RING-LIKE OLIGOMERS OF SYNAPTOTAGMIN1 INVOLVED IN REGULATING NEUROEXOCYTOSIS

BELLO OD; JOUANNOT O; WANG J; ZANETTI MN; LI F; CHAUDHURI A; STROEVA E; COLEMAN J; ROTHMAN, JE; KRISHNAKUMAR, S

Londres

Simposio; 2017 Neuroscience Symposium; 2017

University Collegue London

The synaptic vesicle protein, Synaptotagmin-1 (Syt1) is required to couple Ca2+ influx to the membrane fusion machinery. However, the structural mechanism underlying this process is unclear. Using negative stain electron microscopy, we find that the Syt1 assembles into ring-like oligomeric structures on lipid monolayers under physiological ionic strength and lipid composition in the absence of free Ca2+. These rings oligomers have an average size of 30 ± 5 nm, corresponding to ~17 molecules of Syt1. The ring assembly is intrinsic property of Syt1 and is also a general and conserved structural aspect of many C2 domain proteins. It is triggered by molecularly defined binding of polyphosphates (PIP2 or ATP) to the polylysine patch on the C2B domain. Further, the ring oligomers are sensitive to Ca2+ and are disrupted rapidly in the physiological concentration range. Ca2+ binding to the C2B domain and re-orientation/insertion into the membrane, both required for triggering synaptic transmission, disrupts the ring oligomers. Based on this, we advance a simple and novel mechanism wherein Syt1 ring oligomer act as reversible washer/spacer to synchronize neurotransmitter release to Ca2+ influx. Supporting this hypothesis, we find mutations in Syt1 that specifically disrupt the ring oligomer formation results in dysregulation neuroexocytosis in PC12 cells.