Two putative peroxidases of bacterial origin in the hydrogenosomes of the anaerobic protozoan Trichomonas vaginalis

Trichomonas vaginalis is an anaerobic protozoan parasite of the human urogenital tract. It lacks functional mitochondria but contains hydrogenosomes, anaerobic forms of mitochondria that generate ATP from the fermentative degradation of pyruvate. To determine the similarities and differences between hydrogenosomes and mitochondria, we are characterizing the proteome of purified hydrogenosomes from T. vaginalis by 2D electrophoresis and ESI‐Q‐TOF MS/MS. In the process, we have identified two proteins of bacterial origin that may function as peroxidases and this may be part of the answer to the unsolved question of how hydrogensomes in T. vaginalis are protected against the detrimental effects of oxygen: rubrerythrin is a non‐heme iron protein found predominantly in anaerobic bacteria that can reduce H 2 O 2 and was shown to complement catalase‐deficient E. coli mutants. Among eukaryotes we have found only one further rubrerythrin homologue in the anaerobic, amitochondriate amoeba Entamoeba histolytica . Peroxiredoxins are ubiquitous peroxidases using thiols to reduce alkyl hydroperoxides. T. vaginalis hydrogenosomal thiol peroxidase (Tpx) shows 65% homology to bacterial 20‐kDa Tpx. These peroxidases contain three highly conserved Cys residues, Cys 62 , Cys 82 , and Cys 95 , and belong to a peroxiredoxin subfamily that previously contained eubacterial sequences only. The finding of two putative bacterial‐type peroxidases in T. vaginalis hydrogenosomes suggests that proteins involved in peroxide detoxification in these anaerobic organelles may have been acquired laterally from eubacteria.