Front view and top view of the TM domains of the active-state GABAB receptor (PDB:7EB2). Numerical labels denote helices TM1-TM7; circled labels mark the helices that potentially mediate inter-subunit interactions. The GABAB1 and TAS1R2 subunits (highlighted in boxes) were used for the alignment between the two receptors. The GABAB 7TMs display approximate C2 symmetry (180 degree rotational symmetry) between subunits; in contrast, the TAS1R3-TM and TAS1R2-TM domains are related by a 137 degree rotation.
