Proteins in this family contain SH3 and fibronectin type III (FN3) domains, with the FN3 domains inserted within the SH3 domains. Members include peripheral-type benzodiazepine receptor-associated protein 1 (PRAX-1, TSPOAP1 or RIMBP1, also known as RIMS-binding protein 1 or TSPO-associated protein 1) and RIMS-binding protein 2 (RIMBP2). PRAX-1 interacts with the peripheral benzodiazepine receptor []. RIMBP2 interacts with subunits of the voltage-gated Ca(2+) channels [].RIMs binding proteins (RBPs, RIM-BPs) associate with calcium channels present in photoreceptors, neurons, and hair cells; they interact simultaneously with specific calcium channel subunits, and active zone proteins, RIM1 and RIM2 []. RIMs are part of the matrix at the presynaptic active zone and are associated with synaptic vesicles through their interaction with the small GTPase Rab3 []. RIM-BPs play a role in regulating synaptic transmission by serving as adaptors and linking calcium channels with the synaptic vesicle release machinery []. RIM-BPs contain three SH3 domains and two to three fibronectin III repeats. Invertebrates contain one, while vertebrates contain at least two RIM-BPs, RIM-BP1 and RIM-BP2. RIM-BP1 is also called peripheral-type benzodiazapine receptor associated protein 1 (PRAX-1). Mammals contain a third protein, RIM-BP3 []. RIM-BP1 and RIM-BP2 are predominantly expressed in the brain where they display overlapping but distinct expression patterns, while RIM-BP3 is almost exclusively expressed in the testis and is essential in spermiogenesis []. The SH3 domains of RIM-BPs bind to the PxxP motifs of RIM1, RIM2, and L-type (alpha1D) and N-type (alpha1B) calcium channel subunits [].
