Synaptotagmin-4 (SYT4) belongs to the synaptotagmin family, which is a group of membrane-trafficking proteins that contain two C-terminal C2 domains. Most of the synaptotagmins have a unique N-terminal domain that is involved in membrane anchoring or specific ligand binding. This entry represents SYT4 from chordates. SYT4 is a Ca2+-sensor in the fly but not in the rat. Like all synaptotagmins, SYT4 contains the highly conserved C2A and C2B calcium-binding domains, but an amino acid substitution found in the C2A domain decreases SYT4's affinity for calcium under some conditions. In adult hypothalamic oxytocin neurons, SYT4 is specifically induced by high-fat diet, and this negatively regulates oxytocin exocytosis, which is associated with obesity. In humans the SYT4 gene is localised to a locus linked to schizophrenia and bipolar disorder.