(A) Cartoon of β1AR (grey) depicting the positions of ordered water molecules (red spheres), Na+ ions (purple spheres), lipids (green sticks) and cyanopindolol (stick representation: carbon, yellow; nitrogen, blue; oxygen, red). The extracellular surface is at the top of the figure with the N-terminus (N) and C-terminus (C) labelled appropriately. (B) Detail of the Na+ binding site with portions of H2 and H3 removed for clarity: red spheres, water molecules; purple sphere, Na+ ion; green sticks, amino acid side chains; yellow sticks, cyanopindolol; red dashed lines, polar contacts, as defined by PyMOL. (C) Diagrammatic representation of the hydrogen bond network. Hydrogen bonds are assigned as displayed in COOT with a maximum distance of 3.5 Å. Where more than four interactions are shown, those with more favourable distances and geometry have been selected, with the exception of waters coordinating the Na+ ion, where up to 5 interactions are shown. Only the last two digits of the water numbers are shown.