Interaction of lipid A with antilipid A immunoglobulin G and normal immunoglobulin G in mixed monolayers

In situ characterization of lipid A interaction with antimicrobial peptides using surface X-ray scattering

Lipid A structure at the air-aqueous interface has been studied using pressure-area isotherm methods coupled with the surface X-ray scattering techniques of X-ray reflectivity (XR) and grazing incidence X-ray diffraction (GIXD). Lipid A monolayers were formed at the air-aqueous interface to represent the lipid moiety of the outer membrane of Gram-negative bacteria. Lipid A structure was characterized at surface pressures between 10 and 35 mN/m. Interactions of alpha-helical antimicrobial peptides LL-37, SMAP-29 and D2A22 with lipid A monolayers were subsequently studied. Although insertion into the lipid A monolayers was observed with the alpha-helical peptides, little change was seen from the X-ray data, suggesting that the lipid A hydrocarbon chains are involved in reorientation during insertion and that the hydrocarbon chains have a relatively rigid structure.

Quantitative measurements of the interaction between monosialoganglioside monolayers and wheat germ agglutinin (WGA) by a quartz-crystal microbalance

Monosialogangliosides (GM1, GM2, GM3 and GM4) were reconstituted in lipid monolayers at the air-water interface. The binding amounts and the initial binding rates of wheat germ agglutinin (WGA) to the monosialoganglioside monolayers were quantitatively studied by use of a quartz-crystal microbalance (QCM). A QCM was horizontally attached to the monolayer from the air phase, and the binding behavior (mass increase) was followed by the frequency decrease of the QCM. WGA binding affinities for the ganglioside monolayers were influenced by hydrophilic head groups of lipid matrices, densities of gangliosides, and sequences of oligosaccharide in gangliosides. Binding of WGA to the gangliosides reconstituted in a phosphatidylcholine (sphingomyelin and distearoylphosphatidylcholine) matrix was strongly suppressed, but not in a neutral glycolipids (GlcCer, GalCer, and LacCer), dipalmitoylphosphatidylethanolamine, and dipalmitoylphosphatidylethanolamine matrix. WGA showed high affinity for monolayers containing 20 mol% gangliosides, but only low affinity for 100% ganglioside monolayers. WGA preferably binds to gangliosides in the following sequence: GM3 > GM4 >> GM2 = GM1. No affinities of WGA for GM2 and GM1 were observed. The combined techniques of monolayer and QCM have the advantages of investigating recognition properties of gangliosides.

Binding of influenza A virus to monosialoganglioside (GM3) reconstituted in glucosylceramide and sphingomyelin membranes

The binding of influenza A virus to GM3-containing monolayers at an air/water interface was quantitatively investigated by use of a quartz crystal microbalance (QCM). A QCM was horizontally attached to the monolayer from the air phase and the binding behavior of influenza virus was followed by the frequency changes of the QCM. GM3 was reconstituted in the momolayer of sphingomyelin (SM) or glucosylceramide (GlcCer). When the mole fraction of GM3 was below 30 mol%, the binding rate of the influenza A virus to the GM3/GlcCer membrane was significantly faster than that to GM3/SM membranes. When the mole fraction of GM3 in SM was below 20 mol%, specific binding of influenza virus was not observed at all. Binding of the virus to the GM3/GlcCer mixed membrane was inhibited by the addition of sialyllactose (Neu5Ac alpha 2-3Gal beta 1-4Glc). The virus binding was also visually observed by scanning electron microscopy. Viruses selectively bound to GM3/GlcCer (20:80, by mol%) membrane, but not to GM3/SM (20:80, by mol%) membrane. Furthermore, it was suggested that specific binding of influenza virus to the GM3/GlcCer membrane induced the changes in morphology of virus. It was clearly demonstrated that binding of influenza virus to GM3 was influenced by matrix lipids surrounding GM3.