Comparison of sulphate-binding residues in var2CSA DBL domains. A4 DBL 3X crystal structure is used as control and all residues involved in binding to sulphate ion are coloured blue (PDB codes: 3BQK and 3CPZ). Residues which are conserved in other domains are also colored blue. Residues which are replaced with acidic amino acids are coloured red. Residues replaced by other residue types are coloured cyan.