Structures of Human A1 and A2A Adenosine Receptors with Xanthines Reveal Determinants of Selectivity

The adenosine A(1) and A(2A) receptors belong to the purinergic family of G protein-coupled receptors, and regulate diverse functions of the cardiovascular, respiratory, renal, inflammation, and CNS. Xanthines such as caffeine and theophylline are weak, nonselective antagonists of adenosine receptors. Here we report the structure of a thermostabilized human A(1) receptor at 3.3 angstrom resolution with PSB36, an A(1)-selective xanthine-based antagonist. This is compared with structures of the A(2A) receptor with PSB36 (2.8 angstrom resolution), caffeine (2.1 angstrom), and theophylline (2.0 angstrom) to highlight features of ligand recognition which are common across xanthines. The structures of A(1)R and A(2A)R were analyzed to identify the differences that are important selectivity determinants for xanthine ligands, and the role of T270(7.35) in A(1)R (M270(7.35) in A(2A)R) in conferring selectivity was confirmed by mutagenesis. The structural differences confirmed to lead to selectivity can be utilized in the design of new subtype-selective A(1)R or A(2A)R antagonists.