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球孢白僵菌Beauveria bassiana是一种可寄生在多种昆虫上具较强致病性的真菌,已被广泛用作防治森林、农作物虫害的生物农药[1-2];它产生大量如非核糖体多肽、聚酮类等次生代谢产物,可抑制多种腐生或寄生线虫[3-4]。聚酮、非核糖体多肽及其杂合化合物如聚酮中的红霉素[5]、四环素[6];非核糖体多肽中的青霉素、头孢霉素[7-8];聚酮和非核糖体多肽的杂合化合物如他克莫司[9]、雷帕霉素[10]、博来霉素[11]、埃博霉素[12]等具有免疫抑制剂或抗肿瘤等生理活性[13]。迄今为止,球孢白僵菌中的聚酮和非核糖体多肽杂合型化合物仅有卵孢白僵菌素经基因敲除和异源表达鉴定的报道[3]。聚酮类和非核糖体肽是2类典型的小分子天然次生代谢化合物,分别由聚酮合酶(polyketide synthases, PKS)、非核糖体肽合成酶(nonribosomal peptide synthetases, NRPS)催化简单单体脂肪酸或氨基酸缩合形成[13-14]。真菌聚酮合酶主要属于Ⅰ型PKS[13, 15],其结构域通常包括酮体合成酶(ketosynthase, KS),酰基转移酶(acyltransferase, AT),脱水酶(dehydratase, DH),甲基转移酶(methyltransferase, MT),烯酯酰还原酶(enoylreductase, ER),酮体还原酶(ketoreductase, KR),酰基载体蛋白(acyl carier pretein, ACP)和末端释放酶等[13],短链醇脱氢酶(short chain dehydrogenase/reductase,SDR)家族在PKS中属末端释放酶[16],PKS中的SDR结构域对底物选择具一定的特异性[17];NRPS是一种由多模块组成的多酶复合体,由腺苷酰化结构域(adenylation domain, A),肽酰载体蛋白结构域(phosphopantetheine attachment site, PP)和缩合结构域(condensation domain, C)等3个核心结构域按照特定的时空顺序排列组成[18]。真菌PKS/NRPS酶蛋白复合物含有N端的PKS组件和C端的NRPS组件[19],可催化生成含有酰基和氨酰基构件的聚酮和氨基酸或肽类型化合物的生物合成[9, 20];同时聚酮和氨基酸或肽类化合物能够通过它们化学属性的混合,扩展其产物的生物活性,埃博霉素(epothilone)、雷帕霉素(rapamycin)和博来霉素(bleomycin)是这类混合分子中重要代表,编码这些化合物的PKS/NRPS基因大小均约10 kb[21]。随着高通量测序技术的发展,真菌基因组数据不断增加,基因组数据显示目前已通过结构鉴定、表型筛选和生物活性测定等传统方法分离的天然次生代谢产物仅为冰山一角,真菌基因组中尚有大量的天然次生代谢产物生物合成基因存在;该类基因大多数条件下处于沉默状态,其参与合成的化合物大多尚未被鉴定[22];应用基因组挖掘技术可将这些沉默的生物合成基因分离出来,再通过改变培养基配方和条件或进行遗传学修饰等方式诱导以激发它们全部的次生代谢潜力[23-24]。为了发掘球孢白僵菌中聚酮和非核糖体多肽杂合类化合物的生物合成基因,本研究采用基因组挖掘的方式从其基因组数据中获得1条PKS/NRPS基因(命名Bbpks2),通过生物信息学分析预测其潜在功能,尝试寻找该基因的表达条件,为最终确定其天然产物及对其异源表达奠定基础。
Gene cloning of a PKS/NRPS gene with an SDR domain
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摘要: 聚酮和非核糖体多肽的复合化合物具有独特的生理活性,它们由聚酮合酶/非核糖体肽合成酶(PKS/NRPS)催化合成。目前球孢白僵菌Beauveria bassiana中含SDR结构域的PKS/NRPS酶的生物合成机制尚不清楚,采用基因挖掘技术从球孢白僵菌基因组中分离得到1个PKS/NRPS基因(命名Bbpks2),利用生物信息学分析对其功能进行预测并检测该基因在以6.0 g·L-1麦芽提取物和3.0 g·L-1酵母提取物为基本氮源培养基,7种碳源添加物和以1.8 g·L-1麦芽糖和6.0 g·L-1葡萄糖为基本碳源培养基,4种氮源添加物培养基上的具体表达情况,其中每种添加物含量为4.0 g·L-1。结果显示:Bbpks2基因长度为12 051 bp,编码4 016个氨基酸;其结构域组织顺序为KS-AT-DH-MT-KR-ACP-C-A-PP-SDR,是一种含有SDR结构域的PKS/NRPS;系统进化分析发现,BbPKS2与球孢白僵菌JEF007菌株(PMB64475.1)、头状虫草Tolypocladium capitatum(PNY25600.1)等的PKS/NRPS蛋白聚在同个分支中,可能参与一种聚酮/非核糖体多肽类化合物的生物合成;比较不同氮源、碳源添加物对Bbpks2基因表达的影响,发现该基因在添加了乳糖的培养基上的表达量是其他碳源添加物的3.4倍以上,添加了牛肉浸粉的培养基上表达量是其他氮源添加物的1.3倍以上。该研究为下一步通过异源表达鉴定Bbpks2基因的具体功能,及其调控机理研究和基因资源利用奠定基础。
