In addition to the default ion models (Ca 2+ , K + , Cl -) of the CHARMM force ield, we utilized the recently developed multisite Ca 2+ model that was optimized to achieve more accurate binding afinity with proteins. The temperature was kept constant at 310 K using the Nose-Hoover thermostat. The pressure was maintained at 1 bar using the semi-isotropic Parinello-Rahman barostat, with a time constant of 1 ps and compressibility of 4.5 × 10 -5 bar -1 . A cutoff of 1.2 nm was used for the Lennard-Jones interaction, with a smooth shift function from 1.0 to 1.2 nm. The particle mesh Ewald (PME) method was used for the long-range electrostatics. After energy minimization, we ran 200-ps NVT and 500-ps NPT simulations to preliminarily equilibrate the systems, and then we carried out 400-ns production simulations for the single-membrane systems and 500-ns production simulations for the double-membrane systems (Table ).