75(P59) 高等植物におけるステロール及びトリテルペンの生合成 : トリテルペン合成酵素の分子進化(ポスター発表の部)

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The cyclizations of oxidosqualene into tetra- and pentacyclic carbon skeleton of sterols and triterpenes are one of the most complex and fascinating reactions found in nature which are catalyzed by the enzyme termed as oxidosqualene cyclases (OSCs). In order to obtain insights in molecular evolution of triterpene synthases and their catalytic mechanisms, cDNA cloning of triterpene synthases from Panax ginseng, Olea europaea, Taraxacum officinale, Betula platyphylla, Cucurbita pepo, Glycyrrhiza glabra, Luffa cylindrica, Pisum sativum and Allium macrostemon, was conducted. Homology based PCR method was attempted to obtain the cDNA of OSCs. So far, 24 clones were obtained from the above plants. To determine the enzyme functions of the translates, they were expressed in ERG7 deficient yeast mutant. Accumulation of β-amyrin (clone Y), lupeol (clone W) or cucurbitadienol (clone Q) in the cells of yeast transformants proved clone Y, W and Q to encode β-amyrin synthase, lupeol synthase and cucurbitadienol synthase proteins, respectively. In order to clarify the evolutional relationships among plant OSCs, sequence homologies between all the cloned plant OSCs have been calculated and a phylogenetic tree constructed. Cycloartenol synthase clones form one big cluster in a phylogenetic tree, clearly demonstrating that plants have acquired cycloartenol synthase gene before diverged into individual species during the course of evolution, and that triterpene synthase genes have evolved from cycloartenol synthase genes. Lupeol and β-amyrin synthases from various plants also form an each cluster respectively in the tree. It is very interesting to note that unlike mono-, sesqui- and diterpene cyclases, plant triterpene synthases show correlation between molecular evolution and reaction mechanism.
天然有機化合物討論会の論文
1999-09-01

75(P59) 高等植物におけるステロール及びトリテルペンの生合成 : トリテルペン合成酵素の分子進化(ポスター発表の部)

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