Interaction of NE-dlg/SAP102, a neuronal and endocrine tissue-specific membrane-associated guanylate kinase protein, with calmodulin and PSD-95/SAP90- A possible regulatory role in molecular clustering at synaptic sites

NE-dlg/SAP102, a neuronal and endocrine tissue-specific membrane-associated guanylate kinase family protein, is known to bind to C-terminal ends of N- methyl-D-aspartate receptor 2B (NR2B) through its PDZ (PSD-95/Dlg/ZO-1) dom ains. NE-dlg/SAP102 and NR2B colocalize at synaptic sites in cultured rat h ippocampal neurons, and their expressions increase in parallel with the ons et of synaptogenesis, me have identified that NE-dlg/SAP102 interacts with calmodulin in a Ca2+-dependent manner. The binding site for calmodulin has been determined to he at the putative basic cr-helix region located around the src homology 3 (SH3) domain of NE-dlg/SAP102. Using a surface plasmon r esonance measurement system, we detected specific binding of recombinant NE -dlg/SAP102 to the immobilized calmodulin with a K-d value of 44 nM. Howeve r, the binding of Ca2+/calmodulin to NE-dlg/SAP102 did not modulate the int eraction between PDZ domains of NE-dlg/SAP102 and the C-terminal end of rat NR2B. We have also identified that the region near the calmodulin binding site of NE-dlg/SAP102 interacts with the GUK-like domain of PSD-95/SAP90 by two-hybrid screening. Pull down assay revealed that NE-dlg/SAP102 can inte ract with PSD-95/SAP90 in the presence of both Ca2+ and calmodulin. These f indings suggest that the Ca2+/calmodulin modulates interaction of neuronal membrane-associated guanylate kinase proteins and regulates clustering of n eurotransmitter receptors at central synapses.