Structural and Functional Survey of Environmental Aminoglycoside Acetyltransferases Reveals Functionality of Resistance Enzymes

Aminoglycoside N-acetyltransferases (AACs) confer resistance against the clinical use of aminoglycoside antibiotics. The origin of AACs can be traced to environmental microbial species representing a vast reservoir for new and emerging resistance enzymes, which are currently undercharacterized. Here, we performed detailed structural characterization and functional analyses of four metagenomic AAC (meta-AACs) enzymes recently identified in a survey of agricultural and grassland soil microbiomes (Forsberg et al. Nature 2014, 509, 612). These enzymes are new members of the Gcn5-Related-N-Acetyltransferase superfamily and confer resistance to the aminoglycosides gentamicin C, sisomicin, and tobramycin. Moreover, the meta-AAC0020 enzyme demonstrated activity comparable with an AAC(3)-I enzyme that serves as a model AAC enzyme identified in a clinical bacterial isolate. The crystal structure of meta-AAC0020 in complex with sisomicin confirmed an unexpected AAC(6′) regiospecificity of this enzyme and revealed a ...