Overexpression and Characterization of an Aminoglycoside 6'-N-Acetyltransferase with Broad Specificity from an -Poly-L-lysine Producer, Streptomyces albulus IFO14147

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Abstract
Streptomyces albulus IFO14147 produces ε-poly-l-lysine, which exhibits antimicrobial activity. In the MIC studies with antibiotics, S. albulus IFO14147 was shown to be resistant to kanamycin and amikacin, which are aminoglycoside (AG) antibiotics. We report here the isolation of the AG-resistance gene from S. albulus IFO14147 and the substrate specificity of the gene product, AAC(6′)-Isa, which catalyzes N-acetylation at the 6′ position of AGs, thereby inactivating them. Kinetic studies revealed that this enzyme has remarkably wide substrate specificity. The Vmax/Km values determined for AGs vary by a factor of up to 6,300, a much wider range than those observed for the AAC(6′)s from Enterococcus faecium [AAC(6′)-Ii] and Salmonella enteritidis [AAC(6′)-Iy]. In addition, AAC(6′)-Isa was able to acetylate lividomycin A, which has a hydroxy group at the 6′ position. Enzymatically acetylated lividomycin A was found to be highly susceptible to mild base hydrolysis, suggesting that the enzyme also catalyzes O-acetyltransfer.

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