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
(Neu5Acα2-3(Galβ1-3GalNAcβ1-4)Galβ1-4Glcβ1Cer)) 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.