Molecular characterisation of mitochondrial and cytosolic trypanothione-dependent tryparedoxin peroxidases in Trypanosoma brucei

In trypanosomatids, removal of hydrogen peroxide and other aryl and alkyl peroxides is achieved by the NADPH-dependent trypanothione peroxidase system, whose components are trypanothione reductase (TRYR), trypanothione, tryparedoxin (TRYX) and tryparedoxin peroxidase (TRYP). Here, we report the cloning of a multi-copy tryparedoxin peroxidase gene (TRYP1) from Trypanosoma brucei brucei encoding a protein with two catalytic VCP motifs similar to the cytosolic TRYP from Crithidia fasciculata. In addition, we characterise a novel single copy gene encoding a second tryparedoxin peroxidase (TRYP2). TRYP2 shows 51% similarity to TRYP1, possesses a putative mitochondrial import sequence at its N-terminus and has a variant IPC motif replacing the second VCP motif implicated in catalysis in other 2-Cys peroxiredoxins. TRYP1 and TRYP2 were expressed in Escherichia coli, and the purified recombinant proteins shown to utilise hydrogen peroxide in the presence of NADPH, trypanothione, TRYR and TRYX from T. brucei, similar to the C. fasciculata cytoplasmic system. Western blots showed that TRYX, TRYP1 and TRYP2 are expressed in both bloodstream and procyclic forms of the life cycle. To determine the precise localisation of TRYX, TRYP1 and TRYP2 in the parasite, polyclonal antibodies to purified recombinant TRYX and TRYP1 and monoclonal antibody to TRYP2 were generated in mice. In-situ immunofluorescence and immunoelectron microscopy revealed a colocalisation of TRYX and TRYP1 in the cytosol, whereas TRYP2 was principally localised in the mitochondrion.