To measure effective SMAC:lipid interactions, we have counted the number of bead contacts (<0.5 nm) between both groups (SMAC beads and lipid beads), normalized by the number of SMACs in each simulation (see figure ). In cases with poor or low SMAC:lipid interactions, the SMAC-driven stabilization of the fusion pore did not take place and the pore closed (simulations #5 and #6). A snapshot of simulation #5 (figure , left) just before pore closure (0.19 µs) suggests insufficient SMA-membrane interactions, unlike the snapshot of simulation #3 (figure , left) at the same time with two SMACs already fully inserted in the membranes, parallel to each lipid-water intra-organelle interface.