Biosynthesis of the (2S,3R)-3-methyl glutamate residue of nonribosomal lipopeptides

J Am Chem Soc. 2006 Aug 30;128(34):11250-9. doi: 10.1021/ja062960c.

Abstract

The calcium-dependent antibiotics (CDAs) and daptomycin are therapeutically relevant nonribosomal lipopeptide antibiotics that contain penultimate C-terminal 3-methyl glutamate (3-MeGlu) residues. Comparison with synthetic standards showed that (2S,3R)-configured 3-MeGlu is present in both CDA and daptomycin. Deletion of a putative methyltransferase gene glmT from the cda biosynthetic gene cluster abolished the incorporation of 3-MeGlu and resulted in the production of Glu-containing CDA exclusively. However, the 3-MeGlu chemotype could be re-established through feeding synthetic 3-methyl-2-oxoglutarate and (2S,3R)-3-MeGlu, but not (2S,3S)-3-MeGlu. This indicates that methylation occurs before peptide assembly, and that the module 10 A-domain of the CDA peptide synthetase is specific for the (2S,3R)-stereoisomer. Further mechanistic analyses suggest that GlmT catalyzes the SAM-dependent methylation of alpha-ketoglutarate to give (3R)-methyl-2-oxoglutarate, which is transaminated to (2S,3R)-3-MeGlu. These insights will facilitate future efforts to engineer lipopeptides with modified glutamate residues, which may have improved bioactivity and/or reduced toxicity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chromatography, Liquid
  • Genetic Complementation Test
  • Glutamic Acid / analogs & derivatives*
  • Glutamic Acid / biosynthesis
  • Glutamic Acid / chemistry
  • Lipoproteins / chemical synthesis*
  • Mass Spectrometry
  • Nuclear Magnetic Resonance, Biomolecular
  • Peptides / chemical synthesis*
  • Spectrometry, Mass, Electrospray Ionization
  • Stereoisomerism
  • Streptomyces coelicolor / genetics
  • Streptomyces coelicolor / metabolism

Substances

  • 3-methylglutamic acid
  • Lipoproteins
  • Peptides
  • Glutamic Acid