Distribution of Ganglioside G_M1 between Two-Component, Two-Phase Phosphatidylcholine Monolayers

Abstract

The distribution of the ganglioside GM1, at low concentrations, in phase-separated 1:1 dioleoyl phosphatidylcholine (DOPC)/dipalmitoylphosphatidylcholine (DPPC) Langmuir−Blodgett (LB) films transferred on mica was examined by atomic force microscopy (AFM). For concentrations below 1 mol %, GM1 distributes exclusively in the liquid-condensed DPPC phase where it forms nanometer-scale patches of round and filamentous shapes both at the boundary and toward the middle of DPPC macrodomains. Raising the GM1 concentration up to 4% increases the number of patches and creates fence like structures at the DOPC/DPPC boundary, whereas some GM1 clusters might also emerge from the liquid-expanded DOPC phase. Immiscibility of GM1 with DOPC was confirmed by examination of GM1/DOPC LB films. These data strongly support the hypothesis of the existence of GM1-enriched domains in biological membranes. They further emphasize the usefulness of the coupling of LB films with AFM detection for the investigation of complex lipid mixtures.