Human A2A Adenosine Receptor Research Articles

Dual Targeting of Adenosine A2A Receptors and Monoamine Oxidase B by 4H-3,1-Benzothiazin-4-ones

Blockade of A2A adenosine receptors (A2AARs) and inhibition of monoamine oxidase B (MAO-B) in the brain are considered attractive strategies for the treatment of neurodegenerative diseases such as Parkinson's disease (PD). In the present study, benzothiazinones, e.g., 2-(3-chlorophenoxy)-N-(4-oxo-4H-3,1-benzothiazin-2-yl)acetamide (13), were identified as a novel class of potent MAO-B inhibitors (IC50 human MAO-B: 1.63 nM). Benzothiazinones with large substituents in the 2-position, e.g., methoxycinnamoylamino, phenylbutyrylamino, or chlorobenzylpiperazinylbenzamido residues (14, 17, 27, and 28), showed high affinity and selectivity for A2AARs (Ki human A2AAR: 39.5-69.5 nM). By optimizing benzothiazinones for both targets, the first potent, dual-acting A2AAR/MAO-B inhibitors with a nonxanthine structure were developed. The best derivative was N-(4-oxo-4H-3,1-benzothiazin-2-yl)-4-phenylbutanamide (17, Ki human A2A, 39.5 nM; IC50 human MAO-B, 34.9 nM; selective versus other AR subtypes and MAO-A), which inhibited A2AAR-induced cAMP accumulation and showed competitive, reversible MAO-B inhibition. The new compounds may be useful tools for validating the A2AAR/MAO-B dual target approach in PD.

Ligand-dependent activation and deactivation of the human adenosine A(2A) receptor.

G-protein-coupled receptors (GPCRs) are membrane proteins with critical functions in cellular signal transduction, representing a primary class of drug targets. Acting by direct binding, many drugs modulate GPCR activity and influence the signaling pathways associated with numerous diseases. However, complete details of ligand-dependent GPCR activation/deactivation are difficult to obtain from experiments. Therefore, it remains unclear how ligands modulate a GPCR's activity. To elucidate the ligand-dependent activation/deactivation mechanism of the human adenosine A2A receptor (AA2AR), a member of the class A GPCRs, we performed large-scale unbiased molecular dynamics and metadynamics simulations of the receptor embedded in a membrane. At the atomic level, we have observed distinct structural states that resemble the active and inactive states. In particular, we noted key structural elements changing in a highly concerted fashion during the conformational transitions, including six conformational states of a tryptophan (Trp246(6.48)). Our findings agree with a previously proposed view that, during activation, this tryptophan residue undergoes a rotameric transition that may be coupled to a series of coherent conformational changes, resulting in the opening of the G-protein binding site. Further, metadynamics simulations provide quantitative evidence for this mechanism, suggesting how ligand binding shifts the equilibrium between the active and inactive states. Our analysis also proposes that a few specific residues are associated with agonism/antagonism, affinity, and selectivity, and suggests that the ligand-binding pocket can be thought of as having three distinct regions, providing dynamic features for structure-based design. Additional simulations with AA2AR bound to a novel ligand are consistent with our proposed mechanism. Generally, our study provides insights into the ligand-dependent AA2AR activation/deactivation in addition to what has been found in crystal structures. These results should aid in the discovery of more effective and selective GPCR ligands.

Insight into the binding mode and the structural features of the pyrimidine derivatives as human A2A adenosine receptor antagonists

The interaction of 278 monocyclic and bicyclic pyrimidine derivatives with human A2A adenosine receptor (AR) was investigated by employing molecular dynamics, thermodynamic analysis and three-dimensional quantitative structure–activity relationship (3D-QSAR) approaches. The binding analysis reveals that the pyrimidine derivatives are anchored in TM2, 3, 5, 6 and 7 of A2A AR by the aromatic stacking and hydrogen bonding interactions. The key residues involving Phe168, Glu169, and Asn253 stabilize the monocyclic and bicyclic cores of inhibitors. The thermodynamic analysis by molecular mechanics/Poisson Boltzmann surface area (MM-PBSA) approach also confirms the reasonableness of the binding modes. In addition, the ligand-/receptor-based comparative molecular similarity indices analysis (CoMSIA) models of high statistical significance were generated and the resulting contour maps correlate well with the structural features of the antagonists essential for high A2A AR affinity. A minor/bulky group with negative charge at C2/C6 of pyrimidine ring respectively enhances the activity for all these pyrimidine derivatives. Particularly, the higher electron density of the ring in the bicyclic derivatives, the more potent the antagonists. The obatined results might be helpful in rational design of novel candidate of A2A adenosine receptor antagonist for treatment of Parkinson's disease.

