Figure 2.

Sequence alignment of the four human AR subtypes. Transmembrane (TM), intracellular loop (IL), extracellular loop (EL), and C-terminal (C-TERM) domains are indicated; * symbols indicate sequence identity in all the four subtypes; C letters indicate cysteine residues involved in the disulfide bridge conserved among the four AR subtypes; letters coloured in yellow, cyan, and green indicate the A_2BAR binding site residues involved in ligand interaction (the colour indexing refers to the binding site subdivision described in Figure 5, see its legend for details).