PT - JOURNAL ARTICLE AU - Ward G. Walkup, 4th AU - Tara Mastro AU - Leslie T. Schenker AU - Jost Vielmetter AU - Rebecca Hu AU - Ariella Iancu AU - Meera Reghunathan AU - B. Dylan Bannon AU - B. Kennedy Mary TI - Binding of synGAP to PDZ Domains of PSD-95 is Regulated by Phosphorylation and Shapes the Composition of the Postsynaptic Density AID - 10.1101/058016 DP - 2016 Jan 01 TA - bioRxiv PG - 058016 4099 - http://biorxiv.org/content/early/2016/06/09/058016.short 4100 - http://biorxiv.org/content/early/2016/06/09/058016.full AB - SynGAP is a Ras/Rap GTPase-activating protein (GAP) present in high concentration in postsynaptic densities (PSDs) from mammalian forebrain where it binds to all three PDZ (PSD-95, Discs-large, ZO-1) domains of PSD-95. We show that phosphorylation of synGAP by Ca2+/calmodulin-dependent protein kinase II (CaMKII) decreases its affinity for the PDZ domains as much as 10-fold, measured by surface plasmon resonance. SynGAP is abundant enough in postsynaptic densities (PSDs) to occupy about one third of the PDZ domains of PSD-95. Therefore, we hypothesize that phosphorylation by CaMKII reduces synGAP’s ability to restrict binding of other proteins to the PDZ domains of PSD-95. We support this hypothesis by showing that three critical postsynaptic signaling proteins that bind to the PDZ domains of PSD-95 are present at a higher ratio to PSD-95 in PSDs isolated from synGAP heterozygous mice.