As proposed before, lipid tails beads are a convenient group to induce membrane fusion. By pulling from tail beads, lipids are tilted and reorganized to fuse radially displacing cytosolic waters. This pulling mechanism splays the nearest lipids towards the fusion patch, inducing a hydrophobic core. Therefore, for POPC and POPS lipids, collective variable ξ f pulls from C4A and C4B tail beads, while for PIP 2 it pulls from C4B and C5A tail beads (see supporting information for beads labels). Subsequently, for fusion pore nucleation, collective variable ξ n pulls from intra-organelle water beads (W) and lipid phosphate heads (PO4). Finally, for fusion pore expansion ξ e makes the water channel to widen and the fusion pore to expand by radially pulling from intra-organelle water beads (W) and lipid phosphate heads (PO4). However, the generalization of eq. 3 for the fusion pore from its original purpose to expand a hydrophilic pore in a single bilayer, required the following modifications: