Examining the Functional Consequences of the Flexibility of Aminoglycoside Phosphotransferase (3’)-IIIa

The use of aminoglycoside antibiotics began in 1940 with the discovery of streptomycin. The overuse and misuse of antibiotics has resulted in prevalent cases of antibiotic resistance. The most common source of aminoglycoside resistance is the presence of enzymes that covalently modify the antibiotics at specific locations. One such enzyme, APH(3′)-IIIa [the aminoglycoside phosphotransferase three prime three a] conveys resistance by transferring the γ-phosphate [gamma phosphate] from ATP [adenosine triphosphate] onto the 3′ [three prime] carbon of the aminoglycoside antibiotic sugar ring. APH(3′)-IIIa has been shown to be flexible in solution and this flexibility is proposed to be responsible for its large substrate profile. Upon binding the aminoglycoside, APH(3′)-IIIa adopts a well-defined structure. All previous experiments were conducted in vitro. Here, various aspects associated with the flexibility of APH(3′)-IIIa are further examined in vivo. In-cell NMR [nuclear magnetic resonance] experiments are used to determine the protein dynamics of APH(3′)-IIIa in the crowded environment of the cell. Next, the flexibility of APH(3′)-IIIa is examined when binding more rigid aminoglycoside antibiotics: sisomicin and netilmicin in vitro.