Role of oxidants in microbial pathophysiology

The impact of inducing germination of Bacillus anthracis and Bacillus thuringiensis spores on potential secondary decontamination strategies

AIMS

Decontamination and remediation of a site contaminated by the accidental or intentional release of fully virulent Bacillus anthracis spores are difficult, costly and potentially damaging to the environment. Development of novel decontamination strategies that have minimal environmental impacts remains a high priority. Although ungerminated spores are amongst the most resilient organisms known, once exposed to germinants, the germinating spores, in some cases, become susceptible to antimicrobial environments. We evaluated the concept that once germinated, B. anthracis spores would be less hazardous and significantly easier to remediate than ungerminated dormant spores.

METHODS AND RESULTS

Through in vitro germination and sensitivity assays, we demonstrated that upon germination, B. anthracis Ames spores and Bacillus thuringiensis Al Hakam spores (serving as a surrogate for B. anthracis) become susceptible to environmental stressors. The majority of these germinated B. anthracis and B. thuringiensis spores were nonviable after exposure to a defined minimal germination-inducing solution for prolonged periods of time. Additionally, we examined the impact of potential secondary disinfectant strategies including bleach, hydrogen peroxide, formaldehyde and artificial UV-A, UV-B and UV-C radiation, employed after a 60-min germination-induction step. Each secondary disinfectant employs a unique mechanism of killing; as a result, germination-induction strategies are better suited for some secondary disinfectants than others.

CONCLUSIONS

These results provide evidence that the deployment of an optimal combination strategy of germination-induction/secondary disinfection may be a promising aspect of wide-area decontamination following a B. anthracis contamination event.

SIGNIFICANCE AND IMPACT OF THE STUDY

By inducing spores to germinate, our data confirm that the resulting cells exhibit sensitivities that can be leveraged when paired with certain decontamination measures. This increased susceptibility could be exploited to devise more efficient and safe decontamination measures and may obviate the need for more stringent methods that are currently in place.

MRP8/14 induces autophagy to eliminate intracellular Mycobacterium bovis BCG

OBJECTIVE

To explore the role of myeloid-related protein 8/14 in mycobacterial infection.

METHODS

The mRNA and protein expression levels of MRP8 or MRP14 were measured by real-time PCR and flow cytometry, respectively. Role of MRP8/14 was tested by overexpression or RNA interference assays. Flow cytometry and colony forming unit were used to test the phagocytosis and the survival of intracellular Mycobacterium bovis BCG (BCG), respectively. Autophagy mediated by MRP8/14 was detected by Western blot and immunofluorescence. The colocalization of BCG phagosomes with autophagosomes or lysosomes was by detected by confocal microscopy. ROS production was detected by flow cytometry.

RESULTS

MRP8/14 expressions were up-regulated in human monocytic THP1 cells and primary macrophages after mycobacterial challenge. Silencing of MRP8/14 suppressed bacterial killing, but had no influence on the phagocytosis of BCG. Importantly, silencing MRP8/14 decreased autophagy and BCG phagosome maturation in THP1-derived macrophages, thereby increasing the BCG survival. Additionally, we demonstrated that MRP8/14 promoted autophagy in a ROS-dependent manner.

CONCLUSIONS

The present study revealed a novel role of MRP8/14 in the autophagy-mediated elimination of intracellular BCG by promoting ROS generation, which may provide a promising therapeutic target for tuberculosis and other intracellular bacterial infectious diseases.

IscR regulation of capsular polysaccharide biosynthesis and iron-acquisition systems in Klebsiella pneumoniae CG43

IscR, an Fe–S cluster-containing transcriptional factor, regulates genes involved in various cellular processes. In response to environmental stimuli such as oxidative stress and iron levels, IscR switches between its holo and apo forms to regulate various targets. IscR binding sequences are classified into two types: the type 1 IscR box that is specific for holo-IscR binding, and the type 2 IscR box that binds holo- and apo-IscR. Studying Klebsiella pneumoniae CG43S3, we have previously shown that iron availability regulates capsular polysaccharide (CPS) biosynthesis and iron-acquisition systems. The present study investigated whether IscR is involved in this regulation. Compared with that in CG43S3, the amount of CPS was decreased in AP001 (ΔiscR) or AP002 (iscR_3CA), a CG43S3-derived strain expressing mutated IscR mimicked apo-IscR, suggesting that only holo-IscR activates CPS biosynthesis. Furthermore, a promoter-reporter assay verified that the transcription of cps genes was reduced in AP001 and AP002. Purified IscR::His₆, but not IscR_3CA::His₆, was also found to bind the predicted type 1 IscR box specifically in the cps promoter. Furthermore, reduced siderophore production was observed in AP004 (Δfur-ΔiscR) but not in AP005 (Δfur-iscR_3CA), implying that apo-IscR activates iron acquisition. Compared with those in AP004, mRNA levels of three putative iron acquisition systems (fhu, iuc, and sit) were increased in AP005, and both purified IscR::His₆ and IscR_3CA::His₆ bound the predicted type 2 IscR box in the fhuA, iucA, and sitA promoters, whereas IscR_3CA::His₆ displayed a lower affinity. Finally, we analyzed the effect of external iron levels on iscR expression. The transcription of iscR was increased under iron-depleted conditions as well as in AP001 and AP002, suggesting an auto-repression exerted by apo-IscR. Our results show that in K. pneumoniae, IscR plays a dual role in the regulation of CPS biosynthesis and iron-acquisition systems in response to environmental iron availability.

Impact of Acinetobacter baumannii superoxide dismutase on motility, virulence, oxidative stress resistance and susceptibility to antibiotics

Acinetobacter baumannii is a Gram-negative bacterium appearing as an opportunistic pathogen in hospital settings. Superoxide dismutase (SOD) contributes to virulence in several pathogenic bacteria by detoxifying reactive oxygen species released in the course of host defense reactions. However, the biological role of SODs in A. baumannii has not yet been elucidated. Here, we inactivated in A. baumannii ATCC 17978 gene A1S_2343, encoding a putative SOD of the Fe-Mn type by transposon insertion, resulting in mutant ATCC 17978 sod2343::Km. The mutation was also introduced in two naturally competent A. baumannii isolates by transformation with chromosomal DNA derived from mutant ATCC 17978 sod2343::Km. We demonstrate that inactivation of sod2343 leads to significant motility defects in all three A. baumannii strains. The mutant strains were more susceptible to oxidative stress compared to their parental strains. Susceptibility to colistin and tetracycline was increased in all mutant strains while susceptibility of the mutants to gentamicin, levofloxacin and imipenem was strain-dependent. In the Galleria mellonella infection model the mutant strains were significantly attenuated. In conclusion, sod2343 plays an important role in motility, resistance to oxidative stress, susceptibility to antibiotics and virulence in A. baumannii.

