Fig. 1. Structural properties of TgSODB2. (A) Comparison of amino acid sequences of TgSODB2 (accession no. AY176062), Perkinsus marinus FeSOD (PmSOD1, AY095212), TgSODB (AAC63943), Plasmodium falciparum FeSOD (PfFeSODB, CAA89971) and Vibrio cholerae FeSOD (VcFeSOD, NP_231679). Protein sequences were aligned using the ClustalW program (DNAStar-Megalign) and identical residues among sequences are shaded. TgSODB2 contains all residues deemed important for enzyme function (marked with #) and metal ion binding (marked with ^*) and shows extensive similarity with TgSODB and other FeSODs. The N-terminal hydrophobic sequence of TgSODB2 is boxed and the single basic residue (arg¹²) within this region is indicated with an arrow. (B) Schematic representation of the TgSODB2 N-terminal extension containing a hydrophobic sequence (HS) and presequence (PS). The HS is predicted by SignalP to be a signal peptide for targeting to the secretory pathway, the PS is predicted by iPSORT to be a mitochondrial or chloroplast targeting sequence, and the entire N-terminal extension is predicted to be an apicoplast targeting sequence. (C) Helical wheel projections (Webgenetics; http://webgenetics.com/cgibin/wg?form=wheel&ID=0) of TgSODB2 amino acids 1 to 30 (TgSODB2^1-30) and 31 to 60 (TgSODB2^31-60) and TgHSP70 amino acids 1-30 (TgHSP70^1-30). Arrows denote charged residues, all of which are basic amino acids. Note that TgSODB2^1-30 is predicted to form a hydrophobic helix with only one charged residue (arg¹²) whereas TgSODB2^31-60 exhibits the properties of an amphipathic helix that is similar to the mitochondrial import presequence of TgHSP70.