Selective Expansion of the GM3 Glycolipid Monolayer Induced by Carbohydrate−Carbohydrate Interaction with Gg3 Trisaccharide-Bearing Glycoconjugate Polystyrene at the Air−Water Interface

Abstract

Carbohydrate−carbohydrate interactions between GM3 and Gg3 were investigated using surface pressure−area (π− A ) isotherms of glycolipid monolayers in contact with glycoconjugate polystyrenes at the air−water interface. The GM3 monolayer was greatly expanded by the Gg3-trisaccharide (GalNAcβ1−4Galβ1−4Glc)-bearing glycoconjugate polystyrene [PN(Gg3)] and moderately expanded by lactose-bearing polystyrene, while little or no expansion was observed with GalLac (Galβ1−4Galβ1−4Glc)- or cellobiose-bearing polystyrenes or Gg3-trisaccharide-bearing styrene monomer. The PN(Gg3)-induced expansion of π− A isotherms of sphingolipid monolayers was maximal with GM3 and decreased in the following order: (KDN)GM3 > GM2 ≈ LacCer > GD3 ≈ 2,6-isoGM3 ≈ GM4 ≈ GM1 ≈ sphingomyelin (SM). The extent of expansion reflected the strength of carbohydrate−carbohydrate interactions with Gg3, which were amplified by the clustering effect of carbohydrates in the glycoconjugate polystyrenes. The expansion of various proportions of GM3/SM mixed monolayers by PN(Gg3) was smaller than that of the GM3 monolayer, indicating the importance of clustered carbohydrates in the monolayer. The PN(Gg3)-induced expansion of the GM3 monolayer required no calcium ion, and the expansion was strongly inhibited in the presence of urea and N -acetamido sugars. These observations reveal a new aspect of the mechanism of the carbohydrate−carbohydrate interactions where the N -acetyl groups and hydrogen bonds between the carbohydrate moieties play important roles. The π− A isotherms using glycoconjugate polystyrenes have been demonstrated to be useful as a molecular probe for the carbohydrate−carbohydrate interactions.