An iron superoxide dismutase (FeSOD) gene of the protozoan parasite Trypanosoma brucei has been cloned and its gene product functionally characterized. The gene encodes a protein of 198 residues which shows 80% identity with FeSODs from other trypanosomatids. Inhibitor studies with purified recombinant FeSOD expressed in Escherichia coli confirmed that the enzyme is an iron-containing SOD. The FeSOD is developmentally regulated in the parasite, expression being lowest in the cell-cycle-arrested, short stumpy bloodstream forms. Differential expression of the FeSOD protein contrasts with only minor quantitative changes in the FeSOD mRNA, indicating post-transcriptional regulation of the enzyme. As the level of FeSOD increases during differentiation of cell-cycle-arrested short stumpy into dividing procyclic forms, it is suggested that the enzyme is only required in proliferating stages of the parasite for the elimination of superoxide radicals which are released during the generation of the iron-tyrosyl free-radical centre in the small subunit of ribonucleotide reductase.
- life cycle
- ribonucleotide reductase
- superoxide radical
↵1 Present address: Aventis Pharma, Mainzerlandstrasse 500, D-65795 Hattersheim, Germany.
↵2 Present address: Interdisziplinäres Forschungszentrum, Justus-Liebig-Universität, Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany.
Abbreviations used: Ni2+-NTA, Ni2+-nitrilotriacetic acid; 3′-RACE, rapid amplification of 3′ cDNA ends; SOD, superoxide dismutase; Cu,ZnSOD, copper/zinc-containing SOD; MnSOD, manganese-containing SOD; FeSOD, iron-containing SOD; DTPA, diethylenetriaminepenta-acetic acid.
- The Biochemical Society, London ©2001