Biosynthesis, Mechanism of Action, and Inhibition of the Enterotoxin Tilimycin Produced by the Opportunistic Pathogen Klebsiella oxytoca

ACS Infect Dis. 2020 Jul 10;6(7):1976-1997. doi: 10.1021/acsinfecdis.0c00326. Epub 2020 Jun 24.


Tilimycin is an enterotoxin produced by the opportunistic pathogen Klebsiella oxytoca that causes antibiotic-associated hemorrhagic colitis (AAHC). This pyrrolobenzodiazepine (PBD) natural product is synthesized by a bimodular nonribosomal peptide synthetase (NRPS) pathway composed of three proteins: NpsA, ThdA, and NpsB. We describe the functional and structural characterization of the fully reconstituted NRPS system and report the steady-state kinetic analysis of all natural substrates and cofactors as well as the structural characterization of both NpsA and ThdA. The mechanism of action of tilimycin was confirmed using DNA adductomics techniques through the detection of putative N-2 guanine alkylation after tilimycin exposure to eukaryotic cells, providing the first structural characterization of a PBD-DNA adduct formed in cells. Finally, we report the rational design of small-molecule inhibitors that block tilimycin biosynthesis in whole cell K. oxytoca (IC50 = 29 ± 4 μM) through the inhibition of NpsA (KD = 29 ± 4 nM).

Keywords: Klebsiella oxytoca; adenylation; microbiome; nonribosomal peptide synthetase; pyrrolobenzodiazepine; tilimycin.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Toxins*
  • Benzodiazepines
  • Enterotoxins
  • Kinetics
  • Klebsiella oxytoca* / genetics
  • Pyrroles


  • Bacterial Toxins
  • Enterotoxins
  • Pyrroles
  • tilimycin
  • Benzodiazepines