Alignment of five different CXCR4 proteins.

<p>Seven-transmembrane domains and conserved cysteines are boxed. Extracellular loops are shadowed and marked with the first, second and third extracellular loops (ECL1, ECL2 and ECL3, respectively). Identical amino acid residues are marked by an asterisk. Conserved and semi-conserved residues are indicated by a colon and period respectively. Dashes indicate gaps introduced into the sequences to optimize alignment.