Physical Properties of Bacterial Outer Membrane Models: Neutron Reflectometry & Molecular Simulation

Abstract

The outer membrane (OM) of Gram-negative bacteria is an asymmetric bilayer having phospholipids in the inner leaflet and lipopolysaccharides in the outer leaflet. This unique asymmetry and the complex carbohydrates in lipopolysaccharides make it a daunting task to study the asymmetrical OM structure and dynamics, its interactions with OM proteins, and its roles in translocation of substrates, including antibiotics. In this study, we combine neutron reflectometry and molecular simulation to explore the physical properties of OM mimetics. There is excellent agreement between experiment and simulation, allowing experimental testing of the conclusions from simulations studies and also atomistic interpretation of the behavior of experimental model systems, such as the degree of lipid asymmetry, the lipid component (tail, head, and sugar) profiles along the bilayer normal, and lateral packing (i.e., average surface area per lipid). Therefore, the combination of both approaches provides a powerful new means to explore the biological and biophysical behavior of the bacterial OM.

Role of the lipid bilayer in outer membrane protein folding in Gram-negative bacteria

“…However, the exact thermotropic response of LPS in the outer leaflet may vary, depending on the composition (particularly the presence of hydrogen bond donors and acceptors) and size of the polysaccharide region of the LPS molecules incorporated ( 78 , 229 , 231 , 232 ). In vitro models of the OM using an asymmetric bilayer deposited on silicon or lipid-coated gold surfaces showed that the membrane has unusual mixed characteristics with elements of both liquid- and gel-phase lipids ( 233 , 234 ). The OM in these studies comprised “rough” LPS (containing the conserved polysaccharide core but lacking the O-antigen) ( Fig.…”

Bacterial cell wall material properties determine E. coli resistance to sonolysis

“…The outer membrane is another important structural element that in combination with peptidoglycan resist turgor pressure fluctuations [38] , [39] . The outer membrane has asymmetrical composition with an inner leaflet rich in phospholipids and an outer leaflet predominantly composed of polyanionic lipopolysaccharides (LPS) [40] , [41] . The polyanionic nature of LPS with numerous phosphate and acid sugar groups is stabilised by divalent cations (Mg 2+ and Ca 2+ ).…”

Phytantriol-Based Cubosome Formulation as an Antimicrobial against Lipopolysaccharide-Deficient Gram-Negative Bacteria

“…We have used NR to investigate this in detail. Previous studies have shown that an asymmetric d-DPPC (inner leaflet): Ra-LPS (outer leaflet) bilayer has been well established to mimic the wild-type Gram-negative bacterial OM (Figure A). − Deuterated DPPC (d-DPPC) has been chosen to offer enough isotopic contrast between inner and outer leaflets under neutron measurements and provide a stable platform for the Ra-LPS outer leaflet to be deposited onto. Therefore we have investigated the interactions of cubosomes (32 μg/mL) with the d-DPPC: Ra-LPS OM, Ab 5075D OM and Ab 19609R OM using NR, whereby d-DPPC: Ra-LPS OM was devoted to representing those LPS-rich Gram-negative bacteria, i.e., A.…”