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.