Exocytotic membrane fusion of synaptic vesicles is driven by the SNAREs syntaxin, SNAP-25, and synaptobrevin/VAMP, which assemble in trans between the membranes in a zipper-like fashion, thus pulling the membranes together and overcoming the energy barrier for fusion. In addition, regulatory proteins including synaptotagmin, Munc18, and complexin interact both with the SNAREs and the participating membranes, thus controlling SNARE reactivity and shaping the specific features of cacium-dependent exocytosis of synaptic vesicles. While the zippering model is intuitively satisfying and confirmed by a large body of evidence, the precise sequence of protein-protein interactions and the site of action of the regulatory proteins along the fusion pathway is still only partially understood and controversially discussed. Here we use in-vitro fusion of native secretory vesicles and liposomes reconstituted with purified proteins to isolate partial reactions of the fusion pathway, to understand the structure, dynamics and stoichiometries of the intermediate states of the participating proteins, and to determine the parameters affecting kinetics of each reaction. In the previous funding period, we solved the ci7stal structure of the neuronal SNARE complex with its linkers and transmembrane domains and characterized the interaction of synaptotagmin with SNARE-containing liposomes. Moreover, we developed refined assays for measuring fusion intermediates including fluorescence cross-correlation and cryo electron microscopy, studied the fusion of synaptic vesicles with SNARE-containing liposomes, and interfered with SNARE assembly at the partially or fully zippered state, thus gaining access to intermediate states of the fusion pathway. We now propose to take advantage of these achievements to characterize the intermediate steps in SNARE-mediated fusion and to determine the precise step at which the regulatory proteins synaptotagmin 1, complexin 1, and Munc18-1 operate on membrane fusion catalyzed by neuronal SNAREs. In the first specific aim, we plan to elucidate how SNARE assembly and zippering is connected to membrane docking, hemifusion, and fusion using native and artificial vesicles. In the second specific aim, we will determine the steps in SNARE nucleation and zippering that are acted upon by the regulatory proteins synaptotagmin, MunclS, and complexin. The program will be carried out in close collaboration with Projects 2 and 3 in which complementary approaches are pursued. We expect to obtain essential mechanistic information about the molecular mechanism of neuronal exocytosis that is not obtainable by other approaches..

Public Health Relevance

; SNARE-mediated exocytosis is fundamental for synaptic transmission at every central and peripheral synapse of our body. Furthermore, mutations within several of the proteins, particularly MunclS and SNAP- 25, are associated with neurological diseases such as alcoholism, schizophrenia, and attention deficit disorder. Understanding how these proteins work will facilitate new therapeutic approaches.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Program Projects (P01)
Project #
5P01GM072694-09
Application #
8706170
Study Section
Special Emphasis Panel (ZRG1)
Project Start
Project End
Budget Start
2014-07-01
Budget End
2015-06-30
Support Year
9
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of Virginia
Department
Type
DUNS #
City
Charlottesville
State
VA
Country
United States
Zip Code
22904
Witkowska, Agata; Jahn, Reinhard (2017) Rapid SNARE-Mediated Fusion of Liposomes and Chromaffin Granules with Giant Unilamellar Vesicles. Biophys J 113:1251-1259
Kreutzberger, Alex J B; Kiessling, Volker; Liang, Binyong et al. (2017) Asymmetric Phosphatidylethanolamine Distribution Controls Fusion Pore Lifetime and Probability. Biophys J 113:1912-1915
Katti, Sachin; Nyenhuis, Sarah B; Her, Bin et al. (2017) Non-Native Metal Ion Reveals the Role of Electrostatics in Synaptotagmin 1-Membrane Interactions. Biochemistry 56:3283-3295
Kreutzberger, Alex J B; Kiessling, Volker; Liang, Binyong et al. (2017) Reconstitution of calcium-mediated exocytosis of dense-core vesicles. Sci Adv 3:e1603208
Zdanowicz, Rafal; Kreutzberger, Alex; Liang, Binyong et al. (2017) Complexin Binding to Membranes and Acceptor t-SNAREs Explains Its Clamping Effect on Fusion. Biophys J 113:1235-1250
Yang, Sung-Tae; Kreutzberger, Alex J B; Lee, Jinwoo et al. (2016) The role of cholesterol in membrane fusion. Chem Phys Lipids 199:136-143
Kreutzberger, Alex J B; Liang, Binyong; Kiessling, Volker et al. (2016) Assembly and Comparison of Plasma Membrane SNARE Acceptor Complexes. Biophys J 110:2147-50
Liang, Binyong; Tamm, Lukas K (2016) NMR as a tool to investigate the structure, dynamics and function of membrane proteins. Nat Struct Mol Biol 23:468-74
Dawidowski, Damian; Cafiso, David S (2016) Munc18-1 and the Syntaxin-1 N Terminus Regulate Open-Closed States in a t-SNARE Complex. Structure 24:392-400
Milovanovic, Dragomir; Platen, Mitja; Junius, Meike et al. (2016) Calcium Promotes the Formation of Syntaxin 1 Mesoscale Domains through Phosphatidylinositol 4,5-Bisphosphate. J Biol Chem 291:7868-76

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