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Trypanothione biosynthesis in Leishmania major.
Sandra L Oza1, Matthew P Shaw, Susan Wyllie
1Division of Biological Chemistry and Molecular Microbiology, School of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, UK. s.l.oza@dundee.ac.uk
Molecular and Biochemical Parasitology
|December 22, 2004
Summary
Leishmania major utilizes a single enzyme, trypanothione synthetase (TryS), to produce trypanothione, essential for cellular defense. This contrasts with other organisms and suggests evolutionary adaptation in Leishmania.
Area of Science:
- Biochemistry
- Parasitology
- Molecular Biology
Background:
- Trypanothione is vital for thiol redox balance and stress defense in trypanosomatids.
- Crithidia fasciculata uses two enzymes (GspS and TryS) for trypanothione synthesis.
- Trypanosoma species employ a single broad-specificity enzyme for trypanothione production from glutathione (GSH) and spermidine.
Purpose of the Study:
- To identify and characterize genes encoding trypanothione synthesis enzymes in Leishmania major.
- To elucidate the enzymatic activity, kinetics, and localization of the identified Leishmania major trypanothione synthetase (TryS).
- To understand the evolutionary relationship of trypanothione synthesis pathways in trypanosomatids.
Main Methods:
- Gene identification and sequence analysis in Leishmania major.
- Heterologous expression and purification of the putative Leishmania major TryS enzyme.
- Enzymatic assays to determine substrate specificity, kinetics, and inhibition patterns.
- Sub-cellular localization studies using immunofluorescence and fractionation.
Main Results:
- Two genes with similarity to GspS and TryS were identified in Leishmania major; GspS is a pseudogene.
- The Leishmania major TryS enzyme catalyzes trypanothione formation from GSH and spermidine or glutathionylspermidine.
- TryS exhibits substrate inhibition by GSH and specific kinetic parameters for spermidine, glutathionylspermidine, and MgATP.
- Leishmania major TryS localizes to the cytosol.
- Phylogenetic analysis suggests TryS evolved to replace the GspS/TryS complex in trypanosomatids.
Conclusions:
- Leishmania major employs a single, broad-specificity TryS enzyme for trypanothione synthesis, indicating an evolutionary divergence from the GspS/TryS system found in C. fasciculata.
- The presence of a redundant GspS pseudogene suggests ongoing genome evolution and potential gene loss in Leishmania major.
- The characterized TryS enzyme and its cytosolic localization provide insights into the parasite's defense mechanisms against oxidative stress.