A peptide permease mutant of Mycobacterium bovis BCG resistant to the toxic peptides glutathione and S-nitrosoglutathione

An oligopeptide permease, OppABCD, requires an iron-sulfur cluster domain for functionality

Oligopeptide permease, OppABCD, belongs to the type I ABC transporter family. Its role is to import oligopeptides into bacteria for nutrient uptake and to modulate the host immune response. OppABCD consists of a cluster C substrate-binding protein (SBP), OppA, membrane-spanning OppB and OppC subunits, and an ATPase, OppD, that contains two nucleotide-binding domains (NBDs). Here, using cryo-electron microscopy, we determined the high-resolution structures of Mycobacterium tuberculosis OppABCD in the resting state, oligopeptide-bound pre-translocation state, AMPPNP-bound pre-catalytic intermediate state and ATP-bound catalytic intermediate state. The structures show an assembly of a cluster C SBP with its ABC translocator and a functionally required [4Fe-4S] cluster-binding domain in OppD. Moreover, the ATP-bound OppABCD structure has an outward-occluded conformation, although no substrate was observed in the transmembrane cavity. Here, we reveal an oligopeptide recognition and translocation mechanism of OppABCD, which provides a perspective on how this and other type I ABC importers facilitate bulk substrate transfer across the lipid bilayer.

Unraveling the metabolism of Mycobacterium caprae using comparative genomics

In our laboratory, Mycobacterium caprae has poor growth in standard medium (SM) 7H9-OADC supplemented with pyruvate and Tween-80. Our objectives were to identify mutations affecting M. caprae metabolism and use this information to design a culture medium to improve its growth. We selected 77 M. caprae genomes and sequenced M. caprae NLA000201913 used in our experiments. Mutations present in >95% of the strains compared to Mycobacterium tuberculosis H37Rv were analyzed in silico for their deleterious effects on proteins of metabolic pathways. Apart from the known defect in the pyruvate kinase, M. caprae has important lesions in enzymes of the TCA cycle, methylmalonyl cycle, B₁₂ metabolism, and electron-transport chain. We provide evidence of enzymatic redundancy elimination and epistatic mutations, and possible production of toxic metabolites hindering M. caprae growth in vitro. A newly designed SM supplemented with l-glutamate allowed faster growth and increased final microbial mass of M. caprae. However, possible accumulation of metabolic waste-products and/or nutritional limitations halted M. caprae growth prior to a M. tuberculosis-like stationary phase. Our findings suggest that M. caprae relies on GABA and/or glyoxylate shunts for in vitro growth in routine media. The newly developed medium will improve experiments with this bacterium by allowing faster growth in vitro.

Biophysical analysis of the Mycobacteria tuberculosis peptide binding protein DppA reveals a stringent peptide binding pocket

The peptide binding protein DppA is an ABC transporter found in prokaryotes that has the potential to be used as drug delivery tool for hybrid antibiotic compounds. Understanding the motifs and structures that bind to DppA is critical to the development of these bivalent compounds. This study focused on the biophysical analysis of the MtDppA from M. tuberculosis. Analysis of the crystal structure revealed a SVA tripeptide was co-crystallized with the protein. Further peptide analysis demonstrated MtDppA shows very little affinity for dipeptides but rather preferentially binds to peptides that are 3-4 amino acids in length. The structure-activity relationships (SAR) between MtDppA and tripeptides with varied amino acid substitutions were evaluated using thermal shift, SPR, and molecular dynamics simulations. Efforts to identify novel ligands for use as alternative scaffolds through the thermal shift screening of 35,000 compounds against MtDppA were unsuccessful, indicating that the MtDppA binding pocket is highly specialized for uptake of peptides. Future development of compounds that seek to utilize MtDppA as a drug delivery mechanism, will likely require a tri- or tetrapeptide component with a hydrophobic -non-acidic peptide sequence.

Augmentation of the Riboflavin-Biosynthetic Pathway Enhances Mucosa-Associated Invariant T (MAIT) Cell Activation and Diminishes Mycobacterium tuberculosis Virulence

Mucosa-associated invariant T (MAIT) cells play a critical role in antimicrobial defense. Despite increased understanding of their mycobacterial ligands and the clinical association of MAIT cells with tuberculosis (TB), their function in protection against Mycobacterium tuberculosis infection remains unclear. Here, we show that overexpressing key genes of the riboflavin-biosynthetic pathway potentiates MAIT cell activation and results in attenuation of M. tuberculosis virulence in vivo. Further, we observed greater control of M. tuberculosis infection in MAIT^hi CAST/EiJ mice than in MAIT^lo C57BL/6J mice, highlighting the protective role of MAIT cells against TB. We also endogenously adjuvanted Mycobacterium bovis BCG with MR1 ligands via overexpression of the lumazine synthase gene ribH and evaluated its protective efficacy in the mouse model of M. tuberculosis infection. Altogether, our findings demonstrate that MAIT cells confer host protection against TB and that overexpression of genes in the riboflavin-biosynthetic pathway attenuates M. tuberculosis virulence. Enhancing MAIT cell-mediated immunity may also offer a novel approach toward improved vaccines against TB. IMPORTANCE Mucosa-associated invariant T (MAIT) cells are an important subset of innate lymphocytes that recognize microbial ligands derived from the riboflavin biosynthesis pathway and mediate antimicrobial immune responses. Modulated MAIT cell responses have been noted in different forms of tuberculosis. However, it has been unclear if increased MAIT cell abundance is protective against TB disease. In this study, we show that augmentation of the mycobacterial MAIT cell ligands leads to higher MAIT cell activation with reduced M. tuberculosis virulence and that elevated MAIT cell abundance confers greater control of M. tuberculosis infection. Our study also highlights the potential of endogenously adjuvanting the traditional BCG vaccine with MR1 ligands to augment MAIT cell activation. This study increases current knowledge on the roles of the riboflavin-biosynthetic pathway and MAIT cell activation in M. tuberculosis virulence and host immunity against TB.

Peptide transporter-related protein 2 plays an important role in glutathione transport of Streptococcus thermophilus

Streptococcus thermophilus is widely used as a starter culture in the fermentation of yogurt. Glutathione (GSH; γ-glutamyl-cysteinyl-glycine), as a tripeptide, has an important physiological role for Strep. thermophilus. However, the scope of the GSH transport proteins is still unexplored in this species. In the present study, 5 peptide transporter-related proteins (Ptrp) of Strep. thermophilus strain ST-1 were selected and then inactivated by gene insertion, respectively. Through detection and comparison of intracellular GSH content of mutant strain and wild strain, we identified 2 proteins, named Ptrp-2 and Ptrp-4, that might be related to GSH transport. Reverse-transcriptase quantitative PCR was performed to verify the gene expressions of these 2 possible GSH transport-related proteins, and it was finally determined that Ptrp-2 plays an important role in GSH transport of Strep. thermophilus. Milk fermentation experiments were further conducted to test the effect of Ptrp-2 on the characteristics of yogurt. The results showed that the fermented milk hardly curds using the mutant strain, indicating that Ptrp-2 is important for Strep. thermophilus as a yogurt starter.

