Plays an essential role in docking and fusion steps of regulated exocytosis (By similarity). At the presynaptic level, RPH3A is recruited by RAB3A to the synaptic vesicle membrane in a GTP-dependent manner where it modulates synaptic vesicle trafficking and calcium-triggered neurotransmitter release (By similarity). In the post-synaptic compartment, forms a ternary complex with GRIN2A and DLG4 and regulates NMDA receptor stability. Also plays a role in the exocytosis of arginine vasopressin hormone (By similarity). Interacts with RAB3B, RAB3C, RAB3D, RAB8A, RAB27A and RAB27B (PubMed:12578829). Interacts with RAB3A; this interaction recruits RPH3A to synaptic vesicules (By similarity). Interacts (via C2B domain) with SNAP25 (By similarity). Interacts with deubiquitinating enzyme CAND1; this interaction results in the deubiquitination of RPH3A (By similarity). Interacts with GRIN2A and DLG4; this ternary complex regulates NMDA receptor composition at postsynaptic membranes (By similarity). Interacts with SNCA (By similarity). Specifically expressed in brain. Binds calcium via the C2 domains. The calcium-bound C2 domains mediate interactions with phospholipid bilayers. Ubiquitinated. Deubiquitinated by CAND1 to prevent its degradation. No visible phenotype. Mice are viable and fertile and do not display any physiological impairment. Additionally, synaptic properties seem unaffected.