SPAL, a Rap‐specific GTPase activating protein, is present in the NMDA receptor‐PSD‐95 complex in the hippocampus

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Abstract
Background: The PSD‐95 family of proteins possesses multiple protein binding domains, including three PDZ domains, an SH3 domain, a HOOK domain and a guanylate kinase‐like (GK) domain. The PSD‐95 proteins function as scaffolding proteins that link ion channels such as the N‐methyl‐d‐aspartate‐receptors (NMDA‐Rs) with cytoskeletal networks and signalling molecules, thereby controlling synaptic plasticity and learning. Results: We found that the PSD‐95 family proteins interact via their GK domains with SPA‐1‐like protein (SPAL), a GTPase‐activating protein (GAP) that is specific for Rap1. SPAL was contained within the NMDA‐R‐PSD‐95 complex, and co‐localized with PSD‐95 and NMDA‐R at the synapses in cultured hippocampal neurones. Furthermore, NMDA stimulation induced the dephosphorylation of SPAL in cultured hippocampal neurones. Conclusion: Our findings suggest that SPAL may be involved in the NMDA‐mediated organization of cytoskeletal networks and signal transduction.