Structural Characterization of a Model Gram-Negative Bacterial Surface Using Lipopolysaccharides from Rough Strains of Escherichia coli

Abstract

Lipopolysaccharides (LPS) make up approximately 75% of the Gram-negative bacterial outer membrane (OM) surface, but because of the complexity of the molecule, there are very few model OMs that include LPS. The LPS molecule consists of lipid A, which anchors the LPS within the OM, a core polysaccharide region, and a variable O-antigen polysaccharide chain. In this work we used RcLPS (consisting of lipid A plus the first seven sugars of the core polysaccharide) from a rough strain of Escherichia coli to form stable monolayers of LPS at the air–liquid interface. The vertical structure RcLPS monolayers were characterized using neutron and X-ray reflectometry, while the lateral structure was investigated using grazing incidence X-ray diffraction and Brewster angle microscopy. It was found that RcLPS monolayers at surface pressures of 20 mN m–1 and above are resolved as hydrocarbon tails, an inner headgroup, and an outer headgroup of polysaccharide with increasing solvation from tails to outer headgroups. The lateral organization of the hydrocarbon lipid chains displays an oblique hexagonal unit cell at all surface pressures, with only the chain tilt angle changing with surface pressure. This is in contrast to lipid A, which displays hexagonal or, above 20 mN m–1, distorted hexagonal packing. This work provides the first complete structural analysis of a realistic E. coli OM surface model.

Native lysozyme and dry-heated lysozyme interactions with membrane lipid monolayers: Lateral reorganization of LPS monolayer, model of the Escherichia coli outer membrane

“…By grating the LPS (data not shown), the monolayer thickness could be measured and corresponds to 5 nm. The monolayer thickness is in coherence with the one found by Le Brun et al [26]. Table 1 Binding parameters calculated for N-L and DH-L adsorption at a LPS monolayer: maximal insertion pressure (MIP), synergy factor, and theoretical pressure increase in the absence of lipids (Δπ 0 ); these parameters were extrapolated from the Δπ vs. π initial plots for 0.1 μM lysozyme.…”

Nano-engineering the Antimicrobial Spectrum of Lantibiotics: Activity of Nisin against Gram Negative Bacteria

“…The outer membrane is mainly composed of glycolipids (lipopolysaccharides, LPS) that form 75% of their surface 29 . Due to the phosphate and carboxylate groups in sugar acids the cell surface is negatively charged 30 .…”

Bacterial Cell Mechanics

“…34,35 LPS-containing membranes are stabilized by the presence of divalent cations, which increase the level of order and rigidity of multilamellar LPS layers. 35,36 Addition of Ca 2+ to a “deep-rough” LPS monolayer containing only lipid A and two Kdo sugars (Figure 2) produces a cross-linked elastic gel. 37 Furthermore, increasing the polysaccharide length of the LPS enabled the formation of a similar gel in the absence of Ca 2+ , possibly because of an increased extent of hydrogen bonding, and resulted in additional lateral compression of the LPS monolayer.…”