Multiple sequence alignment of selected representatives of proteins families predicted to belong to the PD-(D/E)XK superfamily. The selection of representative sequences includes members of all families analyzed in this article (see Table 1). Amino acids are colored according to the physico-chemical properties of their side-chains (negatively charged: red, positively charged: blue, polar: magenta, hydrophobic: green). The putative catalytic Asp/Glu and Lys/Arg residues are highlighted. The variable termini and insertions are not shown. The number of omitted residues is indicated in parentheses. Elements of secondary structure (helices and strands predicted individually for each family) are indicated by H and E, respectively.