May link the scaffolding protein CASK to downstream intracellular effectors. Binds the CaM kinase domain of CASK. Forms a ternary complex with CASK and LIN7A, LIN7B or LIN7C. Competes with APBA1 that forms a similar complex with CASK and LIN7 proteins. The tripartite complex CASKIN1/CASK/LIN7(A/B/C) binds the cytoplasmic tail of NRXN1 (By similarity). Polymerizes, via the tandem SAM domains, to form long, 8 nM wide fibers, upon which other proteins can assemble.