Alignment of the amino acid sequences for the five known cyanases. Accession numbers are given in parentheses. Residues conserved in all cyanases are in boldface and labeled with an asterisk, less conserved residues are labeled with colons and full stops. Arg96, Glu99, Ser122 (proposed active-site residues) are shown in red. Secondary structure assignments were derived using the Kabsch and Sander DSSP algorithm [64]: h/H, α helix; t/T, turn; eE, β strand; and S, bend. The aligned sequences are Synechocystis PCC6803 (GenBank accession number Q55367) [29]; Synechococcus PCC7942 (BAA19515) [28]; Aquifex aeolicus (AACO6548) [25]; E. coli (AAA23629) [8]; and Arabidopsis thaliana (BAA21660) [32].