Role of microRNAs in the immunity process of the flat oyster Ostrea edulis against bonamiosis

MicroRNAs (miRNAs) are small (∼22nt) non-coding regulatory single strand RNA molecules that reduce stability and/or translation of sequence-complementary target. miRNAs are a key component of gene regulatory networks and have been involved in a wide variety of biological processes, such as signal transduction, cell proliferation and apoptosis. Many miRNAs are broadly conserved among the animal lineages and even between invertebrates and vertebrates. The European flat oyster Ostrea edulis is highly susceptible to infection with Bonamia ostreae, an intracellular parasite able to survive and proliferate within oyster haemocytes. Mollusc haemocytes play a key role in the immune response of molluscs as main cellular effectors. The roles of miRNAs in the immune response of O. edulis to bonamiosis were analysed using a commercial microarray platform (miRCURY LNA™ v2, Exiqon) for miRNAs. Expression of miRNAs in haemocytes from oysters with different bonamiosis intensity was compared. Differential expression was detected in 63 and 76 miRNAs when comparing heavily-affected with non-affected oysters and with lightly-affected ones, respectively. Among them, 19 miRNAs are known to be linked to immune response, being responsible of proliferation and activation of macrophages, inflammation, apoptosis and/or oxidative damage, which is consistent with the modulation of their expression in oyster haemocytes due to bonamiosis.

The recA operon: A novel stress response gene cluster in Bacteroides fragilis

Bacteroides fragilis, an opportunistic pathogen of humans, is a leading cause of bacteraemias and anaerobic abscesses which are often treated with metronidazole, a drug which damages DNA. This study investigated the responses of the B. fragilis recA three gene operon to the stress experienced during metronidazole treatment and exposure to reactive oxygen species simulating those generated by the host immune system during infection. A transcriptionally regulated response was observed using quantitative RT-PCR after metronidazole and hydrogen peroxide treatment, with all three genes being upregulated under stress conditions. In vivo and in vitro analysis of the functional role of the second gene of the operon was done using heterologous complementation and protein expression (in Escherichia coli), with subsequent biochemical assay. This gene encoded a functional bacterioferritin co-migratory protein (BCP) which was thiol-specific and had antioxidant properties, including protection of the glutamine synthetase III enzyme. This in vitro data supports the hypothesis that the genes of the operon may be involved in protection of the bacteria from the oxidative burst during tissue invasion and may play a significant role in bacterial survival and metronidazole resistance during treatment of B. fragilis infections.

Antifungal and antihepatotoxic effects of sepia ink extract against oxidative stress as a risk factor of invasive pulmonary aspergillosis in neutropenic mice

BACKGROUND

There is a great need for novel strategies to overcome the high mortality associated with invasive pulmonary aspergillosis (IPA) in immunocompromised patients. To evaluate the antifungal and antihepatotoxic potentials of Sepia ink extract, its effect on liver oxidative stress levels was analyzed against IPA in neutropenic mice using amphotercin B as a reference drug.

MATERIALS AND METHODS

Eighty neutropenic infected mice were randomly assigned into four main groups. The 1(st) group was treated with saline, neutropenic infected (NI), the 2(nd) group was treated with ink extract (200 mg/kg) (IE) and the 3(rd) group was treated with amphotericin B (150 mg/kg) (AMB) and 4(th) group was treated with IE plus AMB. Treatment was started at 24 h after fungal inoculation (1×10(9) conidia/ml).

RESULTS

The present study revealed good in vitro and in vivo antifungal activity of IE against A. fumigatus. IE significantly reduced hepatic fungal burden and returns liver function and histology to normal levels. Compared with the untreated infected group, mice in the IE, AMB, and IE+ AMB groups had increased glutathione reduced (GSH) and superoxide dismutase (SOD) and significantly reduced malondialdehyde (MDA) levels at 24 and 72 h after inoculation with A. fumigatus conidia.

CONCLUSION

It is then concluded that in combination with antifungal therapy (AMB), IE treatment can reduce hepatic fungal burden, alleviate hepatic granulomatous lesions and oxidative stress associated with IPA in neutropenic mice.

Antibacterial responses of retinal Müller glia: production of antimicrobial peptides, oxidative burst and phagocytosis

BACKGROUND

We have previously shown that, in response to microbial infection, activated Müller glia secrete inflammatory cytokines/chemokines and exhibit antimicrobial properties. The aim of this study is to understand the mechanisms and the key components involved in this response.

METHODS

Immortalized human retinal Müller glia (MIO-M1 cells) were challenged with Staphylococcus (S) aureus, the leading cause of severe intraocular infection followed by RT2 profile PCR array analysis. The expression of human β-defensin 1 (HBD1), 2 (HBD2), 3 (HBD3), hepcidine and cathelicidin LL37 was checked by RT-PCR and quantified by Taqman qPCR. The expression of AMPs was confirmed at protein level by dot-blot analysis. The production of ROS was measured by dicholoro-dihydro-fluorescein diacetate (DCFH-DA) staining by flow cytometry as well as fluorescence microscopy. The level of nitric oxide (NO) was measured by measuring a stable metabolite, nitrite using the Griess reagent. In vitro killing assay was performed by Live/Dead BacLight staining as well as by dilution plating in suspension and adherent conditions following S. aureus infection. Phagocytosis was measured by CFU enumeration following infection.

RESULTS

PCR array data showed that, in comparison to uninfected control cells, bacterial challenge significantly (> two-fold) induced the expression of 26 genes involved in cytokine/chemokine, antimicrobials, Toll-like receptor, apoptotic, and NF-κB signaling. RT-PCR analysis showed time-dependent increased expression of HBD1, HBD2, HBD3, LL-37, and hepcidin mRNA in bacteria-challenged Müller glia. The expression of these antimicrobial molecules was also increased at the protein level in the culture supernatant, as detected by dot-blot analysis. Additionally, the bacteria-stimulated Müller glia were found to produce reactive oxygen (ROS) and reactive nitrogen (RNS) species. In vitro, killing assays revealed that Müller glia exhibited bactericidal activity against S. aureus in both adherent and suspension cultures. Furthermore, our data demonstrated that Müller glia can phagocytize and kill the bacteria in a time-dependent manner.

