Le Tung B K, Fiedler Hans-Peter, den Hengst Chris D, Ahn Sang Kyun, Maxwell Anthony, Buttner Mark J
Department of Molecular Microbiology, John Innes Centre, Colney Lane, Norwich NR4 7UH, UK.
Mol Microbiol. 2009 Jun;72(6):1462-74. doi: 10.1111/j.1365-2958.2009.06735.x. Epub 2009 May 15.
Because most antibiotics are potentially lethal to the producing organism, there must be mechanisms to ensure that the machinery responsible for export of the mature antibiotic is in place at the time of biosynthesis. Simocyclinone D8 is a potent DNA gyrase inhibitor produced by Streptomyces antibioticus Tü 6040. Within the simocyclinone biosynthetic cluster are two divergently transcribed genes, simR and simX, encoding proteins that resemble the TetR/TetA repressor-efflux pump pair that cause widespread resistance to clinically important tetracyclines. Engineered expression of simX from a strong, heterologous promoter conferred high level simocyclinone D8 resistance on Streptomyces lividans, showing that simX encodes a simocyclinone efflux pump. Transcription of simX is controlled by SimR, which directly represses the simX and simR promoters by binding to two operator sites in the simX-simR intergenic region. Simocyclinone D8 abolishes DNA binding by SimR, providing a mechanism that couples the biosynthesis of simocyclinone to its export. In addition, an intermediate in the biosynthetic pathway, simocyclinone C4, which is essentially inactive as a DNA gyrase inhibitor, also induces simX expression in vivo and relieves simX repression by SimR in vitro.
由于大多数抗生素对产生它们的生物体具有潜在的致死性，所以必须存在一些机制来确保在生物合成时，负责输出成熟抗生素的机制已经就位。西莫环素D8是由抗生素链霉菌Tü 6040产生的一种有效的DNA回旋酶抑制剂。在西莫环素生物合成基因簇中，有两个反向转录的基因simR和simX，它们编码的蛋白质类似于TetR/TetA阻遏物-外排泵对，这对蛋白会导致对临床上重要的四环素产生广泛耐药性。从一个强的异源启动子对simX进行工程表达，可使淡紫链霉菌对西莫环素D8产生高水平抗性，这表明simX编码一个西莫环素外排泵。simX的转录受SimR控制，SimR通过结合simX-simR基因间区域的两个操纵位点直接抑制simX和simR启动子。西莫环素D8可消除SimR与DNA的结合，提供了一种将西莫环素的生物合成与其输出相耦合的机制。此外，生物合成途径中的一种中间体西莫环素C4，作为一种DNA回旋酶抑制剂基本上没有活性，但它在体内也能诱导simX表达，并在体外解除SimR对simX的抑制。
