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

在小檗科、罂粟科和毛茅科植物中，四氢苄基异喹啉衍生物碱来源于两个主要氨基酸L酪氨酸分子。异喹啉部分中的氮原子是由L酪氨酸分子中的一个提供的。然而，异喹啉生物碱的碳骨架来自于醋酸酯，而不是L酪氨酸。通过对编码生物合成酶的基因进行序列分析和比较，可以最好地理解异喹啉生物碱的这种奇怪的另类进化起源。盾叶连翘中的萘基异喹啉生物碱是由乙酸酯衍生而成。一个假定的聚酮合成酶(S)应该催化形成萘基和异喹啉分子。在成环过程中，一个未知来源的氮原子必须插入到折叠聚酮链中才能形成杂环。本项目的目的是通过酶学和分子遗传学方法来确定盾叶树多酮合成酶是否与细菌I、II或植物III型PKS有关，并建立氮原子的直接来源。另一个目标是确定催化C-C苯酚偶联反应的酶的性质。

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.