CONCLUSIONS

These data suggest that retinal Müller glia behave like classical innate immune cells by producing a variety of antimicrobial molecules in response to bacterial challenge, suggesting their pivotal role in retinal innate defense.

IscR is a global regulator essential for pathogenesis of Vibrio vulnificus and induced by host cells

A mutant that exhibited less cytotoxic activity toward INT-407 human intestinal epithelial cells than the wild type was screened from a random transposon mutant library of Vibrio vulnificus, and an open reading frame encoding an Fe-S cluster regulator, IscR, was identified using a transposon-tagging method. A mutational analysis demonstrated that IscR contributes to mouse mortality as well as cytotoxicity toward the INT-407 cells, indicating that IscR is essential for the pathogenesis of V. vulnificus. A whole-genome microarray analysis revealed that IscR influenced the expression of 67 genes, of which 52 were upregulated and 15 were downregulated. Among these, 12 genes most likely involved in motility and adhesion to host cells, hemolytic activity, and survival under oxidative stress of the pathogen during infection were selected and experimentally verified to be upregulated by IscR. Accordingly, the disruption of iscR resulted in a significant reduction in motility and adhesion to INT-407 cells, in hemolytic activity, and in resistance to reactive oxygen species (ROS) such as H2O2 and tert-butyl hydroperoxide (t-BOOH). Furthermore, the present study demonstrated that iscR expression was induced by exposure of V. vulnificus to the INT-407 cells, and the induction appeared to be mediated by ROS generated by the host cells during infection. Consequently, the combined results indicated that IscR is a global regulator that contributes to the overall success in the pathogenesis of V. vulnificus by regulating the expression of various virulence and survival genes in addition to Fe-S cluster genes.

The physiological role of reversible methionine oxidation

Sulfur-containing amino acids such as cysteine and methionine are particularly vulnerable to oxidation. Oxidation of cysteine and methionine in their free amino acid form renders them unavailable for metabolic processes while their oxidation in the protein-bound state is a common post-translational modification in all organisms and usually alters the function of the protein. In the majority of cases, oxidation causes inactivation of proteins. Yet, an increasing number of examples have been described where reversible cysteine oxidation is part of a sophisticated mechanism to control protein function based on the redox state of the protein. While for methionine the dogma is still that its oxidation inhibits protein function, reversible methionine oxidation is now being recognized as a powerful means of triggering protein activity. This mode of regulation involves oxidation of methionine to methionine sulfoxide leading to activated protein function, and inactivation is accomplished by reduction of methionine sulfoxide back to methionine catalyzed by methionine sulfoxide reductases. Given the similarity to thiol-based redox-regulation of protein function, methionine oxidation is now established as a novel mode of redox-regulation of protein function. This article is part of a Special Issue entitled: Thiol-Based Redox Processes.

Antioxidant supplementation enhances bacterial peritonitis in mice by inhibiting phagocytosis

Antioxidants are known to exhibit numerous health benefits including anti-ageing, anti-apoptotic and immuno-stimulatory effects. However, we present the data showing counterproductive effects of therapeutically relevant antioxidants on bacterial clearance by the immune system in a murine peritonitic model. The antioxidants ascorbic acid, glutathione and N-acetylcysteine augmented morbidity and mortality in mice carrying Eshcerichia coli-induced acute bacterial peritonitis. Treatment of peritonitic mice with antioxidants significantly increased their bacterial load in the range of 0.3-2 logs. Antioxidant administration to peritonitic mice resulted in decreased numbers of macrophages, B-cells and dendritic cells at the primary site of infection and increased neutrophil infiltration. Serum TNF-α levels were also decreased in antioxidant-treated peritonitic mice. In vitro experiments showed that antioxidants reduced the phagocytic efficacy of peritoneal macrophages by ~60-75% and also decreased E. coli-induced oxidative burst in macrophages cells. Taken together, our data indicate that the antioxidants increased the severity of peritonitis by decreasing the phagocytic efficiency, oxidative burst, and TNF-α production, and increasing neutrophil infiltration. Based on these results, we propose that antioxidant supplementation during the course of bacterial infection is not recommended as it could be detrimental for the host. In addition, the present study underlines the importance of timing and context of antioxidant administration rather than indiscriminate usage to gain the best possible therapeutic advantage of these redox compounds.

Photodynamic biofilm inactivation by SAPYR--an exclusive singlet oxygen photosensitizer

Prevention and control of biofilm-growing microorganisms are serious problems in public health due to increasing resistances of some pathogens against antimicrobial drugs and the potential of these microorganisms to cause severe infections in patients. Therefore, alternative approaches that are capable of killing pathogens are needed to supplement standard treatment modalities. One alternative is the photodynamic inactivation of bacteria (PIB). The lethal effect of PIB is based on the principle that visible light activates a photosensitizer, leading to the formation of reactive oxygen species, e.g., singlet oxygen, which induces phototoxicity immediately during illumination. SAPYR is a new generation of photosensitizers. Based on a 7-perinaphthenone structure, it shows a singlet oxygen quantum yield ΦΔ of 99% and is water soluble and photostable. Moreover, it contains a positive charge for good adherence to cell walls of pathogens. In this study, the PIB properties of SAPYR were investigated against monospecies and polyspecies biofilms formed in vitro by oral key pathogens. SAPYR showed a dual mechanism of action against biofilms: (I) it disrupts the structure of the biofilm even without illumination; (II) when irradiated, it inactivates bacteria in a polymicrobial biofilm after one single treatment with an efficacy of ≥ 99.99%. These results encourage further investigation on the potential of PIB using SAPYR for the treatment of localized infectious diseases.

