Occurrence, phylogeny, structure, and function of catalases and peroxidases in cyanobacteria

Cyanobacteria have evolved similar to 3x10(9) years ago from ancient phototrophic microorganisms that already lived on our planet Earth. By opening the era of an aerobic, oxygen-containing biosphere, they are the true pacemakers of geological and biological evolution. Cyanobacteria must have been among the first organisms to elaborate mechanisms for the detoxification of partially reduced oxygen species including (hydrogen) peroxide. Since there is still an suprising lack of knowledge on the type, role, and mechanism(s) of peroxide-degrading enzymes in these bacteria, all 44 fully or partially sequenced genomes for haem and non-haem catalases and peroxidases have been critically analysed based on well known structure-function relationships of the corresponding oxidoreductases. It is demonstrated that H2O2-dismutating enzymes are mainly represented by bifunctional (haem) catalase-peroxidases and (binuclear) manganese catalases, with the latter being almost exclusively found in diazotrophic species. Several strains even lack a gene that encodes an enzyme with catalase activity. Two groups of peroxidases are found. Genes encoding putative (primordial) haem peroxidases (with homology to corresponding mammalian enzymes) and vanadium-containing iodoperoxidases are found only in a few species, whereas genes encoding peroxiredoxins (1-Cys, 2-Cys, type II, and Q-type) are ubiquitous in cyanobacteria. In addition, similar to 70% contain NADPH-dependent glutathione peroxidase-like proteins. The occurrence and phylogeny of these enzymes is discussed, as well as the present knowledge of their physiological role(s).