The synaptotagmin family has been implicated in calcium-dependent neurotransmitter release, although Synaptotagmin I (Syt I) is the only isoform that controls synaptic vesicle fusion. Synaptotagmins have calcium-dependent membranetrafficking functions on both sides of the synapse. Synaptotagmins also play key roles in synaptic vesicle endocytosis. Synaptotagmin