Abstract
The purpose of our studies is to define the physicochemical parameters involved in the activation of host cells by endotoxin and to characterize the processes operative during endotoxin/membrane interaction with the aim of understanding transmembrane signal transduction mechanisms. To this end, we determined the molecular conformation of the lipid A component of various endotoxins (endotoxic conformation) using X-ray small angle diffraction, their intercalation into reconstituted macrophage membranes with fluorescence resonance energy transfer spectroscopy, and their IL-6 inducing capacity in whole blood. We also investigated their influence on ion channels as a possible primary event in cell activation applying patch-clamp techniques to macrophages. We found a strong influence of the molecular charge on the molecular conformation, and we could show that the presence of charged groups and a cone- or wedge-like molecular conformation of lipid A are prerequisites for the expression of bioactivity. We also obtained strong evidence supporting the idea that the interaction of endotoxin with ion channels is one of the very early events in the interaction with the cell and, most likely, in signal transduction.