1. Volume 19, Issue 9, Pages 1283-1293 (September 2011)
Structure of the Adenosine A2A Receptor in Complex with ZM and the Xanthines XAC and Caffeine 
Andrew S. Doré, Nathan Robertson, James C. Errey, Irene Ng, Kaspar Hollenstein, Ben Tehan, Edward Hurrell, Kirstie Bennett, Miles Congreve, Francesca Magnani, Christopher G. Tate, Malcolm Weir, Fiona H. Marshall 
Structure 
Volume 19, Issue 9, Pages (September 2011)
DOI: /j.str
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2. Structure 2011 19, 1283-1293DOI: (10.1016/j.str.2011.06.014)
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3. Figure 1
The Effect of StaR Mutations on Receptor Thermostability and Their Location on the Receptor
(A) Thermostability plots of the wild-type adenosine A2A receptor (purple circles), A2A-T4L (orange squares), A2A-StaR1 (previously Rant21, yellow triangles), A2A-T4L engineered to include the A2A-StaR1 mutations in combination with the T4L fusion (A54L2.52/T88A3.36/K122A4.43/V239A6.41) (green triangles), and versus A2A-StaR2 (blue diamonds). Error bars are derived from standard deviation and calculated from duplicated temperature points (n = 2) within a single experiment.
(B) Sequence of the wild-type A2A receptor in relation to the secondary structure determined from the structure of A2A-StaR2. Thermostabilizing residues are shown in red circles and the glycosylation site mutation N154A in blue. Disulfide bonds are in yellow. Numbers refer to the first and last residue in each transmembrane helix (TM) (blue boxes) with the Ballesteros-Weinstein numbering in superscript (same for all subsequent figures).
See also Figure S2 and Table S2.
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4. Figure 2
Pharmacological Characterization of the StaR Receptor and the Ligands Used in Crystallization
(A) Comparison of the pharmacology of A2A-StaR2 with the wild-type adenosine A2A receptor. Radioligand competition binding assays for a range of antagonists (closed circles) and agonists (open circles) were carried out with [3H]-ZM on membranes from cells transiently transfected with receptors.
(B) Effects of the ligands ZM (filled squares), XAC (filled circles), caffeine (open circles), and istradefylline (open squares) on the levels of cAMP measured after overexpression of the wild-type A2A receptor that results in high levels of constitutive activity and elevated levels of cAMP. All ligands are inverse agonists although istradefylline is a weak partial inverse agonist compared to ZM241385, XAC, and caffeine.
See also Table S1.
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5. Figure 3 Overall Structure of the Adenosine A2A Receptor
(A) Structure of A2A-StaR2-ZM in rainbow coloration (blue to red) from the N terminus to the C terminus, ZM is represented as a stick model (blue), oxygen atoms are red and nitrogen atoms deep blue. The visible extracellular and intracellular loops are labeled. The disordered portion of ECL2 is shown as a dashed line. Dotted lines denote approximate boundaries of the plasma membrane.
(B) TM5 and TM6 of the A2A-StaR2 (pale green) with ICL3 represented as a stick model. The potential H-bonding network connecting the two TM helices is shown (dashed red lines) involving Arg /Met /Gln214/Pro217.
See also Figure S1. Individual TMs are numbered using Roman numerals and in all figures forthwith.
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6. Figure 4
Comparison of A2A-StaR2-ZM with A2A-T4L-ZM and Rhodopsin
(A) Superposition of A2A-StaR2-ZM (pale green) with A2A-T4L-ZM (dark red) using consensus Cα atoms of TM1-7, note the difference in TM5/6 helical trajectory. Inset: close-up of interactions across the DRY motif of A2A-StaR2 and A2A-T4L structures demonstrating ionic lock formation in the A2A-StaR2 (potential hydrogen bonds represented as dashed red lines). See also Figure S3A.
(B) Superposition of A2A-StaR2-ZM (pale green) with bovine rhodopsin (orange-1F88) using consensus Cα atoms of TM1-7. Inset: close up of interactions across the A2A-StaR2 DRY and Rhodopsin ERY motif illustrating the similarity of the ionic lock (second subscript residue numbers refer to rhodopsin 1F88).
