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Figure 1. Lipid A is the major lipid of the outer leaflet of the outer membrane of Gram-negative bacteria and an important agent of morbidity and mortality in humans. Lipid A activates the innate immune systems of a variety of higher metazoans, including arthropods and mammals. This illustration depicts LPS from E. coli K-12, with its proximate lipid A moiety, which is conjugated with two molecules of 3-deoxy-D-manno-oct-2-ulosonic acid (KDO I and KDO II) sugar, and the sugar moieties of the inner core oligosaccharide chain (Hep, heptose; Gal, galactose; Glc, glucose and the phospho-amino compound pyrophosphate-ethanolamine, PPE. Lipid A has multiple, fully saturated acyl chains (bottom) that attach by amide and ester bonds to two residues of the phosphorylated glucosamine backbone (GlcN). Biochemical studies provide evidence for lipids from the green alga, Chlorella, with several diagnostic characters of bacterial lipid A. The present study uses lipid A binding agents from fungi and arthropods to demonstrate the presence of this lipid in chloroplasts of algae and vascular plants. Adapted from Fig. 1
of Ferguson et al. (1998) Science 282, 2215–2220, kindly supplied by Professor Ulrich Zahringer and used with his permission.
