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) and other dense-core vesicles by acting as a PtdIns(4,5)P2-binding protein that acts at prefusion step following ATP-dependent priming and participates in DCVs-membrane fusion. However, it may also participate in small clear synaptic vesicles (SVs) exocytosis and it is unclear whether its function is related to Ca(2+) triggering (By similarity). Homodimer. Interacts with the dopamine receptor DRD2 (By similarity). Interacts with RASL10B. Membrane-associated to vesicles. Strongly enriched in synaptic fractions. Preferentially binds to dense core vesicles but not to synaptic vesicles. Binds phosphoinosides, with a strong selectivity for PtdIns(4,5)P2 over PtdIns(3,4,5)P3. Probably localizes to different vesicles compared to CADPS2. Present in brain and adrenal glands (at protein level). Specifically expressed in neural and endocrine secretory tissues. Strongly expressed in almost all nerve cells of the brain, although it is absent from glial cells. Expressed in the cardiac atria, but not ventricles. During brain development, its expression is similar to that of synaptic markers. Expression is first detectable late in embryogenesis (14 dpc) and increases to reach a plateau about 20 days after birth, when most synapses have been formed (at protein level). In the heart, up-regulated by hypertrophic stimuli. The PH domain is essential for regulated exocytosis and binds phospholipids and plasma membrane. It however does not mediate binding to DCVs (By similarity). Mice die within 30 minutes after birth but do not display obvious developmental or biochemical abnormalities. They show a strong reduction in the frequency of amperometrically detectable release events of transmitter-filled vesicles, while the total number of fusing vesicles, as judged by capacitance recordings or total internal reflection microscopy, remains unchanged. The sequence differs from that shown due to a duplication of 90 bp after position 107. Extended N-terminus.