LAL家族转录因子对莫能菌素生物合成途径的调控机理研究

Biosynthesis of the sacondary metabolites is initiated by the pathway-specific regulators activiating or desuppressing the transcription of the biosynthetic gene clusters. The function of the transcriptional factors is the one of the key scentific issues to be probed. Here we will study the regulatory patterns of the transcriptional factor MonH on monensin biosynthetic gene cluster (mon). MonH belongs to the large ATP-binding regulators of the LuxR family (LAL). The regulatory effects of MonH on the transcription of mon cluster and the monensin biosynthesis will be examined by the in vivo knockout, complementation, and overexpression of monH and the promoter probing. The regulated genes of MonH on the mon cluster and their promoter activities will be ascertained. The interaction between MonH and the promoters of the target genes will be elucidated by the in vitro DNase I footpring and electrophoretic mobility shift assay (EMSA). Recognition and binding sites of MonH on promoter sequences will be identified. The fine regulatory mechanism of MonH on monensin biosynthetic pathway will be established. This project has important roles in the fundamental research and practical application. The results of this project would not only provide the new theoretical knowledge for our understanding the regulation of the secondary metabolism, but also be applicable in the strain improvement to increase the quality and productivity of antibiotics.

链霉菌次级代谢产物的生成是通过调节因子对生物合成基因簇的转录激活或阻遏解除来实现的，转录因子的功能研究是次级代谢途径特异性调控的关键科学问题之一。本项目以莫能菌素生物合成基因簇（mon）为模式，研究LuxR家族大ATP结合调控因子（LAL）MonH的调控特征。通过转录因子基因monH敲除、回补、过表达菌株的转录分析和启动子探测等体内分析，研究MonH对莫能菌素生物合成基因簇转录、产物合成的影响，发现所调控的功能基因及启动子活性和级联调控关系；通过电泳迁移阻滞和DNase I足迹等体外分析，研究转录因子MonH与靶基因启动子区域的相互作用，发现和鉴定出MonH识别并结合的DNA序列；从而探明MonH对莫能菌素次级代谢途径的特异性调控机理。一方面将丰富次级代谢调控的基础理论和积累新知识，另一方面可用于菌种改造，提高抗生素的产量和质量。因此，本项目具有重大科学意义和重要应用价值。

莫能菌素是肉桂地链霉菌产生的聚醚类抗生素，用于球虫病防治，还可作为促进生长剂而广泛应用于养殖业。莫能菌素生物合成基因簇包括I型聚酮合成基因（monAI-AX）、II型硫酯酶基因（monAIX、monAX、monCII）、后修饰基因（monBI-II，monCI、monD、monE）、推定的抗性基因(monT)和3个途径特异性调控基因(monH、monRI、monRII)。针对莫能菌素生物合成调控机理不清的问题，研究了MonH 和DasR的精细调控机理。鉴定出了整个莫能菌素生物合成基因簇有8个转录单元，发现MonH、MonRI、MonRII 3个途径特异性转录因子都正调控莫能菌素生物合成，它们之间是级联调控关系，MonH调控MonRII，MonRII调控MonRI。它们还调控了monCII-monE、monAX和monD、monT的转录。在富营养条件下，DasR是正向调控莫能菌素生物合成的全局转录因子，呈现双层调控，既调控途径特异性调控基因monRII，也调控功能基因monAIX、monE、monT。组合过表达途径特异性和全局性调控基因，显著提高了莫能菌素的产量。本研究丰富了链霉菌抗生素生物合成的级联调控机理，为高产莫能菌素菌种改造提供了依据。