Crystal Structures of the <i>Acinetobacter baumannii</i> Macrolide Phosphotransferase E

<i>Acinetobacter baumannii</i> (<i>A. baumannii</i>) challenges clinical infection treatment due to its resistance to various antibiotics. Multiple resistance genes in the core genome or mobile elements contribute to multidrug resistance in <i>A. baumannii</i>. Macrolide phosphotransferase gene <i>mphE</i> has been identified in <i>A. baumannii</i>, which is particularly relevant to macrolide antibiotics. Here, we determined the structure of MphE protein in three states: the apo state, the complex state with erythromycin and guanosine triphosphate (GTP), and the complex state with azithromycin and guanosine. Interestingly, GTP and two magnesium ions were observed in the erythromycin-bound MphE complex. This structure captured the active state of MphE, in which the magnesium ions stabilized the active site and assisted the transfer of phosphoryl groups. Based on these structures, we verified that the conserved residues Asp29, Asp194, His199, and Asp213 play an important role in the catalytic phosphorylation of MphE leading to drug resistance. Our work helps to understand the molecular basis of drug resistance and provides reference targets for optimizing macrolide antibiotics.