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Updated: May 20, 2026

Analysis of SNARE-mediated Membrane Fusion Using an Enzymatic Cell Fusion Assay
Published on: October 19, 2012
SNAREpin assembly by Munc18-1 requires previous vesicle docking by synaptotagmin 1
Daniel Parisotto1, Jörg Malsam, Andrea Scheutzow
1Heidelberg University Biochemistry Center, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany.
Abstract:
Regulated exocytosis requires the general membrane fusion machinery-soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) and Sec1/Munc18 (SM) proteins. Using reconstituted giant unilamellar vesicles containing preassembled t-SNARE proteins (syntaxin 1·SNAP-25), we determined how Munc18-1 controls the docking, priming, and fusion of small unilamellar vesicles containing the v-SNARE VAMP2 and the Ca(2+) sensor synaptotagmin 1. In vitro assays allowed us to position Munc18-1 in the center of a sequential reaction cascade; vesicle docking by synaptotagmin 1 is a prerequisite for Munc18-1 to accelerate trans-SNARE complex (SNAREpin) assembly and membrane fusion. Complexin II stalls SNAREpin zippering at a late stage and, hence, contributes to synchronize membrane fusion in a Ca(2+)- and synaptotagmin 1-dependent manner. Thus, at the neuronal synapse, the priming factor Munc18-1 may accelerate the conversion of docked synaptic vesicles into a readily releasable pool by activating SNAREs for efficient membrane fusion.
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