Fig. 4: Relationship between M3 gate and Q/R ion binding site.

a Overlay of the gating cores (grey: desensitized; red: active), showing the GluA2 M3 constriction points (spheres) relative to the selectivity filter. Values of M3 dilation at Thr621 and Ile613 are depicted (in Å). Inset: Ile613 side chains are in van der Waals distance to the Q/R side chain Cγ,δ, the Q/R side chains form a polar constriction above the selectivity filter. b cryo-EM maps showing the relationship of Ile613 and Arg586 (desensitized map: blue; open map: orange). c Example current traces recorded from outside-out patches evoked by 200 ms pulse of 10 mM glutamate (20 individual responses in gray, average current in black). The plot in the middle shows normalised and averaged current-variance relationship for wild-type (open circles) and I609A mutant (closed circles) GluA1i_TARPγ8. The dashed lines are parabolic fits to the experimental points. Two boxplots on the right show single-channel conductance current peak, and open probability estimates for the wild-type and mutant receptor; the red horizontal line indicates the median; the boxes show the 25th and 75th percentiles; the whiskers enclose the points that fall within 1.5 times of the interquartile range. Source data are provided as a Source Data file. d Density maps revealing ion density in the selectivity filter (sites 1–3). Note the additional density peak in the gate of the desensitized map (blue). e Modelled Na⁺ ions in density peaks, coordinated the Q/R site side chains and main chain carbonyls. Distances of ion coordination are shown and imply (at least partial) Na⁺ hydration.