Glutathione Supplementation as an Adjunctive Therapy in COVID-19

Morbidity and mortality of coronavirus disease 2019 (COVID-19) are due in large part to severe cytokine storm and hypercoagulable state brought on by dysregulated host-inflammatory immune response, ultimately leading to multi-organ failure. Exacerbated oxidative stress caused by increased levels of interleukin (IL)-6 and tumor necrosis factor α (TNF-α) along with decreased levels of interferon α and interferon β (IFN-α, IFN-β) are mainly believed to drive the disease process. Based on the evidence attesting to the ability of glutathione (GSH) to inhibit viral replication and decrease levels of IL-6 in human immunodeficiency virus (HIV) and tuberculosis (TB) patients, as well as beneficial effects of GSH on other pulmonary diseases processes, we believe the use of liposomal GSH could be beneficial in COVID-19 patients. This review discusses the epidemiology, transmission, and clinical presentation of COVID-19 with a focus on its pathogenesis and the possible use of liposomal GSH as an adjunctive treatment to the current treatment modalities in COVID-19 patients.

ATP-binding cassette (ABC) import systems of Mycobacterium tuberculosis: target for drug and vaccine development

Nutrient procurement specifically from nutrient-limiting environment is essential for pathogenic bacteria to survive and/or persist within the host. Long-term survival or persistent infection is one of the main reasons for the overuse of antibiotics, and contributes to the development and spread of antibiotic resistance. Mycobacterium tuberculosis is known for long-term survival within the host, and develops multidrug resistance. Before and during infection, the pathogen encounters various harsh environmental conditions. To cope up with such nutrient-limiting conditions, it is crucial to uptake essential nutrients such as ions, sugars, amino acids, peptides, and metals, necessary for numerous vital biological activities. Among the various types of transporters, ATP-binding cassette (ABC) importers are essentially unique to bacteria, accessible as drug targets without penetrating the cytoplasmic membrane, and offer an ATP-dependent gateway into the cell by mimicking substrates of the importer and designing inhibitors against substrate-binding proteins, ABC importers endeavour for the development of successful drug candidates and antibiotics. Alternatively, the production of antibodies against substrate-binding proteins could lead to vaccine development. In this review, we will emphasize the role of M. tuberculosis ABC importers for survival and virulence within the host. Furthermore, we will elucidate their unique characteristics to discover emerging therapies to combat tuberculosis.

Defining the Environmental Adaptations of Genus Devosia: Insights into its Expansive Short Peptide Transport System and Positively Selected Genes

Devosia are well known for their dominance in soil habitats contaminated with various toxins and are best characterized for their bioremediation potential. In this study, we compared the genomes of 27 strains of Devosia with aim to understand their metabolic abilities. The analysis revealed their adaptive gene repertoire which was bared from 52% unique pan-gene content. A striking feature of all genomes was the abundance of oligo- and di-peptide permeases (oppABCDF and dppABCDF) with each genome harboring an average of 60.7 ± 19.1 and 36.5 ± 10.6 operon associated genes respectively. Apart from their primary role in nutrition, these permeases may help Devosia to sense environmental signals and in chemotaxis at stressed habitats. Through sequence similarity network analyses, we identified 29 Opp and 19 Dpp sequences that shared very little homology with any other sequence suggesting an expansive short peptidic transport system within Devosia. The substrate determining components of these permeases viz. OppA and DppA further displayed a large diversity that separated into 12 and 9 homologous clusters respectively in addition to large number of isolated nodes. We also dissected the genome scale positive evolution and found genes associated with growth (exopolyphosphatase, HesB_IscA_SufA family protein), detoxification (moeB, nifU-like domain protein, alpha/beta hydrolase), chemotaxis (cheB, luxR) and stress response (phoQ, uspA, luxR, sufE) were positively selected. The study highlights the genomic plasticity of the Devosia spp. for conferring adaptation, bioremediation and the potential to utilize a wide range of substrates. The widespread toxin-antitoxin loci and ‘open’ state of the pangenome provided evidence of plastic genomes and a much larger genetic repertoire of the genus which is yet uncovered.

The prominent alteration in transcriptome and metabolome of Mycobacterium bovis BCG str. Tokyo 172 induced by vitamin B1

BACKGROUND

Vitamin B1 (VB1) is a crucial dietary nutrient and essential cofactor for several key enzymes in the regulation of cellular and metabolic processes, and more importantly in the activation of immune system. To date, the precise role of VB1 in Mycobacterium tuberculosis remains to be fully understood.

RESULTS

In this study, the transcriptional and metabolic profiles of VB1-treated Mycobacterium. bovis BCG were analyzed by RNA-sequencing and LC-MS (Liquid chromatography coupled to mass spectrometry). The selection of BCG strain was based on its common physiological features shared with M. tuberculosis. The results of cell growth assays demonstrated that VB1 inhibited the BCG growth rate in vitro. Transcriptomic analysis revealed that the expression levels of genes related to fatty acid metabolism, cholesterol metabolism, glycolipid catabolism, DNA replication, protein translation, cell division and cell wall formation were significantly downregulated in M. bovis BCG treated with VB1. In addition, the metabolomics LC-MS data indicated that most of the amino acids and adenosine diphosphate (ADP) were decreased in M. bovis BCG strain after VB1 treatment.

CONCLUSIONS

This study provides the molecular and metabolic bases to understand the impacts of VB1 on M.bovis BCG.

Transcriptional Approach for Decoding the Mechanism of rpoC Compensatory Mutations for the Fitness Cost in Rifampicin-Resistant Mycobacterium tuberculosis

Multidrug-resistant tuberculosis (TB), defined as TB resistant to the two first-line drugs, isoniazid and rifampin, is a serious challenge to global TB eradication efforts. Although mutations in rpoA or rpoC have been proposed to compensate for this fitness cost due to rpoB mutation in rifampicin-resistant Mycobacterium tuberculosis mutants, whether the compensatory effect exists and the underlying mechanisms of compensation remain unclear. Here, we used RNA sequencing to investigate the global transcriptional profiles of 6 rifampin-resistant clinical isolates with either single mutation in rpoB or dual mutations in rpoB/rpoC, as well as 3 rifampin-susceptible clinical isolates, trying to prove the potential compensatory effect of rpoC by transcriptomic alteration. In rifampin-free conditions, rpoC mutation was associated with M. tuberculosis upregulation of ribosomal protein-coding genes, dysregulation of growth-related essential genes and balancing the expression of arginine and glutamate synthesis-associated genes. Upon rifampin exposure of M. tuberculosis isolates, rpoC mutations were associated with the upregulation of the oxidative phosphorylation machinery, which was inhibited in the rpoB single mutants, as well as stabilization of the expression of rifampin-regulated essential genes and balancing the expression of genes involved in metabolism of sulfur-containing amino acids. Taken together, our data suggest that rpoC mutation may compensate for the fitness defect of rifampicin-resistant M. tuberculosis by altering gene expression in response to rifampin exposure.

Glutathione as a Marker for Human Disease

Glutathione (GSH), often referred to as "the master antioxidant," participates not only in antioxidant defense systems, but many metabolic processes, and therefore its role cannot be overstated. GSH deficiency causes cellular risk for oxidative damage and thus as expected, GSH imbalance is observed in a wide range of pathological conditions including tuberculosis (TB), HIV, diabetes, cancer, and aging. Consequently, it is not surprising that GSH has attracted the attention of biological researchers and pharmacologists alike as a possible target for medical intervention. Here, we discuss the role GSH plays amongst these pathological conditions to illuminate how it can be used as a marker for human disease.

Global gene-expression profiles of intracellular survival of the BruAb2_1031 gene mutated Brucella abortus in professional phagocytes, RAW 264.7 cells

Background

Since recognizing the interaction between Brucella and host cells is crucial to the elucidation of the infectious process, Brucella researches have prioritized the investigation of genes related to pathogenicity. To demonstrate the roles of Brucella genes, RAW 264.7 cells were infected with the Brucella abortus wild-type and mutant strains (generated using transposon mutagenesis), after which the different transcriptional responses of the infected cells were determined using microarray.

