The Charge of Endotoxin Molecules Influences Their Conformation and IL-6-Inducing Capacity

• Published in: The Journal of immunology (1950) 1998-11, Vol.161 (10), p.5464-5471
• Main Authors: Schromm, Andra B, Brandenburg, Klaus, Loppnow, Harald, Zahringer, Ulrich, Rietschel, Ernst Th, Carroll, Stephen F, Koch, Michel H. J, Kusumoto, Shoichi, Seydel, Ulrich
• Format: Article
• Language: English
• Subjects: Acute-Phase Proteins; Animals; Biological Transport; Carrier Proteins - chemistry; Cattle; Endotoxins - chemistry; Endotoxins - pharmacology; Energy Transfer; Humans; Interleukin-6 - biosynthesis; Interleukin-6 - blood; Leukocytes, Mononuclear - metabolism; Lipid A - chemistry; Lipid A - pharmacology; Lipopolysaccharides - chemistry; Lipopolysaccharides - pharmacology; Macromolecular Substances; Membrane Glycoproteins; Phospholipids - chemistry; Protein Conformation; Spectrometry, Fluorescence; Surface Properties; Synchrotrons; X-Ray Diffraction
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.161.10.5464

The activation of cells by endotoxin (LPS) is one of the early host responses to infections with Gram-negative bacteria. The lipid A part of LPS molecules is known to represent the endotoxic principle; however, the specific requirements for the expression of biologic activity are still not fully understood. We previously found that a specific molecular conformation (endotoxic conformation) is a prerequisite for lipid A to be biologically active. In this study, we have investigated the interdependence of molecular charge and conformation of natural and chemically modified LPS and lipid A and its transport and intercalation into phospholipid membranes mediated by human LPS-binding protein, as well as IL-6 production after stimulation of whole blood or PBMCs. We found that the number, nature, and location of negative charges strongly modulate the molecular conformation of endotoxin. In addition, the LPS-binding protein-mediated transport of LPS into phospholipid membranes depends on the presence of net negative charge, yet charge is only a necessary, but not a sufficient, prerequisite for transport and intercalation. The biologic activity is determined mainly by the molecular conformation: only conical molecules are highly biologically active, whereas cylindrical ones are largely inactive. We could demonstrate that the net negative charge of the lipid A component and its distribution within the hydrophilic headgroup strongly influence the molecular conformation and, therefore, also the biologic activity.