The charge of endotoxin molecules influences their conformation and IL-6-inducing capacity.
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.
Schromm
A B
AB
Research Center Borstel, Center for Medicine and Biosciences, Department of Immunochemistry and Biochemical Microbiology, Germany.
Brandenburg
K
K
Loppnow
H
H
Zähringer
U
U
Rietschel
E T
ET
Carroll
S F
SF
Koch
M H
MH
Kusumoto
S
S
Seydel
U
U
D000209:Acute-Phase Proteins; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry; D002417:Cattle; D004731:Endotoxins / Q000737:chemistry* / Q000494:pharmacology; D004735:Energy Transfer; D006801:Humans; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000097:blood; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008050:Lipid A / Q000737:chemistry / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000737:chemistry / Q000494:pharmacology; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D010743:Phospholipids / Q000737:chemistry; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013499:Surface Properties; D017356:Synchrotrons; D014961:X-Ray Diffraction; D000099231:Lipopolysaccharide-Binding Protein
D000209:Acute-Phase Proteins; D002352:Carrier Proteins; D004731:Endotoxins; D015850:Interleukin-6; D008050:Lipid A; D008070:Lipopolysaccharides; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D010743:Phospholipids; D000099231:Lipopolysaccharide-Binding Protein