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

在小檗科、罂粟科和毛茛科植物中，四氢苄基异喹啉衍生的生物碱来源于两个初级氨基酸l -酪氨酸分子。异喹啉部分中的氮原子是由一个l -酪氨酸分子提供的。然而，异喹啉类生物碱的碳骨架来源于乙酸酯而不是l -酪氨酸。这种奇特的异喹啉生物碱的进化起源可以通过对编码生物合成酶的基因的序列分析和比较来最好地理解。peltatum（三phyophyllum peltatum）中的萘基异喹啉生物碱是由醋酸盐衍生而来的。假定的聚酮合成酶应该催化萘和异喹啉基团的形成。在成环过程中，必须在折叠的聚酮链中插入一个来源不明的氮原子，才能形成杂环。本项目旨在通过酶学和分子遗传学的方法确定T. peltatum聚酮合成酶是否与细菌I-型、II-型或植物III型PKSs有关，并确定氮原子的直接来源。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.