The overall goal of this program project is to elucidate the precise molecular mechanism and regulation of the fusion machine that drives exocytosis for the controlled release of neurotransmitter at nerve terminals. The assembly of SNARE molecules residing in the synaptic vesicle and presynaptic plasma membrane takes center stage and provides the driving energy for this process. Even though we know the structure of the fully assembled cis-SNARE complex after fusion in atomic detail and have detailed conformational models for several of the SNAREs before fusion, we do not precisely know how (i) they are conditioned with regulatory proteins such as Munc18 and Munc13 to form an active acceptor complex on the plasma membrane, (ii) how this acceptor SNARE complex engages with the synaptic vesicle SNARE upon encounter, and (iii) how this high-energy trans-SNARE complex is ultimately triggered by the synaptic vesicle protein synaptotagmin and calcium to proceed to full assembly and fusion. Three projects led by three expert leaders in the biochemistry, structural biology, and biophysics of neuronal exocytotic membrane fusion are designed to jointly unravel the precise molecular interactions that drive the neuronal fusion machine through the vesicle docking, priming, and fusion steps with the highest possible structural and time resolution. The team will seek to define the structures and configurations of the active presynaptic acceptor SNARE complex and the fusion-restricted trans-SNARE complex between two membranes, and the team will strive to uncover the molecular mechanism, by which calcium-synaptotagmin engages with the membranes and/or complex to release their fusion-restriction. To achieve this goal the team will use a unique combination of approaches ranging from highly innovative biochemical procedures to reconstitute the relevant proteins, EPR, DEER, and NMR spectroscopy to characterize the pertinent structures in membrane environments, and FLIC and single vesicle TIRF microscopy to measure membrane topology and read out fusion on the millisecond timescale.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Program Projects (P01)
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Special Emphasis Panel (ZRG1)
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University of Virginia
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Yang, Sung-Tae; Lim, Sung In; Kiessling, Volker et al. (2016) Site-specific fluorescent labeling to visualize membrane translocation of a myristoyl switch protein. Sci Rep 6:32866
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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Park, Yongsoo; Seo, Jong Bae; Fraind, Alicia et al. (2015) Synaptotagmin-1 binds to PIP(2)-containing membrane but not to SNAREs at physiological ionic strength. Nat Struct Mol Biol 22:815-23
Kiessling, Volker; Liang, Binyong; Tamm, Lukas K (2015) Reconstituting SNARE-mediated membrane fusion at the single liposome level. Methods Cell Biol 128:339-63
Kiessling, Volker; Yang, Sung-Tae; Tamm, Lukas K (2015) Supported lipid bilayers as models for studying membrane domains. Curr Top Membr 75:1-23
Kreutzberger, Alex J B; Kiessling, Volker; Tamm, Lukas K (2015) High cholesterol obviates a prolonged hemifusion intermediate in fast SNARE-mediated membrane fusion. Biophys J 109:319-29
Milovanovic, Dragomir; Honigmann, Alf; Koike, Seiichi et al. (2015) Hydrophobic mismatch sorts SNARE proteins into distinct membrane domains. Nat Commun 6:5984

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