Results

Following infection, enhanced strategies for intracellular survival, such as down-regulation of genes associated with cytokine responses and apoptosis, were observed in RAW 264.7 cells infected with C3 mutant strain when compared to the transcriptional responses of wild-type infected cells. Using sequence analysis, we determined the mutation site of a C3 mutant strain as the ATP-binding cassette transporter permease (BruAb2_1031). These results were evidenced by an increased level of intracellular survival of the C3 mutant strain.

Conclusions

Characteristics of each mutant strain including bacterial growth rate, abilities to induce cytokine production in macrophages after infection, internalization, and levels of intracellular survival and replication, were investigated by performing RAW 264.7 cell infection experiments. Our results indicate that the BruAb2_1031 gene might be closely related with intracellular survival of B. abortus in RAW 264.7 cells.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1223-7) contains supplementary material, which is available to authorized users.

xCT increases tuberculosis susceptibility by regulating antimicrobial function and inflammation

The physiological functions of macrophage, which plays a central role in the pathogenesis of tuberculosis, depend on its redox state. System xc-, a cystine-glutamate transporter, which consists of xCT and CD98, influences many ROS-dependent pathways by regulating the production of the antioxidant glutathione. xCT's ability to alter this critical host redox balance by increasing the glutathione synthesis aspect of phagocyte physiology suggested that it might influence tuberculosis pathogenesis. In this study, we found that the xCT expression was increased in peripheral blood monocyte of active tuberculosis. xCT expression in macrophage was induced by Mycobacterium tuberculosis (Mtb) through TLR2/Akt- and p38-dependent signaling pathway. Importantly, xCT deficiency conferred protection against tuberculosis, as xCT knock out mice displayed increased Mtb load and reduced pulmonary pathology in lung compared to wild type mice. xCT disruption enhanced the mycobateriacidal activity of macrophage through increasing the mycothiol oxidation. Importantly, chemical inhibition of xCT with sulfasalazine, a specific xCT inhibitor that is already approved by the FDA for treatment of inflammatory bowel disease, produces similar protective effects in vivo and in vitro, indicating xCT might be a novel and useful target for host-directed TB treatment strategy.

Contributions of the oligopeptide permeases in multistep of Vibrio alginolyticus pathogenesis

Vibrio alginolyticus has been associated with several diseases of cultivated marine animals, and has led to considerable economic losses. The oligopeptide permease (Opp) has been proven to play a variety of important roles in nutrition and virulence in several bacteria. In our previous research, the opp gene cluster was identified in Vibrio alginolyticus with transcriptome sequence, which also indicated that the Opp system might play roles in the regulation of adhesion. In this study, the relationship between V. alginolyticus virulence and the opp gene cluster was determined using gene silencing followed by RT‐qPCR, in vitro adhesion assay, growth curves detection in the presence of glutathione (GSH) as a toxic substrate, hemolysis assay, biofilm assay, and artificial infection. Silencing these genes led to deficiencies in adhesion, peptide internalization, biofilm production, hemolytic activity, and virulence. The expression levels of hapr, hapa, tlh, and hlya, which are important genes closely related to the hemolytic activity of Vibrio, were significantly downregulated in all of the RNAi groups. Furthermore, the expression of oppA, oppB, oppC, oppD, and oppF was significantly influenced by temperature, starvation, and pH. These results indicate that (1) oppABCDF contributed in multistep of V. alginolyticus pathogenesis, including adhesion, biofilm production, and hemolytic activity; (2) oppABCDF was sensitive to different temperatures, changes in pH, and increased starvation time.

N-acetyl-cysteine exhibits potent anti-mycobacterial activity in addition to its known anti-oxidative functions

Background

Mycobacterium tuberculosis infection is thought to induce oxidative stress. N-acetyl-cysteine (NAC) is widely used in patients with chronic pulmonary diseases including tuberculosis due to its mucolytic and anti-oxidant activities. Here, we tested whether NAC exerts a direct antibiotic activity against mycobacteria.

Methods

Oxidative stress status in plasma was compared between pulmonary TB (PTB) patients and those with latent M. tuberculosis infection (LTBI) or healthy uninfected individuals. Lipid peroxidation, DNA oxidation and cell death, as well as accumulation of reactive oxygen species (ROS) were measured in cultures of primary human monocyte-derived macrophages infected with M. tuberculosis and treated or not with NAC. M. tuberculosis, M. avium and M. bovis BCG cultures were also exposed to different doses of NAC with or without medium pH adjustment to control for acidity. The anti-mycobacterial effect of NAC was assessed in M. tuberculosis infected human THP-1 cells and bone marrow-derived macrophages from mice lacking a fully functional NADPH oxidase system. The capacity of NAC to control M. tuberculosis infection was further tested in vivo in a mouse (C57BL/6) model.

Results

PTB patients exhibited elevated levels of oxidation products and a reduction of anti-oxidants compared with LTBI cases or uninfected controls. NAC treatment in M. tuberculosis-infected human macrophages resulted in a decrease of oxidative stress and cell death evoked by mycobacteria. Importantly, we observed a dose-dependent reduction in metabolic activity and in vitro growth of NAC treated M. tuberculosis, M. avium and M. bovis BCG. Furthermore, anti-mycobacterial activity in infected macrophages was shown to be independent of the effects of NAC on the host NADPH oxidase system in vitro. Short-term NAC treatment of M. tuberculosis infected mice in vivo resulted in a significant reduction of mycobacterial loads in the lungs.

Conclusions

NAC exhibits potent anti-mycobacterial effects and may limit M. tuberculosis infection and disease both through suppression of the host oxidative response and through direct antimicrobial activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0872-7) contains supplementary material, which is available to authorized users.

Persistent Mycobacterium bovis-BCG is resistant to glutathione induced reductive stress killing

This study focuses on the redox stress response in mycobacteria elicited by a host-derived, thiol-based detoxification molecule, glutathione (GSH). Although the growth and viability of Mycobacterium bovis-BCG (BCG) was hampered by exposure to 8 mM GSH, oxygen depleted, persistent BCG (NRP BCG) resisted GSH-mediated killing. Fast growing mycobacteria also resisted GSH-mediated killing. To determine the mechanisms behind these observations, we evaluated the levels of intracellular ATP in both BCG and NRP BCG exposed to 8 mM GSH. Intracellular ATP levels increased from 0.13 to 2.3 μM in BCG upon exposure to GSH. The levels of ATP remained low and unchanged when NRP BCG was exposed to GSH. Using both HPLC and a cell-based thiol detection assay, it was determined that GSH stimulates the production of mycothiol (MSH) by BCG approximately 5.7 fold. The levels of MSH did not change upon exposure of NRP BCG to GSH. MSH is an alternative, thiol-based detoxification molecule employed by mycobacteria. Changes in the cytoplasmic concentrations of this molecule are suggestive of redox imbalances. Together, GSH and MSH may introduce excess reducing equivalents into the mycobacterial cytoplasm; leading to reductive stress. The modulation of NAD(+) levels through alterations in ATP metabolism can enhance the cells ability to bind excess reducing equivalents and serve as a mechanism to restore the cellular redox balance when cells experience reductive stress. These data suggest that killing of BCG by GSH may result from reductive stress that cannot be controlled. NRP BCG appears to be resistant to GSH-induced reductive stress.

