Talk abstracts

Talk on Friday 04:30-04:45pm submitted by Aditya Kulkarni

Biosynthesis of a Trojan Horse Antibiotic - Albomycin δ2

Aditya S Kulkarni (Department of Biological Sciences, Ohio University , Athens, OH), Yu Zeng (Department of Biological Sciences, Ohio University , Athens, OH), Preeti B Patil (Department of Biological Sciences, Ohio University , Athens, OH), Wei Zhou (Department of Biological Sciences, Ohio University , Athens, OH), Shawn Chen (Department of Biological Sciences, Ohio University , Athens, OH)

Abstract:
Albomycin δ2 is a potent antibiotic produced by Streptomyces sp. ATCC 700974. Albomycin enters the bacterial cell using a ferrichrome transporter and releases a seryl-tRNA synthetase inhibitor on cleavage by cellular proteases. This “Trojan horse” mechanism allows it to stall bacterial protein synthesis at very low MICs, <~0.005 µg/mL in case of E.coli. Albomycin possesses a peptidyl nucleoside structure with unique modifications of N4-carbamylation and N3-methylation on cytosine. Cytosine is linked to a thioxylo-furanose ring which has not been reported in any other natural/synthetic product. The albomycin (abm) biosynthetic gene cluster was identified from Streptomyces sp. ATCC 700974 using a probe based on sidA, encoding an N5-L-Ornithine monooxygenase, a gene involved in ferrichrome biosynthesis. Genes encoding a methyltransferase (abmI) and a carbamoyltransferase (abmE) were found in the gene cluster. A homologous gene cluster (ctj) was found in the sequenced genome of Streptomyces sp.C . The ctj gene cluster also encodes methyltransferase(ctjF) and carbamoyltransferase (ctjE) homologs. The ctj gene cluster likely encodes a Trojan horse antibiotic with a modified nucleobase and thioxylo-furanose ring. A ΔabmE mutant of Streptomyces sp. ATCC 700974 strain resulted in a loss of production of wild type albomycin δ2. Heterologously expressed AbmE was shown to carbamylate the cytosine nucleoside of an unmodified albomycin intermediate at the N4 position in vitro. Wild type albomycin production in the ΔabmE mutant was restored by ctjE or abmE on plasmid. A ΔabmI mutant strain produced a desmethyl-descarbamoyl analogue of albomycin. AbmI, heterologously expressed and purified from E.coli, flexible in substrate specificity, was shown to methylate a variety of cytosine nucleosides. In summary, we discovered and identified the gene cluster involved in albomycin biosynthesis . The discovery of two nucleoside base modification genes involved in albomycin biosynthesis sets the stage to apply them to modify nucleoside antibiotics.

References:
1.Zeng Y, Kulkarni A,Yang Z,Patil PB, Zhou W, Chi X,Van Lanen S,Chen S. Biosynthesis of Albomycinδ2 Provides a Template for Assembling Siderophore and Aminoacyl-tRNA Synthetase Inhibitor Conjugates. ACS Chemical Biology DOI: 10.1021/cb300173x

2. Yu Zeng, Hervé Roy, Preeti B. Patil, Michael Ibba, and Shawn Chen Characterization of Two Seryl-tRNA Synthetases in Albomycin-Producing Streptomyces sp. Strain ATCC 700974 ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Nov. 2009, p. 4619–4627

Keywords: Nucleoside antibiotics, Base Modification, tRNA synthetase inhibitor