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Synergistic roles of Synaptotagmin-1 and complexin in calcium-regulated neuronal exocytosis.

eLife (2020-05-14)
Sathish Ramakrishnan, Manindra Bera, Jeff Coleman, James E Rothman, Shyam S Krishnakumar
ABSTRACT

Calcium (Ca2+)-evoked release of neurotransmitters from synaptic vesicles requires mechanisms both to prevent un-initiated fusion of vesicles (clamping) and to trigger fusion following Ca2+-influx. The principal components involved in these processes are the vesicular fusion machinery (SNARE proteins) and the regulatory proteins, Synaptotagmin-1 and Complexin. Here, we use a reconstituted single-vesicle fusion assay under physiologically-relevant conditions to delineate a novel mechanism by which Synaptotagmin-1 and Complexin act synergistically to establish Ca2+-regulated fusion. We find that under each vesicle, Synaptotagmin-1 oligomers bind and clamp a limited number of 'central' SNARE complexes via the primary interface and introduce a kinetic delay in vesicle fusion mediated by the excess of free SNAREpins. This in turn enables Complexin to arrest the remaining free 'peripheral' SNAREpins to produce a stably clamped vesicle. Activation of the central SNAREpins associated with Synaptotagmin-1 by Ca2+ is sufficient to trigger rapid (<100 msec) and synchronous fusion of the docked vesicles.

MATERIALS
Product Number
Brand
Product Description

Avanti
18:1 PS (DOPS), 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (sodium salt), chloroform