Mechanistic Insights into Neurotransmitter Release and Presynaptic Plasticity from the Crystal Structure of Munc13-1 C1C2BMUN
- University of Texas Southwestern Medical Center, United States
- Charité-Universitätsmedizin Berlin, Germany
- Huazhong University of Science and Technology, China
Abstract
Munc13-1 acts as a master regulator of neurotransmitter release, mediating docking-priming of synaptic vesicles and diverse presynaptic plasticity processes. It is unclear how the functions of the multiple domains of Munc13-1 are coordinated. The crystal structure of a Munc13-1 fragment including its C1, C2B and MUN domains (C1C2BMUN) reveals a 19.5 nm-long multi-helical structure with the C1 and C2B domains packed at one end. The similar orientations of the respective diacyglycerol- and Ca2+-binding sites of the C1 and C2B domains suggest that the two domains cooperate in plasma-membrane binding and that activation of Munc13-1 by Ca2+ and diacylglycerol during short-term presynaptic plasticity are closely interrelated. Electrophysiological experiments in mouse neurons support the functional importance of the domain interfaces observed in C1C2BMUN. The structure imposes key constraints for models of neurotransmitter release and suggests that Munc13-1 bridges the vesicle and plasma membranes from the periphery of the membrane-membrane interface.
Data availability
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C1C2BMUN structurePublicly available at the Protein Data Bank (accession no: 5UE8).
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Refined MUN domain structurePublicly available at the Protein Data Bank (accession no: 5UF7).
Article and author information
Author details
Christian Rosenmund
Funding
National Institutes of Health (R35 NS097333)
- Josep Rizo
Welch Foundation (I-1304)
- Josep Rizo
German Research Council (SFB958)
- Christian Rosenmund
German Research Council (SFB665)
- Christian Rosenmund
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: Animal welfare committees of Charité Medical University and the Berlin state government Agency for Health and Social Services approved all protocols for animal maintenance and experiments (license no. T 0220/09).
Reviewing Editor
- Reinhard Jahn, Max Planck Institute for Biophysical Chemistry, Germany
Publication history
- Received: October 21, 2016
- Accepted: February 7, 2017
- Accepted Manuscript published: February 8, 2017 (version 1)
- Version of Record published: March 9, 2017 (version 2)
Copyright
© 2017, Xu et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Mechanistic Insights into Neurotransmitter Release and Presynaptic Plasticity from the Crystal Structure of Munc13-1 C1C2BMUN
eLife 6:e22567.
https://doi.org/10.7554/eLife.22567
Further reading
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- Structural Biology and Molecular Biophysics
The acidic luminal pH of lysosomes, maintained within a narrow range, is essential for proper degrative function of the organelle and is generated by the action of a V-type H+ ATPase, but other pathways for ion movement are required to dissipate the voltage generated by this process. ClC-7, a Cl-/H+ antiporter responsible for lysosomal Cl- permeability, is a candidate to contribute to the acidification process as part of this ‘counterion pathway’ The signaling lipid PI(3,5)P2 modulates lysosomal dynamics, including by regulating lysosomal ion channels, raising the possibility that it could contribute to lysosomal pH regulation. Here, we demonstrate that depleting PI(3,5)P2 by inhibiting the kinase PIKfyve causes lysosomal hyperacidification, primarily via an effect on ClC-7. We further show that PI(3,5)P2 directly inhibits ClC-7 transport and that this inhibition is eliminated in a disease-causing gain-of-function ClC-7 mutation. Together, these observations suggest an intimate role for ClC-7 in lysosomal pH regulation.
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- Structural Biology and Molecular Biophysics
Synaptic vesicles are primed into a state that is ready for fast neurotransmitter release upon Ca2+-binding to Synaptotagmin-1. This state likely includes trans-SNARE complexes between the vesicle and plasma membranes that are bound to Synaptotagmin-1 and complexins. However, the nature of this state and the steps leading to membrane fusion are unclear, in part because of the difficulty of studying this dynamic process experimentally. To shed light into these questions, we performed all-atom molecular dynamics simulations of systems containing trans-SNARE complexes between two flat bilayers or a vesicle and a flat bilayer with or without fragments of Synaptotagmin-1 and/or complexin-1. Our results need to be interpreted with caution because of the limited simulation times and the absence of key components, but suggest mechanistic features that may control release and help visualize potential states of the primed Synaptotagmin-1-SNARE-complexin-1 complex. The simulations suggest that SNAREs alone induce formation of extended membrane-membrane contact interfaces that may fuse slowly, and that the primed state contains macromolecular assemblies of trans-SNARE complexes bound to the Synaptotagmin-1 C2B domain and complexin-1 in a spring-loaded configuration that prevents premature membrane merger and formation of extended interfaces, but keeps the system ready for fast fusion upon Ca2+ influx.