Defining the nitrogen regulated transcriptome of Mycobacterium smegmatis using continuous culture

BACKGROUND

Nitrogen is essential for microbial growth and its importance is demonstrated by the complex regulatory systems used to control the transport, assimilation and metabolism of nitrogen. Recent studies are beginning to shed light on how mycobacteria respond to nitrogen limitation and several regulators (e.g., GlnR, PII) have been characterized at a molecular level. However, despite this progress, our knowledge of the transcriptional response of mycobacteria to nitrogen limitation and its regulation is confined to batch culture.

METHODS

To gain further insight into the response of mycobacteria to nitrogen limitation, we developed a nitrogen-limited chemostat. We compared the transcriptional response of nitrogen-limited cells to carbon-limited cells using RNA-seq analysis in a continuous culture model at a constant growth rate.

CONCLUSIONS

Our findings revealed significant changes in the expression of 357 genes (208 upregulated, 149 downregulated; >2-fold change, false discovery rate <5 %) in response to nitrogen limitation in continuous culture. The vast majority of the GlnR regulon (68 %) was differentially expressed under nitrogen limitation in continuous culture and approximately 52 % of the 357 genes overlapped with a previously published study investigating the response of M. smegmatis to nitrogen limitation in batch culture, while expression of only 17 % of the genes identified in batch culture were affected in our chemostat model. Moreover, we identified a unique set of 45 genes involved in the uptake and metabolism of nitrogen that were exclusive to our chemostat model. We observed strong downregulation of pathways for amino acid catabolism (i.e., alanine, aspartate, valine, proline and lysine), suggesting preservation of these amino acids for critical cellular function. We found 16 novel transcriptional regulators that were directly or indirectly involved in the global transcriptomic response of M. smegmatis to nitrogen limitation and identified several non-coding RNAs that might be involved in the transcriptional or post-transcriptional regulation of nitrogen-regulated gene expression.

RESULTS

Using nitrogen-limited continuous culture we identified the nitrogen-responsive transcriptome of M. smegmatis, including a number of small non-coding RNAs implicated in controlling nitrogen-regulated gene expression.

MntR(Rv2788): a transcriptional regulator that controls manganese homeostasis in Mycobacterium tuberculosis

The pathogenic mycobacterium Mycobacterium tuberculosis encodes two members of the DtxR/MntR family of metalloregulators, IdeR and SirR. IdeR represses gene expression in response to ferrous iron, and we here demonstrate that SirR (Rv2788), although also annotated as an iron-dependent repressor, functions instead as a manganese-dependent transcriptional repressor and is therefore renamed MntR. MntR regulates transporters that promote manganese import and genes that respond to metal ion deficiency such as the esx3 system. Repression of manganese import by MntR is essential for survival of M. tuberculosis under conditions of high manganese availability, but mntR is dispensable during infection. In contrast, manganese import by MntH and MntABCD was found to be indispensable for replication of M. tuberculosis in macrophages. These results suggest that manganese is limiting in the host and that interfering with import of this essential metal may be an effective strategy to attenuate M. tuberculosis.

Nitrogen metabolism in Mycobacterium tuberculosis physiology and virulence

Several major pathogens, including Mycobacterium tuberculosis, parasitize host cells and exploit host-derived nutrients to sustain their own metabolism. Although the carbon sources that are used by M. tuberculosis have been extensively studied, the mechanisms by which mycobacteria capture and metabolize nitrogen, which is another essential constituent of biomolecules, have only recently been revisited. In this Progress article, we discuss central nitrogen metabolism in M. tuberculosis, the mechanisms that are used by this pathogen to obtain nitrogen from its host and the potential role of nitrogen capture and metabolism in virulence.

Neonatal bacillus Calmette-Guerin vaccination and environmental mycobacteria in sensitizing antimycobacterial activity of macrophages

An immunoepidemiological study was performed to evaluate the effect of neonatal bacillus Calmette-Guérin (BCG) vaccination and tuberculin response on macrophage killing profile against Mycobacterium tuberculosis. In this epidemiological field work, the study subjects were drawn from in and around Chennai city, South India. The descriptive epidemiological pattern of neonatal BCG vaccination and its impact on tuberculin skin test were studied. The study subjects for the immunologic laboratory experiments were recruited based on the skin test (Mantoux) outcome and were grouped in to 4 natural study groups that include vaccinated reactors, vaccinated nonreactors, nonvaccinated reactors and nonvaccinated nonreactors. In immunologic laboratory work part, the elucidation of macrophage killing profile was studied for all the 4 groups, and appropriate intercomparisons were made. The parameters used for the macrophage killing profile were (1) glutathione assay, (2) measurement of phagocytosis, (3) intracellular growth kinetics of M. tuberculosis H37Rv, (4) tumor necrosis factor-α assay and (5) interferon-γ assay. The results found that in the BCG-vaccinated tuberculin reactors the macrophage responses were significantly higher than the BCG-vaccinated tuberculin nonreactors. There was no significant difference in the responses among the BCG-vaccinated tuberculin reactors when compared with the nonvaccinated tuberculin reactors. The immune responses of nonvaccinated tuberculin reactors were significantly higher than the vaccinated tuberculin nonreactors. These findings show that the immune response among the adolescents/young adults is elicited by exposure to mycobacteria and not by the neonatal BCG vaccination.

Characterization of the Opp peptide transporter of Corynebacterium pseudotuberculosis and its role in virulence and pathogenicity

Despite the economic importance of caseous lymphadenitis (CLA), a chronic disease caused by Corynebacterium pseudotuberculosis, few genes related to the virulence of its etiologic agent have been characterized. The oligopeptide permease (Opp) transporters are located in the plasma membrane and have functions generally related to the uptake of peptides from the extracellular environment. These peptide transporters, in addition to having an important role in cell nutrition, also participate in the regulation of various processes involving intercellular signaling, including the control of the expression of virulence genes in pathogenic bacteria. To study the role of Opp in C. pseudotuberculosis, an OppD deficient strain was constructed via simple crossover with a nonreplicative plasmid carrying part of the oppD gene sequence. As occurred to the wild-type, the ΔoppD strain showed impaired growth when exposed to the toxic glutathione peptide (GSH), indicating two possible scenarios: (i) that this component can be internalized by the bacterium through an Opp-independent pathway or (ii) that there is toxicity while the peptide is extracellular. Additionally, the ΔoppD mutant presented a reduced ability to adhere to and infect macrophages compared to the wild-type, although both strains exhibit the same potential to colonize spleens and cause injury and death to infected mice.

New targets and inhibitors of mycobacterial sulfur metabolism

The identification of new antibacterial targets is urgently needed to address multidrug resistant and latent tuberculosis infection. Sulfur metabolic pathways are essential for survival and the expression of virulence in many pathogenic bacteria, including Mycobacterium tuberculosis. In addition, microbial sulfur metabolic pathways are largely absent in humans and therefore, represent unique targets for therapeutic intervention. In this review, we summarize our current understanding of the enzymes associated with the production of sulfated and reduced sulfur-containing metabolites in Mycobacteria. Small molecule inhibitors of these catalysts represent valuable chemical tools that can be used to investigate the role of sulfur metabolism throughout the Mycobacterial lifecycle and may also represent new leads for drug development. In this light, we also summarize recent progress made in the development of inhibitors of sulfur metabolism enzymes.

