Gram-negative bacteria gain resistance by modifying the lipid A moiety present on their outer membrane. One such modification is the addition of phosphoethanolamine to lipidA brought about by an enzyme called lipid A phosphoethanolamine transferase (EptA). The crystal structure of EptA was determined revealing a helical transmembrane domain linked to a periplasmicfacing soluble domain with the active site comprising residues from both domains. Biophysical studies suggest the enzyme adopts multiple conformations essential for binding two different sized lipid substrates. This study will aid in the design of novel therapeutic agents for the treatment of antimicrobial resistant bacterial infections.