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Journal of Bacteriology, October 2007, p. 6796-6805, Vol. 189, No. 19
0021-9193/07/$08.00+0     doi:10.1128/JB.00644-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Mycothiol Import by Mycobacterium smegmatis and Function as a Resource for Metabolic Precursors and Energy Production

Krzysztof P. Bzymek, Gerald L. Newton, Philong Ta, and Robert C. Fahey^*

Department of Chemistry and Biochemistry, University of California, San Diego, California

Received 24 April 2007/ Accepted 15 July 2007

Mycothiol ([MSH] AcCys-GlcN-Ins, where Ac is acetyl) is the major thiol produced by Mycobacterium smegmatis and other actinomycetes. Mutants deficient in MshA (strain 49) or MshC (transposon mutant Tn1) of MSH biosynthesis produce no MSH. However, when stationary phase cultures of these mutants were incubated in medium containing MSH, they actively transported it to generate cellular levels of MSH comparable to or greater than the normal content of the wild-type strain. When these MSH-loaded mutants were transferred to MSH-free preconditioned medium, the cellular MSH was catabolized to generate GlcN-Ins and AcCys. The latter was rapidly converted to Cys by a high deacetylase activity assayed in extracts. The Cys could be converted to pyruvate by a cysteine desulfhydrase or used to regenerate MSH in cells with active MshC. Using MSH labeled with [U-¹⁴C]cysteine or with [6-³H]GlcN, it was shown that these residues are catabolized to generate radiolabeled products that are ultimately lost from the cell, indicating extensive catabolism via the glycolytic and Krebs cycle pathways. These findings, coupled with the fact the myo-inositol can serve as a sole carbon source for growth of M. smegmatis, indicate that MSH functions not only as a protective cofactor but also as a reservoir of readily available biosynthetic precursors and energy-generating metabolites potentially important under stress conditions. The half-life of MSH was determined in stationary phase cells to be 50 h in strains with active MshC and 16 ± 3 h in the MshC-deficient mutant, suggesting that MSH biosynthesis may be a suitable target for drugs to treat dormant tuberculosis.

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* Corresponding author. Mailing address: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0314. Phone: (858) 534-2163. Fax: (858) 534-4864. E-mail: rcfahey{at}ucsd.edu

Published ahead of print on 20 July 2007.

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Journal of Bacteriology, October 2007, p. 6796-6805, Vol. 189, No. 19
0021-9193/07/$08.00+0     doi:10.1128/JB.00644-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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