A) Homology model of the CASK PSG supramodule (left), based on PALS1-Crumbs PSG supramodule structure (right; 4wsi.pdb). PDZ domain, purple. SH3 domain, yellow. Hinge region, orange. CASK GuK domain, gray. PALS1 GuK domain, lavender. β strand containing site of G659D mutation, green. Crumbs, cyan. B) GST pull-down using either GST or GST-neurexin cytosolic tail (GST-NX) fusion protein from HEK293FT cell lysates transfected with cDNA indicated at the top. ‘Start’ indicates the cell lysate. The precipitated proteins were immunoblotted for CASK. * indicates CASK endogenously expressed in HEK293FT cells.