Plays a role in vesicle maturation during exocytosis as a target of the diacylglycerol second messenger pathway. Is involved in neurotransmitter release by acting in synaptic vesicle priming prior to vesicle fusion and participates in the activity-depending refilling of readily releasable vesicle pool (RRP) (By similarity). Essential for synaptic vesicle maturation in a subset of excitatory/glutamatergic but not inhibitory/GABA-mediated synapses (By similarity). In collaboration with UNC13A, facilitates neuronal dense core vesicles fusion as well as controls the location and efficiency of their synaptic release (By similarity). Interacts with RIMS1. Localized to synapses. Translocated to the plasma membrane in response to phorbol ester binding. Isoform 1 is ubiquitously expressed. Isoform 2 is expressed in brain, predominantly in cerebral cortex, hippocampus and striatum. First detected at birth, after which expression level is steadily increasing until it reaches a plateau at P15. The C2 domains are not involved in calcium-dependent phospholipid binding. Belongs to the unc-13 family.