Lipopolysaccharide chemical layers

Cell envelopes of archaea diifer distinctly from those of bacteria and show remarkable structural and chemical diversity. Murein, the typical sacculus-forming polymer of bacteria, and lipopolysaccharide-containing outer membranes, characteristic of gramnegative bacteria, are not found in archaea. Crystalline surface layers (S-layers) are common in both prokaryotic domains and they consist of protein or glycoprotein subunits (Table 1). However, S-layers in archaea have a form-stabilizing function especially when they are the only envelope layer outside the cytoplasmic membrane, while in bacteria S-layers have no distinct form-stabilizing function. 

Purified endotoxin consists only of lipopolysaccharide. This itself has three distinct chemical regions an inner core called lipid A. an intermediate polysaccharide layer, and an outer polysaccharide side chain. Lipid A, a highly substituted disaccharide of gluct amiiie, is responsible for pyrogenicity and other immunological and biological properties associated with endotoxin. 

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