Beyond the MUN domain, Munc13 controls priming and depriming of synaptic vesicles

• DOI: 10.1016/j.celrep.2024.114026
• Publication Date: 2024-05-21T03:05:31Z
• Authors: Jeremy Leitz; Chuchu Wang; Luis Esquivies; Richard A. Pfuetzner; John Jacob Peters; Sergio Couoh-Cardel; Austin L. Wang; Axel T. Brunger
• Keywords: Neurons; 0301 basic medicine; QH301-705.5; Nerve Tissue Proteins; Membrane Fusion; Article; Exocytosis; Mice, Inbred C57BL; Mice; 03 medical and health sciences; Protein Domains; CP: Neuroscience; CP: Cell biology; Animals; Calcium; Synaptic Vesicles; Biology (General); SNARE Proteins

Synaptic vesicle docking and priming are dynamic processes. At the molecular level, SNAREs (soluble NSF attachment protein receptors), synaptotagmins, and other factors are critical for Ca2+-triggered vesicle exocytosis, while disassembly factors, including NSF (N-ethylmaleimide-sensitive factor) and α-SNAP (soluble NSF attachment protein), disassemble and recycle SNAREs and antagonize fusion under some conditions. Here, we introduce a hybrid fusion assay that uses synaptic vesicles isolated from mouse brains and synthetic plasma membrane mimics. We included Munc18, Munc13, complexin, NSF, α-SNAP, and an ATP-regeneration system and maintained them continuously-as in the neuron-to investigate how these opposing processes yield fusogenic synaptic vesicles. In this setting, synaptic vesicle association is reversible, and the ATP-regeneration system produces the most synchronous Ca2+-triggered fusion, suggesting that disassembly factors perform quality control at the early stages of synaptic vesicle association to establish a highly fusogenic state. We uncovered a functional role for Munc13 ancillary to the MUN domain that alleviates an α-SNAP-dependent inhibition of Ca2+-triggered fusion.