial H2S oxidation pathway. Rhodanese catalyzes the transfer of sulfane sulfur from glutathione persulfide (GSSH) to sulfite generating thiosulfate and from thiosulfate to cyanide generating thiocyanate. Two polymorphic variations have been identified in the rhodanese coding sequence in the French Caucasian population. The first, 306A→C, has an allelic frequency of 1% and results in an E102D substitution in the encoded protein. The second polymorphism, 853C→G, has an allelic frequency of 5% and leads to a P285A substitution. In this study, we have examined differences in the stability between wild-type rhodanese and the E102D and P285A variants and in the kinetics of the sulfur transfer reactions. The Asp-102 and Ala-285 variants are more stable than wild-type rhodanese and exhibit kcat/Km,CN values that are 17- and 1.6-fold higher, respectively. All three rhodanese forms preferentially catalyze sulfur transfer from GSSH to sulfite, generating thiosulfate and glutathione. The kcat/Km,sulfite values for the variants in the sulfur transfer reaction from GSSH to sulfite were 1.6- (Asp-102) and 4-fold (Ala-285) lower than for wild-type rhodanese, whereas the kcat/Km,GSSH values were similar for all three enzymes. Thiosulfate-dependent H2S production in murine liver lysate is low, consistent with a role for rhodanese in sulfide oxidation. Our studies show that polymorphic variations that are distant from the active site differentially modulate the sulfurtransferase activity of human rhodanese to cyanide versus sulfite and might be important in differences in susceptibility to diseases where rhodanese dysfunction has been implicated, e.g. inflammatory bowel diseases.