1. The Picower Center for Learning and Memory, RIKEN-MIT Neuroscience Research Center, Howard Hughes Medical Institute, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
2. Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA

Correspondence to: Morgan Sheng¹Thomas Walz² Correspondence and requests for materials should be addressed to M.S. (Email: msheng@mit.edu) and T.W. (Email: twalz@hms.harvard.edu).

Abstract

Ionotropic glutamate receptors mediate fast excitatory synaptic transmission in the central nervous system^{1, 2}. Their modulation is believed to affect learning and memory, and their dysfunction has been implicated in the pathogenesis of neurological and psychiatric diseases^{1, 2}. Despite a wealth of functional data, little is known about the intact, three-dimensional structure of these ligand-gated ion channels. Here, we present the structure of native AMPA receptors (-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid; AMPA-Rs) purified from rat brain, as determined by single-particle electron microscopy. Unlike the homotetrameric recombinant GluR2 (ref. 3), the native heterotetrameric AMPA-R adopted various conformations, which reflect primarily a variable separation of the two dimeric extracellular amino-terminal domains. Members of the stargazin/TARP family of transmembrane proteins co-purified with AMPA-Rs and contributed to the density representing the transmembrane region of the complex. Glutamate and cyclothiazide markedly altered the conformational equilibrium of the channel complex, suggesting that desensitization is related to separation of the N-terminal domains. These data provide a glimpse of the conformational changes of an important ligand-gated ion channel of the brain.

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