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Abstract
Bacterial lipopolysaccharides (LPS) typically consist of a hydrophobic domain known
as lipid A (or endotoxin), a nonrepeating "core" oligosaccharide, and a distal polysaccharide
(or O-antigen). Recent genomic data have facilitated study of LPS assembly in diverse
Gram-negative bacteria, many of which are human or plant pathogens, and have established
the importance of lateral gene transfer in generating structural diversity of O-antigens.
Many enzymes of lipid A biosynthesis like LpxC have been validated as targets for
development of new antibiotics. Key genes for lipid A biosynthesis have unexpectedly
also been found in higher plants, indicating that eukaryotic lipid A-like molecules
may exist. Most significant has been the identification of the plasma membrane protein
TLR4 as the lipid A signaling receptor of animal cells. TLR4 belongs to a family of
innate immunity receptors that possess a large extracellular domain of leucine-rich
repeats, a single trans-membrane segment, and a smaller cytoplasmic signaling region
that engages the adaptor protein MyD88. The expanding knowledge of TLR4 specificity
and its downstream signaling pathways should provide new opportunities for blocking
inflammation associated with infection.