Multidomain scaffolding Mg(2+)-independent protein kinase that catalyzes the phosphotransfer from ATP to proteins such as NRXN1, and plays a role in synaptic transmembrane protein anchoring and ion channel trafficking (By similarity). Contributes to neural development and regulation of gene expression via interaction with the transcription factor TBR1. Binds to cell-surface proteins, including amyloid precursor protein, neurexins, and syndecans. May mediate a link between the extracellular matrix and the actin cytoskeleton via its interaction with syndecan and with the actin/spectrin-binding protein 4.1. Component of the LIN-10-LIN-2-LIN-7 complex, which associates with the motor protein KIF17 to transport vesicles containing N-methyl-D-aspartate (NMDA) receptor subunit NR2B along microtubules (PubMed:10846156). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Unlike other protein kinases, does not require a divalent cation such as magnesium for catalytic activity. Differs from archetypal CaMK members in that the kinase domain exhibits a constitutively active conformation and the autoinhibitory region does not engage in direct contact with the ATP-binding cleft, although it still binds Ca(2+)/CAM. CASK and LIN7 form a tripartite complex with CASKIN1 (By similarity). Component of the brain-specific heterotrimeric complex (LIN-10-LIN-2-LIN-7 complex) composed of at least APBA1, CASK, and LIN7, which associates with the motor protein KIF17 to transport vesicles along microtubules (PubMed:10846156). Forms a heterotrimeric complex with DLG1 and LIN7B via their L27 domains (PubMed:22337881, PubMed:15863617). Identified in a complex with ACTN4, IQGAP1, MAGI2, NPHS1, SPTAN1 and SPTBN1 (By similarity). Part of a complex containing CASK, TBR1 and TSPYL2 (PubMed:10749215, PubMed:15066269). Interacts with WHRN (By similarity). Interacts (via the PDZ, SH3 and guanylate kinase-like domains) with NRXN1 (via C-terminus) (PubMed:25385611). Interacts with CASKIN1, APBA1, LIN7(A/B/C), and L27 domain of DLG1 and isoform 2 of DLG4 (By similarity). Interacts with FCHSD2 (By similarity). Interacts with KIRREL3 (By similarity). Interacts with TBR1 (By similarity). Interacts with TSPYL2 (PubMed:15066269). The first L27 domain binds DLG1 and the second L27 domain probably binds LIN7. The protein kinase domain mediates the interaction with FCHSD2. In the N-terminal section; belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. CaMK subfamily. Belongs to the MAGUK family.