Cyanide Insensitive Oxidase Confers Hydrogen Sulfide and Nitric Oxide Tolerance to Aerobic Respiration.

Hydrogen sulfide (HS) and nitric oxide (NO) are long-known inhibitors of terminal oxidases in the respiratory chain. Yet, they exert pivotal signaling roles in physiological processes, and in several bacterial pathogens have been reported to confer resistance against oxidative stress, host immune responses, and antibiotics. , an opportunistic pathogen causing life-threatening infections that are difficult to eradicate, has a highly branched respiratory chain including four terminal oxidases of the haem-copper type (, , , and ) and one oxidase of the -type (cyanide-insensitive oxidase, CIO).

Hydrogen sulfide production does not affect antibiotic resistance in .

Hydrogen sulfide (HS) has been proposed to protect bacteria from antibiotics, pointing to HS-producing enzymes as possible targets for the development of antibiotic adjuvants. Here, MIC assays performed with mutants producing altered HS levels demonstrate that HS does not affect antibiotic resistance in this bacterium. Moreover, correlation analyses in a large collection of cystic fibrosis isolates argue against the protective role of HS from antibiotic activity during chronic lung infection.

Human Cystathionine γ-Lyase Is Inhibited by -Nitrosation: A New Crosstalk Mechanism between NO and HS.

The 'gasotransmitters' hydrogen sulfide (HS), nitric oxide (NO), and carbon monoxide (CO) act as second messengers in human physiology, mediating signal transduction via interaction with or chemical modification of protein targets, thereby regulating processes such as neurotransmission, blood flow, immunomodulation, or energy metabolism. Due to their broad reactivity and potential toxicity, the biosynthesis and breakdown of HS, NO, and CO are tightly regulated. Growing evidence highlights the active role of gasotransmitters in their mutual cross-regulation.

The multifaceted roles of sulfane sulfur species in cancer-associated processes.

Sulfane sulfur species comprise a variety of biologically relevant hydrogen sulfide (HS)-derived species, including per- and poly-sulfidated low molecular weight compounds and proteins. A growing body of evidence suggests that HS, currently recognized as a key signaling molecule in human physiology and pathophysiology, plays an important role in cancer biology by modulating cell bioenergetics and contributing to metabolic reprogramming. This is accomplished through functional modulation of target proteins via HS binding to heme iron centers or HS-mediated reversible per- or poly-sulfidation of specific cysteine residues.

Nitric Oxide Does Not Inhibit but Is Metabolized by the Cytochrome - Supercomplex.

Nitric oxide (NO) is a well-known active site ligand and inhibitor of respiratory terminal oxidases. Here, we investigated the interaction of NO with a purified chimeric - supercomplex composed of cytochrome and -type terminal oxidase. Strikingly, we found that the enzyme in turnover with O and reductants is resistant to inhibition by the ligand, being able to metabolize NO at 25 °C with an apparent turnover number as high as ≈303 mol NO (mol enzyme) min at 30 µM NO.

Bacterial Oxidases of the Cytochrome Family: Redox Enzymes of Unique Structure, Function, and Utility As Drug Targets.

Cytochrome is a ubiquinol:oxygen oxidoreductase of many prokaryotic respiratory chains with a unique structure and functional characteristics. Its primary role is to couple the reduction of molecular oxygen, even at submicromolar concentrations, to water with the generation of a proton motive force used for adenosine triphosphate production. Cytochrome is found in many bacterial pathogens and, surprisingly, in bacteria formally denoted as anaerobes.

Hydrogen Sulfide Metabolism and Signaling in the Tumor Microenvironment.

Hydrogen sulfide (HS), while historically perceived merely as a toxicant, has progressively emerged as a key regulator of numerous processes in mammalian physiology, exerting its signaling function essentially through interaction with and/or modification of proteins, targeting mainly cysteine residues and metal centers. As a gaseous signaling molecule that freely diffuses across aqueous and hydrophobic biological milieu, it has been designated the third 'gasotransmitter' in mammalian physiology. HS is synthesized and detoxified by specialized endogenous enzymes that operate under a tight regulation, ensuring homeostatic levels of this otherwise toxic molecule.

In the respiratory chain of Escherichia coli cytochromes bd-I and bd-II are more sensitive to carbon monoxide inhibition than cytochrome bo.

Bacteria can not only encounter carbon monoxide (CO) in their habitats but also produce the gas endogenously. Bacterial respiratory oxidases, thus, represent possible targets for CO. Accordingly, host macrophages were proposed to produce CO and release it into the surrounding microenvironment to sense viable bacteria through a mechanism that in Escherichia (E.

-Acetylcysteine Serves as Substrate of 3-Mercaptopyruvate Sulfurtransferase and Stimulates Sulfide Metabolism in Colon Cancer Cells.

