Presynaptic protein involved in the synaptic transmission tuning. Regulates synaptic release probability by decreasing the calcium sensitivity of release. Forms homomultimers (PubMed:23723986). Multimerization appears to be important for presynaptic targeting (PubMed:23723986). Interacts with BSN (By similarity). Highest levels in brain with lower levels in testis. Weakly expressed in heart, spleen and liver. In the hippocampal CA3 region, localizes to mossy fiber terminals but is absent from inhibitory nerve terminals. Localizes to inhibitory terminals throughout the cerebellar cortex (at protein level) (PubMed:17869247). Expressed in the calyx of Held (PubMed:26212709). Phosphorylated. Phosphorylation promotes association with synaptic vesicle membranes. Belongs to the TPRG1 family.