Structural and Functional Characterization of the LPS Transport Complex LptDE from Pathogenic Gram-negative Bacteria

摘要

Lipopolysaccharide (LPS) is critical component of the asymmetric outer membrane of Gram-negative bacteria. It plays a number of roles, including shielding the bacterium from harmful compounds capable of diffusing across symmetric phospholipid bilayers and allowing the bacterium to inhabit harsh environments. In doing so LPS, is a major factor contributing to the pathogenicity of Gram-negative species. Because LPS is essential, the cellular machinery required to synthesize and transport it is also essential. Among this machinery are the proteins LptD and LptE. Like LPS, LptD and LptE are localized to the outer membrane where they form an intimate complex responsible for the final step of LPS installation. Because the LptDE complex is surface exposed, it represents a promising target for the development of new antimicrobial therapies that are desperately required to address the growing threat of drug-resistant Gram-negative species. As a first step toward targeting LptDE for drug development, we have determined four x-ray crystal structures of the LptDE complex from three pathogenic Gram-negative species: Yersinia pestis, Klebsiella pneumoniae, and Pseudomonas aeruginosa. These structures have shed light on the mechanism of LPS installation into the outer membrane. In addition, we developed a phage-based tool to study LptD function in vivo using targeted LptD mutations and a knockout/complementation strategy.