MprF from <i>Pseudomonas aeruginosa</i> is a promiscuous lipid scramblase with broad substrate specificity

The multiple peptide resistance factor (MprF) is a bifunctional membrane protein found in many bacteria, including <i>Pseudomonas aeruginosa</i> and <i>Staphylococcus aureus</i>. MprF modifies inner leaflet lipid headgroups through aminoacylation and translocates modified lipid to the outer leaflet. This activity provides increased resistance to antimicrobial agents. MprF presents a promising target in multiresistant pathogens, but structural information is limited and both substrate specificity and energization of MprF-mediated lipid transport are poorly understood. Here, we present the cryo-EM structure of MprF from <i>P. aeruginosa</i> (<i>Pa</i>MprF) bound to a synthetic nanobody. <i>Pa</i>MprF adopts an "open" conformation with a wide, lipid-exposed groove on the periplasmic side that induces a local membrane deformation in molecular dynamics simulations. Using an in vitro liposome transport assay, we demonstrate that <i>Pa</i>MprF translocates a wide range of different lipids without an external energy source. This suggests that <i>Pa</i>MprF is the first dedicated lipid scramblase to be characterized in bacteria.