Backbone resonance assignments of a promiscuous aminoglycoside antibiotic resistance enzyme; the aminoglycoside phosphotransferase(3′)-IIIa

The aminoglycoside phosphotransferase(3′)-IIIa (APH) is a promiscuous enzyme and renders a large number of structurally diverse aminoglycoside antibiotics useless against infectious bacteria. A remarkable property of this ~31 kDa enzyme is in its unusual dynamic behavior in solution; the apo-form of the enzyme exchanges all of its backbone amide protons within 15 h of exposure to D 2 O while aminoglycoside-bound forms retain ~40% of the amide protons even after >90 h of exposure. Moreover, the number of observable peaks and their dispersion in HSQC spectra varies with each aminoglycoside, rendering the resonance assignments very challenging. Therefore, the binary APH–tobramycin complex, which shows the largest number of well-resolved peaks, was used for the backbone resonance assignments (Cα, C, N, H, and some Cβ) of this protein (BMRB-16337).