Abstact

AMPA-type ionotropic glutamate receptors (AMPARs) are integral to fast excitatory synaptic transmission and play vital roles in synaptic plasticity, motor coordination, learning, and memory1. While extensive structural studies have been conducted on recombinant AMPARs and native calcium impermeable (CI)-AMPARs alongside their auxiliary proteins2-5, the molecular architecture of native calcium permeable (CP)-AMPARs has remained undefined. To elucidate the subunit composition, physiological architecture, and gating mechanisms of CP-AMPARs, here we present the first visualization of these receptors, immunoaffinity purified from rat cerebella, and resolve their structures using cryo-electron microscopy (cryo-EM). Our results indicate that the predominant assembly consists of GluA1 and GluA4 subunits, with the GluA4 subunit occupying the B and D positions, while auxiliary subunits, including TARPs, are located at the B'/D' positions and CNIHs or TARPs at the A'/C' positions. Furthermore, we resolved the structure of the Noelin 1-GluA1/A4 complex, wherein Noelin 1 (Noe 1) specifically binds to the GluA4 subunit at the B and D positions. Notably, Noe 1 stabilizes the amino-terminal domain (ATD) layer without affecting receptor gating properties. Noe 1 contributes to AMPAR function by forming dimeric-AMPAR assemblies that likely engage in extracellular networks, clustering receptors within synaptic environments and modulating receptor responsiveness to synaptic inputs.