Characterization of aminoglycoside phosphotransferase APH(3')-IIIa, an enterococcal enzyme conferring resistance to aminoglycoside antibiotics

Abstract

<p>Aminoglycosides antibiotics are a clinically relevant class of antibiotics that continue to find use despite the appearance of organisms resistant to these therapeutic agents. Resistance to aminoglycosides may be manifested through several mechanisms including alteration of the ribosomal target, active efflux of the compounds or chemical modification of the antibiotics. The latter mechanism of resistance can occur through O -adenylation, N -acetylation or O -phosphorylation. An aminoglycoside phosphotransferase, APH(3' )-IIIa modifies a broad range of aminoglycoside antibiotics through ATP dependent phosphorylation of the 3' hydroxyl group rendering these antibiotics inoffensive to the bacterium. In an attempt to gain a more thorough understanding of the molecular mechanisms of this drug modification, studies were initiated to determine its substrate specificity and identify residues required for substrate recognition and enzyme activity. The results reported herein, identify residues which line the ATP binding pocket as well as identify substrate structures required for enzyme/substrate interactions. These mechanistic studies further identify a functional similarity between APH(3' )-IIIa and eukaryotic protein kinases. These data have mapped both enzyme and substrate structures required for aminoglycoside detoxification and form the basis for further rational drug design studies.</p>