Interaction of hemoglobin with enterobacterial lipopolysaccharide and lipid A. Physicochemical characterization and biological activity.
The interaction of hemoglobin (Hb) with endotoxins [i.e. with enterobacterial deep rough mutant lipopolysaccharide (LPS) Re and the "endotoxic principle" of LPS, lipid A] was investigated using a variety of physical techniques and with two biological assays, tumor necrosis factor (TNF)-alpha induction in human mononuclear cells and the Limulus amebocyte lysate (LAL) assay. Fourier-transform IR-spectroscopic experiments indicate nonelectrostatic binding to the hydrophobic moiety with a slight rigidification of the lipid A acyl chains, and an increase in the inclination of the lipid A backbone with respect to the membrane surface from 35 degrees to more than 40 degrees due to Hb binding, but no change of the predominantly alpha-helical secondary structures of Hb due to LPS binding. From isothermal titration calorimetry, the molar [Hb] : [endotoxin] binding ratio lies between 1 : 3 and 1 : 5 molar. Synchrotron radiation X-ray diffraction measurements indicate a reorientation of the lipid A aggregates from one cubic structure to another, the final structure belonging to space group Q224. The LPS-induced TNF-alpha production of mononuclear cells is enhanced by Hb, whereas in the LAL assay an LPS concentration-dependent increase or decrease was observed. Although a detailed mechanism of action cannot be given, the enhancement of LPS bioactivity can be understood in the light of the previously presented conformational concept; Hb induces an increase in the conical shape of the lipid A moiety of LPS, higher cross-section of the hydrophobic than the hydrophilic part, and of the inclination angle of the diglucosamine backbone with respect to the direction of the acyl chains.
Jürgens
G
G
Forschungszentrum Borstel, Division of Biophysics, D-23845 Borstel, Germany.
Müller
M
M
Koch
M H
MH
Brandenburg
K
K
D000818:Animals; D002151:Calorimetry; D004305:Dose-Response Relationship, Drug; D004754:Enterobacter / Q000737:chemistry*; D004926:Escherichia coli / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism*; D006737:Horseshoe Crabs / Q000737:chemistry; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008050:Lipid A / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D008070:Lipopolysaccharides / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D014409:Tumor Necrosis Factor-alpha / Q000737:chemistry; D014961:X-Ray Diffraction
D006454:Hemoglobins; D008050:Lipid A; D008055:Lipids; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha