Composition and structure of lipopolysaccharide-human plasma low density lipoprotein complex. Analytical ultracentrifugation, 31P-NMR, ESR and fluorescence spectroscopy studies.
Complexes of Salmonella typhimurium lipopolysaccharide toxin (LPS) with low density lipoproteins (LDL) prepared in vitro have been analyzed. LPS-LDL complexes were found to comprise approx. 0.24 mg LPS/mg LDL protein. The major protein of complexes was apolipoprotein apoB-100 (greater than or equal to 90-95%). Incorporation of LPS molecules into LDL was accompanied by small changes in lipid composition, i.e. the phosphatidylcholine content was diminished by approx. 11% and the free fatty acid concentration was raised 2-fold. Analytical ultracentrifugation showed that insertion of LPS into LDL results in the increase of a portion of particles with higher density (lower flotation coefficient) compared to initial LDL. As was evidenced by ESR, in LPS-LDL complexes, the phospholipid hydrocarbon chains are more ordered than in LDL. 31P-NMR spectra indicated that in LPS-LDL complexes the mobility of phospholipid polar headgroups is restricted in comparison with LDL. Application of the shift reagent (Pr3+) revealed that phospholipid molecules form a monolayer structure on the surface of complexes. Upon binding of LPS to LDL, a maximum of the apoB intrinsic fluorescence was slightly red-shifted (1-2 nm) which may testify that the localization of apoB remains nearly unchanged. For LPS-LDL complexes, the accessibility of apoB fluorophores to quenchers (I-, Cs+, acrylamide) did not dramatically differ from that of LDL. It is concluded that rather large amounts of LPS (about 9-10 molecules) can accommodate in one LDL particle without severely perturbing its original composition and structure. Moreover, in the LPS-LDL complexes, oligosaccharide chains of LPS screen notably neither phospholipid polar headgroups nor, what is very important, apoB. LPS-LDL complexes are suggested to be able in vivo to bind to cellular apoB/E receptors, possible LPS receptors and scavenger-receptors of macrophages (monocytes).
Victorov
A V
AV
Central Research Institute of Epidemiology, USSR Ministry of Public Health, Moscow.
Medvedeva
N V
NV
Gladkaya
E M
EM
Morozkin
A D
AD
Podrez
E A
EA
Kosykh
V A
VA
Yurkiv
V A
VA
D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D008070:Lipopolysaccharides / Q000032:analysis*; D008077:Lipoproteins, LDL / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D013050:Spectrometry, Fluorescence; D014461:Ultracentrifugation
D008070:Lipopolysaccharides; D008077:Lipoproteins, LDL