Abstract
Rieske non-heme iron oxygenases, which have a Rieske-type [2Fe–2S] cluster and a non-heme catalytic iron center, are an important family of oxidoreductases involved mainly in regio- and stereoselective transformation of a wide array of aromatic hydrocarbons. Though present in all domains of life, the most widely studied Rieske non-heme iron oxygenases are found in mesophilic bacteria. The present study explores the potential for isolating novel Rieske non-heme iron oxygenases from thermophilic sources. Browsing the entire bacterial genome database led to the identification of 45 homologs from thermophilic bacteria distributed mainly among Chloroflexi, Deinococcus–Thermus and Firmicutes. Thermostability, measured according to the aliphatic index, showed higher values for certain homologs compared with their mesophilic relatives. Prediction of substrate preferences indicated that a wide array of aromatic hydrocarbons could be transformed by most of the identified oxygenase homologs. Further identification of putative genes encoding components of a functional oxygenase system opens up the possibility of reconstituting functional thermophilic Rieske non-heme iron oxygenase systems with novel properties.
Highlights
Rieske non-heme iron oxygenases (ROs) constitute a large family of oxidoreductase enzymes involved primarily in the oxygenation of various aromatic compounds
Blast searches against all thermophile genomes initially led to the identification of 95 putative large subunit of RO terminal oxygenase (ROox) α-subunit homologs distributed among 20 different genera
Though the thermophilic RO homologs identified in this study were present among taxonomically close organisms, their distributions were very specific for certain phyla, often with very low abundance (Fig. 1)
Summary
Rieske non-heme iron oxygenases (ROs) constitute a large family of oxidoreductase enzymes involved primarily in the oxygenation of various aromatic compounds. Regio- and stereoselective cis-dihydroxylation of aromatic compounds, catalyzed by ROs, generate impressive chiral intermediates in the synthesis. Members of the RO family are usually either two- or three-component systems in which one or two soluble electron transport (ET) proteins (such as ferredoxin and reductase) transfer electrons from reduced nucleotides, such as NAD(P)H, to the terminal oxygenase component (a large α-subunit, often accompanied by a small β-subunit),which in turn catalyzes the di- or mono-oxygenation of the aromatic nucleus of the substrate (Mason and Cammack 1992; Ferraro et al 2005). Found in all three domains of life, studies have shown that ROs occur more commonly in bacteria compared with archaea and eukaryotes
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