Incorporation of iron into Tritrichomonas foetus cell compartments reveals ferredoxin as a major iron-binding protein in hydrogenosomes

Abstract

The intracellular transport of iron and its incorporation into organelles are poorly understood processes in eukaryotes and virtually unknown in parasitic protists. The transport of iron is of particular interest in trichomonads, which possess hydrogenosomes instead of mitochondria. The metabolic functions of hydrogenosomes, which contain a specific set of FeS proteins, entirely depend on iron acquisition. In this work the incorporation of iron into the cattle parasite Tritrichomonas foetus was monitored. Iron was efficiently taken up from 59Fe-nitrilotriacetic acid and accumulated in the cytosol (88·9 %) and hydrogenosomes (4·7 % of the total radioactivity). Using atomic absorption spectrophotometry, an unusually high steady-state iron concentration in hydrogenosomes was determined [54·4±1·1 nmol Fe (mg protein)−1]. The concentration of iron in the cytosol was 13·4±0·5 nmol Fe (mg protein)−1. Qualitative analysis of incorporated iron was performed using native gradient PAGE. The majority of the 59Fe in the cytosol appeared as the labile-iron pool, which represents weakly bound iron associated with compounds of molecular mass ranging from 5000 to 30 000 Da. Ferritin was not observed in Tt. foetus, nor in two other anaerobic protists, Entamoeba histolytica and Giardia intestinalis. Analysis of Tt. foetus hydrogenosomes showed at least nine iron-binding compounds, which were absent in metronidazole-resistant mutants. The major iron-binding compound was identified as [2Fe–2S] ferredoxin of the adrenodoxin type.

Mitochondrial-type iron–sulfur cluster biosynthesis genes (IscS and IscU) in the apicomplexan Cryptosporidium parvum

“…Recent evidence has shown, for example, that 59 Fe can be incorporated into the hydrogenosome of the cattle parasite Tritrichomonas foetus, and that this requires ferredoxin and other peptides within the [Fe-S] machinery (Suchan et al, 2003). Whether C. parvum might also incorporate iron into the relict mitochondrion is not yet known, but certainly the fact that this apicomplexan possesses IscS, IscU, ferredoxin and mtHsp70 homologues with mitochondrial targeting signals suggests that [Fe-S] biogenesis may be one of the essential biochemical pathways of the endosymbiont retained by parasitic protists after reductive evolution of the mitochondrial relict.…”

Mitochondrial-type assembly of FeS centers in the hydrogenosomes of the amitochondriate eukaryote Trichomonas vaginalis

“…Hydrogenosomes contain high amounts of Fe associated with FeS proteins and an Fe pool of unknown molecular character that may represent intrahydrogenosomal Fe storage (34). Not surprisingly, [FeS] cluster formation was observed even when no Fe was added to the reaction (Fig.…”

Transferrin Binding Proteins as a Means to Obtain Iron in Parasitic Protozoa

“…Accordingly, iron from 59 Fe-TF was efficiently accumulated into T. foetus, specifically in the labile iron pool (LIP). Interestingly, the concentration of protein-bound iron that restored 50% cell growth (5 μM for Fe-TF) was approximately 5-fold lower than that of low molecular weight iron complexes [Tachezy et al, 1996;Suchan et al, 2003], indicating that T. foetus uses TF iron more efficiently. This finding agrees with results in studies of other pathogens that require higher iron concentrations from these complexes than those from host proteins (holoLF and HG) [Wilson et al, 1994;Jarosik et al, 1998].…”