Calcium-binding protein involved in exocytosis of vesicles filled with neurotransmitters and neuropeptides. Probably acts upstream of fusion in the biogenesis or maintenance of mature secretory vesicles. Regulates catecholamine loading of DCVs. May specifically mediate the Ca(2+)-dependent exocytosis of large dense-core vesicles (DCVs) (By similarity). Homodimer. Membrane-associated to vesicles. Strongly enriched in synaptic fractions. Preferentially binds to DCVs but not to SVs. Binds phosphoinosides. The PH domain is essential for regulated exocytosis and binds phospholipids.