Two representative orientation/organization of GM1 in a DPPC bilayer. The angle formed by the vector Gal2 : C1→Gal5 : C4 with the Z-axis is 56° (a) and 105° (b). Likewise, the angle formed by the vector Gal2 : C1→NeuAc3 : C5 with the Z-axis is 39° (a) and 47° (b). GM1 forms 7 (a) and 10 (b) hydrogen bonds with DPPC. The carbonyl oxygen atoms of DPPC fatty acid chains are rendered as tiny yellow spheres and these represent the approximate lipid-solvent interface. Carbon atoms of GM1 and DPPC molecules are rendered in green and orange sticks. The atoms Gal2 : C1, Gal5 : C4, and NeuAc3 : C5 are rendered as cyan, green, and gray spheres, respectively. Hydrogen bonds between GM1 and DPPC molecules are rendered with thick magenta connector. The snapshots, rendered using VMD [35], are from the simulations with starting conformation C (at 4 ns; (a)) and G (at 7 ns; (b)) [20].