SAP-102 (also known as DLG3) is a PDZ containing domain protein that is also a member of the membrane-associated guanylate kinase (MAGUK) family of multi-domain adaptor proteins^1,2.

PDZ domains are conserved protein domains of about 90 amino acids involved in protein–protein recognition, protein targeting and assembly of multi-protein complexes. The name PDZ derives from the first three proteins in which these domains were identified: PSD-95 (a 95 kDa protein involved in signaling at the post-synaptic density), DLG (the Drosophila melanogaster Discs large protein) and ZO-1 (the zonula occludens 1 protein involved in maintenance of epithelial polarity)^1,2.

MAGUKs are scaffolding proteins that comprise several modular protein binding motifs including one or more PDZ domains, a Src homology 3 (SH3) domain, and a catalytically inactive guanylate kinase-like domain^1,2.

The multidomain nature of PDZ-containing proteins enables them to interact with multiple binding partners and hence organize larger signaling protein complexes.

SAP-102 has been shown to participate in the postsynaptic density, a dedicated structure formed in postsynaptic nerve terminals that includes a specialized assembly of ion channels, receptors and signaling molecules that are involved in information processing and the modulation of synaptic plasticity^1,2. Moreover, mutations in the SAP102 gene have been linked with a form of mental retardation³.