Discovery of C-Glycosylpyranonaphthoquinones in Streptomyces sp. MBT76 by a Combined NMR-Based Metabolomics and Bioinformatics Workflow

J Nat Prod. 2017 Feb 24;80(2):269-277. doi: 10.1021/acs.jnatprod.6b00478. Epub 2017 Jan 27.

Abstract

Mining of microbial genomes has revealed that actinomycetes harbor far more biosynthetic potential for bioactive natural products than anticipated. Activation of (cryptic) biosynthetic gene clusters and identification of the corresponding metabolites has become a focal point for drug discovery. Here, we applied NMR-based metabolomics combined with bioinformatics to identify novel C-glycosylpyranonaphthoquinones in Streptomyces sp. MBT76 and to elucidate the biosynthetic pathway. Following activation of the cryptic qin gene cluster for a type II polyketide synthase (PKS) by constitutive expression of its pathway-specific activator, bioinformatics coupled to NMR profiling facilitated the chromatographic isolation and structural elucidation of qinimycins A-C (1-3). The intriguing structural features of the qinimycins, including 8-C-glycosylation, 5,14-epoxidation, and 13-hydroxylation, distinguished these molecules from the model pyranonaphthoquinones actinorhodin, medermycin, and granaticin. Another novelty lies in the unusual fusion of a deoxyaminosugar to the pyranonaphthoquinone backbone during biosynthesis of the antibiotics BE-54238 A and B (4, 5). Qinimycins showed weak antimicrobial activity against Gram-positive bacteria. Our work shows the utility of combining bioinformatics, targeted activation of cryptic gene clusters, and NMR-based metabolic profiling as an effective pipeline for the discovery of microbial natural products with distinctive skeletons.

MeSH terms

  • Actinobacteria / chemistry*
  • Anti-Bacterial Agents / chemistry
  • Anti-Bacterial Agents / isolation & purification*
  • Anti-Bacterial Agents / pharmacology*
  • Bacillus subtilis / drug effects
  • Computational Biology
  • Escherichia coli / drug effects
  • Glycosides / chemistry
  • Glycosides / isolation & purification*
  • Glycosides / pharmacology*
  • Metabolomics
  • Microbial Sensitivity Tests
  • Molecular Structure
  • Naphthoquinones / chemistry*
  • Naphthoquinones / isolation & purification*
  • Nuclear Magnetic Resonance, Biomolecular
  • Pseudomonas aeruginosa / drug effects
  • Pyrrolizidine Alkaloids / chemistry
  • Pyrrolizidine Alkaloids / isolation & purification*
  • Pyrrolizidine Alkaloids / pharmacology*
  • Staphylococcus aureus / drug effects
  • Streptomyces / chemistry*

Substances

  • Anti-Bacterial Agents
  • BE 54238B
  • Glycosides
  • Naphthoquinones
  • Pyrrolizidine Alkaloids
  • BE 54238A