Early evolutionary loss of the lipid A modifying enzyme PagP resulting in innate immune evasion in <i>Yersinia pestis</i>.

Abstract

Immune evasion through membrane remodeling is a hallmark of <i>Yersinia pestis</i> pathogenesis. <i>Yersinia</i> remodels 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 <i>Yersinia pseudotuberculosis</i> (<i>Ypt</i>) and <i>Yersinia enterocolitica</i> (<i>Ye</i>), as well as the causative agent of plague, <i>Yersinia pestis</i> (<i>Yp</i>). Addition of a C16 fatty acid (palmitate) to lipid A by the outer membrane acyltransferase enzyme PagP occurs in immunostimulatory <i>Ypt</i> and <i>Ye</i> strains, but not in immune-evasive <i>Yp</i> Analysis of <i>Yp pagP</i> gene 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 <i>Ypt</i> and <i>Ye</i>, lipid A isolated from a <i>Yp pagP+</i> 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 <i>Yp</i>, 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 <i>Yp</i> infectivity, pathogenesis, and host innate immune evasion.