Synaptic vesicle phosphoprotein that enhances spontaneous neurotransmitter release but does not effect induced neurotransmitter release (By similarity). Unlike other synaptotagmins, it does not bind Ca(2+) or phospholipids (By similarity). Essential for mossy-fiber long-term potentiation in the hippocampus (By similarity). Homodimer (By similarity). Can also form heterodimers (By similarity). Interacts with SYT1 (By similarity). Phosphorylation of Ser-97 is required for mossy-fiber long-term potentiation. Belongs to the synaptotagmin family.