Major constituent of the PSD essential for postsynaptic signaling. Inhibitory regulator of the Ras-cAMP pathway. Member of the NMDAR signaling complex in excitatory synapses, it may play a role in NMDAR-dependent control of AMPAR potentiation, AMPAR membrane trafficking and synaptic plasticity. Regulates AMPAR-mediated miniature excitatory postsynaptic currents. Exhibits dual GTPase-activating specificity for Ras and Rap. May be involved in certain forms of brain injury, leading to long-term learning and memory deficits (By similarity). Interacts KLHL17, CAMK2A and CAMK2B. Interacts with MPDZ (By similarity). Mostly in excitatory glutamatergic synapses (By similarity). receptor activation or SYNGAP1/MPDZ complex disruption. Phosphorylation by PLK2 promotes its activity (By similarity). The C2 domain is required for RapGAP activity.