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7. Figure 5
Residues Involved in Ligand Binding of the Xanthines and ZM241385
Two-dimensional schematics of the A2A-StaR2 ligand binding interactions; (A) ZM241385, (B) XAC, and (C) caffeine. Diagrams were generated using the LigPlot software (Wallace et al., 1995).
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8. Figure 6
Comparison of Ligand Positions in the A2A-StaR2 Cocrystal Structure Binding Site Cavity
The structure of A2A-StaR2 is depicted as a gray surface, cut away to reveal the ligand binding pocket with TM2 and TM5 depicted as green helices. The ligands are represented as sticks (gray), oxygen atoms are red, and nitrogen atoms blue. Amino acid side chains are similarly depicted with carbons in purple, oxygen in red, and nitrogen in blue. Specific hydrogen bonds are marked as dashed red lines with Asn and Ala shown. Structures are A2A-StaR2 in complex with (A) ZM241385, (B) XAC, and (C) caffeine.
See also Figure S3 and Figure S4.
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9. Figure 7
Comparison of Specific Interactions in the Ligand Binding Site between the A2A-StaR2-ZM241385/XAC/Caffeine Costructures
(A) Superposition of A2A-StaR2 (pale green) bound to ZM (blue) with A2A-StaR2 (orange) bound to XAC (green).
(B) Superposition of A2A-StaR2 (orange) bound to XAC (green) with A2A-StaR2 (yellow) bound to caffeine (bright yellow).
(C) Superposition of A2A-StaR2 (pale green) bound to ZM (blue) with A2A-StaR2 (yellow) bound to caffeine (bright yellow). A2A-StaR2 is shown in helical representation with specific side chains making important ligand receptor interactions marked. Specific hydrogen bonds are marked as dashed red lines. Ligands are represented as stick models (colored according to the ligand) with oxygen atoms red and nitrogen atoms blue.
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10. Figure 8
Comparison of the Conformations of Different A2A Receptor Structures
(A) Superposition of the A2A-StaR2-ZM (pale green) (PDB code: 3PWH), A2A-T4L-ZM (dark red) (PDB code: 3EML), A2AR-GL31 (yellow) (PDB code: 2YDV), and agonist-β2AR Nb80 (gray) (PDB code: 3P0G) structures in cartoon representation, ligands have been omitted. The N- and C-termini are marked, and TM5 and 6 are labeled. Inset: close-up view of TM6 illustrating the degree of helix rotation from the ground state (3PWH) to R∗ (3P0G). 3EML and 2YDV sit at intermediate points on the activation pathway.
(B) Superposition of the A2AR structures, colored and represented as in (A); close-up view of the extracellular side of the receptor, demonstrating the conformational changes occurring in ECL1 and 2 on activation.
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11. Figure 9 Activation Mechanism of the Adenosine A2A Receptor
(A) Close-up of the ligand binding sites of the A2AR structures superposed and colored as in Figure 8 (ECL regions have been omitted for clarity). Only the ZM and NECA ligands are shown in blue and green stick representation, respectively. Specific hydrogen bonds made between A2AR-GL31 and NECA are marked as dashed red lines. Residues implicated in ligand binding and transmission of conformational changes through the receptor are labeled and only shown for 3PWH and 2YDV. Transmembrane helices are denoted by green discs. The black arrows show transmembrane helical movements occurring on activation. In summary, agonist binding leads to inward shifts of TM1, 5, and 7, an upward movement (toward the extracellular side of the receptor) of TM3 and a rigid body rotation of TM4.
(B) Superposition of A2AR-GL31-NECA (yellow cartoon and ligand in green stick representation) and A2A-StaR2-ZM (green cartoon and ligand in blue stick representation) TMs 2, 6, and 7 labeled. Only the A2AR-GL31 is depicted as a gray surface, cut away to reveal the NECA agonist binding deeper in the receptor ligand binding pocket compared to the ZM inverse agonist.
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