Identification of a developmentally regulated iron superoxide dismutase ofTrypanosoma brucei

An iron superoxide dismutase (FeSOD) gene of the protozoan parasite Trypano soma 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 recombin ant FeSOD expressed in Escherichia coli confirmed that the enzyme is an iro n-containing SOD. The FeSOD is developmentally regulated in the parasite, e xpression being lowest in the cell-cycle-arrested, short stumpy bloodstream forms. Differential expression of the FeSOD protein contrasts with only mi nor quantitative changes in the FeSOD mRNA, indicating posttranscriptional regulation of the enzyme. As the level of FeSOD increases during differenti ation of cell-cycle-arrested short stumpy into dividing procyclic forms, it is suggested that the enzyme is only required in proliferating stages of t he parasite for the elimination of superoxide radicals which are released d uring the generation of the iron-tyrosyl free-radical centre in the small s ubunit of ribonucleotide reductase.