Abstract

Regulation of AMPA receptor (AMPAR) trafficking results in changes in receptor number at the postsynaptic membrane, and hence modifications in synaptic strength, which are proposed to underlie learning and memory. NMDA receptor-mediated postsynaptic Ca²⁺ influx enhances AMPAR internalisation, but the molecular mechanisms that trigger such trafficking are not well understood. We investigated whether AMPAR-associated protein–protein interactions known to regulate receptor surface expression may be directly regulated by Ca²⁺. PICK1 binds the AMPAR GluR2 subunit and is involved in AMPAR internalisation and LTD. We show that PICK1 is a Ca²⁺-binding protein, and that PICK1–GluR2 interactions are enhanced by the presence of 15 M Ca²⁺. Deletion of an N-terminal acidic domain in PICK1 reduces its ability to bind Ca²⁺, and renders the GluR2–PICK1 interaction insensitive to Ca²⁺. Overexpression of this Ca²⁺-insensitive mutant occludes NMDA-induced AMPAR internalisation in hippocampal neurons. This work reveals a novel postsynaptic Ca²⁺-binding protein that provides a direct mechanistic link between NMDAR-mediated Ca²⁺ influx and AMPAR endocytosis.