πD . This radius is calculated dynamically at each simulation step using the number of intra-organelle water beads n p (r) inside a horizontal layer (parallel to the membranes) of height D, placed at the local Z center (Z l ) of all lipids inside a cylinder of radius R max around the nucleated fusion pore (see figure ). R(r) is then the radius of a cylinder of volume πDR(r) 2 which, when normalized by the volume of one W Martini bead (v0 = 0.076879nm 3 ), equals the amount of water molecules inside the fusion pore n p (r).