Synthesis, biological activity and molecular modelling studies of tricyclic alkylimidazo-, pyrimido- and diazepinopurinediones.

Syntheses and biological activities of imidazo-, pyrimido- and diazepino[2,1-f]purinediones containing N-alkyl substituents (with straight, branched or unsaturated chains) are described. Tricyclic derivatives were synthesized by the cyclization of 8-bromo-substituted 7-(2-bromoethyl)-, 7-(3-chloropropyl)- or 7-(4-bromobutyl)-theophylline with primary amines under various conditions. Compound 22 with an ethenyl substituent was synthesized by dehydrohalogenation of 9-(2-bromoethyl)-1,3-dimethyltetrahydropyrimido[2,1-f]purinedione. The obtained derivatives (5–35) were initially evaluated for their affinity at rat A1 and A2A adenosine receptors (AR), showing moderate affinity for both adenosine receptor subtypes. The best ligands were diazepinopurinedione 28 (K i = 0.28 μM) with fivefold A2A selectivity and the non-selective A1/A2A AR ligand pyrimidopurinedione 35 (K i A1 = 0.28 μM and K i A2A = 0.30 μM). The compounds were also evaluated for their affinity at human A1, A2A, A2B and A3 ARs. All of the obtained compounds were docked to the A2A AR X-ray structure in complex with the xanthine-based, potent adenosine receptor antagonist—XAC. The likely interactions of imidazo-, pyrimido- and diazepino[2,1-f]purinediones with the residues forming the A2A binding pocket were discussed. Furthermore, the new compounds were tested in vivo as anticonvulsants in maximal electroshock, subcutaneous pentylenetetrazole (ScMet) and TOX tests in mice (i.p.). Pyrimidopurinediones showed anticonvulsant activity mainly in the ScMet test. The best derivative was compound 11, showing 100 % protection at a dose of 100 mg/kg without symptoms of neurotoxicity. Compounds 6, 7, 8 and 14 with short substituents showed neurotoxicity and caused death. In rat tests (p.o.), 9 was characterized by a high protection index (>13.3). AR affinity did not apparently correlate with the antiepileptic potency of the compounds.Electronic supplementary materialThe online version of this article (doi:10.1007/s11302-013-9358-3) contains supplementary material, which is available to authorized users.

Novel adenosine A2A receptor ligands: A synthetic, functional and computational investigation of selected literature adenosine A2A receptor antagonists for extending into extracellular space

Growing evidence has suggested a role in targeting the adenosine A2A receptor for the treatment of Parkinson’s disease. The literature compounds KW 6002 (2) and ZM 241385 (5) were used as a starting point from which a series of novel ligands targeting the adenosine A2A receptor were synthesized and tested in a recombinant human adenosine A2A receptor functional assay. In order to further explore these molecules, we investigated the biological effects of assorted linkers attached to different positions on selected adenosine A2A receptor antagonists, and assessed their potential binding modes using molecular docking studies. The results suggest that linking from the phenolic oxygen of selected adenosine A2A receptor antagonists is relatively well tolerated due to the extension towards extracellular space, and leads to the potential of attaching further functionality from this position.

SKCa Channels Blockage Increases the Expression of Adenosine A2AReceptor in Jurkat Human T Cells

Adenosine is a nucleoside displaying various biological effects via stimulation of four G-protein–coupled receptors, A1, A2A, A2B, and A3. Adenosine also modulates voltage-gated (Kv) and small conductance calcium-activated (SKCa) potassium channels. The effect of these potassium channels on the expression of adenosine receptors is poorly understood. We evaluated the action of BgK (a natural Kv channel blocker) and Lei-Dab7 (a synthetic SKCa channel blocker) on the expression of adenosine A2A receptors (A2AR) in Jurkat human T cells. We found that Lei-Dab7, but not BgK, increased the maximal binding value of the tritiated ligand ZM241385 to A2AR in a dose-dependent manner (+45% at 5 nM; +70% at 50 nM as compared to control). These results were further confirmed by Western blotting using a specific monoclonal antibody to human A2AR. The ligand affinity-related dissociation constant and A2AR mRNA amount were not significantly modified by either drug. We suggest that modulation of SKCa channels can influence membrane expression of A2AR and thus has a therapeutic potential.

