Fig. 2. Protein interactions regulating NO signaling at neuronal synapses. PDZ domain interactions (pink) function to bring nNOS to the NMDA receptor, allowing specific activation of nNOS in response to glutamate-induced calcium influx. Binding of nNOS to PSD-95 leaves the nNOS PDZ domain peptide-binding pocket free to interact with other proteins such as Capon. The NO produced in association with NMDA receptor activity diffuses to presynaptic nerve terminals and nitrosylates Dexras associated with Capon. Abbreviations: Arg, arginine; CaM, calmodulin; GK, guanylate kinase domain.