A plant type III polyketide synthase that produces pentaketide chromone

J Am Chem Soc. 2005 Feb 9;127(5):1362-3. doi: 10.1021/ja0431206.


A novel plant-specific type III polyketide synthase (PKS) that catalyzes formation of a pentaketide chromone, 5,7-dihydroxy-2-methylchromone, from five molecules of malonyl-CoA, was cloned and sequenced from aloe (Aloe arborescens). Site-directed mutagenesis revealed that Met207 (corresponding to Thr197 in CHS) determines the polyketide chain length and the product specificity of the enzyme; remarkably, replacement of a single amino acid residue, Met207, with Gly yielded a mutant enzyme that efficiently produces aromatic octaketides, SEK4 and SEK4b, the products of the minimal PKS for actinorhodin (act from Streptomyces coelicolor), from eight molecules of malonyl-CoA. This provided new insights into the catalytic functions and specificities of the CHS-superfamily type III PKS enzymes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acyltransferases / chemistry
  • Acyltransferases / genetics
  • Acyltransferases / metabolism*
  • Aloe / enzymology
  • Aloe / genetics
  • Amino Acid Sequence
  • Chromones / metabolism*
  • Kinetics
  • Malonyl Coenzyme A / metabolism
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Plant Proteins / chemistry
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Substrate Specificity


  • Chromones
  • Plant Proteins
  • Malonyl Coenzyme A
  • Acyltransferases
  • flavanone synthetase