Simulation boxes are repeated in all directions by periodic images. (A) Lipid bilayer interacting with apolipoprotein CII mimetic peptides, one on each leaflet. (B) Nanodisc stabilized by a double belt of APOA1. Both systems are surrounded by water and ions. Orange lines show box boundaries. Only one simulation box is shown in (B). Representation codes: Lipids, sticks; proteins and peptides, surface; water and ions, beads (Oxygen of water, blue; Na+, yellow; CI−, green).