Distribution and infection-related functions of bacillithiol in Staphylococcus aureus

Bacillithiol (Cys-GlcN-malate, BSH) serves as a major low molecular weight thiol in low GC Gram-positive bacteria including Bacillus species and a variety of Staphylococcus aureus strains. These bacteria do not produce glutathione (GSH). In this study, HPLC analyses were used to determine BSH levels in different S. aureus strains. Furthermore, the role of BSH in the resistance against oxidants and antibiotics and its function in virulence was investigated. We and others (Newton, G.L., Fahey, R.C., Rawat, M., 2012. Microbiology 158, 1117-1126) found that BSH is not produced by members of the S. aureus NCTC8325 lineage, such as strains 8325-4 and SH1000. Using bioinformatics we show that the BSH-biosynthetic gene bshC is disrupted by an 8-bp duplication in S. aureus NCTC8325. The functional bshC-gene from BSH-producing S. aureus Newman (NWMN_1087) was expressed in S. aureus 8325-4 to reconstitute BSH-synthesis. Comparison of the BSH-producing and BSH-minus strains revealed higher resistance of the BSH-producing strain against the antibiotic fosfomycin and the oxidant hypochlorite but not against hydrogen peroxide or diamide. In addition, a higher bacterial load of the BSH-producing strain was detected in human upper-airway epithelial cells and murine macrophages. This indicates a potential role of BSH in protection of S. aureus during infection.

Nitrosothiols in bacterial pathogens and pathogenesis

SIGNIFICANCE

The formation and degradation of S-nitrosothiols (SNOs) are important mechanisms of post-translational protein modification and appear to be ubiquitous in biology. These processes play well-characterized roles in eukaryotic cells, including a variety of pathologies and in relation to chronic conditions. We know little of the roles of these processes in pathogenic and other bacteria.

RECENT ADVANCES

It is clear, mostly from growth and transcriptional studies, that bacteria sense and respond to exogenous SNOs. These responses are phenotypically and mechanistically distinct from the responses of bacteria to nitric oxide (NO) and NO-releasing agents, as well as peroxynitrite. Small SNOs, such as S-nitrosoglutathione (GSNO), are accumulated by bacteria with the result that intracellular S-nitrosoproteins (the 'S-nitrosoproteome') are detectable. Recently, conditions for endogenous SNO formation in enterobacteria have been described.

CRITICAL ISSUES

The propensity of intracellular proteins to form SNOs is presumably constrained by the same rules of selectivity that have been discovered in eukaryotic systems, but is also influenced by uniquely bacterial NO detoxification systems, exemplified by the flavohemoglobin Hmp in enterobacteria and NO reductase of meningococci. Furthermore, the bacterial expression of such proteins impacts upon the formation of SNOs in mammalian hosts.

FUTURE DIRECTIONS

The impairment during bacterial infections of specific SNO events in the mammalian host is of considerable interest in the context of proteins involved in innate immunity and intracellular signalling. In bacteria, numerous mechanisms of S-nitrosothiol degradation have been reported (e.g., GSNO reductase); others are thought to operate, based on consideration of their mammalian counterparts. The nitrosothiols of bacteria and particularly of pathogens warrant more intensive investigation.

Glutathione transporters

BACKGROUND

Glutathione (GSH) is synthesized in the cytoplasm but there is a requirement for glutathione not only in the cytoplasm, but in the other organelles and the extracellular milieu. GSH is also imported into the cytoplasm. The transports of glutathione across these different membranes in different systems have been biochemically demonstrated. However the molecular identity of the transporters has been established only in a few cases.

SCOPE OF REVIEW

An attempt has been made to present the current state of knowledge of glutathione transporters from different organisms as well as different organelles. These include the most well characterized transporters, the yeast high-affinity, high-specificity glutathione transporters involved in import into the cytoplasm, and the mammalian MRP proteins involved in low affinity glutathione efflux from the cytoplasm. Other glutathione transporters that have been described either with direct or indirect evidences are also discussed.

MAJOR CONCLUSIONS

The molecular identity of a few glutathione transporters has been unambiguously established but there is a need to identify the transporters of other systems and organelles. There is a lack of direct evidence establishing transport by suggested transporters in many cases. Studies with the high affinity transporters have led to important structure-function insights.

GENERAL SIGNIFICANCE

An understanding of glutathione transporters is critical to our understanding of redox homeostasis in living cells. By presenting our current state of understanding and the gaps in our knowledge the review hopes to stimulate research in these fields. This article is part of a Special Issue entitled Cellular functions of glutathione.

Virulence factors of the Mycobacterium tuberculosis complex

The Mycobacterium tuberculosis complex (MTBC) consists of closely related species that cause tuberculosis in both humans and animals. This illness, still today, remains to be one of the leading causes of morbidity and mortality throughout the world. The mycobacteria enter the host by air, and, once in the lungs, are phagocytated by macrophages. This may lead to the rapid elimination of the bacillus or to the triggering of an active tuberculosis infection. A large number of different virulence factors have evolved in MTBC members as a response to the host immune reaction. The aim of this review is to describe the bacterial genes/proteins that are essential for the virulence of MTBC species, and that have been demonstrated in an in vivo model of infection. Knowledge of MTBC virulence factors is essential for the development of new vaccines and drugs to help manage the disease toward an increasingly more tuberculosis-free world.

The diversity of microbial responses to nitric oxide and agents of nitrosative stress close cousins but not identical twins

Nitric oxide and related nitrogen species (reactive nitrogen species) now occupy a central position in contemporary medicine, physiology, biochemistry, and microbiology. In particular, NO plays important antimicrobial defenses in innate immunity but microbes have evolved intricate NO-sensing and defense mechanisms that are the subjects of a vast literature. Unfortunately, the burgeoning NO literature has not always been accompanied by an understanding of the intricacies and complexities of this radical and other reactive nitrogen species so that there exists confusion and vagueness about which one or more species exert the reported biological effects. The biological chemistry of NO and derived/related molecules is complex, due to multiple species that can be generated from NO in biological milieu and numerous possible reaction targets. Moreover, the fate and disposition of NO is always a function of its biological environment, which can vary significantly even within a single cell. In this review, we consider newer aspects of the literature but, most importantly, consider the underlying chemistry and draw attention to the distinctiveness of NO and its chemical cousins, nitrosonium (NO(+)), nitroxyl (NO(-), HNO), peroxynitrite (ONOO(-)), nitrite (NO(2)(-)), and nitrogen dioxide (NO(2)). All these species are reported to be generated in biological systems from initial formation of NO (from nitrite, NO synthases, or other sources) or its provision in biological experiments (typically from NO gas, S-nitrosothiols, or NO donor compounds). The major targets of NO and nitrosative damage (metal centers, thiols, and others) are reviewed and emphasis is given to newer "-omic" methods of unraveling the complex repercussions of NO and nitrogen oxide assaults. Microbial defense mechanisms, many of which are critical for pathogenicity, include the activities of hemoglobins that enzymically detoxify NO (to nitrate) and NO reductases and repair mechanisms (e.g., those that reverse S-nitrosothiol formation). Microbial resistance to these stresses is generally inducible and many diverse transcriptional regulators are involved-some that are secondary sensors (such as Fnr) and those that are "dedicated" (such as NorR, NsrR, NssR) in that their physiological function appears to be detecting primarily NO and then regulating expression of genes that encode enzymes with NO as a substrate. Although generally harmful, evidence is accumulating that NO may have beneficial effects, as in the case of the squid-Vibrio light-organ symbiosis, where NO serves as a signal, antioxidant, and specificity determinant. Progress in this area will require a thorough understanding not only of the biology but also of the underlying chemical principles.

