Comparison of sulphate binding site in all the CSA-binding var2CSA DBL domains. (a) Superposition of all CSA-binding DBL domains onto the A4 DBL 3X crystal structure (PDB code: 3BQK). The sulphate-binding site is highlighted. (b) Close view of the sulphate-binding site. The loop region bearing the important Gly and Lys residues is magnified. This loop is either absent or is in a different orientation in all CSA-binding domains except A4 (magenta) and 3D7 (green) DBL 3X.