Ligand-dependent cholesterol interactions with the human A2A adenosine receptor

We present nearly 10μs of all-atom simulation data of a G-protein coupled receptor, the human A2A adenosine receptor, bound to four different ligands. Our focus is on binding of cholesterol to the “cholesterol consensus motif,” a cluster of five amino acids on the second and fourth transmembrane helices, which interact with two cholesterols in the intracellular leaflet of the bilayer. We find evidence for a ligand-specific interaction between the CCM and cholesterol, mediated by the rotameric dynamics and configuration of Trp129. Binding of the synthetic agonist UK432097 disrupts hydrogen bonding between Trp129 and Ser47, which activates the rotameric dynamics of Trp129 and disrupts the interaction with one of the two cholesterols. We also investigate the effect of four thermostabilizing mutations, three of which are located on helix two. The conformational stability of helix two has been proposed to be sensitive to interaction with cholesterol in the CCM, suggesting a mechanism for the thermostabilization. However, our data are instead suggestive of a force-field dependent “straightening” of helix two, and therefore offer no basis for rationalizing the effect of the quadruple mutant.

Identification of Novel Amino Acid Derived CCK-2R Antagonists As Potential Antiulcer Agent: Homology Modeling, Design, Synthesis, and Pharmacology

The present study revisited the three-dimensional (3D) homology model of CCK-2R using human A(2a) adenosine receptor and the resolved NMR based structure of the third extracellular loop of the CCK-2R as templates. Further in order to identify novel antiulcer agents, rational designing have been performed utilizing the substructure of a well-known CCK-2R antagonist benzotript as a lead molecule and submitted to the combined docking and simulation studies. This led to the understanding of the essential structure requirement as well as variation of binding mode among conformational isomers of small molecule CCK-2R antagonists. In the next step, preparation of each configurational isomer of these molecules was carried out and submitted for their in vitro activity followed by in vivo screening into antiulcer rat model. The biological screening of these compounds has not only validated the developed homology model of CCK-2R but also led to the identification of highly potent CCK-2R antagonist 6a as an orally active and safe candidate molecule having better antiulcer properties than the well-known drug benzotript.

Ligand-Perturbed Allosteric Communication within the Human A2A Adenosine Receptor

The human A2A adenosine receptor (A2AR) is a member of Class A G protein-coupled receptors (GPCRs). Activation of A2A adenosine receptor leads to the stimulation of adenylyl cyclase (AC), and thereby increases the formation of cyclic adenosine monophosphate (cAMP). It has been recognized that A2A adenosine receptor is a potential therapeutic target for the treatment of Parkinson's disease, Huntington's disease, schizophrenia, and other neurodegenerative diseases. In 2008, the first human A2A adenosine receptor was crystalized in complex with its high affinity selective antagonist ZM241385. In 2011, six more A2A adenosine receptor structures were published. Three of them co-crystallized with its agonists (UK432097, adenosine, and NECA) and three of the others co-crystallized with its antagonists (ZM241385, xanthine amine congener, and caffeine). In this study, the changes of allosteric communication inside the A2A adenosine receptor induced by these agonists and antagonists are examined by molecular dynamics simulations. We found that agonists are able to switch the torsion angle of W2466.48, and the correlated motions within the A2A adenosine receptor are also perturbed by this rotamer toggle switch. In addition to conventional dynamical cross-correlation matrix analysis, we also investigated the time-lagged correlated motions to see the persistence time of autocorrelation and cross-correlation, and to examine the causality relationships between different dynamics states of the receptor.1. Huang, N.-K.; Lin, J.-H. ….Chern Y. A new drug design targeting the adenosinergic system for Huntington's disease. PLoS. ONE 2011, 6, e20934.2. Chen, J.-B.;. ….Lin, J.-H., Fang J.-M. Design and synthesis of novel dual-action compounds targeting adenosine A2A receptor for neuroprotection. ChemMedChem 2011, 6, 1390-1400.

