The dual role of lipopolysaccharide as effector and target molecule

Lipopolysaccharides (LPS) are major integral components of the outer membra ne of Gram-negative bacteria being exclusively located in its outer leaflet facing the bacterial environment. Chemically they consist in different bac terial strains of a highly variable O-specific chain, a less variable core oligosaccharide, and a lipid component, termed lipid A, with low structural variability, LPS participate in the physiological membrane functions and a re, therefore, essential for bacterial growth and viability. They contribut e to the low membrane permeability and increase the resistance towards hydr ophobic agents. They are also the primary target for the attack of antibact erial drugs and proteins such as components of the host's immune response. When set free LPS elicit, in higher organisms, a broad spectrum of biologic al activities. They play an important role in the manifestation of Gram-neg ative infection and are therefore termed endotoxins. Physico-chemical param eters such as the molecular conformation and the charges of the lipid A por tion, which is responsible for endotoxin-typical biological activities and is therefore termed the 'endotoxic principle' of LPS, are correlated with t he biological activity of chemically different LPS.