The WALP peptides were aligned vertically in order to start the simulation in ideal TM configurations. The peptides were then inserted, using the insane.py script , into a 10 × 10 nm 2 square membrane of DMPC phosopholipids (dimirystoylphosphatidylcholine), with 9 nm simulation box height. Water was added to fill the box, together with an NaCl ionic strength of 0.15 M. In the Martini 2 systems, 10% of water beads were changed to the 'antifreeze' type to prevent freezing, as recommended .