Rehabilitation Studies for withdrawn Drugs from the Market: Derivation of Non-hERG1 Channel Blocker Cisapride Analogues using Multi-Faceted Approaches

The human ether-a-go-go related gene 1 (hERG1) potassium ion channel is a key element for the cardiac delayed rectified potassium current IKr and it plays an important role in the normal repolarization of the action potential. Diverse types of organic compounds used both in common cardiac and noncardiac medications can reduce the IKr and may lead to ventricular arrhythmia. Therefore, several approved drugs have been withdrawn from the market because of their effects on QT interval prolongation. Since most of these drugs have high potency for their principal targets, “rehabilitation” studies for decreasing their high hERG1 blocking affinities while keeping them active at the binding site of their targets may lead re-use of these drugs. For this aim, a gastroprokinetic agent, cisapride, is studied. Cisapride is withdrawn from the market because of its high hERG1 blocking affinity. In this study, analyses of fragment interactions of cisapride at the human A2A adenosine receptor and hERG1 central cavities is investigated using in silico applications (molecular docking, molecular dynamics simulations, de novo drug design) and novel and safer (with low hERG1 blocking affinities) of cisapride derivatives are proposed for their synthesis and their biological tests.

Conopeptide ρ-TIA Defines a New Allosteric Site on the Extracellular Surface of the α1B-Adrenoceptor

The G protein-coupled receptor (GPCR) superfamily is an important drug target that includes over 1000 membrane receptors that functionally couple extracellular stimuli to intracellular effectors. Despite the potential of extracellular surface (ECS) residues in GPCRs to interact with subtype-specific allosteric modulators, few ECS pharmacophores for class A receptors have been identified. Using the turkey β(1)-adrenergic receptor crystal structure, we modeled the α(1B)-adrenoceptor (α(1B)-AR) to help identify the allosteric site for ρ-conopeptide TIA, an inverse agonist at this receptor. Combining mutational radioligand binding and inositol 1-phosphate signaling studies, together with molecular docking simulations using a refined NMR structure of ρ-TIA, we identified 14 residues on the ECS of the α(1B)-AR that influenced ρ-TIA binding. Double mutant cycle analysis and docking confirmed that ρ-TIA binding was dominated by a salt bridge and cation-π between Arg-4-ρ-TIA and Asp-327 and Phe-330, respectively, and a T-stacking-π interaction between Trp-3-ρ-TIA and Phe-330. Water-bridging hydrogen bonds between Asn-2-ρ-TIA and Val-197, Trp-3-ρ-TIA and Ser-318, and the positively charged N terminus and Glu-186, were also identified. These interactions reveal that peptide binding to the ECS on transmembrane helix 6 (TMH6) and TMH7 at the base of extracellular loop 3 (ECL3) is sufficient to allosterically inhibit agonist signaling at a GPCR. The ligand-accessible ECS residues identified provide the first view of an allosteric inhibitor pharmacophore for α(1)-adrenoceptors and mechanistic insight and a new set of structural constraints for the design of allosteric antagonists at related GPCRs.

Loop prediction for a GPCR homology model: Algorithms and results

We present loop structure prediction results of the intracellular and extracellular loops of four G-protein-coupled receptors (GPCRs): bovine rhodopsin (bRh), the turkey β1-adrenergic (β1Ar), the human β2-adrenergic (β2Ar) and the human A2a adenosine receptor (A2Ar) in perturbed environments. We used the protein local optimization program, which builds thousands of loop candidates by sampling rotamer states of the loops' constituent amino acids. The candidate loops are discriminated between with our physics-based, all-atom energy function, which is based on the OPLS force field with implicit solvent and several correction terms. For relevant cases, explicit membrane molecules are included to simulate the effect of the membrane on loop structure. We also discuss a new sampling algorithm that divides phase space into different regions, allowing more thorough sampling of long loops that greatly improves results. In the first half of the paper, loop prediction is done with the GPCRs' transmembrane domains fixed in their crystallographic positions, while the loops are built one-by-one. Side chains near the loops are also in non-native conformations. The second half describes a full homology model of β2Ar using β1Ar as a template. No information about the crystal structure of β2Ar was used to build this homology model. We are able to capture the architecture of short loops and the very long second extracellular loop, which is key for ligand binding. We believe this the first successful example of an RMSD validated, physics-based loop prediction in the context of a GPCR homology model.

Homology Modeling and Antagonist Binding Site Study of the Human Histamine H2 Receptor

On the basis of the high resolution crystal structures of bovine rhodopsin, human beta2-adrenergic receptor and human A(2a) adenosine receptor, three-dimensional structure of the human histamine H2 receptor (HHR2) was developed by homology modeling. Results of the evaluations suggest that a high quality homology model for HHR2 has been obtained. Three antagonists, cimetidine, ranitidine and nizatidine, were applied to binding site study with this model through molecular docking, molecular dynamics simulations and the molecular mechanics-Poisson-Boltzmann surface area calculations. One aspartic acid, Asp98 in transmembrane domain 7 (TM3), has been identified as major contributors to ligand binding by H-bond interactions. Asn159 in TM4 and Asp186 in TM5 are of great importance in stabilizing HHR2- antagonist complexes. Two hydrophobic sites especially two residues, Val99 in TM3 and Phe254 in TM6, were identified to be essential for their strong hydrophobic interactions with antagonists. The findings reported here are in agreement with available experimental mutagenesis data. This study should be very helpful for a better understanding of the action mode of the antagonist and for guiding further drug design and mutagenesis studies.

