Oxidative cleavage of premithramycin B is one of the last steps in the biosynthesis of the antitumor drug mithramycin

Laura Prado, Ernestina Fernández, Ulrike Weißbach, Gloria Blanco, Luis M. Quirós, Alfredo F. Braña, Carmen Méndez, Jürgen Rohr, José A. Salas

Research output: Contribution to journalArticlepeer-review

74 Scopus citations


Background: Mithramycin is a member of the clinically important aureolic acid group of antitumor drugs that interact with GC-rich regions of DNA nonintercalatively. These drugs contain a chromophore aglycon that is derived from condensation of ten acetate units (catalyzed by a type II polyketide synthase). The aglycones are glycosylated at two positions with different chain length deoxyoligosaccharides, which are essential for the antitumor activity. During the early stages of mithramycin biosynthesis, tetracyclic intermediates of the tetracycline-type occur, which must be converted at later stages into the tricyclic glycosylated molecule, presumably through oxidative breakage of the fourth ring. Results: Two intermediates in the mithramycin biosynthetic pathway, 4-demethylpremithramycinone and premithramycin B, were identified in a mutant lacking the mithramycin glycosyltransferase and methyltransferase genes and in the same mutant complemented with the deleted genes, respectively. Premithramycin B contains five deoxysugars moieties (like mithramycin), but contains a tetracyclic aglycon moiety instead of a tricyclic aglycon. We hypothesized that transcription of mtmOIV (encoding an oxygenase) was impaired in this strain, preventing oxidative breakage of the fourth ring of premithramycin B. Inactivating mtmOIV generated a mithramycin nonproducing mutant that accumulated premithramycin B instead of mithramycin. In vitro assays demonstrated that MtmOIV converted premithramycin B into a tricyclic compound. Conclusions: In the late stages of mithramycin biosynthesis by Strepyomyces argillaceus, a fully glycosylated tetracyclic tetracycline-like intermediate (premithramycin B) is converted into a tricyclic compound by the oxygenase MtmOIV. This oxygenase inserts an oxygen (Baeyer-Villiger oxidation) and opens the resulting lactone. The following decarboxylation and ketoreduction steps lead to mithramycin. Opening of the fourth ring represents one of the last steps in mithramycin biosynthesis.

Original languageEnglish
Pages (from-to)19-30
Number of pages12
JournalChemistry and Biology
Issue number1
StatePublished - Jan 1999

Bibliographical note

Funding Information:
This work was suooorted bv arants of the Eurooean Communitv to J.A.S. and J.R. (Bl04-CT96-0068): the Spanish Ministry of Educatron and Science to J.A.S. through the Plan National en Biotecnologia (BiOQ7-0771) and by grants from the Deutsche Forschungsgemeinschaft (SFB 416) and the Medical University of South Carolina to J.R. R. Machinek and G. Udvarnoki (University of Gtittingen, Germany) are thanked for their excellent help with NMR and mass spectroscopy experiments, respectively.


  • Antitumor agents
  • Aureolic acid
  • Biosynthesis
  • Polyketide synthase
  • Polyketides

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Medicine
  • Molecular Biology
  • Pharmacology
  • Drug Discovery
  • Clinical Biochemistry


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