Fig. 1. Physiology and architecture of the GluA1/2_γ8 /CNIH2 complex.

a,b, Auxiliary subunits slow desensitization rates of recombinant receptors (a, left). Native AMPARs show diverse properties (a, right), with A1/2_γ8 +CNIH2 recapitulating CA1 & CA3-like kinetics (b, weighted τ_des (ms), mean ± SEM). Recombinant receptors: GluA1/2: 6.01 ± 0.31, n=9; +γ8: 9.29 ± 0.53, n=12; +CNIH2+γ8: 19.71 ± 1.27, n=9. Neuronal receptors: CA1 pyramidal: 21.03 ± 1.19, n=14; CA3 pyramidal 24.51 ± 1.69, n=5; DG granule cell: 8.38 ± 1.01, n=6; CA1 stratum radiatum interneurons: 4.48 ± 0.55, n=8; Welch’s ANOVA tests with Dunnett’s multiple comparisons test - Recombinant: W(2,15.11) = 60.68, p<0.0001; Neurons: W(3,11.60) = 76.28, p<0.0001; see Supplementary Table 1 for details). Boxes represent 25 % to 75 % percentile, whiskers minimum/maximum values and central line median. c-e, Cryo-EM maps, depicting the LBD and TMD domain layers. Core subunits positioned to AC/BD, and auxiliary subunits at A’C’/B’D’ sites are shown. (c) Front view, depicting γ8 at the B’D’ sites. (d) Side view, visualising CNIH2 at A’C’ sites. Inset: lipids concentrating at the TMD, beneath the GluA2 pre-M1 helix. (e) Bottom view, highlighting CNIH2 binding to GluA2 transmembrane helices M1-3 (red), and γ8 to the GluA1 M1-3 helices (blue). f, Model of CNIH2, including the M1/2 and M3/4 cytosolic loops, docking to its binding site (M1_GluA2 [red] M4_GluA1 [blue]). g, CNIH2 Phe3, -5, -8 slotting into its binding site close to Cys528 (GluA2) and Leu785 (GluA1). h, CNIH2 contacts at the bottom of the binding site, mediated by Phe23 and Lys66; lipid (UL1) penetrates the A’C’ site and interacts with GluA2 Phe546. i, A’C’ (left) and B’D’ (right) site surface representation. M1^A2 and M4^A1 residues contacted by CNIH2 are coloured depending on the number of atoms contributing to the interaction (red: high, blue: low). Contacts were counted using ‘findNeighbors’ in ProDy³⁸’, with a 4.5 Å cutoff between heavy atoms.