PIP₂electrostatically triggers vesicle fusion: arresting full SNARE assembly and vesicle fusion by PIP₂-masking

Abstract SNARE proteins drive vesicle fusion and neurotransmitters release. Given that exocytosis is fast, and vesicle docking is tight, SNARE proteins are likely pre-assembled before fusion. However, the molecular mechanisms of the partially-assembled SNARE complex remain controversial. We use amperometry and the reconstitution of native vesicle fusion to show that MARCKS arrests basal fusion by masking PIP 2 in a vesicle docking state where the SNARE complex is partially assembled. Ca 2+ /CaM or PKC-epsilon unmask PIP 2 through the MARCKS dissociation, and thus rescue basal fusion and potentiates synaptotagmin-1-mediated Ca 2+ -dependent vesicle fusion. Our data provide the novel model that PIP 2 electrostatically triggers vesicle fusion by lowering the hydration energy, and that masking PIP 2 arrests vesicle fusion in a state of the partial SNARE assembly. Vesicle-mimicking liposomes fail to arrest vesicle fusion by masking PIP 2 , indicating that native vesicles are essential for the reconstitution of physiological vesicle fusion. One Sentence Summary Masking PIP 2 by MARCKS arrests the full SNARE assembly and vesicle fusion.