Of receptors, channels, and watching the red cell center lose hold

Of receptors, channels, and watching the red cell center lose hold

Structural Basis for Allosteric Regulation of GPCRs by Sodium Ions

Pharmacological responses of G protein-coupled receptors (GPCRs) can be fine-tuned by allosteric modulators. Structural studies of such effects have been limited due to the medium resolution of GPCR structures. We reengineered the human A(2A) adenosine receptor by replacing its third intracellular loop with apocytochrome b(562)RIL and solved the structure at 1.8 angstrom resolution. The high-resolution structure allowed us to identify 57 ordered water molecules inside the receptor comprising three major clusters. The central cluster harbors a putative sodium ion bound to the highly conserved aspartate residue Asp(2.50). Additionally, two cholesterols stabilize the conformation of helix VI, and one of 23 ordered lipids intercalates inside the ligand-binding pocket. These high-resolution details shed light on the potential role of structured water molecules, sodium ions, and lipids/cholesterol in GPCR stabilization and function.

Ligand-specific homology modeling of human cannabinoid (CB1) receptor

Cannabinoid (CB1) receptor is a therapeutic drug target, and its structure and conformational changes after ligand binding are of great interest. To study the protein conformations in ligand bound state and assist in drug discovery, CB1 receptor homology models are needed for computer-based ligand screening. The known CB1 ligands are highly diverse structurally, so CB1 receptor may undergo considerable conformational changes to accept different ligands, which is challenging for molecular docking methods. To account for the flexibility of CB1 receptor, we constructed four CB1 receptor models based on four structurally distinct ligands, HU-210, ACEA, WIN55212-2 and SR141716A, using the newest X-ray crystal structures of human β2 adrenergic receptor and adenosine A2A receptor as templates. The conformations of these four CB1–ligand complexes were optimized by molecular dynamics (MD) simulations. The models revealed interactions between CB1 receptor and known binders suggested by experiments and could successfully discriminate known ligands and non-binders in our docking assays. MD simulations were used to study the most flexible ligand, ACEA, in its free and bound states to investigate structural mobility achieved by the rearrangement of the fatty acid chain. Our models may capture important conformational changes of CB1 receptor to help improve accuracy in future CB1 drug screening.

New chromene scaffolds for adenosine A2A receptors: Synthesis, pharmacology and structure–activity relationships

In silico screening of a collection of 1584 academic compounds identified a small molecule hit for the human adenosine A2A receptor (pKi = 6.2) containing a novel chromene scaffold (3a). To explore the structure–activity relationships of this new chemical series for adenosine receptors, a focused library of 43 2H-chromene-3-carboxamide derivatives was synthesized and tested in radioligand binding assays at human adenosine A1, A2A, A2B and A3 receptors. The series was found to be enriched with bioactive compounds for adenosine receptors, with 14 molecules showing submicromolar affinity (pKi ≥ 6.0) for at least one adenosine receptor subtype. These results provide evidence that the chromene scaffold, a core structure present in natural products from a wide variety of plants, vegetables, and fruits, constitutes a valuable source for novel therapeutic agents.

Prediction of Binding Mode between Chemokine Receptor CCR2 and Its Known Antagonists using Ligand Supported Homology Modeling

