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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Title
Bases of biocontrol: Sequence predicts synthesis and mode of action of agrocin 84, the Trojan Horse antibiotic that controls crown gall
Author(s)
J G Kim; B K Park; Sung Uk Kim; Doil Choi; B H Nahm; Jae Sun Moon; J S Reader; S K Farrand; I Hwang
Bibliographic Citation
Proceedings of National Academy of Sciences of United States of America, vol. 103, no. 23, pp. 8846-8851
Publication Year
2006
Abstract
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, agnB2 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.
Keyword
Agrobacterium radiobacterBiological controlpAgK84
ISSN
0027-8424
Publisher
Natl Acad Sciences
DOI
http://dx.doi.org/10.1073/pnas.0602965103
Type
Article
Appears in Collections:
Division of Research on National Challenges > Plant Systems Engineering Research > 1. Journal Articles
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