Plays a role in the synaptic transmission as bifunctional linker that interacts simultaneously with RIMS1, RIMS2, CACNA1D and CACNA1B. Interacts with RIMS1, RIMS2, CACNA1D and CACNA1B, and potentially with other Ca(2+) channel alpha-1 isoforms. Synaptic plasma membrane. The SH3 domains mediate binding to a proline-rich motif in RIMS1, RIMS2, CACNA1D and CACNA1B. Belongs to the RIMBP family.