A trans-dominant mutational strategy was used to down-regulate trypanothione reductase (TR) activity levels in Leishmania donovani, the causative agent of visceral leishmaniasis in humans. TR, regarded as an ideal drug target against trypanosomatid infections, is a homodimeric flavoprotein oxidoreductase unique to these organisms that plays a central role in the enzymatic regeneration of the thiol pool. Extrachromosomal, heterologous expression of a trans-dominant mutant version of the Trypanosoma cruzi enzyme in L. donovani resulted in the formation of inactive cross-species heterodimers and in a dramatic decrease of endogenous TR activity levels. Recombinant cells depleted of up to 85% of TR activity were significantly impaired in their ability to regenerate dihydrotrypanothione from trypanothione disulfide following oxidation with diamide. Nonetheless trans-dominant mutant recombinants were still capable of maintaining a reduced intracellular environment during cell growth in culture and were able to metabolize hydrogen peroxide at wild-type rates in vitro. Importantly, however, cells expressing the trans-dominant mutant enzyme displayed a decreased ability to survive inside activated macrophages in a murine model of Leishmania infection. The apparent inability of Leishmania to modulate the expression of active TR homodimers in response to the expression of trans-dominant mutant protein suggests that specific inhibitors of this enzyme should be useful anti-leishmanial agents
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