2014.07.21【英译中】SCI 连载之七

小妮丫头 (流火) 路人甲
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发表于:2014-07-21 15:09 [只看楼主] [划词开启]

2014.07.21【英译中】SCI 连载之七


LAL regulatory system

LAL调节系统

Constitutive overexpression of a putative pathway-specific LAL regulator was shown to successfully induce the expression of the silent type I modular polyketide synthase (PKS) gene cluster in Streptomyces ambofaciens 23877, enabling the identification of a unique structural class of polyketides with promising antitumor activity (Laureti et al.2011). S. ambofaciens 23877 produces two antibiotics, the macrolide spiramycin and the pyrrole-amide congocidine. Sequence analysis of its genome showed that S. ambofaciens 23877 contains several secondary metabolite biosynthetic gene clusters, including a giant type I modular PKS gene cluster. This cluster is composed of 25 genes, nine of which encode PKSs, and spans almost 150 kb, making it one of the largest polyketide biosynthetic gene clusters described to date. The metabolic product(s) of this gene cluster have not been determined and transcriptional analyses showed that this cluster is not expressed under laboratory growth conditions. The constitutive expression of a regulatory gene within this cluster, encoding a protein that is similar to the LAL family of proteins, triggered the expression of the biosynthetic genes. This led to the identification of four 51-membered glycosylated macrolides, named stambomycins A–D, as metabolic products of the gene cluster (Laureti et al.2011). Database searches have identified genes that encode LAL regulators within numerous cryptic biosynthetic gene clusters in actinomycete genomes, for which metabolic product(s) remain to be discovered, suggesting that constitutive expression of such pathway-specific activators represents a powerful approach for the discovery of novel bioactive natural products.

假定途径特异性LAL调节子的结构性过表达,已经成功显示其能够诱导Streptomyces ambofaciens 23877中的I型聚合酮酶沉默基因簇表达,并且已经见顶了一系列结构唯一的具有抗癌抗生素活性的聚酮化合物。S. ambofaciens 23877产生两种抗生素,大环内酯类螺旋霉素和吡咯酰胺类刚果杀菌素。对S. ambofaciens 23877进行基因组序列分析发现其含有一些次级代谢产物基因簇,当中就包括IPKS基因簇。这个基因簇有25个基因组成,其中有9个负责编码聚合酮酶,大小有150kb之多,成为目前最大的聚合酮酶合成基因簇。迄今为止,这个基因簇的代谢产物还没有被检测到。对其进行转录水平分析,这个基因簇在实验室的生长条件下还没有表达。该基因簇的调节基因负责编码类似于LAL蛋白家族的一种蛋白质,其结构性表达能够出发合成基因的表达。这样,我们从该基因簇的次级代谢产物中分离鉴定出451环的糖基化的大环内酯类化合物——stambomycins A-D。在目前发现次级代谢产物数据库中搜索发现了放线菌基因组中有很多由潜在生物合成基因簇编码的LAL调节子基因,这表明这种途径的特异性调节子的结构性表达代表了一种发现新的活性天然产物的强有力的方法。

 

The metabolism-remodeling approach

代谢-重建方法

Although activation of biosynthetic genes at the transcriptional level is primarily important for exploiting useful metabolites, perturbation of biosynthesis by modulating, for example, the supply of precursors may also be a promising approach to enhancing the cell’s capability to produce secondary metabolites, a process termed metabolic engineering (Olano et al.2008). One method of enhancing the yields of secondary metabolites consists of modulating fatty acid biosynthesis using small molecules. For example, screening of a large number (>30,000) of small molecules, seeking candidates that might “remodel” the yields of actinorhodin in S. coelicolor, identified 19 compounds that caused elevated or precocious production of actinorhodin (Craney et al.2012). Further examination of four of these 19 molecules, antibiotic remodeling compounds (ARC)2, 3, 4, and 5, showed that (1) low concentrations of ARC2 enhanced the yield of actinorhodin, (2) the ARC2 effect can be observed in other actinomycetes, suggesting that the molecular target and mechanism of ARC2 is conserved in various actinomycetes, and (3) several of the most active molecules are structurally similar to the known antimicrobial agent triclosan, an inhibitor of fatty acid synthesis. The ARC2 effects therefore involve the inhibition of the enoyl reductase activity of FabI, an enzyme that catalyzes the final and rate-limiting step in fatty acid biosynthesis. Since fatty acid and polyketide synthesis share the precursors acetyl-CoA and malonyl-CoA, partial inhibition of fatty acid synthesis could recruit those acyl-CoAs preferentially to polyketide biosynthesis.

虽然转录水平上的生物合成基因的激活对开发有用代谢产物十分的重要,调整生物合成途径,就如为强化细胞产生次级代谢产物的能力而提供前体化合物也是一种十分有用的方法,这种方法也被称作代谢工程学。一种提高次级代谢产物产量的方法其中包括利用小模块的模块化脂肪酸生物合成。比如说,在筛选大量小分子化合物(>30,000)的过程中我们发现,S. coelicolor中利用探针筛选出的可能能够重新改造放线紫红素产量的化合物,分离鉴定出了19种能够提高或者早一步形成放线紫红素的化合物。对这19种化合物重点4个进行进一步检测发现,抗生素重建的化合物(ARC)2, 3, 45表现了如下几个特征:(1)、低浓度的ARC2就能提高放线紫红素的产量;(2)ARC2能够在其他放线菌中检测到,说明ARC2分子的作用靶点和作用机制在多种放线菌中十分保守;(3)、一些活性较强的分子在结构上与已知的抗菌药剂三氯生十分相似,是一种脂肪酸合成的抑制剂。因此,ARC2分子的作用影响包括对FabI烯(酯)酰还原酶活性的影响,这种酶在脂肪酸合成途径中负责催化最后一步,是一个限速步骤。由于脂肪酸合成和聚合酮合成途径有共同的乙酰辅酶A和丙二酸单酰辅酶A前体,对脂肪酸合成代谢的部分抑制作用会优先使聚合酮合成途径在乙酰辅酶A的供给上优先得到满足。

分类: 英语

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