Common phylogeny of catalase-peroxidases and ascorbate peroxidases

Catalase-peroxidases belong to Class I of the plant, fungal, bacterial pero xidase superfamily, together with yeast cytochrome c peroxidase and ascorba te peroxidases. Obviously these bifunctional enzymes arose via gene duplica tion of an ancestral hydroperoxidase. A 230-residues long homologous region exists in all eukaryotic members of Class I, which is present twice in bot h prokaryotic and archaeal catalase-peroxidases. The overall structure of e ukaryotic Class I peroxidases may be retained in both halves of catalase-pe roxidases, with major insertions in several loops, some of which may partic ipate in inter-domain or inter-subunit interactions. Interspecies distances in unrooted phylogenetic trees, analysis of sequence similarities in distinct structural regions, as well as hydrophobic cluste r analysis (HCA) suggest that one single tandem duplication had already occ urred in the common ancestor prior to the segregation of the archaeal and e ubacterial lines. The C-terminal halves of extant catalase-peroxidases clea rly did not accumulate random changes, so prolonged periods of independent evolution of the duplicates can be ruled out. Fusion of both copies must ha ve occurred still very early or even in the course of the duplication. We s uggest that the sparse representatives of eukaryotic catalase-peroxidases g o back to lateral gene transfer, and that, except for several fungi, only s ingle copy hydroperoxidases occur in the eukaryotic lineage. The N-terminal halves of catalase-peroxidases, which reveal higher homology with the single-copy members of the superfamily, obviously are catalytical ly active, whereas the C-terminal halves of the bifunctional enzymes presum ably control the access to the haem pocket and facilitate stable folding. T he bifunctional nature of catalase-peroxidases can be ascribed to several u nique sequence peculiarities conserved among all N-terminal halves, which m ost likely will affect the properties of both haem ligands. (C) 2000 Elsevi er Science B.V. All rights reserved.