Chrysen-2-ol derivative from West Indian Wood Nettle Laportea aestuans (L.) Chew inhibits oxidation and microbial growth in vitro

Bio-active compounds present in West Indian Wood Nettle Laportea aestuans (L.) Chew (Urticaceae), used in ethno medicine as antioxidant and antimicrobial were studied. The aim of this research work was to isolate and characterize the bio-active compounds in the n-hexane fraction of L. aestuans, determine the toxicity and subject it to in-vitro antimicrobial and free radical scavenging activities. The chemical constituents were isolated by gradient elution column chromatographic technique and Ultra Violet/visible (UV), Infrared (IR) and Nuclear Magnetic Resonance (NMR) spectroscopies were used for structural elucidation. The free radical scavenging activity of the isolate was assessed using three methods; scavenging effect on 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), hydroxyl radical generated from hydrogen peroxide and ferric thiocynate method. Antimicrobial screening was done by agar well diffusion method while toxicity was determined by Brine shrimp lethality test. Structures were proposed for the white crystalline solids isolated; (4E)-3,6-dimethylhep-4-en-3-ol (AB) and 1,2,3,4,4a,4b,5,6,6a,7,8,9,10,10a,10b,11-hexadecahydro-1,1,6a,10b-tetramethyl-7-((E)-4,7-dimethyloct-5-enyl) chrysen-2-ol (AC). Percentage yield of AC was 91.2 and was non-toxic with LC50 (µg/ml) value of 1581233000.0. AC significantly scavenged free radical at 0.0625 mg/ml in the DPPH (64.73 %) and hydrogen peroxide (99.22 %) tests. It also showed 65.23 % inhibition at 1.0 mg/ml in the ferric thiocyanate test. AC also inhibited microbial growth significantly when compared with gentamicin and tioconazole which are antibacterial and antifungal standards respectively. The presence of Chrysen-2-ol derivative in L. aestuans which was non-toxic and possessed significant antimicrobial and antioxidant activities supports its ethno medicinal application.

Protective role of the PG1036-PG1037-PG1038 operon in oxidative stress in Porphyromonas gingivalis W83

As an anaerobe, Porphyromonas gingivalis is significantly affected by the harsh inflammatory environment of the periodontal pocket during initial colonization and active periodontal disease. We reported previously that the repair of oxidative stress-induced DNA damage involving 8-oxo-7,8-dihydroguanine (8-oxoG) may occur by an undescribed mechanism in P. gingivalis. DNA affinity fractionation identified PG1037, a conserved hypothetical protein, among other proteins, that were bound to the 8-oxoG lesion. PG1037 is part of the uvrA-PG1037-pcrA operon in P. gingivalis which is known to be upregulated under H2O2 induced stress. A PCR-based linear transformation method was used to inactivate the uvrA and pcrA genes by allelic exchange mutagenesis. Several attempts to inactivate PG1037 were unsuccessful. Similar to the wild-type when plated on Brucella blood agar, the uvrA and pcrA-defective mutants were black-pigmented and beta-hemolytic. These isogenic mutants also had reduced gingipain activities and were more sensitive to H2O2 and UV irradiation compared to the parent strain. Additionally, glycosylase assays revealed that 8-oxoG repair activities were similar in both wild-type and mutant P. gingivalis strains. Several proteins, some of which are known to have oxidoreducatse activity, were shown to interact with PG1037. The purified recombinant PG1037 protein could protect DNA from H2O2-induced damage. Collectively, these findings suggest that the uvrA-PG1037-pcrA operon may play an important role in hydrogen peroxide stress-induced resistance in P. gingivalis.

Kallistatin modulates immune cells and confers anti-inflammatory response to protect mice from group A streptococcal infection

Group A streptococcus (GAS) infection may cause severe life-threatening diseases, including necrotizing fasciitis and streptococcal toxic shock syndrome. Despite the availability of effective antimicrobial agents, there has been a worldwide increase in the incidence of invasive GAS infection. Kallistatin (KS), originally found to be a tissue kallikrein-binding protein, has recently been shown to possess anti-inflammatory properties. However, its efficacy in microbial infection has not been explored. In this study, we transiently expressed the human KS gene by hydrodynamic injection and investigated its anti-inflammatory and protective effects in mice via air pouch inoculation of GAS. The results showed that KS significantly increased the survival rate of GAS-infected mice. KS treatment reduced local skin damage and bacterial counts compared with those in mice infected with GAS and treated with a control plasmid or saline. While there was a decrease in immune cell infiltration of the local infection site, cell viability and antimicrobial factors such as reactive oxygen species actually increased after KS treatment. The efficiency of intracellular bacterial killing in neutrophils was directly enhanced by KS administration. Several inflammatory cytokines, including tumor necrosis factor alpha, interleukin 1β, and interleukin 6, in local infection sites were reduced by KS. In addition, KS treatment reduced vessel leakage, bacteremia, and liver damage after local infection. Therefore, our study demonstrates that KS provides protection in GAS-infected mice by enhancing bacterial clearance, as well as reducing inflammatory responses and organ damage.

The oxidant scavenging capacity of the oral Mycoplasma salivarium

OBJECTIVE

Mycoplasma salivarium is a human oral potential pathogen that preferentially resides in dental plaques and gingival sulci. It has been suggested that this organism may play an etiological role in inflammatory processes in the oral cavity. The aim of this work was to determine whether M. salivarium possesses a potent oxidant scavenging capacity (OSC).

DESIGN

The OSC of M. salivarium was quantified by a highly sensitive luminal-dependent chemiluminescence assay in the presence of cocktails that induced a constant flux of luminescence resulting from the generation of peroxide, hydroxyl radical (cocktail A) and NO, superoxide and peroxynitrites (cocktail B).

RESULTS

M. salivarium markedly reduced oxidative stress by scavenging both free reactive oxygen and nitrogen species. The OSC of M. salivarium was much higher than that of other Mycoplasma species. Most of M. salivarium OSC was confined to the cytosolic fraction and was markedly increased in the presence of tannic acid, red blood cells or mucin. The cytosolic OSC of M. salivarium was heat stable and not affected by sodium azide or prolonged proteolysis. However, it was markedly decreased upon dialysis, suggesting that the major reducing activity is not enzymatic but rather, a low molecular weight compound(s).

CONCLUSIONS

The ability of M. salivarium to scavenge oxidants may play a role in the survival and pathogenicity of this microorganism. The enhanced OSC of M. salivarium in the presence of tannic acid, red blood cells or mucin might have a significant importance to assess complex interactions with polyphenols from nutrients, salivary proteins and red blood cells extravasated from injured capillaries during infection and inflammation in oral tissues.

