State Key Laboratory of Phytochemistry and Plant Resources in West China, CAS Center for Excellence in Molecular Plant Sciences, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650204, China.
Org Biomol Chem. 2019 Jan 16;17(3):477-481. doi: 10.1039/c8ob02847h.
Toxoflavin (1), fervenulin (2), and reumycin (3), known to be produced by plant pathogen Burkholderia glumae BGR1, are structurally related 7-azapteridine antibiotics. Previous biosynthetic studies revealed that N-methyltransferase ToxA from B. glumae BGR1 catalyzed the sequential methylation at N6 and N1 in pyrimido[5,4-e]-as-triazine-5,7(6H,8H)-dione (4) to generate 1. However, the N8 methylation of 4 in the biosynthesis of fervenulin remains unclear. To explore the N-methyltransferases required for the biosynthesis of 1 and 2, we identified and characterized the fervenulin and toxoflavin biosynthetic gene clusters in S. hiroshimensis ATCC53615. On the basis of the structures of intermediates accumulated from the four N-methyltransferase gene inactivation mutants and systematic enzymatic methylation reactions, the tailoring steps for the methylation order in the biosynthesis of 1 and 2 were proposed. The N-methylation order and routes for the biosynthesis of fervenulin and toxoflavin in S. hiroshimensis are more complex and represent an obvious departure from those in B. glumae BGR1.
依赖菌素（1）、 fervenulin（2）和雷美霉素（3），已知由植物病原体 Burkholderia glumae BGR1 产生，是结构相关的 7-氮杂蝶啶抗生素。先前的生物合成研究表明，来自 B. glumae BGR1 的 N-甲基转移酶 ToxA 催化嘧啶并[5,4-e]-as-三嗪-5,7(6H,8H)-二酮（4）中 N6 和 N1 的顺序甲基化，生成 1。然而，在 fervenulin 的生物合成中，4 中 N8 的甲基化仍然不清楚。为了探索 1 和 2 生物合成所需的 N-甲基转移酶，我们鉴定并表征了 S. hiroshimensis ATCC53615 中 fervenulin 和 toxoflavin 生物合成基因簇。基于四个 N-甲基转移酶基因失活突变体积累的中间体结构和系统酶促甲基化反应，提出了 1 和 2 生物合成中甲基化顺序的修饰步骤。S. hiroshimensis 中 fervenulin 和 toxoflavin 的生物合成中的 N-甲基化顺序和途径更加复杂，与 B. glumae BGR1 中的途径明显不同。