Hydrogen sulfide (HS) is an endogenously produced signaling molecule. The enzymes 3-mercaptopyruvate sulfurtransferase (MST), partly localized in mitochondria, and the inner mitochondrial membrane-associated sulfide:quinone oxidoreductase (SQR), besides being respectively involved in the synthesis and catabolism of HS, generate sulfane sulfur species such as persulfides and polysulfides, currently recognized as mediating some of the HS biological effects. Reprogramming of HS metabolism was reported to support cellular proliferation and energy metabolism in cancer cells.

Hydrogen Sulfide Oxidation: Adaptive Changes in Mitochondria of SW480 Colorectal Cancer Cells upon Exposure to Hypoxia.

Hydrogen sulfide (HS), a known inhibitor of cytochrome oxidase (CcOX), plays a key signaling role in human (patho)physiology. HS is synthesized endogenously and mainly metabolized by a mitochondrial sulfide-oxidizing pathway including sulfide:quinone oxidoreductase (SQR), whereby HS-derived electrons are injected into the respiratory chain stimulating O consumption and ATP synthesis. Under hypoxic conditions, HS has higher stability and is synthesized at higher levels with protective effects for the cell.

Screening Pyridine Derivatives against Human Hydrogen Sulfide-synthesizing Enzymes by Orthogonal Methods.

Biosynthesis of hydrogen sulfide (HS), a key signalling molecule in human (patho)physiology, is mostly accomplished by the human enzymes cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (MST). Several lines of evidence have shown a close correlation between increased HS production and human diseases, such as several cancer types and amyotrophic lateral sclerosis. Identifying compounds selectively and potently inhibiting the human HS-synthesizing enzymes may therefore prove beneficial for pharmacological applications.

Substrate-induced conformational change in cytochrome P450 OleP.

The regulation of cytochrome P450 activity is often achieved by structural transitions induced by substrate binding. We describe the conformational transition experienced upon binding by the P450 OleP, an epoxygenase involved in oleandomycin biosynthesis. OleP bound to the substrate analog 6DEB crystallized in 2 forms: one with an ensemble of open and closed conformations in the asymmetric unit and another with only the closed conformation.

Hydrogen Sulfide Biochemistry and Interplay with Other Gaseous Mediators in Mammalian Physiology.

Hydrogen sulfide (HS) has emerged as a relevant signaling molecule in physiology, taking its seat as a bona fide gasotransmitter akin to nitric oxide (NO) and carbon monoxide (CO). After being merely regarded as a toxic poisonous molecule, it is now recognized that mammalian cells are equipped with sophisticated enzymatic systems for HS production and breakdown. The signaling role of HS is mainly related to its ability to modify different protein targets, particularly by promoting persulfidation of protein cysteine residues and by interacting with metal centers, mostly hemes.

The presence of glutamate residues on the PAS sequence of the stimuli-sensitive nano-ferritin improves in vivo biodistribution and mitoxantrone encapsulation homogeneity.

A genetically engineered human ferritin heavy chain (HFt)-based construct has been recently shown by our group to efficiently entrap and deliver doxorubicin to cancer cells. This construct, named HFt-MP-PAS, contained a tumor-selective sequence (MP) responsive to proteolytic cleavage by tumor proteases (MMPs), located between each HFt subunit and an outer shielding polypeptide sequence rich in proline (P), serine (S) and alanine (A) residues (PAS). HFt-MP-PAS displayed excellent therapeutic efficacy in xenogenic pancreatic and head and neck cancer models in vivo, leading to a significant increase in overall animal survivals.

Nitrosative stress defences of the enterohepatic pathogenic bacterium Helicobacter pullorum.

Helicobacter pullorum is an avian bacterium that causes gastroenteritis, intestinal bowel and hepatobiliary diseases in humans. Although H. pullorum has been shown to activate the mammalian innate immunity with release of nitric oxide (NO), the proteins that afford protection against NO and reactive nitrogen species (RNS) remain unknown.

Cytochrome bd and Gaseous Ligands in Bacterial Physiology.

Cytochrome bd is a unique prokaryotic respiratory terminal oxidase that does not belong to the extensively investigated family of haem-copper oxidases (HCOs). The enzyme catalyses the four-electron reduction of O to 2HO, using quinols as physiological reducing substrates. The reaction is electrogenic and cytochrome bd therefore sustains bacterial energy metabolism by contributing to maintain the transmembrane proton motive force required for ATP synthesis.

A Clinically Relevant Variant of the Human Hydrogen Sulfide-Synthesizing Enzyme Cystathionine -Synthase: Increased CO Reactivity as a Novel Molecular Mechanism of Pathogenicity?

The human disease classical homocystinuria results from mutations in the gene encoding the pyridoxal 5'-phosphate- (PLP-) dependent cystathionine -synthase (CBS), a key enzyme in the transsulfuration pathway that controls homocysteine levels, and is a major source of the signaling molecule hydrogen sulfide (HS). CBS activity, contributing to cellular redox homeostasis, is positively regulated by S-adenosyl-L-methionine (AdoMet) but fully inhibited upon CO or NO• binding to a noncatalytic heme moiety. Despite extensive studies, the molecular basis of several pathogenic mutations is not yet fully understood.

