A polyketide synthase of Plumbago indica that catalyzes the formation of hexaketide pyrones

Authors

  • Karin Springob,

    1.  Leibniz-Institut für Pflanzenbiochemie, Halle (Saale), Germany
    2.  Donald Danforth Plant Science Center, St Louis, MO, USA
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  • Supachai Samappito,

    1.  Leibniz-Institut für Pflanzenbiochemie, Halle (Saale), Germany
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    • Present address
      Department of Biotechnology, Faculty of Technology, Mahasarakham University, Mahasarakham 44001, Thailand.

  • Aphacha Jindaprasert,

    1.  Leibniz-Institut für Pflanzenbiochemie, Halle (Saale), Germany
    2.  Department of Pharmacognosy, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, Thailand
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  • Jürgen Schmidt,

    1.  Leibniz-Institut für Pflanzenbiochemie, Halle (Saale), Germany
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  • Jonathan E Page,

    1.  Leibniz-Institut für Pflanzenbiochemie, Halle (Saale), Germany
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    • Plant Biotechnology Institute, National Research Council of Canada, 110 Gymnasium Place, Saskatoon, SK, S7N 0W9 Canada.

  • Wanchai De-Eknamkul,

    1.  Department of Pharmacognosy, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, Thailand
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  • Toni M Kutchan

    1.  Leibniz-Institut für Pflanzenbiochemie, Halle (Saale), Germany
    2.  Donald Danforth Plant Science Center, St Louis, MO, USA
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K. Springob, Donald Danforth Plant Science Center, 975 North Warson Road, St Louis, MO 63132, USA
Fax: +1 314 5871590
Tel: +1 314 5871490
E-mail: kspringob@danforthcenter.org

Abstract

Plumbago indica L. contains naphthoquinones that are derived from six acetate units. To characterize the enzyme catalyzing the first step in the biosynthesis of these metabolites, a cDNA encoding a type III polyketide synthase (PKS) was isolated from roots of P. indica. The translated polypeptide shared 47–60% identical residues with PKSs from other plant species. Recombinant P. indica PKS expressed in Escherichia coli accepted acetyl-CoA as starter and carried out five decarboxylative condensations with malonyl coenzyme A (-CoA). The resulting hexaketide was not folded into a naphthalene derivative. Instead, an α-pyrone, 6-(2′,4′-dihydroxy-6′-methylphenyl)-4-hydroxy-2-pyrone, was produced. In addition, formation of α-pyrones with linear keto side chains derived from three to six acetate units was observed. As phenylpyrones could not be detected in P. indica roots, we propose that the novel PKS is involved in the biosynthesis of naphthoquinones, and additional cofactors are probably required for the biosynthesis of these secondary metabolites in vivo.

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