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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Identification of unique mechanisms for triterpene biosynthesis in Botryococcus braunii
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Identification of unique mechanisms for triterpene biosynthesis in Botryococcus braunii

机译：鉴定Botryococcus braunii中三萜生物合成的独特机制

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Botryococcene biosynthesis is thought to resemble that of squa-lene, a metabolite essential for sterol metabolism in all eukaryotes. Squalene arises from an initial condensation of two molecules of farnesyl diphosphate (FPP) to form presqualene diphosphate (PSPP), which then undergoes a reductive rearrangement to form squalene. In principle, botryococcene could arise from an alternative rearrangement of the presqualene intermediate. Because of these proposed similarities, we predicted that a botryococcene synthase would resemble squalene synthase and hence isolated squalene synthase-like genes from Botryococcus braunii race B. While B. braunii does harbor at least one typical squalene synthase, none of the other three squalene synthase-like (SSL) genes encodes for botryococcene biosynthesis directly. SSL-1 catalyzes the biosynthesis of PSPP and SSL-2 the biosynthesis of bisfar-nesyl ether, while SSL-3 does not appear able to directly utilize FPP as a substrate. However, when combinations of the synthase-like enzymes were mixed together, in vivo and in vitro, robust botryococcene (SSL-1+SSL-3) or squalene biosynthesis (SSL1+SSL-2) was observed. These findings were unexpected because squalene synthase, an ancient and likely progenitor to the other Botryococcus triterpene synthases, catalyzes a two-step reaction within a single enzyme unit without intermediate release, yet in B. braunii, these activities appear to have separated and evolved interde-pendently for specialized triterpene oil production greater than 500 MYA. Coexpression of the SSL-1 and SSL-3 genes in different configurations, as independent genes, as gene fusions, or targeted to intracellular membranes, also demonstrate the potential for engineering even greater efficiencies of botryococcene biosynthesis.
机译：Botryococcene的生物合成被认为与方透镜相似，方透镜是所有真核生物中固醇代谢必不可少的代谢产物。角鲨烯是由两个分子的法呢基二磷酸酯（FPP）最初缩合形成角鲨烯二磷酸酯（PSPP）而产生的，然后再进行还原性重排以形成角鲨烯。原则上，葡萄角鲨烯可能来自角鲨烯中间体的另一种重排。由于这些拟议的相似性，我们预测，Botryococcene合酶将类似于角鲨烯合酶，并因此分离自Botryococcus braunii人种B的角鲨烯合酶样基因。尽管B. braunii确实具有至少一种典型的角鲨烯合酶，但其他三种角鲨烯合酶均不包含类（SSL）基因直接编码葡萄球菌的生物合成。 SSL-1可以催化PSPP的生物合成，而SSL-2可以催化比法萘酯醚的生物合成，而SSL-3似乎不能直接利用FPP作为底物。然而，当将合成酶样酶的组合混合在一起时，在体内和体外，观察到健壮的葡萄球菌（SSL-1 + SSL-3）或角鲨烯生物合成（SSL1 + SSL-2）。这些发现是出乎意料的，因为角鲨烯合酶是其他Botryococcus triterpene合酶的古老且可能的祖先，可在单个酶单元内催化两步反应，而没有中间释放，但在B. braunii中，这些活性似乎已经分离并进化了-专门用于生产大于500 MYA的三萜油。 SSL-1和SSL-3基因以不同的配置作为独立基因，作为基因融合体或以细胞内膜为目标的共表达，也表明有可能工程化更高效率的葡萄球菌生物合成。

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