Peroxisomal Δ32-enoyl CoA isomerases and evolution of cytosolic paralogues in embryophytes

Authors

  • Simon Goepfert,

    1. Département de Biologie Moléculaire Végétale, Biophore, Université de Lausanne, CH-1015 Lausanne, Switzerland
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    • Present address: Research and Development, Philip Morris International, Quai Jeanrenaud 56, 2000 Neuchâtel, Switzerland.

  • Charles Vidoudez,

    1. Département de Biologie Moléculaire Végétale, Biophore, Université de Lausanne, CH-1015 Lausanne, Switzerland
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  • Christian Tellgren-Roth,

    1. Bioinformatics Core, Center for Rural Health Research and Education, University of Wyoming, Laramie, WY 82071, USA
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  • Syndie Delessert,

    1. Département de Biologie Moléculaire Végétale, Biophore, Université de Lausanne, CH-1015 Lausanne, Switzerland
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  • J. Kalervo Hiltunen,

    1. Biocenter Oulu and Department of Biochemistry, University of Oulu, FI-90014 Oulu, Finland
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  • Yves Poirier

    Corresponding author
    1. Département de Biologie Moléculaire Végétale, Biophore, Université de Lausanne, CH-1015 Lausanne, Switzerland
      (fax +41 21 692 4195; e-mail yves.poirier@unil.ch).
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(fax +41 21 692 4195; e-mail yves.poirier@unil.ch).

Summary

Δ32-enoyl CoA isomerase (ECI) is an enzyme that participates in the degradation of unsaturated fatty acids through the β-oxidation cycle. Three genes encoding Δ32-enoyl CoA isomerases and named AtECI1, AtECI2 and AtECI3 have been identified in Arabidopsis thaliana. When expressed heterologously in Saccharomyces cerevisiae, all three ECI proteins were targeted to the peroxisomes and enabled the yeast Δeci1 mutant to degrade 10Z-heptadecenoic acid, demonstrating Δ32-enoyl CoA isomerase activity in vivo. Fusion proteins between yellow fluorescent protein and AtECI1 or AtECI2 were targeted to the peroxisomes in onion epidermal cells and Arabidopsis root cells, but a similar fusion protein with AtECI3 remained in the cytosol for both tissues. AtECI3 targeting to peroxisomes in S. cerevisiae was dependent on yeast PEX5, while expression of Arabidopsis PEX5 in yeast failed to target AtECI3 to peroxisomes. AtECI2 and AtECI3 are tandem duplicated genes and show a high level of amino acid conservation, except at the C-terminus; AtECI2 ends with the well conserved peroxisome targeting signal 1 (PTS1) terminal tripeptide PKL, while AtECI3 possesses a divergent HNL terminal tripeptide. Evolutionary analysis of ECI genes in plants revealed several independent duplication events, with duplications occurring in rice and Medicago truncatula, generating homologues with divergent C-termini and no recognizable PTS1. All plant ECI genes analyzed, including AtECI3, are under negative purifying selection, implying functionality of the cytosolic AtECI3. Analysis of the mammalian and fungal genomes failed to identify cytosolic variants of the Δ32-enoyl CoA isomerase, indicating that evolution of cytosolic Δ32-enoyl CoA isomerases is restricted to the plant kingdom.

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