Claulansine F suppresses apoptosis induced by sodium nitroprusside in PC12 cells

Reactive oxygen species (ROS) are known to be involved in many neurodegenerative diseases. This study assessed the effect of Claulansine F, a new carbazole isolated from Clausena lansium, on sodium nitroprusside (SNP)-treated rat pheochromocytoma PC12 cells. First, it was found that Claulansine F showed more potential on inhibiting the programmed death of PC12 cells than edaravone by cell viability, morphologic observation, and flow cytometric analysis. Further results also showed that Claulansine F attenuated the production of total intracellular ROS formation and lipid peroxidation in PC12 cells, inhibited the mitochondrial membrane potential (MMP) loss, and prevented the programmed cell death event via the P53/Bcl-2 family pathway. Its protective effect was likely medicated by the hydroxyl radical (·OH) scavenging ability, as it appeared to be not involved in the natural antioxidant system. These results suggested a promising potential for Claulansine F as a ROS scavenger in pathologies, where an oxidative stress is involved.

Identification of Besnoitia besnoiti proteins that showed differences in abundance between tachyzoite and bradyzoite stages by difference gel electrophoresis

Bovine besnoitiosis is a chronic and debilitating disease, caused by the apicomplexan parasite Besnoitia besnoiti. Infection of cattle by B. besnoiti is governed by the tachyzoite stage, which is related to acute infection, and the bradyzoite stage gathered into macroscopic cysts located in subcutaneous tissue in the skin, mucosal membranes and sclera conjunctiva and related to persistence and chronic infection. However, the entire life cycle of this parasite and the molecular mechanisms underlying tachyzoite-to-bradyzoite conversion remain unknown. In this context, a different antigenic pattern has been observed between tachyzoite and bradyzoite extracts. Thus, to identify stage-specific proteins, a difference gel electrophoresis (DIGE) approach was used on tachyzoite and bradyzoite extracts followed by mass spectrometry (MS) analysis. A total of 130 and 132 spots were differentially expressed in bradyzoites and tachyzoites, respectively (average ratio ± 1.5, P<0.05 in t-test). Furthermore, 25 differentially expressed spots were selected and analysed by MALDI-TOF/MS. As a result, 5 up-regulated bradyzoite proteins (GAPDH, ENO1, LDH, SOD and RNA polymerase) and 5 up-regulated tachyzoite proteins (ENO2; LDH; ATP synthase; HSP70 and PDI) were identified. The present results set the basis for the identification of new proteins as drug targets. Moreover, the role of these proteins in tachyzoite-to-bradyzoite conversion and the role of the host cell environment should be a subject of further research.

The globins of Campylobacter jejuni

Campylobacter jejuni is a zoonotic Gram-negative bacterial pathogen that is exposed to reactive nitrogen species, such as nitric oxide, from a variety of sources. To combat the toxic effects of this nitrosative stress, C. jejuni upregulates a small regulon under the control of the transcriptional activator NssR, which positively regulates the expression of a single-domain globin protein (Cgb) and a truncated globin protein (Ctb). Cgb has previously been shown to detoxify nitric oxide, but the role of Ctb remains contentious. As C. jejuni is amenable to genetic manipulation, and its globin proteins are easily expressed and purified, a combination of mutagenesis, complementation, transcriptomics, spectroscopic characterisation and structural analyses has been used to probe the regulation, function and structure of Cgb and Ctb. This ability to study Cgb and Ctb with such a multi-pronged approach is a valuable asset, especially since only a small fraction of known globin proteins have been functionally characterised.

dpr and sod in Streptococcus mutans are involved in coexistence with S. sanguinis, and PerR is associated with resistance to H2O2

Large numbers of bacteria coexist in the oral cavity. Streptococcus sanguinis, one of the major bacteria in dental plaque, produces hydrogen peroxide (H(2)O(2)), which interferes with the growth of other bacteria. Streptococcus mutans, a cariogenic bacterium, can coexist with S. sanguinis in dental plaque, but to do so, it needs a means of detoxifying the H(2)O(2) produced by S. sanguinis. In this study, we investigated the association of three oxidative stress factors, Dpr, superoxide dismutase (SOD), and AhpCF, with the resistance of S. sanguinis to H(2)O(2). The knockout of dpr and sod significantly increased susceptibility to H(2)O(2), while the knockout of ahpCF had no apparent effect on susceptibility. In particular, dpr inactivation resulted in hypersensitivity to H(2)O(2). Next, we sought to identify the factor(s) involved in the regulation of these oxidative stress genes and found that PerR negatively regulated dpr expression. The knockout of perR caused increased dpr expression levels, resulting in low-level susceptibility to H(2)O(2) compared with the wild type. Furthermore, we evaluated the roles of perR, dpr, and sod when S. mutans was cocultured with S. sanguinis. Culturing of the dpr or sod mutant with S. sanguinis showed a significant decrease in the S. mutans population ratio compared with the wild type, while the perR mutant increased the ratio. Our results suggest that dpr and sod in S. mutans are involved in coexistence with S. sanguinis, and PerR is associated with resistance to H(2)O(2) in regulating the expression of Dpr.

Stress Response and Pathogenicity of the Necrotrophic Fungal Pathogen Alternaria alternata

The production of host-selective toxins by the necrotrophic fungus Alternaria alternata is essential for the pathogenesis. A. alternata infection in citrus leaves induces rapid lipid peroxidation, accumulation of hydrogen peroxide (H2O2), and cell death. The mechanisms by which A. alternata avoids killing by reactive oxygen species (ROS) after invasion have begun to be elucidated. The ability to coordinate of signaling pathways is essential for the detoxification of cellular stresses induced by ROS and for pathogenicity in A. alternata. A low level of H2O2, produced by the NADPH oxidase (NOX) complex, modulates ROS resistance and triggers conidiation partially via regulating the redox-responsive regulators (YAP1 and SKN7) and the mitogen-activated protein (MAP) kinase (HOG1) mediated pathways, which subsequently regulate the genes required for the biosynthesis of siderophore, an iron-chelating compound. Siderophore-mediated iron acquisition plays a key role in ROS detoxification because of the requirement of iron for the activities of antioxidants (e.g., catalase and SOD). Fungal strains impaired for the ROS-detoxifying system severely reduce the virulence on susceptible citrus cultivars. This paper summarizes the current state of knowledge of signaling pathways associated with cellular responses to multidrugs, oxidative and osmotic stress, and fungicides, as well as the pathogenicity/virulence in the tangerine pathotype of A. alternata.

