Functions in endosome to Golgi retrograde transport. In response to calcium influx, may interact with SNARE fusion receptors and membrane phospholipids to mediate endosome fusion with the trans-Golgi network. By promoting the recycling of secretory vesicle transmembrane proteins, it indirectly controls dense-core secretory vesicle biogenesis, maturation and their ability to mediate the constitutive and regulated secretion of neurotransmitters and hormones. May regulate behavior and food intake by controlling calcium-stimulated exocytosis of neurotransmitters including NPY and serotonin and hormones like insulin (PubMed:28626000). Proposed to play a role in hypothalamic neuronal firing by modulating gamma-aminobutyric acid (GABA)ergic inhibitory neurotransmission (By similarity). Binds 3 Ca(2+) ions per C2 domain. Interacts with ADGRB1; this interaction is direct (PubMed:9790924). Interacts with endosomal SNARE proteins VAMP3, VAMP4, STX6 and STX16; this interaction is increased in the presence of calcium (PubMed:28626000). Rapidly recruited to the plasma membrane and to Golgi structures in response to increased intracellular calcium concentration. Predominantly expressed in brain (PubMed:9790924). Also expressed in nonneural tissues such as breast and testes epithelium (PubMed:12498718). Belongs to the unc-13 family. Extended N-terminus. Truncated C-terminus.