Direct evidence that the rifamycin polyketide synthase assembles polyketide chains processively
Direct evidence that the rifamycin polyketide synthase assembles polyketide chains processively
复制标题
DOI：
10.1073/pnas.96.16.9051
复制
发表时间：
1999-08-03
影响因子：
11.1
通讯作者：
Floss, HG
中科院分区：
文献类型：
--
作者：
Yu, TW;Shen, YM;Floss, HG
利福霉素B的聚酮骨架在由Rifa-rife基因编码的I型利福霉素聚酮合成酶(PKS)上的组装被riff基因的产物终止，riff基因是一种酰胺合成酶，它将完整的十一酮释放为其大环内酰胺。RIFE的失活给出了一个不产生利福霉素B的突变体，它仍然积累了一系列从四酮到十酮的线性多酮，这也在野生型中检测到，这表明PKS以一种过程的方式工作。因此，RifD模块8和RIFE模块9和模块10基因的中断也会导致这种线性多酮的积累。提前终止聚酮组装体。四酮类化合物携带的是未修饰的芳香族发色团，而五到十酮类化合物则发生了氧化环化反应，生成了萘醌，这表明这种修饰发生在PKS组装过程中，而不是在组装之后。其中一个积累的化合物的结构和O-18实验表明，这种氧化环化反应产生了8-羟基-7，8-二氢对苯二酚结构，经过原阿霉素X阶段后，脱氢为8-羟基对苯二酚。
The assembly of the polyketide backbone of rifamycin B on the type I rifamycin polyketide synthase (PKS), encoded by the rifA-rifE genes, is terminated by the product of the rifF gene, an amide synthase that releases the completed undecaketide as its macrocyclic lactam. Inactivation of rifE gives a rifamycin B nonproducing mutant that still accumulates a series of linear polyketides ranging from the tetra- to a decaketide, also detected in the wild type, demonstrating that the PKS operates in a processive manner. Disruptions of the rifD module 8 and rifE module 9 and module 10 genes also result in accumulation of such linear polyketides as a consequence. of premature termination of polyketide assembly. Whereas the tetraketide carries an unmodified aromatic chromophore, the penta- through decaketides have undergone oxidative cyclization to the naphthoquinone, suggesting that this modification occurs during, not after, PKS assembly. The structure of one of the accumulated compounds together with O-18 experiments suggests that this oxidative cyclization produces an 8-hydroxy-7,8-dihydronaphthoquinone structure that, after the stage of proansamycin X, is dehydrogenated to an 8-hydroxynaphthoquinone.