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J. Biol. Chem., Vol. 281, Issue 47, 35894-35903, November 24, 2006

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Identification and Functional Characterization of a Monofunctional Peroxisomal Enoyl-CoA Hydratase 2 That Participates in the Degradation of Even cis-Unsaturated Fatty Acids in Arabidopsis thaliana^*

Simon Goepfert, J. Kalervo Hiltunen, and Yves Poirier¹

From the Département de Biologie Moléculaire Végétale, Biophore Building, Université de Lausanne, CH-1015, Switzerland and the Biocenter Oulu and Department of Biochemistry, University of Oulu, FIN-90014 Oulu, Finland

A gene, named AtECH2, has been identified in Arabidopsis thaliana to encode a monofunctional peroxisomal enoyl-CoA hydratase 2. Homologues of AtECH2 are present in several angiosperms belonging to the Monocotyledon and Dicotyledon classes, as well as in a gymnosperm. In vitro enzyme assays demonstrated that AtECH2 catalyzed the reversible conversion of 2E-enoyl-CoA to 3R-hydroxyacyl-CoA. AtECH2 was also demonstrated to have enoyl-CoA hydratase 2 activity in an in vivo assay relying on the synthesis of polyhydroxyalkanoate from the polymerization of 3R-hydroxyacyl-CoA in the peroxisomes of Saccharomyces cerevisiae. AtECH2 contained a peroxisome targeting signal at the C-terminal end, was addressed to the peroxisome in S. cerevisiae, and a fusion protein between AtECH2 and a fluorescent protein was targeted to peroxisomes in onion cells. AtECH2 gene expression was strongest in tissues with high -oxidation activity, such as germinating seedlings and senescing leaves. The contribution of AtECH2 to the degradation of unsaturated fatty acids was assessed by analyzing the carbon flux through the -oxidation cycle in plants that synthesize peroxisomal polyhydroxyalkanoate and that were over- or underexpressing the AtECH2 gene. These studies revealed that AtECH2 participates in vivo to the conversion of the intermediate 3R-hydroxyacyl-CoA, generated by the metabolism of fatty acids with a cis (Z)-unsaturated bond on an even-numbered carbon, to the 2E-enoyl-CoA for further degradation through the core -oxidation cycle.

Received for publication, July 5, 2006 , and in revised form, September 15, 2006.

^* This work was supported by the Fonds National Suisse de la Recherche Scientifique (Grant 3100A0-105874), the Etat de Vaud, the Université de Lausanne, and the Herbette Foundation (to Y. P.) and by the Academy of Finland and the Sigrid Jusélius Foundation (to J. K. H.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 41-21-692-4222; Fax: 41-21-692-4195; E-mail: yves.poirier{at}unil.ch.

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