Pyrazinone protease inhibitor metabolites from Photorhabdus luminescens

J Antibiot (Tokyo). 2016 Aug;69(8):616-21. doi: 10.1038/ja.2016.79. Epub 2016 Jun 29.

Abstract

Photorhabdus luminescens is a bioluminescent entomopathogenic bacterium that undergoes phenotypic variation and lives in mutualistic association with nematodes of the family Heterorhabditidae. The pair infects and kills insects, and during their coordinated lifecycle, the bacteria produce an assortment of specialized metabolites to regulate its mutualistic and pathogenic roles. As part of our search for new specialized metabolites from the Photorhabdus genus, we examined organic extracts from P. luminescens grown in an amino-acid-rich medium based on the free amino-acid levels found in the circulatory fluid of its common insect prey, the Galleria mellonella larva. Reversed-phase HPLC/UV/MS-guided fractionation of the culture extracts led to the identification of two new pyrazinone metabolites, lumizinones A (1) and B (2), together with two N-acetyl dipeptides (3 and 4). The lumizinones were produced only in the phenotypic variant associated with nematode development and insect pathogenesis. Their chemical structures were elucidated by analysis of 1D and 2D NMR and high-resolution ESI-QTOF-MS spectral data. The absolute configurations of the amino acids in 3 and 4 were determined by Marfey's analysis. Compounds 1-4 were evaluated for their calpain protease inhibitory activity, and lumizinone A (1) showed inhibition with an IC50 (half-maximal inhibitory concentration) value of 3.9 μm.

Publication types

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

MeSH terms

  • Amino Acids / chemistry
  • Animals
  • Chromatography, High Pressure Liquid
  • Inhibitory Concentration 50
  • Lepidoptera / chemistry
  • Magnetic Resonance Spectroscopy
  • Mass Spectrometry
  • Photorhabdus / metabolism*
  • Protease Inhibitors / chemistry
  • Protease Inhibitors / isolation & purification
  • Protease Inhibitors / pharmacology*
  • Pyrazines / chemistry
  • Pyrazines / isolation & purification
  • Pyrazines / pharmacology*
  • Spectrometry, Mass, Electrospray Ionization / methods

Substances

  • Amino Acids
  • Protease Inhibitors
  • Pyrazines