Here, we have generalized the latter methodology to expand a toroid-shaped fusion pore, formed by two independent bilayers (Prof. Hub generously shared with us his source code through personal communication). Through umbrella sampling simulations, we have quantified the effects of Synaptotagmin-1 (Syt1) C2B domains (PDB ID:1K5W 27 ) on the free energy landscape during the expansion of the fusion pore. We have observed that the effects are cumulative: one and two C2B domains progressively lower the free energy needed to expand the metastable fusion pore. Remarkably, C2B domains boost just nucleated, nascent fusion pores in the direction of expansion, though reducing the probability of kiss-and-run events.