Turbocharging synaptic transmission: 12 SNAREpins are required for rapid release of reconstituted synaptic vesicles.

Abstract

Synaptic transmission occurs synchronously with real-world events, far faster than vesicle fusion for hormone release or membrane biogenesis, all mediated by soluble <i>N</i>-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes. How SNAREs cooperate to achieve synchronous neurotransmitter release is a long-standing mystery. Rapid release (<7 milliseconds) has been reconstituted from purified synaptic SNAREs, SNARE-assembling chaperones, and calcium ion sensors in a fully-defined, genetically validated system that enables single-molecule counting in docked vesicles before release. SNAREpin complexes (12 ± 0.3) are found in each such ready-release vesicle, suggesting a regular structure. Several genetic conditions (including point mutation of the synaptic vesicle protein Synaptophysin from a Synaptopathy patient and human and mouse disease mutations of the synaptic vesicle protein vesicle-associated membrane protein-2 (VAMP2) reduce the number of SNAREpins to 6 ± 0.3 and result in profoundly delayed release over 0.1 to 1 seconds. Omitting Synaptophysin, whose hexamers preassemble 12 copies of VAMP2, also yields ~6 SNAREpins and delays release.