Fig. 1.

Schematic of vesicle docking at the pre-fusion stage in BBB exocytosis. (a) Vesicle connects to the endothelial membrane through the first protein bridge (Docking I). Important proteins involved in this bridge are Munc13-4, Rab27A, S100A10, and Annexin A2. (b) The two membranes get closer when Slp4-a binds to Munc18-1 as well as syntaxin2 to form the second docking bridge (Docking II). (c) SNAREs complex formed by the merging of Syntaxin2, VAMP8, and SNAP23 into 4 helix bundle for priming. In this stage, Slp4-a starts to connect with SNAREs and complexin. (d) Calcium ion-dependent pre-fusion, where the protein system could trigger the membrane fusion.