Resistance to aminoglycoside antibiotics is mediated by chemical modifications including phosphorylation, nucleotidylation and acetylation. The largest family of aminoglycoside-modifying enzymes are the amino glycoside 6'-N-acetyltransferase (AAC) enzymes. There are at least 60 of these enzymes but only structural knowledge of five at the time of this structure determination.
Here we present the apo structure of AAC(6')-Ih, an enzyme from the emerging pathogen Acinetobacter baumanni. The dimer is most closely related to the dimeric AAC(6')-Iy (PDB 1S3Z) but shows different active site features from further structural homologs including E. coli AAC(6')-Ib (PDB 1V0C). These active site features may resault in an altered substrate specificity spectrum and will be the focus of further studies.