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关键词:
- 森林保护学 /
- 球孢白僵菌 /
- 杂合PKS/NRPS /
- 生物信息学分析
Abstract: The compound of a hybrid polyketide/nonribosomal peptide, which usually has some particular bioactive activity, is catalyzed by an enzyme of hybrid PKS/NRPS. A hybrid PKS/NRPS containing a SDR domain from Beauveria bassiana has not yet clearly elucidated. To inveastigate this type of gene, the present study obtained a hybrid PKS/NRPS gene (named Bbpks2) from B. bassiana using genome-mining, predicted its gene function with a bioinformatic analysis, and detected the expression level of Bbpks2 in the medium by adding 7 carbon additives(adding 4.0 g·L-1 of every carbon additives) using 6.0 g·L-1 malt extract and 3.0 g·L-1 yeast extract as basic medium, or 4 nitrogen additives(adding 4.0 g·L-1 of every carbon additives) using 1.8 g·L-1 maltose and 6.0 g·L-1 as basic medium, 3 replications every treatment. Results showed that the Bbpks2 gene had 12 051 bp, encoded 4 016 amino acids, and had a sequential domain organization of KS-AT-DH-MT-KR-ACP-C-A-PP-SDR. The proteins of BbPKS2 could belong to a hybrid PKS/NRPS, which was comprised of a short-chain dehydrogenase reductase (SDR) domain. BbPKS2, PMB64475.1 from the strain of B. bassiana JEF007, and PNY25600.1 from Tolypocladium capitatum were three hybrid PKS/NRPS proteins that clustered in the same clade meaning that BbPKS2 could take part in the biosynthesis of a compound belonging to the hybrid polyketides/nonribosomal peptides. Comparing the expression level of the Bbpks2 gene when appending different C or N additives, the expression level of the Bbpks2 gene with lactose added to the basic medium was found to be at least 3.4 times higher than the other C additives, and beef extract 1.3 times higher than the other N additives. The present study could provide some help in further identifying the specific function of the Bbpks2 gene through heterologous expression and could provide a basis for explaining the molecular regulation mechanism when utilizing the gene resource of B. bassiana.-
Key words:
- forest protection /
- Beauveria bassiana /
- hybrid PKS/NRPS /
- bioinformatics analysis
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链接本文:
https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.2019.06.024