Fig. 3. Structural details of the TM heterodimeric interfaces for the inactive and active GABA_B structures.

a, b Side (a) and intracellular (b) views of the inactive TM interface. EM densities (magenta) corresponding to putative cholesterols are shown in surface. c Close view of inactive TM interface proximal to the cytoplasm. H689^3.55 and E790^5.60 of GB1, H579^3.55 and E677^5.60 of GB2 forms salt bridge network to stabilize an inactive conformation. d Detailed interactions of the TM interface in the active state. e, f Cryo-EM density (e) and the detailed interactions (f) of (+)-BHFF (PAM) in the active TM interface. The critical residues are shown as sticks. Hydrogen bonds are depicted as dashed lines.