Bases of biocontrol: Sequence predicts synthesis and mode of action of agrocin 84, the Trojan Horse antibiotic that controls crown gall
Bases of biocontrol: Sequence predicts synthesis and mode of action of agrocin 84, the Trojan Horse antibiotic that controls crown gall
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DOI：
10.1073/pnas.0602965103
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发表时间：
2006-06-06
影响因子：
11.1
通讯作者：
Hwang, Ingyu
中科院分区：
文献类型：
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作者：
Kim, Jung-Gun;Park, Young Keun;Hwang, Ingyu
辐射农杆菌K84在全球范围内被用于生物控制由根癌农杆菌引起的冠胆疾病，它产生一种名为agrocin 84的抗农业细菌化合物。我们报道了pAgK84的核苷酸序列，pAgK84是一个44.42kb的质粒，编码产生这种双取代的腺嘌呤核苷酸抗生素。PAgK84编码36个ORF，其中17个(Agn)编码合成agrocin 84或对其免疫。两个基因，Agn，62和agna，编码氨酰tRNA合成酶同源物。我们已经证明，agrocin 84的毒性部分抑制细胞亮氨酰-tRNA合成酶，而对抗生素具有免疫力的AgNB2是这种酶的耐药形式。AGNA是天冬酰胺基tRNA合成酶的截短同系物，可以催化甲基戊酰胺侧基的前体与核苷酸之间的磷酸酯键。我们建议在AgnB1的催化下，通过先前未曾描述的化学作用，产生这种磷酰胺键所需的前体。AgNC7与核糖核苷酸还原酶有关，可产生核苷的3‘-脱氧阿拉伯糖基。生物信息学表明，agnC3、agnC4和agnC6有助于甲基戊酰胺的成熟，而agnC2可能产生与腺嘌呤环结合的葡萄糖呋喃糖侧基团。AgG与细菌输出子有关。AgnG突变体在细胞内积累了agrocin 84，但不输出抗生素。PAgK84是可传递的，编码连接DNA加工的基因，但缺乏IV型分泌系统，提示pAgK84通过动员进行转移。通过序列分析，pAgK1026中的缺失去除了ORIT和必需的trA基因，证实了这种修饰形式的pAgK84具有更强的环境安全性。
Agrobacterium radiobacter K84, used worldwide to biocontrol crown gall disease caused by Agrobacterium tumefaciens, produces an antiagrobacterial compound called agrocin 84. We report the nucleotide sequence of pAgK84, a 44.42-kb plasmid coding for production of this disubstituted adenine nucleotide antibiotic. pAgK84 encodes 36 ORFs, 17 of which (agn) code for synthesis of or immunity to agrocin 84. Two genes, agn,62 and agnA, encode aminoacyl tRNA synthetase homologues. We have shown that the toxic moiety of agrocin 84 inhibits cellular leucyl-tRNA synthetases and AgnB2, which confers immunity to the antibiotic, is a resistant form of this enzyme. AgnA, a truncated homologue of asparaginyl tRNA synthetase could catalyze the phosphoramidate bond between a precursor of the methyl pentanamide side group and the nucleotide. We propose previously undescribed chemistry, catalyzed by AgnB1, to generate the precursor necessary for this phosphoramidate linkage. AgnC7 is related to ribonucleotide reductases and could generate the 3'-deoxyarabinose moiety of the nucleoside. Bioinformatics suggest that agnC3, agnC4, and agnC6 contribute to maturation of the methyl pentanamide, whereas agnC2 may produce the glucofuranose side group bound to the adenine ring. AgnG is related to bacterial exporters. An agnG mutant accumulated agrocin 84 intracellularly but did not export the antibiotic. pAgK84 is transmissible and encodes genes for conjugative DNA processing but lacks a type IV secretion system, suggesting that pAgK84 transfers by mobilization. By sequence analysis, the deletion engineered into pAgK1026 removed the oriT and essential tra genes, confirming the enhanced environmental safety of this modified form of pAgK84.