Chemokines play a crucial role in the trafficking of leukocytes in the body through the binding to their related receptors. Chemokine Receptor 2 (CCR2) belongs to GProtein Coupled Receptor (GPCR) family and expressed in monocytes, immature dendritic cells, activated T lymphocytes, basophils, and endothelial and vascular smooth-muscle cells. CCR2 binds several chemokines; CCL2, CCL7, CCL8, and CCL13. CCR2 and its ligand have been implicated in the pathophysiology of a number of diseases, including rheumatoid arthritis, multiple sclerosis, atherosclerosis, organ transplant rejection, and insulin resistance. Knowledge of the structural basis on CCR2-ligand interaction could help facilitate the design of novel CCR2 antagonists. We modeled and predicted the binding sites of widely known CCR2 antagonists, TAK-779 and Teijin-lead (Fig. 1), using ligand supported homology modeling method. Homology modeling predicts the three-dimensional structure of a given protein sequence based on its alignment to reference proteins of known three-dimensional structure (socalled templates). It is known as the most successful technique for predicting the three-dimensional protein structure. In conventional homology modeling method, the ligand molecules are not considered in the process of protein model building. After building the protein model, the ligand molecules are docked into the protein model. These approaches often showed the consequence that residue side chains involved in ligand binding are inappropriately modeled. The time-consuming re-modeling of the binding site or docking is required to generate sensible side-chain and ligand orientations. In the case of GPCR, the conventional homology modeling approaches for obtaining the binding site models are more challenging because the number of the available templates is very limited and the sequence identity to the templates is very low. The available templates for GPCR are the solved three-dimensional structures of bovine rhodopsin, β2-adrenergic receptor (β2AR), turkey β1adrenergic receptor, and human adenosine A2A receptor. The homology modeling from those limited number of templates may result in uncertainty not only regarding backbone positioning but also about side chain conformations. One approach to solve this is to optimize the side chains through mechanics and/or dynamics in an empty pocket; however, this method may be inaccurate due to possible disruption of the binding site. Another approach is to use dynamics and ligand data as a restraint. This method also has a possibility of poor quality. Thus, the development of modified homology modeling methods for constructing a plausible ligand binding mode is an important theme in GPCR-ligand modeling research. The incorporation of ligand information from the early stage of homology modeling has been studied as an alternative strategy to the conventional homology modeling. This approach was first developed and termed as ligand supported homology modeling by Klebe and coworkers. Recently, the improved and diversified methods have been published as ligand-steered homology modeling or homology-modeling protein-ligand interactions. The results presented reasonable binding site models. We recently reported the protocol and evaluation for the proprietary CCR2 antagonist by ligand-supported homology modeling. We here employed the protocol to predict the binding mode for known CCR2 antagonists, TAK-779 and Teijin-lead. The method in this study for structure modeling of CCR2 and its antagonists is summarized in Figure 2. In the first place of homology modeling, we retained the bound ligand, carazolol, from the crystal structure of β2AR. Then, carazolol was replaced by the various conformations of the target

G-protein-coupled receptor inactivation by an allosteric inverse-agonist antibody.

G protein-coupled receptors (GPCRs) are the largest class of cell-surface receptors, and these membrane proteins exist in equilibrium between inactive and active states.1-13 Conformational changes induced by extracellular ligands binding to GPCRs result in a cellular response through the activation of G-proteins. The A2A adenosine receptor (A2AAR) is responsible for regulating blood flow to the cardiac muscle and is important in the regulation of glutamate and dopamine release in the brain.14 In this study, we have successfully raised a mouse monoclonal antibody against human A2AAR that prevents agonist but not antagonist binding to the extracellular ligand-binding pocket. The structure of the A2AAR-antibody Fab fragment (Fab2838) complex reveals that the fragment, unexpectedly, recognises the intracellular surface of A2AAR and that its complementarity determining region, CDR-H3, penetrates into the receptor. CDR-H3 is located in a similar position to the G-protein C-terminal fragment in the active opsin structure1 and to the CDR-3 of the nanobody in the active β2 adrenergic receptor structure2 but locks the A2AAR in an inactive conformation. These results shed light on a novel strategy to modulate GPCR activity.

Class A GPCRs: a multifaceted reality

Highlight presented by Maria P. Abbracchio Xu F, Wu H, Katritch V, Han GW, Jacobson KA, Gao ZG, Cherezov V, Stevens RC (2011) Structure of an agonist-bound human A2A adenosine receptor. Science 332:322–327; doi:10.1126/science.1202793 About the Authors Chiara Parravicini is research associate at the Department of Pharmacological Sciences at the University of Milan, Italy. She holds a PhD in pharmacology and her research is on purinergic pharmacology, with particular focus on the P2Y-like receptor GPR17. Cristina Sensi is a bioinformatician at the same University and applies computational tools for solving protein structures. Ivano Eberini is senior research associate at the Department of Pharmacological Sciences at the University of Milan, Italy. He is a molecular pharmacologist with a PhD in biotechnology. He is author/coauthor of more than 65 papers, 15 of which focussed on structure-function relationships in proteins of pharmacological interest.