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. 2009 Apr;50 Suppl(Suppl):S103-8.
doi: 10.1194/jlr.R800060-JLR200. Epub 2008 Oct 29.

Discovery of new biosynthetic pathways: the lipid A story

Christian R H Raetz  1 , Ziqiang Guan, Brian O Ingram, David A Six, Feng Song, Xiaoyuan Wang, Jinshi Zhao
Affiliations

Discovery of new biosynthetic pathways: the lipid A story

Christian R H Raetz et al. J Lipid Res. 2009 Apr.

Abstract

The outer monolayer of the outer membrane of Gram-negative bacteria consists of the lipid A component of lipopolysaccharide (LPS), a glucosamine-based saccharolipid that is assembled on the inner surface of the inner membrane. The first six enzymes of the lipid A pathway are required for bacterial growth and are excellent targets for the development of new antibiotics. Following assembly, the ABC transporter MsbA flips nascent LPS to the periplasmic side of the inner membrane, whereupon additional transport proteins direct it to the outer surface of the outer membrane. Depending on the bacterium, various covalent modifications of the lipid A moiety may occur during the transit of LPS to the outer membrane. These extra-cytoplasmic modification enzymes are therefore useful as reporters for monitoring LPS trafficking. Because of its conserved structure in diverse Gram-negative pathogens, lipid A is recognized as foreign by the TLR4/MD2 receptor of the mammalian innate immune system, resulting in rapid macrophage activation and robust cytokine production.

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Figures

Fig. 1.
Fig. 1.
Schematic representation of the E. coli cell envelope.
Fig. 2.
Fig. 2.
The constitutive pathway of lipid A biosynthesis in E. coli.
Fig. 3.
Fig. 3.
The structure of lipid A in E. coli versus F. novicida.
Fig. 4.
Fig. 4.
Lipid A modification enzymes in F. novicida.
Fig. 5.
Fig. 5.
Topography of lipid A export and modification in F. novicida.
See this image and copyright information in PMC

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