Ion channel clustering by membrane-associated guanylate kinases - Differential regulation by N-terminal lipid and metal binding motifs

The postsynaptic density protein PSD-95 and related membrane-associated guanylate kinase (MAGUK) proteins assemble signal transduction complexes at sites of cell cell contact including synapses. Whereas PSD-95 and PSD-93 occur only at postsynaptic sites in hippocampal neurons, SAP-102 also occurs in axone. In heterologous cells, PSD-95 and PSD-93 mediate cell surface ion channel clustering, but SAP-102 and SAP-97 do not. This selective ion channel clustering activity by MAGUKs is explained by differential palmitoylation, as PSD-93 and PSD-95 are palmitoylated though SAP-97, and SAP-102 are not. Rather than being palmitoylated, we find that N-terminal cysteines from SAP-102 tightly bind to zinc. And, appending the N terminus of SAP-102 to PSD-95 results in localization of the chimera to both axone and dendrites, These data suggest that lipid modifications and heavy metal associations with the N termini of MAGUKs mediate differential functions and subcellular localizations of these synaptic scaffolds.