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 (By similarity). Interacts with RAB3A; this interaction recruits RPH3A to synaptic vesicules (PubMed:15207266). 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 (PubMed:15207266). Binds calcium via the C2 domains. The calcium-bound C2 domains mediate interactions with phospholipid bilayers (By similarity). Ubiquitinated. Deubiquitinated by CAND1 to prevent its degradation.