Cryo-EM reveals structure of AMPA-receptor complexes

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Figure 1. An example aligned micrograph showing GluA2-STZ particles, with some particles circled in red. Below the micrograph are 2D class averages, showing an array of views of the GluA2-STZ particles and secondary structure features.

 

In the brain, trafficking, gating, and pharmacology of AMPA-subtype ionotropic glutamate receptors (AMPARs) are tightly regulated by transmembrane AMPAR regulatory proteins (TARPs). Aberrancies in the formation of AMPAR-TARP lead to disruption of excitatory neurotransmission, resulting in a wide-range of acute and chronic neurodegenerative diseases. Using cryo-electron microscopy (cryo-EM), we investigated how the AMPAR GluA2 assembles with the prototypical TARP protein, stargazin (STZ). An example micrograph, with example 2D class averages is shown in Figure 1. With three-dimensional classification, we were able to identify multiple stoichiometry states of the GluA2-STZ complex, and show that STZ is poised to interact with the receptor protomers that have the most profound effects on GluA2 gating with the highest affinity (Figure 2). Furthermore, we identify the interfaces by which GluA2 and STZ interact, as well as outline an electrostatic trap mechanism that is likely the key regulatory interface for STZ’s effects on AMPAR gating. These insights from cryo-EM have provided critical insights into how AMPAR-TARP complexes assemble in the brain, and we anticipate that this will provide new foundations for the studies of these complexes in disease states. Read the paper in Science.

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Figure 2. Models of the variable stoichiometric states of the GluA2-STZ complex shown in membrane on a micrograph background; purple (stargazin), green (B/D subunits), orange (A/C subunits).