CASK encodes a calcium/calmodulin-dependent serine protein kinase. The encoded protein is a MAGUK protein family member. These proteins are scaffold proteins and the encoded protein is located at synapses in the brain.

CASK encodes a 921-amino acid polypeptide with an N-terminal calcium/calmodulin-dependent protein kinase-like domain, PDZ and SH3 domains, a potential protein 4.1-binding motif, and a domain homologous to guanylate kinase. Human CASK is 99% and 52% identical to rat CASK and C. elegans LIN2, respectively. Northern blot analysis demonstrated that CASK is ubiquitously expressed. Immunofluorescence localized the CASK protein to lateral and/or basal plasma membrane domains in epithelial cells.