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Summary: Methylxanthines, including caffeine and theophylline, are among the most widely consumed stimulant drugs in the world. These effects are mediated primarily via blockade of adenosine receptors. Xanthine analogs with improved properties have been developed as potential treatments for diseases such as Parkinson''s disease. Here we report the structures of a thermostabilized adenosine A2A receptor in complex with the xanthines xanthine amine congener and caffeine, as well as the A2A selective inverse agonist ZM241385. The receptor is crystallized in the inactive state conformation as defined by the presence of a salt bridge known as the ionic lock. The complete third intracellular loop, responsible for G protein coupling, is visible consisting of extended helices 5 and 6. The structures provide new insight into the features that define the ligand binding pocket of the adenosine receptor for ligands of diverse chemotypes as well as the cytoplasmic regions that interact with signal transduction proteins. [Copyright &y& Elsevier]

Summary 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, non-selective antagonists of adenosine receptors. Here we report the structure of a thermostabilized human A 1 receptor at 3.3 Å resolution with PSB36, an A 1 -selective xanthine-based antagonist. This is compared with structures of the A 2A receptor with PSB36 (2.8 Å resolution), caffeine (2.1 Å), and theophylline (2.0 Å) 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. [ABSTRACT FROM AUTHOR]

Virtual screening was performed against experimentallyenabledhomology models of the adenosine A2Areceptor, identifyinga diverse range of ligand efficient antagonists (hit rate 9%). Byuse of ligand docking and Biophysical Mapping (BPM), hits 1and 5were optimized to potent and selective lead molecules(11–13from 5, pKI= 7.5–8.5, 13- to >100-fold selectiveversus adenosine A1; 14–16from 1, pKI= 7.9–9.0,19- to 59-fold selective). [ABSTRACT FROM AUTHOR]

A new approach to generating information on ligand receptor interactions within the binding pocket of G protein-coupled receptors has been developed, called Biophysical Mapping (BPM). Starting from a stabilized receptor (StaR), minimally engineered for thermostability, additional single mutations are then added at positions that could be involved in small molecule interactions. The StaR and a panel of binding site mutants are captured onto Biacore chips to enable characterization of the binding of small molecule ligands using surface plasmon resonance (SPR) measurement. A matrix of binding data for a set of ligands versus each active site mutation is then generated, providing specific affinity and kinetic information (KD, kon, and koff) of receptor–ligand interactions. This data set, in combination with molecular modeling and docking, is used to map the small molecule binding site for each class of compounds. Taken together, the many constraints provided by these data identify key protein–ligand interactions and allow the shape of the site to be refined to produce a high quality three-dimensional picture of ligand binding, thereby facilitating structure based drug design. Results of biophysical mapping of the adenosine A2Areceptor are presented. [ABSTRACT FROM AUTHOR]