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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Molecular Identification and Characterization of the Arabidopsis ^3,5,^2,4-Dienoyl-Coenzyme A Isomerase, a Peroxisomal Enzyme Participating in the -Oxidation Cycle of Unsaturated Fatty Acids¹

Département de Biologie Moléculaire Végétale, Bâtiment de Biologie, Université de Lausanne, CH–1015 Lausanne, Switzerland (S.G., C.V., E.R., Y.P.); and Biocenter Oulu and Department of Biochemistry, University of Oulu, FIN–90570 Oulu, Finland (J.K.H.)

Degradation of unsaturated fatty acids through the peroxisomal -oxidation pathway requires the participation of auxiliary enzymes in addition to the enzymes of the core -oxidation cycle. The auxiliary enzyme ^3,5,^2,4-dienoyl-coenzyme A (CoA) isomerase has been well studied in yeast (Saccharomyces cerevisiae) and mammals, but no plant homolog had been identified and characterized at the biochemical or molecular level. A candidate gene (At5g43280) was identified in Arabidopsis (Arabidopsis thaliana) encoding a protein showing homology to the rat (Rattus norvegicus) ^3,5,^2,4-dienoyl-CoA isomerase, and possessing an enoyl-CoA hydratase/isomerase fingerprint as well as aspartic and glutamic residues shown to be important for catalytic activity of the mammalian enzyme. The protein, named AtDCI1, contains a peroxisome targeting sequence at the C terminus, and fusion of a fluorescent protein to AtDCI1 directed the chimeric protein to the peroxisome in onion (Allium cepa) cells. AtDCI1 expressed in Escherichia coli was shown to have ^3,5,^2,4-dienoyl-CoA isomerase activity in vitro. Furthermore, using the synthesis of polyhydroxyalkanoate in yeast peroxisomes as an analytical tool to study the -oxidation cycle, expression of AtDCI1 was shown to complement the yeast mutant deficient in the ^3,5,^2,4-dienoyl-CoA isomerase, thus showing that AtDCI1 is also appropriately targeted to the peroxisome in yeast and has ^3,5,^2,4-dienoyl-CoA isomerase activity in vivo. The AtDCI1 gene is expressed constitutively in several tissues, but expression is particularly induced during seed germination. Proteins showing high homology with AtDCI1 are found in gymnosperms as well as angiosperms belonging to the Monocotyledon or Dicotyledon classes.

² Present address: Nutrition and Health Department, Functional Microbiology Group, Nestlé Research Center, P.O. Box 44, CH–1000 Lausanne 26, Switzerland.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.064311.

^* Corresponding author; e-mail yves.poirier{at}unil.ch; fax 41–21–692–4195.

Received April 18, 2005; returned for revision May 26, 2005; accepted May 30, 2005.

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