Abstract
Spontaneous mutants of Mycobacterium tuberculosis that were resistant to the anti-tuberculosis drugs ethionamide and isoniazid were isolated and found to map to mshA, a gene encoding the first enzyme involved in the biosynthesis of mycothiol, a major low-molecular-weight thiol in M. tuberculosis. Seven independent missense or frameshift mutations within mshA were identified and characterized. Precise null deletion mutations of the mshA gene were generated by specialized transduction in three different strains of M. tuberculosis. The mshA deletion mutants were defective in mycothiol biosynthesis, were only ethionamide-resistant and required catalase to grow. Biochemical studies suggested that the mechanism of ethionamide resistance in mshA mutants was likely due to a defect in ethionamide activation. In vivo, a mycothiol-deficient strain grew normally in immunodeficient mice, but was slightly defective for growth in immunocompetent mice. Mutations in mshA demonstrate the non-essentiality of mycothiol for growth in vitro and in vivo, and provide a novel mechanism of ethionamide resistance in M. tuberculosis.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Sequence
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Animals
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Antitubercular Agents / pharmacology*
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Bacterial Proteins / chemistry
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Bacterial Proteins / genetics
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Bacterial Proteins / metabolism
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Catalase / genetics
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Catalase / metabolism
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Corynebacterium glutamicum / genetics
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Cysteine / biosynthesis*
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Cysteine / genetics
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Drug Resistance, Bacterial*
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Ethionamide / pharmacology*
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Glycopeptides / biosynthesis*
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Glycopeptides / genetics
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Glycosyltransferases / chemistry
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Glycosyltransferases / genetics
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Glycosyltransferases / metabolism
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Humans
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Inositol / biosynthesis*
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Inositol / genetics
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Isoniazid / pharmacology
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Mice
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Mice, Inbred C57BL
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Mice, SCID
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Microbial Sensitivity Tests
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Mixed Function Oxygenases / genetics
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Mixed Function Oxygenases / metabolism
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Molecular Sequence Data
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Mycobacterium Infections / drug therapy
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Mycobacterium Infections / microbiology*
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Mycobacterium tuberculosis / drug effects*
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Mycobacterium tuberculosis / enzymology
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Mycobacterium tuberculosis / genetics
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Mycobacterium tuberculosis / metabolism*
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Sequence Alignment
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Sequence Deletion
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Tuberculosis, Multidrug-Resistant
Substances
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Antitubercular Agents
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Bacterial Proteins
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Glycopeptides
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mycothiol
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Inositol
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Mixed Function Oxygenases
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Catalase
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Glycosyltransferases
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Cysteine
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Ethionamide
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Isoniazid