Structural analysis of a novel substrate-free form of the aminoglycoside 6′-N-acetyltransferase from Enterococcus faecium

Aminoglycoside acetyltransferases (AACs) catalyze the transfer of an acetyl group between acetyl-CoA and an aminoglycoside, producing CoA and an acetylated aminoglycoside. AAC(6′)-Ii enzymes target the amino group linked to the 6′ C atom in an aminoglycoside. Several structures of the AAC(6′)-Ii from Enterococcus faecium [Ef-AAC(6′)-Ii] have been reported to date. However, the detailed mechanism of its enzymatic function remains elusive. In this study, the crystal structure of Ef-AAC(6′)-Ii was determined in a novel substrate-free form. Based on structural analysis, it is proposed that Ef-AAC(6′)-Ii sequentially undergoes conformational selection and induced fit for substrate binding. These results therefore provide a novel viewpoint on the mechanism of action of Ef-AAC(6′)-Ii.