Abstract: Dragomir Milovanovic

Organization and dynamics of presynaptic membrane

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Dragomir Milovanovic, Alf Honigmann, Stefan W. Hell, Reinhard Jahn

Departments of Neurobiology and NanoBiophotonics, Max Planck Institute for Biophyscal Chemistry, Götingen, Germany.

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Release of neurotransmitters requires a subtle spatial and temporal organization of secretion machinery at the active zone of neurons. The protein machinery that acts in this process has been extensively studied. Overall, it is accepted that exocytosis involves coordinated activity of both SNAREs and calcium sensor synaptotagmin-1. It is becoming clear that these proteins as well as certain bioactive lipids are highly organized in specific domains. Syntaxin-1A and SNAP25 are not uniformly distributed in the plasma membrane, but cluster in ~70 nm-sized membrane domains. Although only a single SNARE complexes, or just a few of them, are needed for synaptic vesicle fusion, organization of these proteins into domains might provide a local enrichment for protein exocytosis. Furthermore, the anionic lipid PIP2 is locally enriched in the inner leaflet of plasma membrane at the sites of exocytosis. The aim of our work is twofold. First, we investigate the interaction of synaptotagmin-1 with syntaxin/PIP2 domains in the membrane. Thus far, we showed calcium-independent binding of synaptotagmin-1 to syntaxin/PIP2 domains in both supported lipid bilayers and in the plasma membrane of PC12 cells. Hence, syntaxin/PIP2 domains serve as a molecular beacon in the recruitment of synaptic vesicles to the plasma membrane. Secondly, we analyze the mechanism behind the spatial organization of syntaxin molecules in the membrane. Here we show that a cholesterol-induced hydrophobic mismatch between the transmembrane helix and the lipid bilayer acts synergistically with polyanionic phosphoinositides in shaping the membrane architecture.