Fig. 3. Structure of the active state GABA_B and the details of agonist and PAM binding.

a, Overall view of GABA_B model and map in the active agonist/PAM-bound conformation. Elongated density interacting with the intracellular part of GB2 resembles the coiled-coil domain. b, Extracellular view of GABA_B TMD in the active conformation. c, Zoom-in on the agonist binding pocket in GB1-VFT. SKF97541 activates GABA_B by interacting with LB1 (blue) and LB2 (teal) of GB1. d, Binding of the PAM (GS39783) further stabilizes GABA_B active state by interacting with TMD residues from both GB1 and GB2. SKF97541 and GS39783 are shown as sticks with carbon atoms colored in sand, oxygen in red, nitrogen in blue, phosphorus in light green, and sulfur in dark green. e, IP₁ production induced by 10 μM GS39783 in intact HEK293 cells expressing the indicated subunit combinations. Values are means ± SD from 7 biologically independent experiments. Data are normalized by GABA response and analyzed using one-way ANOVA with Dunnett’s multiple comparison test to determine significance (compared with WT), with ****P<0.0001 for all, except for GB2-M870A (***P=0.013). f, pKi values for GABA, determined from displacement of CGP54626-DY647 binding in intact cells expressing the indicated subunit combinations in the absence or presence of 1 or 5 μM GS39783 (the number of biologically independent experiments is given in Extended Data Table 2). Data were analyzed using one-way ANOVA with Dunnett’s multiple comparison test to determine significance (compared with no GS39783 for the same combined subunits), with ****P ≤ 0.0001 and ns P > 0.05. For 1 μM (5 μM) GS39783, P = 0.9994 (0.8166) for GB2-Y697A, 0.9672 (0.8849) for GB2-N698A, 0.9934 (0.4946) for GB2-MYN-AAA, 0.5504 (0.2972) for GB1-M807A, 0.9981 (0.5843) for GB1-Y810A, 0.9605 (0.7139) for GB1-N811A, and 0.8819 (0.9318) for GB1-MYN-AAA.