The initial coordinates of ganglioside GM1 were obtained from CHARMM-GUI Glycolipid Modeler [24] (http://www.charmmgui.org/?doc=input/glycolipid), which uses the internal coordinate information of common glycosidic torsion angle values, orientates the ganglioside perpendicular to the membrane, and performs Langevin dynamics with a cylindrical restraint potential to keep the whole GM1 molecule cylindrical, particularly the membrane-embedded ceramide part.