A unique feature of iron loss via close adhesion of Helicobacter pylori to host erythrocytes

Iron deficiency anemia is an extra-stomach disease experienced in H. pylori carriers. Individuals with type A blood are more prone to suffering from H. pylori infection than other individuals. To clarify the molecular mechanisms underlying H. pylori-associated anemia, we collected erythrocytes from A, B, O, and AB blood donors and analyzed morphology, the number of erythrocytes with H. pylori colonies attached to them, and iron contents in erythrocytes and H. pylori (NCTC11637 and SS1 strains) by means of optical microscopy, scanning electron microscopy, and synchrotron radiation soft X-ray imaging. The number of type A erythrocytes with H. pylori attached to them was significantly higher than that of other erythrocytes (P<0.05). Far more iron distribution was observed in H. pylori bacteria using dual energy analysis near the iron L2, 3 edges by soft X-ray imaging. Iron content was significantly reduced in host erythrocytes after 4 hours of exposure to H. pylori. H. pylori are able to adhere more strongly to type A erythrocytes, and this is related to iron shift from the host to the bacteria. This may explain the reasons for refractory iron deficiency anemia and elevated susceptibility to H. pylori infection in individuals with type A blood.

17-AAG kills intracellular Leishmania amazonensis while reducing inflammatory responses in infected macrophages

Background

Leishmaniasis is a neglected endemic disease with a broad spectrum of clinical manifestations. Pentavalent antimonials have been the treatment of choice for the past 70 years and, due to the emergence of resistant cases, the efficacy of these drugs has come under scrutiny. Second-line drugs are less efficacious, cause a range of side effects and can be costly. The formulation of new generations of drugs, especially in developing countries, has become mandatory.

Methodology/Principal Findings

We investigated the anti-leishmanial effect of 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), an HSP90 inhibitor, in vitro. This inhibitor is currently in clinical trials for cancer treatment; however, its effects against intracellular Leishmania remain untested. Macrophages infected with L. amazonensis were treated with 17-AAG (25–500 nM) and parasite load was quantified using optical microscopy. Parasite load declined in 17-AAG-treated macrophages in a dose- and time-dependent manner. Intracellular parasite death became irreversible after 4 h of treatment with 17-AAG, and occurred independent of nitric oxide (NO) and superoxide (O₂⁻) production. Additionally, intracellular parasite viability was severely reduced after 48 h of treatment. Interestingly, treatment with 17-AAG reduced pro-inflammatory mediator production, including TNF-α, IL-6 and MCP-1, yet IL-12 remained unaffected. Electron microscopy revealed morphological alterations, such as double-membrane vacuoles and myelin figures at 24 and 48 h after 17-AAG treatment.

Conclusions/Significance

The HSP90 inhibitor, 17-AAG, possesses high potency under low dosage and reduces both pro-inflammatory and oxidative molecule production. Therefore, further studies are warranted to investigate this inhibitor’s potential in the development of new generations of anti-leishmanials.

Distinct characteristics of two 2-Cys peroxiredoxins of Vibrio vulnificus suggesting differential roles in detoxifying oxidative stress

Peroxiredoxins (Prxs) are ubiquitous antioxidant enzymes reducing toxic peroxides. Two distinct 2-Cys Prxs, Prx1 and Prx2, were identified in Vibrio vulnificus, a facultative aerobic pathogen. Both Prxs have two conserved catalytic cysteines, C(P) and C(R), but Prx2 is more homologous in amino acid sequences to eukaryotic Prx than to Prx1. Prx2 utilized thioredoxin A as a reductant, whereas Prx1 required AhpF. Prx2 contained GGIG and FL motifs similar to the motifs conserved in sensitive Prxs and exhibited sensitivity to overoxidation. MS analysis and C(P)-SO(3)H specific immunoblotting demonstrated overoxidation of C(P) to C(P)-SO(2)H (or C(P)-SO(3)H) in vitro and in vivo, respectively. In contrast, Prx1 was robust and C(P) was not overoxidized. Discrete expression of the Prxs implied that Prx2 is induced by trace amounts of H(2)O(2) and thereby residential in cells grown aerobically. In contrast, Prx1 was occasionally expressed only in cells exposed to high levels of H(2)O(2). A mutagenesis study indicated that lack of Prx2 accumulated sufficient H(2)O(2) to induce Prx1. Kinetic properties indicated that Prx2 effectively scavenges low levels of peroxides because of its high affinity to H(2)O(2), whereas Prx1 quickly degrades higher levels of peroxides because of its high turnover rate and more efficient reactivation. This study revealed that the two Prxs are differentially optimized for detoxifying distinct ranges of H(2)O(2), and proposed that Prx2 is a residential scavenger of peroxides endogenously generated, whereas Prx1 is an occasional scavenger of peroxides exogenously encountered. Furthermore, genome sequence database search predicted widespread coexistence of the two Prxs among bacteria.

Green tea polyphenols function as prooxidants to inhibit Pseudomonas aeruginosa and induce the expression of oxidative stress-related genes

Green tea polyphenols (GTP) are widely believed to function as antioxidants and antimicrobial agents. Here we observed that GTP and epigallocatechin gallate, the most abundant catechin in GTP, could also function as prooxidants and produce hydrogen peroxide (H2O2) to inhibit the growth of Pseudomonas aeruginosa. pH value of the medium was the key factor that affected prooxidant versus antioxidant property of GTP. Under weakly acidic conditions (pH 5.5-6.5), GTP showed antioxidant activity by eliminating H2O2; whereas, under neutral and weakly alkaline conditions (pH 7.0-8.0), GTP showed prooxidant activity and inhibited the growth of P. aeruginosa. Furthermore, we studied the effects of GTP on gene expression profiles of a few oxidative stress-related genes by quantitative real-time PCR analysis. After 10 min to 1 h of exposure under weakly alkaline condition, GTP significantly up-regulated expression levels of katB, sodM, ohr, lexA, and recN gene. These findings highlight that the pH-dependent H2O2 production by GTP contributes to the antibacterial activity and can induce oxidative stress-related responses in P. aeruginosa.

Oxidative stress and tryptophan degradation pattern of acute Toxoplasma gondii infection in mice

Toxoplasma gondii is a very common obligate single-cell protozoan parasite which induces overproduction of interferon (IFN)-gamma and of other proinflammatory cytokines. Although immunomodulatory role of IFN-gamma favors tryptophan (Trp) degradation via indoleamine-2,3-dioxygenase (IDO) activity and is related with nitric oxide (NO) synthesis, the mechanism of antitoxoplasma activity is complex. In order to characterize the Trp degradation pattern during the acute T. gondii infection, serum Trp, kynurenine (Kyn), and urinary biopterin levels of mice were measured. The possible oxidative status was evaluated by the liver, spleen, brain, and serum malondialdehyde (MDA) and NO levels. Increased free radical toxicity may cause elevation in tissue MDA in T. gondii-infected mice, while unchanged serum MDA might indicate the increased oxidative stress due to T. gondii infection restricted to intracellular area. Elevated serum NO most probably might be due to the formation of reactive nitrogen radicals. The Kyn/Trp ratio was higher in T. gondii-infected mice compared to healthy animals (p < 0.05); however, it was not correlated with urinary biopterin. These results suggested that Trp degradation might be promoted by a pathway other than IDO during T. gondii infection and the reduction of Trp concentration favors the local immunosuppression and systemic tolerance.

