Presynaptic protein involved in the synaptic transmission tuning. Regulates synaptic release probability by decreasing the calcium sensitivity of release. Forms homomultimers (By similarity). Multimerization appears to be important for presynaptic targeting (By similarity). Interacts with BSN (PubMed:17869247). Phosphorylated. Phosphorylation promotes association with synaptic vesicle membranes. Belongs to the TPRG1 family.