Research Article

X-ray structures of AMPA receptor–cone snail toxin complexes illuminate activation mechanism

Science  29 Aug 2014:
Vol. 345, Issue 6200, pp. 1021-1026
DOI: 10.1126/science.1258409

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Activating a receptor to excite a neuron

Transmitting signals between nerve cells, occuring at structures known as synapses, is critical to processes such as learning and memory. Fast transmission occurs when glutamate is released from a presynaptic neuron and binds to ionotropic glutamate receptors (iGluRs) in the cell membrane of a postsynaptic neuron. The iGluR contains an ion channel that is transiently opened, to activate the postsynaptic neuron, but then closes rapidly. Chen et al. and Yelshanskaya et al. report crystal structures in a range of conformations that together provide insight into how glutamate binding causes the channel to open and how other molecules that bind to the receptor modulate this. The information could aid in the design of drugs to treat cognitive impairment or seizure disorders

Science, this issue p. 1021 and p. 1070

Abstract

AMPA-sensitive glutamate receptors are crucial to the structural and dynamic properties of the brain, to the development and function of the central nervous system, and to the treatment of neurological conditions from depression to cognitive impairment. However, the molecular principles underlying AMPA receptor activation have remained elusive. We determined multiple x-ray crystal structures of the GluA2 AMPA receptor in complex with a Conus striatus cone snail toxin, a positive allosteric modulator, and orthosteric agonists, at 3.8 to 4.1 angstrom resolution. We show how the toxin acts like a straightjacket on the ligand-binding domain (LBD) “gating ring,” restraining the domains via both intra- and interdimer cross-links such that agonist-induced closure of the LBD “clamshells” is transduced into an irislike expansion of the gating ring. By structural analysis of activation-enhancing mutants, we show how the expansion of the LBD gating ring results in pulling forces on the M3 helices that, in turn, are coupled to ion channel gating.

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