Role of glutathione in immunity and inflammation in the lung

Reactive oxygen species and thiol antioxidants, including glutathione (GSH), regulate innate immunity at various levels. This review outlines the redox-sensitive steps of the cellular mechanisms implicated in inflammation and host defense against infection, and describes how GSH is not only important as an antioxidant but also as a signaling molecule. There is an extensive literature of the role of GSH in immunity. Most reviews are biased by an oversimplified picture where “bad” free radicals cause all sorts of diseases and “good” antioxidants protect from them and prevent oxidative stress. While this may be the case in certain fields (eg, toxicology), the role of thiols (the topic of this review) in immunity certainly requires wearing scientist’s goggles and being prepared to accept a more complex picture. This review aims at describing the role of GSH in the lung in the context of immunity and inflammation. The first part summarizes the history and basic concepts of this picture. The second part focuses on GSH metabolism/levels in pathology, the third on the role of GSH in innate immunity and inflammation, and the fourth gives 4 examples describing the importance of GSH in the response to infections.

An oligopeptide transporter of Mycobacterium tuberculosis regulates cytokine release and apoptosis of infected macrophages

Background

The Mycobacterium tuberculosis genome encodes two peptide transporters encoded by Rv3665c-Rv3662c and Rv1280c-Rv1283c. Both belong to the family of ABC transporters containing two nucleotide-binding subunits, two integral membrane proteins and one substrate-binding polypeptide. However, little is known about their functions in M. tuberculosis. Here we report functional characterization of the Rv1280c-Rv1283c-encoded transporter and its substrate-binding polypeptide OppA_MTB.

Methodology/Principal Findings

OppA_MTB was capable of binding the tripeptide glutathione and the nonapeptide bradykinin, indicative of a somewhat broad substrate specificity. Amino acid residues G109, N110, N230, D494 and F496, situated at the interface between domains I and III of OppA, were required for optimal peptide binding. Complementaton of an oppA knockout mutant of M. smegmatis with OppA_MTB confirmed the role of this transporter in importing glutathione and the importance of the aforesaid amino acid residues in peptide transport. Interestingly, this transporter regulated the ability of M. tuberculosis to lower glutathione levels in infected compared to uninfected macrophages. This ability was partly offset by inactivation of oppD. Concomitantly, inactivation of oppD was associated with lowered levels of methyl glyoxal in infected macrophages and reduced apoptosis-inducing ability of the mutant. The ability to induce the production of the cytokines IL-1β, IL-6 and TNF-α was also compromised after inactivation of oppD.

Conclusions

Taken together, these studies uncover the novel observations that this peptide transporter modulates the innate immune response of macrophages infected with M. tuberculosis.

Mycobacterium tuberculosis modulates its cell surface via an oligopeptide permease (Opp) transport system

Bacterial species utilize a vast repertoire of surface structures to interact with their surroundings and employ a number of strategies to reconfigure the cellular envelope according to specific stimuli. Gram-positive bacteria, exemplified by Streptomyces and Bacillus species, control production of some exposed molecules by importing oligopeptide signals via permeases (Opp). Such oligopeptides modulate intracellular signaling pathways. In this work, we functionally characterized an Opp of the human pathogen Mycobacterium tuberculosis (Mtb) and propose its reannotation. Using genome-wide transcriptional profiling, we found that Opp was required to modulate (fold-change ranging from -3.5 to 2.0) the expression of several genes, most of them encoding surface-exposed molecules. These included the virulence-associated lipids mycolic acids and phthiocerol dimycocerosates (PDIMs) as well as PE-family proteins. By thin-layer chromatography and MALDI-TOF-MS we confirmed changes in the lipid profile, including an altered accumulation of triacylglycerides and an affected ratio of mycolic acids to PDIMs. An Opp loss of function mutant showed no in vitro growth defect, but had diminished burden during chronic infection and produced a slightly delayed time to death of animals when compared to WT Mtb infection.

Mycothiol: synthesis, biosynthesis and biological functions of the major low molecular weight thiol in actinomycetes

Actinomycetes produce mycothiol as their major low molecular weight thiol, which parallels the functions of glutathione found in prokaryotes and most Gram-negative bacteria. This review covers progress that has so far been made in terms of its distribution, biosynthesis and metabolic functions, as well as chemical syntheses of mycothiol and alternative substrates and inhibitors of mycothiol biosynthesis and mycothiol-dependent enzymes. 152 references are cited.

Selection of genes of Mycobacterium tuberculosis upregulated during residence in lungs of infected mice

In sequel to previous report [Srivastava V, Rouanet C, Srivastava R, Ramalingam B, Locht C, Srivastava BS. Macrophage-specific Mycobacterium tuberculosis genes: identification by green fluorescent protein and kanamycin resistance selection. Microbiology 2007;153:659-66], the genes of Mycobacterium tuberculosis upregulated during residence in lungs of infected mice were identified in an in vivo expression system based on kanamycin resistance. A promoter library of M. tuberculosis was constructed in a promoter trap shuttle vector pLL192 containing an artificial bicistronic operon composed of promoterless green fluorescent protein gene followed by kanamycin resistance gene. The library was introduced in M. bovis BCG and then infected in mice by intravenous route. Mice were treated twice daily with 40 mg/kg dose of kanamycin by intramuscular route for 21 days. Recombinant BCG recovered from the lungs were reinfected in mice to enrich clones surviving kanamycin treatment in the lung but sensitive to killing by kanamycin in vitro. After nucleotide sequencing of inserts from these clones, 20 genes belonging to fatty acids metabolism, membrane transport, nitric oxide defence and PE_PGRS/PPE family were identified. Real-time PCR analysis using RNA isolated from M. tuberculosis grown in vitro and from the lungs, confirmed upregulation of genes from 2 to 20-fold in vivo compared to growth in vitro. Several of these select 20 genes were also found upregulated ex vivo in macrophage-like cell line J774A.1, thus, suggesting a correlation in mycobacterial gene expression between ex vivo and in vivo conditions.

BCG-induced rabbit alveolar macrophages are endowed with strengthened antioxidant metabolic pathways

Following i.v. BCG infection, a new population of macrophages are recruited in the rabbit lung. These macrophages, known as activated macrophages, substitute the resident macrophages and can play a key role in the defence against mycobacteria. We report here that BCG-activated alveolar macrophages are equipped with a more active hexose monophosphate pathway, which can maintain an optimal intracellular concentration of NADPH and GSH, and allow to produce mycobactericidal free radicals and to become resistant to mycobacterium-induced programmed cell death. These findings suggest that sustaining the anti-oxidant properties of macrophages could represent a candidate process to be considered as a good therapeutic target in fighting Mycobacterium spp infections.

Drug targets in mycobacterial sulfur metabolism

The identification of new antibacterial targets is urgently needed to address multidrug resistant and latent tuberculosis infection. Sulfur metabolic pathways are essential for survival and the expression of virulence in many pathogenic bacteria, including Mycobacterium tuberculosis. In addition, microbial sulfur metabolic pathways are largely absent in humans and therefore, represent unique targets for therapeutic intervention. In this review, we summarize our current understanding of the enzymes associated with the production of sulfated and reduced sulfur-containing metabolites in Mycobacteria. Small molecule inhibitors of these catalysts represent valuable chemical tools that can be used to investigate the role of sulfur metabolism throughout the Mycobacterial lifecycle and may also represent new leads for drug development. In this light, we also summarize recent progress in the development of inhibitors of sulfur metabolism enzymes.

