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 parasiteTritrichomonas foetuswas monitored. Iron was efficiently taken up from59Fe-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 the59Fe 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 inTt. foetus, nor in two other anaerobic protists,Entamoeba histolyticaandGiardia intestinalis. Analysis ofTt. foetushydrogenosomes 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.