Isolation, structural elucidation and biosynthesis of 3-hydroxy-6-dimethylallylindolin-2-one, a novel prenylated indole derivative from Actinoplanes missouriensis
作者:Ryutaro Satou、Miho Izumikawa、Yohei Katsuyama、Misato Matsui、Motoki Takagi、Kazuo Shin-ya、Yasuo Ohnishi
DOI:10.1038/ja.2013.116
日期:2014.3
Many prenylated indole derivatives are widely distributed in nature. Recently, two Streptomyces prenyltransferases, IptA and its homolog SCO7467, were identified in the biosynthetic pathways for 6-dimethylallylindole (DMAI)-3-carbaldehyde and 5-DMAI-3-acetonitrile, respectively. Here, we isolated a novel prenylated indole derivative, 3-hydroxy-6-dimethylallylindolin (DMAIN)-2-one, based on systematic purification of metabolites from a rare actinomycete, Actinoplanes missouriensis NBRC 102363. The structure of 3-hydroxy-6-DMAIN-2-one was determined by HR-MS and NMR analyses. We found that A. missouriensis produced not only 3-hydroxy-6-DMAIN-2-one but also 6-dimethylallyltryptophan (DMAT) and 6-DMAI when grown in PYM (peptone-yeast extract-MgSO4) medium. We searched the complete genome of A. missouriensis for biosynthesis genes of these compounds and found a gene cluster composed of an iptA homolog (AMIS_22580, named iptA-Am) and a putative tryptophanase gene (AMIS_22590, named tnaA-Am). We constructed a tnaA-Am-deleted (ÎtnaA-Am) strain and found that it produced 6-DMAT but did not produce 6-DMAI or 3-hydroxy-6-DMAIN-2-one. Exogenous addition of 6-DMAI to mutant ÎtnaA-Am resulted in the production of 3-hydroxy-6-DMAIN-2-one. Furthermore, in vitro enzyme assays using recombinant proteins produced by Escherichia coli demonstrated that 6-DMAI was synthesized from tryptophan and dimethylallyl pyrophosphate in the presence of both IptA-Am and TnaA-Am, and that IptA-Am preferred tryptophan to indole as the substrate. From these results, we concluded that the iptA-AmâtnaA-Am gene cluster is responsible for the biosynthesis of 3-hydroxy-6-DMAIN-2-one. Presumably, tryptophan is converted into 6-DMAT by IptA-Am and 6-DMAT is then converted into 6-DMAI by TnaA-Am. 6-DMAI appears to be converted into 3-hydroxy-6-DMAIN-2-one by the function of some unknown oxidases in A. missouriensis.
自然界中广泛分布着许多前酰基吲哚衍生物。最近,在 6-二甲基烯丙基吲哚(DMAI)-3-甲醛和 5-DMAI-3-乙腈的生物合成途径中发现了两种链霉菌前炔基转移酶 IptA 及其同源物 SCO7467。在这里,我们通过系统纯化稀有放线菌--密苏里放线菌(Actinoplanes missouriensis NBRC 102363)的代谢产物,分离出了一种新型前酰基吲哚衍生物--3-羟基-6-二甲基烯丙基吲哚啉(DMAIN)-2-酮。通过 HR-MS 和 NMR 分析确定了 3-hydroxy-6-DMAIN-2-one 的结构。我们发现,当 missouriensis 在PYM(蛋白胨-酵母提取物-硫酸镁)培养基中生长时,不仅会产生 3-羟基-6-DMAIN-2-酮,还会产生 6-二甲基烯丙基色氨酸(DMAT)和 6-DMAI。我们在 A. missouriensis 的完整基因组中搜索了这些化合物的生物合成基因,发现了一个由一个 iptA 同源物(AMIS_22580,命名为 iptA-Am)和一个推测的色氨酸酶基因(AMIS_22590,命名为 tnaA-Am)组成的基因簇。我们构建了一个 tnaA-Am 缺失(δtnaA-Am)菌株,发现它能产生 6-DMAT,但不产生 6-DMAI 或 3-羟基-6-DMAIN-2-酮。在突变体δtnaA-Am 中外源添加 6-DMAI 会产生 3-羟基-6-DMAIN-2-酮。此外,利用大肠杆菌产生的重组蛋白进行的体外酶测定表明,在 IptA-Am 和 TnaA-Am 存在的情况下,6-DMAI 是由色氨酸和焦磷酸二甲基烯丙基酯合成的,而且 IptA-Am 更喜欢以色氨酸而不是吲哚作为底物。根据这些结果,我们得出结论:iptA-AmâtnaA-Am 基因簇负责 3-hydroxy-6-DMAIN-2-one 的生物合成。据推测,色氨酸通过 IptA-Am 转化为 6-DMAT,然后 6-DMAT 通过 TnaA-Am 转化为 6-DMAI。6-DMAI 在密苏里金合欢属中似乎通过一些未知氧化酶的作用转化为 3-羟基-6-DMAIN-2-酮。