Molecular genetics of acetate-derived naphtylisoquinoline alkaloid biosynthesis in the liane Triphyophyllum peltatum

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In members of the plant families Berberidaceae, Papaveraceae and Ranunculaceae, tetrahydrobenzylisoquinoline-derived alkaloids originate from two molecules of the primary amino acid L-tyrosine. The nitrogen atom found in the isoquinoline moiety is provided by one of the L-tyrosine molecules. However, the carbon skeleton of isoquinoline alkaloids found in species of the Ancistrocladaceae and Dioncophyllaceae originates from acetate rather than from L-tyrosine. This curious alternative evolutionary origin of isoquinoline alkaloids can best be understood by a sequence analysis and comparison of the genes encoding the biosynthetic enzymes. Naphthylisoquinoline alkaloids in the liane Triphyophyllum peltatum (Doncophyllaceae) are derived form acetate. A putative polyketide synthase(s) should catalyze the formation of the naphthyl- and isoquinoline moietes. During ring formation, a nitrogen atom of unknown origin must be inserted into the folding polyketide chain in order to form the heterocycle. It is aimed in this project to establish by enzymological and molecular genetic methods whether the T. peltatum polyketide synthase is related to bacterial type I-, II- or to plant type III PKSs and to establish the immediate origin of the nitrogen atom. An additional goal is to identify the nature of the enzyme that catalyzes the C-C phenol coupling reaction.