PIP2 electrostatically 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 PIP2 in a vesicle docking state where the SNARE complex is partially assembled. Ca2+/CaM or PKC-epsilon unmask PIP2 through the MARCKS dissociation, and thus rescue basal fusion and potentiates synaptotagmin-1-mediated Ca2+-dependent vesicle fusion. Our data provide the novel model that PIP2 electrostatically triggers vesicle fusion by lowering the hydration energy, and that masking PIP2 arrests vesicle fusion in a state of the partial SNARE assembly. Vesicle-mimicking liposomes fail to arrest vesicle fusion by masking PIP2, indicating that native vesicles are essential for the reconstitution of physiological vesicle fusion. One Sentence SummaryMasking PIP2 by MARCKS arrests the full SNARE assembly and vesicle fusion.