%0 Journal Article %A Ward G. Walkup, 4th %A Tara Mastro %A Leslie T. Schenker %A Jost Vielmetter %A Rebecca Hu %A Ariella Iancu %A Meera Reghunathan %A B. Dylan Bannon %A B. Kennedy Mary %T Binding of synGAP to PDZ Domains of PSD-95 is Regulated by Phosphorylation and Shapes the Composition of the Postsynaptic Density %D 2016 %R 10.1101/058016 %J bioRxiv %P 058016 %X 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. %U https://www.biorxiv.org/content/biorxiv/early/2016/06/09/058016.full.pdf