Interaction of GM₁ glycolipid in phospholipid monolayers with wheat germ agglutinin: Effect of phospholipidic environment and subphase

Mixed monolayers of GM₁ glycolipid and stearoyl-oleoyl-phosphatidylcholine (SOPC) or dipalmitoyl-phosphatidycholine (DPPC) phospholipids were studied by surface pressure measurements. The effects induced by GM₁ on the mean molecular areas of mixtures and DPPC phase transition were followed for GM₁ concentrations ranging from 1 to 20 mol.%. Under our experimental conditions, one main parameter influencing the behavior of phospholipid-GM₁ monolayers is the ionic strength of the subphase. Mixed monolayers are in a more expanded state on buffer than on pure water. This could be due to a change of GM₁ orientation at the interface. The interaction of wheat germ agglutinin (WGA), a lectin recognizing specifically GM₁, with these monolayers was quantified in terms of the Gibbs equation. Specific WGA-GM₁ interactions are clearly reduced in the presence of DPPC as compared with SOPC, probably because of the higher packing density of these monolayers. Phospholipid-GM₁ monolayers could also undergo some rearrangements induced by WGA binding.