Immune evasion through membrane remodeling is a hallmark of
Yersinia pestispathogenesis. Yersiniaremodels its membrane during its life cycle as it alternates between mammalian hosts (37 °C) and ambient (21 °C to 26 °C) temperatures of the arthropod transmission vector or external environment. This shift in growth temperature induces changes in number and length of acyl groups on the lipid A portion of lipopolysaccharide (LPS) for the enteric pathogens Yersinia pseudotuberculosis( Ypt) and Yersinia enterocolitica( Ye), as well as the causative agent of plague, Yersinia pestis( Yp). Addition of a C16 fatty acid (palmitate) to lipid A by the outer membrane acyltransferase enzyme PagP occurs in immunostimulatory Yptand Yestrains, but not in immune-evasive Yp. Analysis of Yp pagPgene sequences identified a single-nucleotide polymorphism that results in a premature stop in translation, yielding a truncated, nonfunctional enzyme. Upon repair of this polymorphism to the sequence present in Yptand Ye, lipid A isolated from a Yp pagP+strain synthesized two structures with the C16 fatty acids located in acyloxyacyl linkage at the 2′ and 3′ positions of the diglucosamine backbone. Structural modifications were confirmed by mass spectrometry and gas chromatography. With the genotypic restoration of PagP enzymatic activity in Yp, a significant increase in lipid A endotoxicity mediated through the MyD88 and TRIF/TRAM arms of the TLR4-signaling pathway was observed. Discovery and repair of an evolutionarily lost lipid A modifying enzyme provides evidence of lipid A as a crucial determinant in Ypinfectivity, pathogenesis, and host innate immune evasion.