摘要/Abstract

在四环素类化合物SF2575的生物合成中, 4-keto-anhydrotetracycline (4-keto-ATC, 2)中C-4的羰基先由SsfF还原为羟基得到(R)-4-hydroxyl-ATC (7), 7经过一系列修饰可以得到最终化合物. 在之前的研究中, 发现基因簇tjh介导了一系列新型四环素类化合物的产生, 而且在ΔtjhO5::2R突变株中得到了三个骨架结构与7类似但C-4构型为S构型的化合物. 生物信息学分析显示TjhD2与SsfF同源性较高, 它们可能有类似的功能. 通过回补SF2575生物合成中编码C-4酮基还原酶的基因ssfF到ΔtjhD2突变株中, 成功得到了两个新的四环素类化合物15和16. 这两个化合物的C-4都发生了异构, 且化合物15是16的苷元. 该组合生物合成策略不仅成功获得了两个新的四环素类似物, 同时也证实了tjhD2的功能. 虽然SsfF和TjhD2在体内展现类似的催化功能, 但其得到的产物构型却相反. 这一结果可以应用到四环素类化合物的改造, 同时也为进一步探寻酮基还原酶立体选择性还原的机制奠定了基础.
关键词: 组合生物合成, 生物合成, II型聚酮类化合物, 四环素, 异构
During the biosynthesis of SF2575, a tetracycline antibiotic, the ketone of C-4 in 4-keto-anhydrotetracycline (4-keto-ATC, 2) is reduced by SsfF to form (R)-4-hydroxyl-ATC (7) which can be further transformed to the final product. According to the previous study, gene cluster tjh mediates the production of a series of new tetracyclines. Three new compounds in ΔtjhO5::2R mutant which are structurally similar with 4-keto-ATC but with (S)-C-4 were obtained. TjhD2 with high similarity with SsfF revealed by bioinformatic analysis indicates that these two enzymes may exhibit the similar enzymatic function. Two new tetracyclines via complementation of ssfF encoding C-4 ketone reductase into ΔtjhD2 mutant were successfully obtained. C-4 of these two compounds is all isomerized and 15 is the aglycone of 16. The combinatorial biosynthesis strategy not only successfully discovers two new natural products, but also verifies the function of TjhD2. Moreover, although TjhD2 and SsfF possess the similar catalytic function, they mediate the production of compounds with different configuration. These results may be applied in modification of tetracyclines and lay the foundation for further exploring the specific mechanism of stereoselective reduction of ketoreductases.
Key words: combinatorial biosynthesis, biosynthesis, type II polyketides, tetracycline, isomerization


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