Structure of the Adenosine A1 Receptor Reveals the Basis for Subtype Selectivity

The adenosine A(1) receptor (A(1)-AR) is a G-proteincoupled receptor that plays a vital role in cardiac, renal, and neuronal processes but remains poorly targeted by current drugs. We determined a 3.2 angstrom crystal structure of the A(1)-AR bound to the selective covalent antagonist, DU172, and identified striking differences to the previously solved adenosine A(2A) receptor (A(2A)-AR) structure. Mutational and computational analysis of A(1)-AR revealed a distinct conformation of the second extracellular loop and a wider extracellular cavity with a secondary binding pocket that can accommodate orthosteric and allosteric ligands. We propose that conformational differences in these regions, rather than amino-acid divergence, underlie drug selectivity between these adenosine receptor subtypes. Our findings provide a molecular basis for AR subtype selectivity with implications for understanding the mechanisms governing allosteric modulation of these receptors, allowing the design of more selective agents for the treatment of ischemia-reperfusion injury, renal pathologies, and neuropathic pain.