CASK (Calcium/calmodulin-dependent serine protein kinase), a conserved multi-domain scaffolding protein, belongs to a MAGUK (membrane-associated guanylate kinase homologs) subfamily and is involved in cell junction organization, tumor suppression and signaling. It is characterized by a novel domain structure that consists of a calcium/calmodulin-dependent protein kinase domain followed by PDZ, SH3 and guanylate kinase-like (GUK) domains. CASK is ubiquitously expressed and significantly greater in brain where it is thought to be involved in signaling at neuronal synapses. CASK interacts with CASKINs and defects in CASK are the cause of mental retardation X-linked CASK-related.Synonyms: Calcium/calmodulin-dependent serine protein kinase, LIN2, Lin-2 homolog, Peripheral plasma membrane protein CASK