Calcium/calmodulin-dependent serine protein kinase (CASK) is a conserved multi-domain scaffolding protein involved in brain development, synapse formation, and establishment of cell polarity. CASKINs (CASK interacting proteins) interact with CASK and are thoμght to play a role in CASK function, specifically by coupling CASK to distinct downstream effectors. CASKIN1 is a multidomain protein containing six N-terminal ankyrin repeats, one SH3 domain, and two sterile alpha motif domains followed by a long proline-rich sequence and a short conserved C-terminal domain. CASKIN1 co-assembles with CASK on the cytoplasmic tail of neurexin 1, sμggesting that CASKIN and CASK coat the cytoplasmic tails of neurexins and other cell-surface proteins.