The association of post-synaptic density protein 95 with the N-methyl-D-aspartate type glutamate receptor: Specificity of PDZ domain interactions and physiological consequences of binding

Post-synaptic Density protein 95 (PSD-95) is a structural protein that binds to NMDA-type glutamate receptors at the post-synaptic site. The essential role of the NMDA receptor in synaptic function, including learning and memory suggests that PSD-95 may be important for these functions.; NMDA receptors bind protein-protein interaction domains on PSD-95 called PDZ domains. In order to study how the primary structure of the NMDA-receptor affects affinity for PDZ domains, we constructed several libraries of peptides based on the PSD-95 binding domain of the NMDA receptor subunit NR2b, systematically substituting at each position archetypical amino acids. Using fluorescence anisotropy, the affinity of the peptides for individual PDZ domains of PSD-95 and SAP 102, a related protein, were determined. From these data, an optimal sequence for binding to the PDZ1 and 2 and PSD-95 and SAP 102 was determined (E/Q-S/T D/E/Q/N-V). Searching the human genome for proteins ending with E/Q-S/T-X-V turned up several proteins. We tested and found several proteins for that had not previously been described to bind PSD-95 and SAP 102.; A peptide based on the C-terminus of NR2a (NR2aCT) could disrupt PSD-95/NMDA receptor interactions in vitro, and a membrane permeable form of NR2aCT could disrupt endogenous PSD-95/NMDA receptor in acute hippocampal slices. Whole cell recordings in acute hippocampal slices show that peptide can make it to post-synaptic sites in a relatively short time frame. However, intracellular perfusion of peptide in this manner did not alter basal synaptic transmission or synaptic plasticity (long-term potentiation of evoked post-synaptic responses). This indicates that either the PSD-95 interaction with NMDA receptor (and other PDZ domain binding proteins) does not affect synaptic function, or the time scale of the recordings did not allow sufficient disruption of the interactions.