Interactions of lipopolysaccharide with lipid membranes, raft models — A solid state NMR study

Abstract

Lipopolysaccharide (LPS) is a major component of the external leaflet of bacterial outer membranes, key pro-inflammatory factor and an important mediator of host-pathogen interactions. In host cells it activates the complement along with a pro-inflammatory response via a TLR4-mediated signalling cascade and shows preference for cholesterol-containing membranes. Here, we use solid state (13)C and (31)P MAS NMR to investigate the interactions of LPS from three bacterial species, Brucella melitensis, Klebsiella pneumoniae and Escherichia coli, with mixed lipid membranes, raft models. All endotoxin types are found to be pyrophosphorylated and Klebsiellar LPS is phosphonylated, as well. Carbon-13 MAS NMR indicates an increase in lipid order in the presence of LPS. Longitudinal (31)P relaxation, providing a direct probe of LPS molecular and segmental mobility, reveals a significant reduction in (31)P T1 times and lower molecular mobility in the presence of ternary lipid mixtures. Along with the ordering effect on membrane lipid, this suggests a preferential partitioning of LPS into ordered bilayer sphingomyelin/cholesterol-rich domains. We hypothesise that this is an important evolutionary drive for the selection of GPI-anchored raft-associated LPS-binding proteins as a first line of response to membrane-associated LPS.

Impact of bacterial endotoxin on the structure of DMPC membranes

“…It has been reported to insert spontaneously into giant unilamellar vesicles generating shape changes and vesicle fission [11]. Further, Kubiak et al have shown that, in vesicles of Escherichia coli lipid extract, LPS causes an expansion of gel-like areas which strongly supports their association with LPS [12].…”

“…In addition, without any co-stimulatory mediators, LPS is supposed to interact in a receptor-independent pathway with lipid membranes with preference to cholesterol-containing lipid rafts [10,11]. It has been reported to insert spontaneously into giant unilamellar vesicles generating shape changes and vesicle fission [11].…”

Introductory Chapter: Obesity—“OMICS” and Endocrinology

“…The LPS-stimulated biological effect on p53-induced apoptosis in the liver [53,54] surpasses the effect of Sirt1 as to the deacetylation of p53, reducing the hepatic lipid turnover. Hence, the p53-mediated downregulation of PXR activity [55,56] is not dependent of the Sirt1/PXR-mediated reactions [57][58][59][60].…”

“…IFγ has also been shown to affect genes, like Sirt1 and p53 apoptosis coupled genes, whose role are being "dissociated" in dysfunctional stages of metabolism [45][46][47][48][49][50][51][52][53]. The impact of IFγ on chromatin modeling stimulates macrophages, controlling gene transcription, thus regulating inflammatory cytokine production in activated macrophages [46,47].…”

“…Sirt1 and its posttranscriptional impact on p53 [42,43] is heavily involved in the differentiation of adipocytes, as well as lipid metabolism in general [44][45][46][47][48], with their implications for abnormal Sirt1 deacetylation of p53, linked to lipid metabolism with its characteristic transformation of adipocytes and ensuing liver disease. Interestingly, both Sirt1 and p53 knockout mice develop NAFLD [49][50][51][52], which alludes to a close connections between adipocyte phenotype "switch" involving Sirt 1 and/or p53 impact on mitochondrial functioning [53][54][55][56].…”