Ring-like oligomers of synaptotagmin-1 involved in calcium regulated neuroexocytosis

O. BELLO; O. JOUANNOT; A. CHAUDHURI; E. STROEVA; J. COLEMAN; J. ROTHMAN; S. S. KRISHNAKUMAR

Washington, DC

Congreso; SNF Neuroscience 2017, Annual Meeting; 2017

Society for Neuroscience

Synchronized rapid release of neurotransmitters at the synapse is a highly orchestrated cellular process. This involves maintaining a pool of synaptic vesicles containing neurotransmitters docked at the pre-synaptic membrane, ready to fuse and release their contents upon the influx of calcium following an action potential. The synaptic vesicle protein, Synaptotagmin-1 (Syt1) is a central component of this coordinated processes, including preventing the spontaneous fusion of vesicles in absence of the appropriate cue. However, the underlying molecular mechanism is still unclear. Here using negative stain electron microscopy combined with targeted mutations, and a functional exocytosis assay, we propose a simple and novel mechanism wherein Syt1 ring-like oligomer act as reversible washer/spacer to synchronize neurotransmitter release to calcium influx. This is prompted by our recent finding that Syt1 assembles into calcium-sensitive ring-like oligomeric structures on lipid monolayers under physiologically relevant conditions. The ring assembly is an intrinsic property of Syt1 and is also a general and conserved structural aspect of many C2 domain proteins. Underscoring the physiological relevancy, both the Syt1 ring assembly and its rapid disruption by calcium involve the well-established functional surfaces on the C2B domain that are important for synaptic transmission. Significantly, we find that mutations in Syt1 that specifically alter the ring oligomer formation results in dysregulation neuroexocytosis, specifically the spontaneous release in PC12 cells in support of our "washer" model.