Ca(2+) sensor specifically required for the Ca(2+)-dependent exocytosis of secretory vesicles containing IGF1 in neurons of the olfactory bulb. Exocytosis of IGF1 is required for sensory perception of smell. Not involved in Ca(2+)-dependent synaptic vesicle exocytosis (By similarity). Acts through Ca(2+) and phospholipid binding to the C2 domain: Ca(2+) induces binding of the C2-domains to phospholipid membranes and to assembled SNARE-complexes; both actions contribute to triggering exocytosis (By similarity). Binds 3 Ca(2+) ions per subunit. The ions are bound to the C2 domains. Homodimer; disulfide-linked via the cysteine motif. Can also form heterodimers with SYT3, SYT6, SYT7 and SYT9. Localizes to neuronal vesicles containing IGF1 that are not enriched at synapses. Does not colocalize with synaptic vesicles or with the Golgi apparatus. Expressed only in pancreas, lung and kidney. The cysteine motif mediates homo- or heterodimer formation via formation of disulfide bonds. The first C2 domain mediates Ca(2+)-dependent phospholipid binding. Belongs to the synaptotagmin family.