Biophysical Society Thematic Meeting| Padova 2019

Quantitative Aspects of Membrane Fusion and Fission

Poster Abstracts

60-POS Board 60 MOLECULAR MECHANISM OF NEUROTRANSMITTER RELEASE: LOCKED UNTIL THE LAST MILLISECOND Qiangjun Zhou 1 ; Thomas C Südhof 1,2 ; Axel T Brunger 1,2 ; 1 Stanford University, Molecular and Cellular Physiology, Stanford, California, USA 2 Howard Hughes Medical Institute, Stanford, California, USA Synaptic transmission is essential for the process of communication between two neurons. It occurs upon fusion of synaptic vesicles with the plasma membrane, a highly regulated and ultrafast process occurring in less than a millisecond. Synaptotagmin, complexin, and neuronal SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) proteins mediate evoked synchronous neurotransmitter release, but the molecular mechanisms mediating the cooperation between these molecules remain unclear. Through a combination of high- resolution structural, biochemical and electrophysiological studies, we showed how these proteins form the primed pre-fusion SNARE–complexin–synaptotagmin-1 complex. Furthermore, combined with functional studies on the dominant-negative effects of certain synaptotagmin-1 mutants, we proposed an unlocking mechanism that is triggered by Ca 2+ binding to the synaptotagmin-1 molecules, leading to SNARE complex zippering and membrane fusion. Finally, these studies also explained the high speed of Ca 2+ -triggered fusion – everything is in the right place until the synaptotagmin-1 “brake” at the tripartite interface is released. However, the molecular organization of the primed pre-fusion complexes, and the association of these complexes with the synaptic and plasma membranes remains unclear. Over the past two years, I have continued my research investigating the synaptic vesicle fusion machinery ex vivo and in situ . My recent work shows more details of the primed state of synaptic vesicles on the plasma membrane in cultured neurons using cellular cryo-electron.

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