Bacterial catalase-peroxidases are gene duplicated members of the plant peroxidase superfamily

Bacterial catalase-peroxidases are enzymes containing 0.5-1.0 heme per subunit. The identical subunits are generally 80 kDa in size, and the sequenced subunits of E. coli, S. typhimurium and B. stearothermophilus contain 726-731 amino acid residues per subunit. The heme-containing peroxidases of plants, fungi and yeast are monomeric, homologous and 290-350 residues in size. Analyses of the amino acid sequences indicate that the double length of the bacterial peroxidases can be ascribed to gene duplication. Each half is homologous to eukaryotic, monomeric peroxidase and can be modelled into the high-resolution crystal structure of yeast cytochrome c peroxidase. The comparisons and modelling have predicted: (1) the C-terminal half does not bind heme, and bacterial peroxidases have one heme per subunit; (2) the ten dominating helices observed in the yeast enzyme are highly conserved and connected by surface loops which are often longer in the bacterial peroxidases; and (3) yeast cytochrome c peroxidase has evolved more slowly than other known peroxidases. The study has revealed ten invariant residues and a number of highly conserved residues present in peroxidases of the plant peroxidase superfamily and provides a basis for rationally engineered peroxidases.