Bioenergetic relevance of hydrogen sulfide and the interplay between gasotransmitters at human cystathionine β-synthase.

Merely considered as a toxic gas in the past, hydrogen sulfide (H2S) is currently viewed as the third 'gasotransmitter' in addition to nitric oxide (NO) and carbon monoxide (CO), playing a key signalling role in human (patho)physiology. H2S can either act as a substrate or, similarly to CO and NO, an inhibitor of mitochondrial respiration, in the latter case by targeting cytochrome c oxidase (CcOX). The impact of H(2)S on mitochondrial energy metabolism crucially depends on the bioavailability of this gaseous molecule and its interplay with the other two gasotransmitters.

The Terminal Oxidase Cytochrome bd Promotes Sulfide-resistant Bacterial Respiration and Growth.

Hydrogen sulfide (H2S) impairs mitochondrial respiration by potently inhibiting the heme-copper cytochrome c oxidase. Since many prokaryotes, including Escherichia (E.) coli, generate H2S and encounter high H2S levels particularly in the human gut, herein we tested whether bacteria can sustain sulfide-resistant O2-dependent respiration.

Evidence for Detrimental Cross Interactions between Reactive Oxygen and Nitrogen Species in Leber's Hereditary Optic Neuropathy Cells.

Here we have collected evidence suggesting that chronic changes in the NO homeostasis and the rise of reactive oxygen species bioavailability can contribute to cell dysfunction in Leber's hereditary optic neuropathy (LHON) patients. We report that peripheral blood mononuclear cells (PBMCs), derived from a female LHON patient with bilateral reduced vision and carrying the pathogenic mutation 11778/ND4, display increased levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS), as revealed by flow cytometry, fluorometric measurements of nitrite/nitrate, and 3-nitrotyrosine immunodetection. Moreover, viability assays with the tetrazolium dye MTT showed that lymphoblasts from the same patient are more sensitive to prolonged NO exposure, leading to cell death.

Antioxidant defence systems in the protozoan pathogen Giardia intestinalis.

The microaerophilic protist Giardia intestinalis is the causative agent of giardiasis, one of the most common intestinal infectious diseases worldwide. The pathogen lacks not only respiratory terminal oxidases (being amitochondriate), but also several conventional antioxidant enzymes, including catalase, superoxide dismutase and glutathione peroxidase. In spite of this, since living attached to the mucosa of the proximal small intestine, the parasite should rely on an efficient antioxidant system to survive the oxidative and nitrosative stress conditions found in this tract of the human gut.

S-Adenosyl-l-methionine Modulates CO and NO• Binding to the Human H2S-generating Enzyme Cystathionine β-Synthase.

Cystathionine β-synthase (CBS) is a key enzyme in human (patho)physiology with a central role in hydrogen sulfide metabolism. The enzyme is composed of a pyridoxal 5'-phosphate-binding catalytic domain, flanked by the following two domains: a heme-binding N-terminal domain and a regulatory C-terminal domain binding S-adenosyl-l-methionine (AdoMet). CO or NO(•) binding at the ferrous heme negatively modulates the enzyme activity.

Superoxide reductase from Giardia intestinalis: structural characterization of the first SOR from a eukaryotic organism shows an iron centre that is highly sensitive to photoreduction.

Superoxide reductase (SOR), which is commonly found in prokaryotic organisms, affords protection from oxidative stress by reducing the superoxide anion to hydrogen peroxide. The reaction is catalyzed at the iron centre, which is highly conserved among the prokaryotic SORs structurally characterized to date. Reported here is the first structure of an SOR from a eukaryotic organism, the protozoan parasite Giardia intestinalis (GiSOR), which was solved at 2.

Antigiardial activity of novel triazolyl-quinolone-based chalcone derivatives: when oxygen makes the difference.

Giardiasis is a common diarrheal disease worldwide caused by the protozoan parasite Giardia intestinalis. It is urgent to develop novel drugs to treat giardiasis, due to increasing clinical resistance to the gold standard drug metronidazole (MTZ). New potential antiparasitic compounds are usually tested for their killing efficacy against G.

Cytochrome bd from Escherichia coli catalyzes peroxynitrite decomposition.

Cytochrome bd is a prokaryotic respiratory quinol oxidase phylogenetically unrelated to heme-copper oxidases, that was found to promote virulence in some bacterial pathogens. Cytochrome bd from Escherichia coli was previously reported to contribute not only to proton motive force generation, but also to bacterial resistance to nitric oxide (NO) and hydrogen peroxide (H2O2). Here, we investigated the interaction of the purified enzyme with peroxynitrite (ONOO(-)), another harmful reactive species produced by the host to kill invading microorganisms.