Allen P. Zinkle, Mariana Bunoro Batista, Carmen M. Herrera, Satchal K. Erramilli, Brian Kloss, Khuram U. Ashraf, Kamil Nosol, Guozhi Zhang, Rosemary J. Cater, Michael T. Marty, Anthony A. Kossiakoff, M. Stephen Trent, Rie Nygaard, Phillip J. Stansfeld, Filippo Mancia
Polymyxins are used to treat infections caused by multidrug-resistant Gram-negative bacteria. They are cationic peptides that target the negatively charged lipid A component of lipopolysaccharides, disrupting the outer membrane and lysing the cell. Polymyxin resistance is conferred by inner-membrane enzymes, such as phosphoethanolamine transferases, which add positively charged phosphoethanolamine to lipid A. Here, we present the structure of MCR-1, a plasmid-encoded phosphoethanolamine transferase, in its liganded form. The phosphatidylethanolamine donor substrate is bound near the active site in the periplasmic domain, and lipid A is bound over 20 Å away, within the transmembrane region. Integrating structural, biochemical, and drug-resistance data with computational analyses, we propose a two-state model in which the periplasmic domain rotates to bring the active site to lipid A, near the preferential phosphate modification site for MCR-1. This enzymatic mechanism may be generally applicable to other phosphoform transferases with large, globular soluble domains.