Only one of four oligopeptide transport systems mediates nitrogen nutrition in Staphylococcus aureus

Oligopeptides internalized by oligopeptide permease (Opp) transporters play key roles in bacterial nutrition, signaling, and virulence. To date, two opp operons, opp-1 and opp-2, have been identified in Staphylococcus aureus. Systematic in silico analysis of 11 different S. aureus genomes revealed the existence of two new opp operons, opp-3 and opp-4, plus an opp-5A gene encoding a putative peptide-binding protein. With the exception of opp-4, the opp operons were present in all S. aureus strains. Within a single strain, the different opp operons displayed little sequence similarity and distinct genetic organization. Transcriptional studies showed that opp-1, opp-2, opp-3, and opp-4 operons were polycistronic and that opp-5A is monocistronic. We designed a minimal chemically defined medium for S. aureus RN6390 and showed that all opp genes were expressed but at different levels. Where tested, OppA protein production paralleled transcriptional profiles. opp-3, which encodes proteins most similar to known peptide transport proteins, displayed the highest expression level and was the only transporter to be regulated by specific amino acids, tyrosine and phenylalanine. Defined deletion mutants in one or several peptide permeases were constructed and tested for their capacity to grow in peptide-containing medium. Among the four putative Opp systems, Opp-3 was the only system able to provide oligopeptides for growth, ranging in length from 3 to 8 amino acids. Dipeptides were imported exclusively by DtpT, a proton-driven di- and tripeptide permease. These data provide a first complete inventory of the peptide transport systems opp and dtpT of S. aureus. Among them, the newly identified Opp-3 appears to be the main Opp system supplying the cell with peptides as nutritional sources.

Thiols in nitric oxide synthase-containing Nocardia sp. strain NRRL 5646

Mycothiol (MSH) [1-D-myo-inosityl-2-(N-acetyl-l-cysteinyl)amido-2-deoxy-alpha-D-glucopyranoside], isolated as the bimane derivative, was established to be the major thiol in Nocardia sp. strain NRRL 5646, a species most closely related to Nocardia brasiliensis strain DSM 43758(T). Thiol formation and detection of MSH-dependent formaldehyde dehydrogenase activity in cell extracts are relevant to the possible modulation of nitric oxide toxicity generated by strain NRRL 5646.

Characterization of a glutathione metabolic mutant of Mycobacterium tuberculosis and its resistance to glutathione and nitrosoglutathione

Glutathione is a tripeptide and antioxidant, synthesized at high levels by cells during the production of reactive oxygen and nitrogen intermediates. Glutathione also serves as a carrier molecule for nitric oxide in the form of S-nitrosoglutathione. Previous studies from this laboratory have shown that glutathione and S-nitrosoglutathione are directly toxic to mycobacteria. Glutathione is not transported into the cells as a tripeptide. Extracellular glutathione is converted to a dipeptide due to the action of transpeptidase, and the dipeptide is then transported into the bacterial cells. The processing of glutathione and S-nitrosoglutathione is brought about by the action of the enzyme gamma-glutamyl transpeptidase. The function of gamma-glutamyl transpeptidase is to cleave glutathione and S-nitrosoglutathione to the dipeptide (Cys-Gly), which is then transported into the bacterium by the multicomponent ABC transporter dipeptide permease. We have created a mutant strain of Mycobacterium tuberculosis lacking this metabolic enzyme. We investigated the sensitivity of this strain to glutathione and S-nitrosoglutathione compared to that of the wild-type bacteria. In addition, we examined the role of glutathione and/or S-nitrosoglutathione in controlling the growth of intracellular M. tuberculosis inside mouse macrophages.

Deletion of the anaerobic regulator HlyX causes reduced colonization and persistence of Actinobacillus pleuropneumoniae in the porcine respiratory tract

Actinobacillus pleuropneumoniae, the etiological agent of porcine pleuropneumonia, is able to persist on respiratory epithelia, in tonsils, and in the anaerobic environment of encapsulated lung sequesters. We have demonstrated previously that putative HlyX-regulated genes, coding for dimethyl sulfoxide (DMSO) reductase and aspartate ammonia lyase, are upregulated during infection and that deletions in these genes result in attenuation of the organism. The study presented here investigates the role of HlyX, the fumarate nitrate reductase regulator (FNR) homologue of A. pleuropneumoniae. By constructing an isogenic A. pleuropneumoniae hlyX mutant, the HlyX protein is shown to be responsible for upregulated expression of both DMSO reductase and aspartate ammonia lyase (AspA) under anaerobic conditions. In a challenge experiment the A. pleuropneumoniae hlyX mutant is shown to be highly attenuated, unable to persist in healthy lung epithelium and tonsils, and impaired in survival inside sequestered lung tissue. Further, using an A. pleuropneumoniae strain carrying the luxAB genes as transcriptional fusion to aspA on the chromosome, the airway antioxidant glutathione was identified as one factor potentially responsible for inducing HlyX-dependent gene expression of A. pleuropneumoniae in epithelial lining fluid.

S-Nitrosoglutathione cytotoxicity toMycobacterium smegmatisand its use to isolate stationary phase survival mutants

We report that stationary phase Mycobacterium smegmatis is more sensitive than exponential phase cells to the nitric oxide donor S-Nitrosoglutathione (GSNO). This finding was used to select for both spontaneous and transposon mutants of M. smegmatis with increased resistance to GSNO in stationary phase. Some of these mutants were also defective in stationary phase survival, demonstrating a link between sensitivity to GSNO and stationary phase survival. Transduction of the disrupted region from seven selected mutants indicated that the transposon insertion was linked to the GSNO-resistance and stationary phase survival phenotypes. For five mutants, the disrupted genes were identified. Three were homologous to genes with possible roles in nutrient scavenging, including: (i) a putative amino acid efflux pump, (ii) a putative thioesterase and (iii) an enoyl-CoA-hydratase. One mutant was disrupted in the atpD gene, encoding the beta chain of F1 F0 ATP synthase. We independently isolated a stationary phase survival mutant disrupted in the atpA gene (encoding the alpha chain) of the F1 F0 ATP synthase of the same operon, suggesting an important role for efficient ATP synthesis in stationary phase survival.

The metabolism of nitrosothiols in the Mycobacteria: identification and characterization of S-nitrosomycothiol reductase

When grown in culture Mycobacterium smegmatis metabolized S-nitrosoglutathione to oxidized glutathione and nitrate, which suggested a possible involvement of an S-nitrosothiol reductase and mycobacterial haemoglobin. The mycothiol-dependent formaldehyde dehydrogenase from M. smegmatis was purified by a combination of Ni2+-IMAC (immobilized metal ion affinity chromatography), hydrophobic interaction, anion-exchange and affinity chromatography. The enzyme had a subunit molecular mass of 38263 kDa. Steady-state kinetic studies indicated that the enzyme catalyses the NAD+-dependent conversion of S-hydroxymethylmycothiol into formic acid and mycothiol by a rapid-equilibrium ordered mechanism. The enzyme also catalysed an NADH-dependent decomposition of S-nitrosomycothiol (MSNO) by a sequential mechanism and with an equimolar stoichiometry of NADH:MSNO, which indicated that the enzyme reduces the nitroso group to the oxidation level of nitroxyl. Vmax for the MSNO reductase reaction indicated a turnover per subunit of approx. 116700 min(-1), which was 76-fold faster than the formaldehyde dehydrogenase activity. A gene, Rv2259, annotated as a class III alcohol dehydrogenase in the Mycobacterium tuberculosis genome was cloned and expressed in M. smegmatis as the C-terminally His6-tagged product. The purified recombinant enzyme from M. tuberculosis also catalysed both activities. M. smegmatis S-nitrosomycothiol reductase converted MSNO into the N -hydroxysulphenamide, which readily rearranged to mycothiolsulphinamide. In the presence of MSNO reductase, M. tuberculosis HbN (haemoglobin N) was converted with low efficiency into metHbN [HbN(Fe3+)] and this conversion was dependent on turnover of MSNO reductase. These observations suggest a possible route in vivo for the dissimilation of S-nitrosoglutathione.

