Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Poster Abstracts

9-POS Board 3 THE ROLE OF MUNC18 IN REGULATING THE SPATIAL ARRANGEMENT OF SYNTAXIN-1A AND SNARE COMPLEX ASSEMBLY. Weronika Tomaka 1,2 ; Volker Kiessling 1,2 ; Lukas K Tamm 1,2 ; 1 University of Virginia, Center for Membrane and Cell Physiology, Charlottesville, VA, USA 2 University of Virginia, Department of Molecular Physiology and Biological Physics, Charlottesville, VA, USA SNARE-mediated membrane fusion between synaptic vesicles and the presynaptic neuronal plasma membrane allows for neurotransmitter release to the synaptic cleft. Many proteins are involved in the process of synaptic vesicle docking, priming, and fusion in response to an influx of intracellular calcium. Here, we focus on the role of Munc18, a cytosolic protein implicated in aiding vesicle docking and SNARE complex assembly. To investigate these two aspects of Munc18 function, we studied Munc18’s effect on the spatial organization of the Q-SNARE Syntaxin in the target membrane and how this organization influences Syntaxin’s interaction with phosphatidylinositol 4,5-bisphosphate (PIP2) and other Q- and R-SNARE proteins. Consistent with previous results in cells and model membranes, we find that the lipid environment greatly affects the oligomerization of Syntaxin and Munc18 binding to Syntaxin. Munc18 dissociates Syntaxin oligomers and changes the orientation of Syntaxin relative to the membrane in a manner that also depends on the lipid environment. The presence of the Q SNARE SNAP25 in reconstituted model membranes modulates the binding of Munc18 implying that Munc18 binding influences the assembly of Q-SNAREs. To correlate states of Q-SNARE assembly with fusion, we show that Munc18 increases SNARE-mediated fusion of Dense Core Vesicles purified from PC12 cells with reconstituted target membranes.

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