Generation and characterization of thiol-deficient Mycobacterium tuberculosis mutants.

Mycothiol (MSH) and ergothioneine (ERG) are thiols able to compensate for each other to protect mycobacteria against oxidative stress. Gamma-glutamylcysteine (GGC), another thiol and an intermediate in ERG biosynthesis has detoxification abilities. Five enzymes are involved in ERG biosynthesis, namely EgtA, EgtB, EgtC, EgtD and EgtE. The role of these enzymes in the production of ERG had been unclear. On the other hand, the enzyme MshA is known to be essential for MSH biosynthesis. In this manuscript, we describe the raw data of the generation and characterization of Mycobacterium tuberculosis (M.tb) mutants harbouring a deletion of the gene coding for each of these enzymes, and the raw data of the phenotypic characterization of the obtained thiol-deficient M.tb mutants. High throughput screening (HTS) of off-patent drugs and natural compounds revealed few compounds that displayed a higher activity against the thiol-deficient mutants relative to the wild-type strain. The mode of action of these drugs was further investigated. Raw data displaying these results are described here.

Ergothioneine protects Streptomyces coelicolor A3(2) from oxidative stresses.

Thiol compounds with low-molecular weight, such as glutathione, mycothiol (MSH), bacillithiol, and ergothioneine (ERG), are known to protect microorganisms from oxidative stresses. Mycobacteria and actinobacteria utilize both MSH and ERG. The biological functions of MSH in mycobacteria have been extensively studied by genetic and biochemical studies, which have suggested it has critical roles for detoxification in cells. In contrast, the biological functions of ERG remain ambiguous because its biosynthetic genes were only recently identified in Mycobacterium avium. In this study, we constructed mutants of Streptomyces coelicolor A3(2), in which either the MSH or ERG biosynthetic gene was disrupted, and examined their phenotypes. A mshC (SCO1663)-disruptant completely lost MSH productivity. In contrast, a disruptant of the egtA gene (SCO0910) encoding γ-glutamyl-cysteine synthetase unexpectedly retained reduced productivity of ERG, probably because of the use of l-cysteine instead of γ-glutamyl-cysteine. Both disruptants showed delayed growth at the late logarithmic phase and were more susceptible to hydrogen peroxide and cumene hydroperoxide than the parental strain. Interestingly, the ERG-disruptant, which still kept reduced ERG productivity, was more susceptible. Furthermore, the ERG-disruptant accumulated 5-fold more MSH than the parental strain. In contrast, the amount of ERG was almost the same between the MSH-disruptant and the parental strain. Taken together, our results suggest that ERG is more important than MSH in S. coelicolor A3(2).

Mycobacterium tuberculosis is extraordinarily sensitive to killing by a vitamin C-induced Fenton reaction.

Drugs that kill tuberculosis more quickly could shorten chemotherapy significantly. In Escherichia coli, a common mechanism of cell death by bactericidal antibiotics involves the generation of highly reactive hydroxyl radicals via the Fenton reaction. Here we show that vitamin C, a compound known to drive the Fenton reaction, sterilizes cultures of drug-susceptible and drug-resistant Mycobacterium tuberculosis, the causative agent of tuberculosis. While M. tuberculosis is highly susceptible to killing by vitamin C, other Gram-positive and Gram-negative pathogens are not. The bactericidal activity of vitamin C against M. tuberculosis is dependent on high ferrous ion levels and reactive oxygen species production, and causes a pleiotropic effect affecting several biological processes. This study enlightens the possible benefits of adding vitamin C to an anti-tuberculosis regimen and suggests that the development of drugs that generate high oxidative burst could be of great use in tuberculosis treatment.

Properties of human vasopressin precursor constructs: inefficient monomer folding in the absence of copeptin as a potential contributor to diabetes insipidus.

These studies were aimed at an initial characterization of the human vasopressin precursor and the evaluation of factors leading to misfolding by the pathological 87STOP mutation. This mutation deletes the precursor's glycosylated copeptin segment, which has been considered unnecessary for folding, and the last seven neurophysin residues. We investigated the role in folding of the last seven neurophysin residues by comparing the properties of the 87STOP precursor and its derivative neurophysin with those of the corresponding wild-type proteins from which copeptin had been deleted, leading to the following conclusions. First, despite modulating effects on several protein properties, the last seven neurophysin residues do not make a significant net thermodynamic contribution to precursor folding; stabilities of the mutant and wild-type precursors to both guanidine denaturation and redox buffer unfolding are similar, as are in vitro folding rates. Second, the monomeric forms of both precursors are unstable and predicted to fold inefficiently at physiological pH and temperature, as evidenced by precursor behavior in redox buffers and by thermodynamic calculations. Third, both precursors are significantly less stable than the bovine oxytocin precursor. These results, together with earlier studies elsewhere of vasopressin precursor behavior within rat neurons, are shown to represent a self-consistent argument for a role for glycosylated copeptin in vasopressin precursor folding in vivo, copeptin most probably assisting refolding by facilitating interaction of misfolded monomers with the calnexin/calreticulin system. This hypothesis provides an explanation for the absence of copeptin in the more stable oxytocin precursor and suggests that the loss of copeptin contributes to 87STOP pathogenicity. Reported cell culture studies of rat precursor folding are also discussed in this context. Most generally, the results emphasize the significance of monomer stability in the folding pathways of oligomeric proteins.