A Backup Plan for Self-Protection: S-Methylation of Holomycin Biosynthetic Intermediates in Streptomyces clavuligerus

Authors

  • Dr. Bo Li,

    1. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115 (USA)
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    • These authors contributed equally to this work.

  • Ry R. Forseth,

    1. Boyce Thompson Institute and Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853 (USA)
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    • These authors contributed equally to this work.

  • Prof. Dr. Albert A. Bowers,

    1. Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, IN 47907 (USA)
    2. Current address: Department of Chemical Biology and Medicinal Chemistry, Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 (USA)
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  • Prof. Dr. Frank C. Schroeder,

    1. Boyce Thompson Institute and Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853 (USA)
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  • Prof. Dr. Christopher T. Walsh

    Corresponding author
    1. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115 (USA)
    • Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115 (USA)
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Abstract

Biosynthesis of the dithiolopyrrolone antibiotic holomycin in Streptomyces clavuligerus involves the closure of a pair of enethiols to a cyclic disulfide. We have shown that the dithiol oxidase HlmI is responsible for the disulfide formation and this enzyme also plays a role in self-protection. In the present study, we examine how S. clavuligerus deals with the proposed toxic dithiol intermediates when hlmI is deleted. We used differential NMR spectroscopy and mass spectrometry to profile the metabolomes of hlmI deletion mutants along with the wild-type strain and a holomycin-overproducing strain. A number of metabolites unique to ΔhlmI strains were identified. In these metabolites the enethiols have been incapacitated by a combination of mono- and di-S-methylation. We also observed an intriguing dimeric thioether adduct in low quantities in the wild-type strain and at much higher levels in the ΔhlmI strains. The structures of these novel metabolites highlight the reactivity of the dihydrodithiolopyrrolone scaffold. Furthermore, bioassays suggest that modification of the enethiol warhead by S-alkylation provides a host strategy for detoxification, one that is shared amongst multiple species producing such bioactive disulfide natural products.

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