A non-canonical caleosin from Arabidopsis efficiently epoxidizes physiological unsaturated fatty acids with complete stereoselectivity

FEBS J. 2012 Oct;279(20):3981-95. doi: 10.1111/j.1742-4658.2012.08757.x. Epub 2012 Sep 14.


In plants, epoxygenated fatty acids (EFAs) are constituents of oil seeds as well as defence molecules and components of biopolymers (cutin, suberin). While the pleiotropic biological activities of mammalian EFAs have been well documented, there is a paucity of information on the physiological relevance of plant EFAs and their biosynthesis. Potential candidates for EFA formation are caleosin-type peroxygenases which catalyze the epoxidation of unsaturated fatty acids in the presence of hydroperoxides as co-oxidants. However, the caleosins characterized so far, which are mostly localized in seeds, are poor epoxidases. In sharp contrast, quantitative RT-PCR analysis revealed that PXG4, a class II caleosin gene, is expressed in roots, stems, leaves and flowers of Arabidopsis. Expressed in yeast, PXG4 encodes a calcium-dependent membrane-associated hemoprotein able to catalyze typical peroxygenase reactions. Moreover, we show here that purified recombinant PXG4 is an efficient fatty acid epoxygenase, catalyzing the oxidation of cis double bonds of unsaturated fatty acids. Physiological linoleic and linolenic acids proved to be the preferred substrates for PXG4; they are oxidized into the different positional isomers of the monoepoxides and into diepoxides. An important regioselectivity was observed; the C-12,13 double bond of these unsaturated fatty acids being the least favored unsaturation epoxidized by PXG4, linolenic acid preferentially yielded the 9,10-15,16-diepoxide. Remarkably, PXG4 catalyzes exclusively the formation of (R),(S)-epoxide enantiomers, which is the absolute stereochemistry of the epoxides found in planta. These findings pave the way for the study of the functional role of EFAs and caleosins in plants.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Biocatalysis
  • Blotting, Western
  • Calcium-Binding Proteins / classification
  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / metabolism*
  • Fatty Acids, Unsaturated / chemistry
  • Fatty Acids, Unsaturated / metabolism*
  • Gene Expression Regulation, Enzymologic
  • Gene Expression Regulation, Plant
  • Linoleic Acids / chemistry
  • Linoleic Acids / metabolism
  • Linolenic Acids / chemistry
  • Linolenic Acids / metabolism
  • Mixed Function Oxygenases / classification
  • Mixed Function Oxygenases / genetics
  • Mixed Function Oxygenases / metabolism*
  • Oxidation-Reduction
  • Oxidoreductases / genetics
  • Oxidoreductases / metabolism*
  • Oxygen / metabolism
  • Phylogeny
  • Reverse Transcriptase Polymerase Chain Reaction
  • Stereoisomerism
  • Substrate Specificity


  • Arabidopsis Proteins
  • Calcium-Binding Proteins
  • Fatty Acids, Unsaturated
  • Linoleic Acids
  • Linolenic Acids
  • Mixed Function Oxygenases
  • Oxidoreductases
  • PXG4 protein, Arabidopsis
  • epoxidase
  • peroxygenase
  • Oxygen