Role of DNA base excision repair in the mutability and virulence of Streptococcus mutans

The oral pathogen, Streptococcus mutans, possesses inducible DNA repair defences for protection against pH fluctuations and production of reactive oxygen metabolites such as hydrogen peroxide (H(2) O(2) ), which are present in the oral cavity. DNA base excision repair (BER) has a critical role in genome maintenance by preventing the accumulation of mutations associated with environmental factors and normal products of cellular metabolism. In this study, we examined the consequences of compromising the DNA glycosylases (Fpg and MutY) and endonucleases (Smx and Smn) of the BER pathway and their relative role in adaptation and virulence. Enzymatic characterization of the BER system showed that it protects the organism against the effects of the highly mutagenic lesion, 7,8-dihydro-8-oxo-2'-deoxyguanine (8-oxo-dG). S. mutans strains lacking a functional Fpg, MutY or Smn showed elevated spontaneous mutation frequencies; and, these mutator phenotypes correlated with the ability of the strains to survive killing by acid and oxidative agents. In addition, in the Galleria mellonella virulence model, strains of S. mutans deficient in Fpg, MutY and Smn showed increased virulence as compared with the parent strain. Our results suggest that, for S. mutans, mutator phenotypes, due to loss of BER enzymes, may confer an advantage to virulence of the organism.

Overexpression of reactive cysteine-containing 2-nitrobenzoate nitroreductase (NbaA) and its mutants alters the sensitivity of Escherichia coli to reactive oxygen species by reprogramming a regulatory network of disulfide-bonded proteins

The effects of redox-sensitive proteins on Escherichia coli were investigated by overexpressing Pseudomonas 2-nitrobenzoate nitroreductase (NbaA) and its mutants. Overexpression of wild-type and mutant NbaA proteins significantly altered the sensitivity of E. coli to antibiotics and reactive oxygen species regardless of the enzyme activity for reduction of 2-nitrobenzoic acid. The overexpressed proteins rendered cells 100-10000-fold more sensitive to superoxide anion (O2(•-))-generating paraquat and 10-100-fold more resistant to H2O2. A significant increase in intracellular levels of O2(•-), but not H2O2, was observed during expression of wild-type and truncated (Δ65-74, Δ193-216, and Δ65-74Δ193-216) NbaA. From two-dimensional nonreducing/reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis and mass spectrometry analyses, 29 abundant proteins in the cytoplasm were identified to form interchain disulfide bonds, when cells were exposed to polymyxin B. Of them, down-regulation and modifications of SodB, KatE, and KatG were strongly associated with elevated cellular O2(•-) levels. Western blotting showed up-regulation of cell death signal sensor, CpxA, and down-regulation of cytoplasmic superoxide dismutase, SodB, with ∼2-fold up-regulation of heterodimeric integration host factor, Ihf. Activity gel assays revealed significant reduction of glyceraldehyde-3-phosphate dehydrogenase with constant levels of 6-phosphogluconate dehydrogenase. These changes would support a high level of NADPH to reduce H2O2-induced disulfide bonds by forced expression of thioredoxin A via thioredoxin reductase. Thus, overexpression of wild-type and truncated NbaA partially compensates for the lack of KatE and KatG to degrade H2O2, thereby enhancing disulfide bond formation in the cytoplasm, and modifies a regulatory network of disulfide-bonded proteins to increase intracellular O2(•-) levels.

Life and death of proteins: a case study of glucose-starved Staphylococcus aureus

The cellular amount of proteins not only depends on synthesis but also on degradation. Here, we expand the understanding of differential protein levels by complementing synthesis data with a proteome-wide, mass spectrometry-based stable isotope labeling with amino acids in cell culture analysis of protein degradation in the human pathogen Staphylococcus aureus during glucose starvation. Monitoring protein stability profiles in a wild type and an isogenic clpP protease mutant revealed that 1) proteolysis mainly affected proteins with vegetative functions, anabolic and selected catabolic enzymes, whereas the expression of TCA cycle and gluconeogenesis enzymes increased; 2) most proteins were prone to aggregation in the clpP mutant; 3) the absence of ClpP correlated with protein denaturation and oxidative stress responses, deregulation of virulence factors and a CodY repression. We suggest that degradation of redundant, inactive proteins disintegrated from functional complexes and thereby amenable to proteolytic attack is a fundamental cellular process in all organisms to regain nutrients and guarantee protein homeostasis.

Modulation of RhoGTPases improves the behavioral phenotype and reverses astrocytic deficits in a mouse model of Rett syndrome

RhoGTPases are crucial molecules in neuronal plasticity and cognition, as confirmed by their role in non-syndromic mental retardation. Activation of brain RhoGTPases by the bacterial cytotoxic necrotizing factor 1 (CNF1) reshapes the actin cytoskeleton and enhances neurotransmission and synaptic plasticity in mouse brains. We evaluated the effects of a single CNF1 intracerebroventricular inoculation in a mouse model of Rett syndrome (RTT), a rare neurodevelopmental disorder and a genetic cause of mental retardation, for which no effective therapy is available. Fully symptomatic MeCP2-308 male mice were evaluated in a battery of tests specifically tailored to detect RTT-related impairments. At the end of behavioral testing, brain sections were immunohistochemically characterized. Magnetic resonance imaging and spectroscopy (MRS) were also applied to assess morphological and metabolic brain changes. The CNF1 administration markedly improved the behavioral phenotype of MeCP2-308 mice. CNF1 also dramatically reversed the evident signs of atrophy in astrocytes of mutant mice and restored wt-like levels of this cell population. A partial rescue of the overexpression of IL-6 cytokine was also observed in RTT brains. CNF1-induced brain metabolic changes detected by MRS analysis involved markers of glial integrity and bioenergetics, and point to improved mitochondria functionality in CNF1-treated mice. These results clearly indicate that modulation of brain RhoGTPases by CNF1 may constitute a totally innovative therapeutic approach for RTT and, possibly, for other disorders associated with mental retardation.

