VAMP2 Binding to Munc18-1 Domain 3a Controls the Nanoscale Reorganization of the Plasma Membrane and Vesicle Interface During Vesicular Priming

SNARE-mediated secretory vesicle (SV) exocytosis underpins neuronal communication. Munc18-1 orchestrates SNARE complex formation by controlling the opening of syntaxin-1A. How the SV-plasma membrane interface becomes fusion competent at nanoscale level is unknown. Here, we propose that the interaction of Munc18-1 with VAMP2 during vesicular docking triggers nanocluster re-organization which renders the SV-plasma membrane interface fusion-competent. We identified and mutated key Munc18-1 residues (A297 and T304) in domain 3a to impair the interaction with VAMP2. This constrained SVs on the plasma membrane and reduced stimulated secretion, under rescue conditions in Munc18-1/2 double knockout neurosecretory cells. Moreover, activity-dependent de-clustering of Munc18-1 and concomitant lateral trapping of syntaxin-1A was lost. The interaction of VAMP2 with Munc18-1 domain 3a therefore controls the re-organization of the nanoscale environment of docked SV-plasma membrane interface, fostering syntaxin-1A opening and Munc18-1 release to ensure that SNARE assembly only occurs within the confinement of docked vesicles.