Losada Armando A, Méndez Carmen, Salas José A, Olano Carlos
Departamento de Biología Funcional e Instituto Universitario de Oncología del Principado de Asturias (I.U.O.P.A), Universidad de Oviedo, C/Julian Claveria s/n, 33006, Oviedo, Asturias, Spain.
Microb Cell Fact. 2017 May 25;16(1):93. doi: 10.1186/s12934-017-0709-6.
The biosynthesis pathway of benzoxazole compounds caboxamycin and nataxazole have been recently elucidated. Both compounds share one of their precursors, 3-hydroxyanthranilate (two units in the case of nataxazole). In addition, caboxamycin structure includes a salicylate moiety while 6-methylsalycilate is the third scaffold in nataxazole. Pathways cross-talk has been identified in caboxamycin producer Streptomyces sp. NTK937, between caboxamycin and enterobactin pathways, and nataxazole producer Streptomyces sp. Tü6176, between nataxazole and coelibactin pathways. These events represent a natural form of combinatorial biosynthesis.
Eleven novel caboxamycin derivatives, and five putative novel derivatives, bearing distinct substitutions in the aryl ring have been generated. These compounds were produced by heterologous expression of several caboxamycin biosynthesis genes in Streptomyces albus J1074 (two compounds), by combinatorial biosynthesis in Streptomyces sp. NTK937 expressing nataxazole iterative polyketide synthase (two compounds) and by mutasynthesis using a nonproducing mutant of Streptomyces sp. NTK937 (12 compounds). Some of the compounds showed improved bioactive properties in comparison with caboxamycin.
In addition to the benzoxazoles naturally biosynthesized by the caboxamycin and nataxazole producers, a greater structural diversity can be generated by mutasynthesis and heterologous expression of benzoxazole biosynthesis genes, not only in the respective producer strains but also in non-benzoxazole producers such as S. albus strains. These results show that the production of a wide variety of benzoxazoles could be potentially achieved by the sole expression of cbxBCDE genes (or orthologs thereof), supplying an external source of salicylate-like compounds, or with the concomitant expression of other genes capable of synthesizing salicylates, such as cbxA or natPK.
苯并恶唑类化合物卡波霉素和纳他霉素的生物合成途径最近已被阐明。这两种化合物共享它们的一种前体，即3-羟基邻氨基苯甲酸（纳他霉素中有两个单位）。此外，卡波霉素的结构包含一个水杨酸部分，而6-甲基水杨酸是纳他霉素中的第三个支架结构。在卡波霉素产生菌链霉菌属NTK937中，已确定卡波霉素和肠杆菌素途径之间存在途径间串扰；在纳他霉素产生菌链霉菌属Tü6176中，已确定纳他霉素和天蓝色菌素途径之间存在途径间串扰。这些事件代表了组合生物合成的一种自然形式。
已产生了11种新型卡波霉素衍生物以及5种推定的新型衍生物，它们在芳环上具有不同的取代基。这些化合物是通过在白色链霉菌J1074中异源表达几个卡波霉素生物合成基因产生的（两种化合物），通过在表达纳他霉素迭代聚酮合酶的链霉菌属NTK937中进行组合生物合成产生的（两种化合物），以及通过使用链霉菌属NTK937的非产生突变体进行突变生物合成产生的（12种化合物）。与卡波霉素相比，一些化合物表现出改善的生物活性特性。
除了由卡波霉素和纳他霉素产生菌天然生物合成的苯并恶唑类化合物外，通过苯并恶唑生物合成基因的突变生物合成和异源表达，不仅在各自的产生菌菌株中，而且在非苯并恶唑产生菌如白色链霉菌菌株中，都可以产生更大的结构多样性。这些结果表明，仅通过表达cbxBCDE基因（或其直系同源基因），提供类似水杨酸化合物的外部来源，或同时表达能够合成水杨酸的其他基因，如cbxA或natPK，就有可能实现多种苯并恶唑类化合物的生产。