Plant defense mechanisms are activated during biotrophic and necrotrophic development of Colletotricum graminicola in maize

Hemibiotrophic plant pathogens first establish a biotrophic interaction with the host plant and later switch to a destructive necrotrophic lifestyle. Studies of biotrophic pathogens have shown that they actively suppress plant defenses after an initial microbe-associated molecular pattern-triggered activation. In contrast, studies of the hemibiotrophs suggest that they do not suppress plant defenses during the biotrophic phase, indicating that while there are similarities between the biotrophic phase of hemibiotrophs and biotrophic pathogens, the two lifestyles are not analogous. We performed transcriptomic, histological, and biochemical studies of the early events during the infection of maize (Zea mays) with Colletotrichum graminicola, a model pathosystem for the study of hemibiotrophy. Time-course experiments revealed that mRNAs of several defense-related genes, reactive oxygen species, and antimicrobial compounds all begin to accumulate early in the infection process and continue to accumulate during the biotrophic stage. We also discovered the production of maize-derived vesicular bodies containing hydrogen peroxide targeting the fungal hyphae. We describe the fungal respiratory burst during host infection, paralleled by superoxide ion production in specific fungal cells during the transition from biotrophy to a necrotrophic lifestyle. We also identified several novel putative fungal effectors and studied their expression during anthracnose development in maize. Our results demonstrate a strong induction of defense mechanisms occurring in maize cells during C. graminicola infection, even during the biotrophic development of the pathogen. We hypothesize that the switch to necrotrophic growth enables the fungus to evade the effects of the plant immune system and allows for full fungal pathogenicity.

Inactivation of the potent Pseudomonas aeruginosa cytotoxin pyocyanin by airway peroxidases and nitrite

Pyocyanin (1-hydroxy-N-methylphenazine, PCN) is a cytotoxic pigment and virulence factor secreted by the human bacterial pathogen, Pseudomonas aeruginosa. Here, we report that exposure of PCN to airway peroxidases, hydrogen peroxide (H(2)O(2)), and NaNO(2) generates unique mononitrated PCN metabolites (N-PCN) as revealed by HPLC/mass spectrometry analyses. N-PCN, in contrast to PCN, was devoid of antibiotic activity and failed to kill Escherichia coli and Staphylococcus aureus. Furthermore, in contrast to PCN, intratracheal instillation of N-PCN into murine lungs failed to induce a significant inflammatory response. Surprisingly, at a pH of ∼7, N-PCN was more reactive than PCN with respect to NADH oxidation but resulted in a similar magnitude of superoxide production as detected by electron paramagnetic resonance and spin trapping experiments. When incubated with Escherichia coli or lung A549 cells, PCN and N-PCN both led to superoxide formation, but lesser amounts were detected with N-PCN. Our results demonstrate that PCN that has been nitrated by peroxidase/H(2)O(2)/NO(2)(-) systems possesses less cytotoxic/proinflammatory activity than native PCN. Yield of N-PCN was decreased by the presence of the competing physiological peroxidase substrates (thiocyonate) SCN(-) (myeloperoxidase, MPO, and lactoperoxidase, LPO) and Cl(-) (MPO), which with Cl(-) yielded chlorinated PCNs. These reaction products also showed decreased proinflammatory ability when instilled into the lungs of mice. These observations add important insights into the complexity of the pathogenesis of lung injury associated with Pseudomonas aeruginosa infections and provide additional rationale for exploring the efficacy of NO(2)(-) in the therapy of chronic Pseudomonas aeruginosa airway infection in cystic fibrosis.

Hsp33 confers bleach resistance by protecting elongation factor Tu against oxidative degradation in Vibrio cholerae

The redox-regulated chaperone Hsp33 protects bacteria specifically against stress conditions that cause oxidative protein unfolding, such as treatment with bleach or exposure to peroxide at elevated temperatures. To gain insight into the mechanism by which expression of Hsp33 confers resistance to oxidative protein unfolding conditions, we made use of Vibrio cholerae strain O395 lacking the Hsp33 gene hslO. We found that this strain, which is exquisitely bleach-sensitive, displays a temperature-sensitive (ts) phenotype during aerobic growth, implying that V. cholerae suffers from oxidative heat stress when cultivated at 43°C. We utilized this phenotype to select for Escherichia coli genes that rescue the ts phenotype of V. cholerae ΔhslO when overexpressed. We discovered that expression of a single protein, the elongation factor EF-Tu, was sufficient to rescue both the ts and bleach-sensitive phenotypes of V. cholerae ΔhslO. In vivo studies revealed that V. cholerae EF-Tu is highly sensitive to oxidative protein degradation in the absence of Hsp33, indicating that EF-Tu is a vital chaperone substrate of Hsp33 in V. cholerae. These results suggest an 'essential client protein' model for Hsp33's chaperone action in Vibrio in which stabilization of a single oxidative stress-sensitive protein is sufficient to enhance the oxidative stress resistance of the whole organism.

Novel NADPH-cysteine covalent adduct found in the active site of an aldehyde dehydrogenase

PaBADH (Pseudomonas aeruginosa betaine aldehyde dehydrogenase) catalyses the irreversible NAD(P)+-dependent oxidation of betaine aldehyde to its corresponding acid, the osmoprotector glycine betaine. This reaction is involved in the catabolism of choline and in the response of this important pathogen to the osmotic and oxidative stresses prevalent in infection sites. The crystal structure of PaBADH in complex with NADPH showed a novel covalent adduct between the C2N of the pyridine ring and the sulfur atom of the catalytic cysteine residue, Cys286. This kind of adduct has not been reported previously either for a cysteine residue or for a low-molecular-mass thiol. The Michael addition of the cysteine thiolate in the 'resting' conformation to the double bond of the α,β-unsaturated nicotinamide is facilitated by the particular conformation of NADPH in the active site of PaBADH (also observed in the crystal structure of the Cys286Ala mutant) and by an ordered water molecule hydrogen bonded to the carboxamide group. Reversible formation of NAD(P)H-Cys286 adducts in solution causes reversible enzyme inactivation as well as the loss of Cys286 reactivity towards thiol-specific reagents. This novel covalent modification may provide a physiologically relevant regulatory mechanism of the irreversible PaBADH-catalysed reaction, preventing deleterious decreases in the intracellular NAD(P)+/NAD(P)H ratios.