Trapped intermediates in crystals of the FMN-dependent oxidase PhzG provide insight into the final steps of phenazine biosynthesis.
Trapped intermediates in crystals of the FMN-dependent oxidase PhzG provide insight into the final steps of phenazine biosynthesis.
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DOI：
10.1107/s0907444913008354
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发表时间：
2013-08
期刊：
影响因子：
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通讯作者：
Ningna Xu;E. Ahuja;P. Janning;D. Mavrodi;L. Thomashow;W. Blankenfeldt
中科院分区：
文献类型：
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作者：
Ningna Xu;E. Ahuja;P. Janning;D. Mavrodi;L. Thomashow;W. Blankenfeldt
吩嗪是许多细菌产生并分泌到环境中的氧化还原活性次级代谢产物。它们是广泛特异性的抗生素，但也作为感染性疾病的毒力和存活因子。吩嗪衍生自氯酸，但其生物合成的重要细节仍不清楚。例如，三个双电子氧化似乎是必要的，在最后的步骤的途径，而只有一个氧化酶，FMN依赖的PhzG，是保守的吩嗪生物合成phz操纵子。在这里，晶体结构的PhzG从荧光假单胞菌2-79和从伯克霍尔德氏菌lata 383在复杂的过量FMN和吩嗪生物合成中间体六氢吩嗪-1，6-二羧酸和四氢吩嗪-1-羧酸在原位产生的报告。与生物化学数据相证实，这些复合物表明，PhzG是吩嗪生物合成中的末端酶，其宽松的底物特异性使其参与吩嗪-1，6-二羧酸（PDC）和吩嗪-1-羧酸（PCA）的生成。这表明，通过PhzG和自发的氧化脱羧黄素依赖性氧化之间的竞争决定的比例的PDC，PCA和未取代的吩嗪的吩嗪生物合成的产品。此外，结果表明，PhzG以其还原形式合成吩嗪。这些还原的分子，而不是完全芳香化的衍生物，是体内可能的终产物，解释了为什么在吩嗪生物合成途径中只需要一种氧化酶。
Phenazines are redox-active secondary metabolites that many bacteria produce and secrete into the environment. They are broad-specificity antibiotics, but also act as virulence and survival factors in infectious diseases. Phenazines are derived from chorismic acid, but important details of their biosynthesis are still unclear. For example, three two-electron oxidations seem to be necessary in the final steps of the pathway, while only one oxidase, the FMN-dependent PhzG, is conserved in the phenazine-biosynthesis phz operon. Here, crystal structures of PhzG from Pseudomonas fluorescens 2-79 and from Burkholderia lata 383 in complex with excess FMN and with the phenazine-biosynthesis intermediates hexahydrophenazine-1,6-dicarboxylate and tetrahydrophenazine-1-carboxylate generated in situ are reported. Corroborated with biochemical data, these complexes demonstrate that PhzG is the terminal enzyme in phenazine biosynthesis and that its relaxed substrate specificity lets it participate in the generation of both phenazine-1,6-dicarboxylic acid (PDC) and phenazine-1-carboxylic acid (PCA). This suggests that competition between flavin-dependent oxidations through PhzG and spontaneous oxidative decarboxylations determines the ratio of PDC, PCA and unsubstituted phenazine as the products of phenazine biosynthesis. Further, the results indicate that PhzG synthesizes phenazines in their reduced form. These reduced molecules, and not the fully aromatized derivatives, are the likely end products in vivo, explaining why only one oxidase is required in the phenazine-biosynthesis pathway.