Behavior of GM3 ganglioside in lipid monolayers mimicking rafts or fluid phase in membranes

We studied the interaction of GM3 ganglioside with sphingomyelin (SM) and palmitoyl-oleoyl-phosphatidylcholine (POPC) in Langmuir monolayers mimicking, respectively, raft and fluid phase of a cellular membrane, by surface pressure measurements and fluorescence microscopy. No difference was observed in the behavior of SM–GM3 and POPC–GM3 monolayers. In both cases, a GM3 threshold concentration has been underlined between 20 and 40 mol%. Below this threshold, SM–GM3 and POPC–GM3 monolayers behave ideally, suggesting that GM3 and host lipid would form separated domains. On the contrary, above the threshold, a condensation of monolayers is observed. This could be due to a partial solubilisation of GM3 in host lipid, leading to a change in orientation of GM3 molecules at the air–water interface.