Fig. 6. Molecular model of the human A_2a receptor containing NECA bound in the proposed binding site, viewed either (A) perpendicularly to the membrane from the extracellular side or (B) as a side view of the residues in TM5, TM6, and TM7 in proximity to the bound ligand.

The model was based on the structure of rhodopsin and minimized using the Discover program (BIOSYM Technologies, San Diego CA, Version 2.90) employing the Amber force field. Side chains in dark green were those residues found in mutation experiments in this study to be essential for ligand binding. Side chains in yellow were those residues found in mutation experiments in this study to be non-essential for ligand binding, thus Ala mutants at these positions were fully functional in binding of both agonist and antagonist radioligands.