Ganglioside GM1 forces the redistribution of cholesterol in a biomimetic membrane

Neutron reflectivity has been applied to investigate different mixed asymmetric lipid systems, in the form of single "supported + floating" bilayers, made of phospholipids, cholesterol and GM1 ganglioside (Neu5Ac alpha 2-3(Gal beta 1-3GalNAc beta 1-4)Gal beta 1-4Glc beta 1Cer)) in bio-similar mole ratios. Bilayer preparation was carried out layer-by-layer with the Langmuir-Blodgett Langmuir-Schaefer techniques, allowing for compositional asymmetry in the system buildup. It is the first time that such a complex model membrane system is reported. Two important conclusions are drawn. First, it is experimentally shown that the presence of GM1 enforces an asymmetry in cholesterol distribution, opposite to what happens for a GM1-free membrane that, submitted to a similar procedure, results in a full symmetrization of cholesterol distribution. We underline that natural cholesterol has been used. Second, and most interesting, our results suggest that a preferential asymmetric distribution of GM1 and cholesterol is attained in a model membrane with biomimetic composition, revealing that a true coupling between the two molecular species occurs. (C) 2012 Elsevier B.V. All rights reserved.