Microcystin biosynthesis in Planktothrix:: Genes, evolution, and manipulation
Microcystin biosynthesis in Planktothrix:: Genes, evolution, and manipulation
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DOI：
10.1128/jb.185.2.564-572.2003
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发表时间：
2003-01-01
影响因子：
3.2
通讯作者：
Dittmann, E
中科院分区：
文献类型：
--
作者：
Christiansen, G;Fastner, J;Dittmann, E
微囊藻毒素是由各种蓝藻非核糖体合成的环状七肽毒素的一个非常大的家族。微囊藻毒素特异性地抑制真核蛋白磷酸酶I和2A。它们突出的可变性使它们特别适用于研究肽合成酶及其基因的结构-功能关系的进化。微囊藻毒素合成酶基因的分析为组合生物合成的潜力和局限性提供了有价值的线索。我们已经测序和分析了55.6 kb的潜在的微囊藻毒素合成酶基因（MCY）簇从丝状蓝藻浮游丝藻agardhii CYA 126。该簇包含肽合成酶（mcyABC）、聚酮合成酶（PKS; mcyD）、由肽合成酶和PKS模块组成的嵌合酶（mcyEG）、推定的硫酯酶（mcyT）、推定的ABC转运蛋白（mcyH）和推定的肽修饰酶（mcyJ）的基因。基因产物中的基因内容和排列以及特定结构域的序列与单细胞蓝藻微囊藻中的MCY簇不同。这些数据表明，mcy簇是从节球藻素（一种相关的五肽）生物合成基因进化而来，而不是向节球藻素基因进化。我们的数据不支持完整的MCY基因簇在属间水平转移的观点。我们已经建立了一个协议，稳定的遗传转化的浮游发菌属，其特征在于多细胞丝表现出连续运动。靶向突变的mcyJ揭示了其作为O-甲基转移酶的基因编码的功能。突变细胞产生一种新的微囊藻毒素变体，其对蛋白磷酸酶的抑制活性降低。
Microcystins represent an extraordinarily large family of cyclic heptapeptide toxins that are nonribosomally synthesized by various cyanobacteria. Microcystins specifically inhibit the eukaryotic protein phosphatases I and 2A. Their outstanding variability makes them particularly useful for studies on the evolution of structure-function relationships in peptide synthetases and their genes. Analyses of microcystin synthetase genes provide valuable clues for the potential and limits of combinatorial biosynthesis. We have sequenced and analyzed 55.6 kb of the potential microcystin synthetase gene (mcy) cluster from the filamentous cyanobacterium Planktothrix agardhii CYA 126. The cluster contains genes for peptide synthetases (mcyABC), polyketide synthases (PKSs; mcyD), chimeric enzymes composed of peptide synthetase and PKS modules (mcyEG), a putative thioesterase (mcyT), a putative ABC transporter (mcyH), and a putative peptide-modifying enzyme (mcyJ). The gene content and arrangement and the sequence of specific domains in the gene products differ from those of the mcy cluster in Microcystis, a unicellular cyanobacterium. The data suggest an evolution of mcy clusters from, rather than to, genes for nodularin (a related pentapeptide) biosynthesis. Our data do not support the idea of horizontal gene transfer of complete mcy gene clusters between the genera. We have established a protocol for stable genetic transformation of Planktothrix, a genus that is characterized by multicellular filaments exhibiting continuous motility. Targeted mutation of mcyJ revealed its function as a gene coding for a O-methyltransferase. The mutant cells produce a novel microcystin variant exhibiting reduced inhibitory activity toward protein phosphatases.