The metabolism of S-nitrosothiols in the trypanosomatids: the role of ovothiol A and trypanothione

It has recently been established that nitrosoglutathione is the preferred substrate of the glutathione-dependent formaldehyde dehydrogenase from divergent organisms. Trypanosomatids produce not only glutathione, but also glutathionylspermidine, trypanothione and ovothiol A. The formaldehyde dehydrogenase activity of Crithidia fasciculata was independent of these thiols and extracts possessed very low levels of nitrosothiol reductase activity with glutathione or its spermidine conjugates as the thiol component. Although ovothiol A did not form a stable nitrosothiol, it decomposed the S -nitroso groups of nitrosoglutathione (GSNO) and dinitrotrypanothione [T(SNO)(2)] with second-order rate constants of 19.12 M(-1) x s(-1) and 8.67 M(-1) x s(-1) respectively. The reaction of T(SNO)(2) with ovothiol A, however, accelerated to a rate similar to that seen with GSNO. Ovothiol A can act catalytically to decompose these nitrosothiols, although non-productive mechanisms exist. The catalytic phase of the reaction was dependent on the production of thiyl radicals, since it was abolished in the presence of 5,5-dimethyl-1-pyrroline- N -oxide and the formation of nitric oxide could be detected by means of the conversion of oxyhaemoglobin into methaemoglobin. The rate-limiting step in the catalytic process was the reduction of oxidized ovothiol species and, in this respect, T(SNO)(2) is a more efficient substrate than GSNO. Trypanothione decomposed GSNO with a second-order rate constant of 0.786 M(-1) x s(-1) and the major nitrogenous end product changed from nitrite to ammonia as the ratio of thiol to nitrosothiol increased. The results indicate that ovothiol A acts in synergy with trypanothione in the decomposition of T(SNO)(2).

Role of glutathione in macrophage control of mycobacteria

Reactive oxygen and nitrogen intermediates are important antimicrobial defense mechanisms of macrophages and other phagocytic cells. While reactive nitrogen intermediates have been shown to play an important role in tuberculosis control in the murine system, their role in human disease is not clearly established. Glutathione, a tripeptide and antioxidant, is synthesized at high levels by cells during reactive oxygen intermediate and nitrogen intermediate production. Glutathione has been recently shown to play an important role in apoptosis and to regulate antigen-presenting-cell functions. Glutathione also serves as a carrier molecule for nitric oxide, in the form of S-nitrosoglutathione. Previous work from this laboratory has shown that glutathione and S-nitrosoglutathione are directly toxic to mycobacteria. A mutant strain of Mycobacterium bovis BCG, defective in the transport of small peptides such as glutathione, is resistant to the toxic effect of glutathione and S-nitrosoglutathione. Using the peptide transport mutant as a tool, we investigated the role of glutathione and S-nitrosoglutathione in animal and human macrophages in controlling intracellular mycobacterial growth.

Human eosinophil peroxidase induces surface alteration, killing, and lysis of Mycobacterium tuberculosis

The antimycobacterial role of eosinophil peroxidase (EPO), one of the most abundant granule proteins in human eosinophils, was investigated. Our data indicate that purified EPO shows significant inhibitory activity towards Mycobacterium tuberculosis H37Rv. On a molar basis, this activity was similar to that exhibited by neutrophil myeloperoxidase (MPO) and was both dose and time dependent. In contrast to the activity of MPO, which requires H(2)O(2), EPO also exhibited anti-M. tuberculosis activity in the absence of exogenously added peroxide. Morphological evidence confirmed that the mechanism of action of EPO against mycobacteria differs from that of MPO. While MPO kills M. tuberculosis H37Rv exclusively in the presence of hydrogen peroxide, it does not induce morphological changes in the pathogen. In contrast, EPO-treated bacteria frequently had cell wall lesions and eventually underwent lysis, either in the presence or in the absence of H(2)O(2).

A putative three-dimensional arrangement of the human serotonin transporter transmembrane helices: a tool to aid experimental studies

The human serotonin transporter is the molecular target for selective serotonin reuptake inhibitor drugs which are being used for treatment of depression. A three-dimensional model of the membrane spanning parts of the transporter was constructed. The transporter was assumed to consist of 12 transmembrane alpha-helices. The model was based on published experimental data of cocaine binding to mutant transporters, amino acid sequence analysis, and interactive molecular graphics. The model suggests that a high affinity cocaine binding site is situated in a region of the model where Asp98 acts like an anchor, while a putative low affinity site is situated in another region with Glu508 as the anchoring amino acid. A series of docking experiments with various reuptake inhibitors were conducted, using interactive molecular graphics techniques combined with energy calculations and analysis of the transporter-ligand complexes. Experiments involving molecular mapping of ligand binding areas may benefit from using the current model in experimental design. From the current model, several amino acids were proposed as prime candidates for mutagenesis and subsequent ligand binding studies. Also for evaluation of results from site directed mutagenesis experiments with SERT and similar transporters we assume the model will be helpful.

The ATP binding cassette (ABC) transport systems of Mycobacterium tuberculosis

We have undertaken the inventory and assembly of the typical subunits of the ABC transporters encoded by the complete genome of Mycobacterium tuberculosis. These subunits, i.e. the nucleotide binding domains (NBDs), the membrane-spanning domains (MSDs) and the substrate binding proteins (SBPs), were identified on the basis of their characteristic stretches of amino acids and/or conserved structure. A total of 45 NBDs present in 38 proteins, of 47 MSDs present in 44 proteins and of 15 SBPs were found to be encoded by M. tuberculosis. Analysis of transcriptional clusters and searches of homology between the identified subunits of the transporters and proteins characterized in other organisms allowed the reconstitution of at least 26 complete (including at least one NBD and one MSD) and 11 incomplete ABC transporters. Sixteen of them were unambiguously classified as importers whereas 21 were presumed to be exporters. By searches of homology with already known transporters from other organisms, potential substrates (peptides, macrolides, carbohydrates, multidrugs, antibiotics, iron, anions) could be attributed to 30 of the ABC transporters identified in M. tuberculosis. The ABC transporters have been further classified in nine different sub-families according to a tree obtained from the clustering of their NBDs. Contrary to Escherichia coli and similarly to Bacillus subtilis, there is an equal representation of extruders and importers. Many exporters were found to be potentially implicated in the transport of drugs, probably contributing to the resistance of M. tuberculosis to many antibiotics. Interestingly, a transporter (absent in E. coli and in B. subtilis) potentially implicated in the export of a factor required for the bacterial attachment to the eukaryotic host cells was also identified. In comparison to E. coli and B. subtilis, there is an under-representation of the importers (with the exception of the phosphate importers) in M. tuberculosis. This may reflect the capacity of this bacterium to synthesize many essential compounds and to grow in the presence of few external nutrients. The genes encoding the ABC transporters occupy about 2.5% of the genome of M. tuberculosis.