Journal
GENE
Volume 296, Issue 1-2, Pages 45-52Publisher
ELSEVIER
DOI: 10.1016/S0378-1119(02)00873-9
Keywords
eukaryotic evolution; hydrogenase; hydrogenosomes; Neocallimastix; anaerobic fungi
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Hydrogenases, oxygen-sensitive enzymes that can make hydrogen gas, are key to the function of hydrogen-producing organelles (hydro-genosomes), which occur in anaerobic eukaryotes scattered throughout the eukaryotic tree. All of the eukaryotic enzymes characterized so far are iron-only [Fe] hydrogenases. In contrast, it has previously been suggested that hydrogenosomes of the best-studied anaerobic fungus Neocallimastix frontalis L2 contain an unrelated iron-nickel-selenium [NiFeSe] hydrogenase. We have isolated a gene from strain L2 that encodes a putative protein containing all of the characteristic features of an iron-only [Fe] hydrogenase, including the cysteine residues required for the co-ordination of the unique 'hydrogen cluster'. As is the case for experimentally verified hydrogenosomal matrix enzymes from N. frontalis, the [Fe] hydrogenase encodes a plausible amino terminal extension that resembles mitochondrial targeting signals. Phylogenetic analyses of an expanded [Fe] hydrogenase dataset reveal a complicated picture that is difficult to interpret in the light of current ideas of species relationships. Nevertheless, our analyses cannot reject the hypothesis that the novel [Fe] hydrogenase gene of Neocallimastix is specifically related to other eukaryote [Fe] hydrogenases, and thus ultimately might be traced to the same ancestral source. (C) 2002 Elsevier Science B.V. All rights reserved.
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