LAUSR

Vesicular exocytosis is a promising pathway for brain drug delivery through blood-brain barrier to treat neurodegenerative diseases. In vesicle exocytosis, the membrane fusion process is initiated by the calcium sensor protein named synaptotagmin-like protein4-a (Slp4-a). Understanding of conformational changes of Slp4-a during prefusion stage of vesicle and endothelial membranes will help to understand nanoparticle-based drug delivery to brain. In this work, we used molecular dynamics (MD) simulations with a hybrid force field coupling united-atom protein model with MARTINI coarse-grained solvent to capture the conformational changes of Slp4-a during the prefusion stage. These hybrid coarse-grained simulations are more efficient than all-atom MD simulations and can capture protein interactions and conformational changes. Our simulation results show that only one calcium ion can remain in each calcium-binding pocket of C2 domains. The C2B domain of calcium-unbound Slp4-a remains parallel to the endothelial membrane, while C2B domain of calcium-bound Slp4-a rotates perpendicular to the endothelial membrane to approach vesicular membrane. For calcium-bound case, three synaptotagmin-like proteins can effectively bend lipid membranes at the prefusion stage, which could later trigger lipid stalk between membranes. This work provides better understanding of how C2 domains of Slp4-a operate during vesicle exocytosis from endothelial cell.