The overall goal of our research is to gain a greater understanding of the dynamics of SNARE assembly underlying Ca2+-triggered synaptic vesicle fusion and the driving forces for directional lipid transport mediated by bridge lipid transfer proteins (LTPs). The synaptic fusion machinery contains three SNARE proteins (syntaxin-1, SNAP-25, and VAMP2), Munc18-1, and at least five regulatory proteins (Munc13-1, synaptotagmin-1 (Syt1), complexin, -SNAP, and NSF). The SNAREs couple their ordered folding and assembly to membrane fusion like a molecular zipper, thereby generating force to bring the synaptic and plasma membranes into close proximity to induce fusion. Other proteins chaperone the initial SNARE assembly and then clamp it to form a primed partially zippered SNARE complex. Ca2+ triggers its further zippering to conclude membrane fusion. However, the composition and structure of this primed SNARE complex remain unclear. In the previous funding cycle, we discovered and characterized a tetrameric complex formed by Munc18-1, Syntaxin-1, VAMP2, and Munc13-1 in solution. Here, we propose to reconstitute the entire primed complex, which additionally contains complexin and the Ca2+ sensor Sty1, and characterize its stability, structure, and dynamics in a membrane environment. As a newly identified category of LTPs in eukaryotes, bridge LTPs are thought to act as a conduit to enable lipids to flow from one membrane to the other at their contact site. The bulk lipid flow causes membrane expansion of certain target membranes, leading to organelle biogenesis. However, the forces that dictate the direction and rate of the lipid flow are unknown. We propose that gradients of membrane tension and membrane protein densities can serve as the long-thought driving forces, which will be tested in our novel lipid transfer assays. SNARE-mediated vesicle fusion and LTP-mediate lipid transfer are two complementary membrane trafficking pathways, whose malfunction has been linked to numerous diseases. A better understanding of their mechanisms has the potential to enable intervention in these diseases.