This is a family of proteins that form part of the CAZ (cytomatrix at the active zone) complex which is involved in determining the site of synaptic vesicle fusion [1]. The C-terminus is a PDZ-binding motif that binds directly to RIM (a small G protein Rab-3A effector). The family also contains four coiled-coil domains [2].

1: CAST2: identification and characterization of a protein structurally related to the presynaptic cytomatrix protein CAST. Deguchi-Tawarada M, Inoue E, Takao-Rikitsu E, Inoue M, Ohtsuka T, Takai Y; Genes Cells. 2004;9:15-23. PMID:14723704

2: A family of RIM-binding proteins regulated by alternative splicing: Implications for the genesis of synaptic active zones. Wang Y, Liu X, Biederer T, Sudhof TC; Proc Natl Acad Sci U S A. 2002;99:14464-14469. PMID:12391317