Abstract
Abstract The microaerophilic protozoan parasite Giardia lamblia occurs globally and causes dysentery in humans and animals. Since it is very sensitive to oxygen and reactive oxygen species, G. lamblia disposes over several enzymatic pathways to counter oxidative stress. One of the enzymes involved is thioredoxin reductase (TrxR), a central redox regulator that indirectly reduces peroxiredoxins via thioredoxin, an electron shuttle protein. Interestingly, the components of the TrxR-mediated redox system, including functional thioredoxins, have so far not been described despite their surmised importance for parasite survival. We aimed at filling this gap and attempted to identify functional thioredoxins and other interaction partners of TrxR in G. lamblia. To this end, we conducted database searches and expressed three recombinant candidate thioredoxins in Escherichia coli for ensuing enzyme assays. Further, co-immunoprecipitation experiments were conducted in order to identify further components of the thioredoxin redox network. Finally, the cellular localization of TrxR and peroxiredoxin 1 was determined by immunofluorescence microscopy. Surprisingly, our endeavours did not result in the identification of a functional thioredoxin or other credible interaction partners of TrxR. We, therefore, conclude that there is currently no evidence for a canonical thioredoxin redox network in G. lamblia.
Highlights
The protist Giardia lamblia is a worldwide occurring zoonotic parasite that causes dysentery in humans and animals
Since the measured activity was very similar to the one determined in an earlier study (Leitsch et al 2012a, b), we concluded that our assay was fully functional and, that none of the three candidate G. lamblia thioredoxins tested is a substrate for G. lamblia thioredoxin reductase (TrxR)
At present our understanding of the thioredoxin system in G. lamblia remains incomplete as there is no evidence for any protein that shuttles electrons from TrxR to peroxiredoxin or any other protein
Summary
The protist Giardia lamblia (syn. duodenalis, intestinalis) is a worldwide occurring zoonotic parasite that causes dysentery in humans and animals. Duodenalis, intestinalis) is a worldwide occurring zoonotic parasite that causes dysentery in humans and animals. It has a microaerophilic/anaerobic lifestyle which renders it vulnerable to oxygen and reactive oxygen species (Gillin and Diamond, 1981; Lloyd et al 2000; Paget et al 2004). It is well established that the thioredoxin-mediated redox system, comprising thioredoxin reductase (TrxR), the electron shuttle protein thioredoxin, and peroxiredoxins (Lu and Holmgren, 2014), plays a central role in the antioxidant defence. Peroxiredoxins reduce harmful hydrogen peroxide to water and molecular oxygen via their catalytic cysteines To this end, their catalytic cysteines need to be reduced by the catalytic cysteines of thioredoxin first. In most organisms, thioredoxin has a large number of protein substrates in addition to peroxiredoxins, including transcription factors and ribonucleotide reductase, rendering it a central redox regulator
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