From bacteria to mammals, different phospholipid species are segregated between the inner and outer leaflets of the cellular membrane by ATP-dependent lipid transporters. Disruption of this asymmetry by ATP-independent phospholipid scrambling is a key step in cellular signaling, e.g., in apoptosis and in blood coagulation. Using molecular dynamics simulations with NAMD coupled with experimental assays, a recent collaborative study with H. Criss Hartzell (Emory University) published in eLife shows how a hydrophilic track formed on the surface of scramblases serves as the pathway for both lipid and ion translocations and how Ca²⁺ controls the open/closed transition of the track. The results of the simulations were used to successfully engineer scramblase activity in a homologous Ca²⁺ activated ion channel member of the family. This work provides a microscopic view of how lipids and other lipophilic molecules can permeate specialized proteins to travel between the two leaflets of the cellular membrane. Further details of the study can be found here.