The role of queuine as a nutritional regulator of the response of Entamoeba histolyticato oxidative stress

Amebiasis is an intestinal disease transmitted by the protist parasite, Entamoeba histolytica, following the ingestion of contaminated food and water. Many infected patients (90%) are asymptomatic but for unknown reasons, these trophozoites can become virulent and invasive, cause amebic dysentery, and migrate to the liver, via the portal veins, where they cause hepatocellular damage. We have recently reported that Escherichia coli can modulate E.histolytica 's virulence and resistance to oxidative stress (OS) via the production of oxaloacetate. Queuosine is a naturally occurring modified nucleoside and is found in the first position of the anticodon of the transfer RNAs for Asp, Asn, His and Tyr. Lower and higher eukaryotes are supplied with queuine (the base of queuosine) in the diet or by the intestinal flora. Here, we have tested the hypothesis that queuine being a micronutrient offers an advantage to E.histolytica during OS. Queuine which is efficiently incorporated in E.histolytica’s tRNAs leads to significant modifications of the parasite’s transcriptome, to hypermethylation of C38 in tRNAAspGTC and consequently to OS resistance. While queuine leads to the translation of proteins during OS, we found that that it inhibits protein synthesis otherwise. Localization studies with an antibody against EhTGT in queuine-treated trophozoites revealed the presence of small granular structures. We have biochemically characterized the parasite’s tRNA-guanine transglycosylase (TGT), the enzyme that catalyzes the modification of Q-tRNAs. Trophozoites silenced for TGT expression have a growth defect and they are less resistant to OS compared to control trophozoites. queuine with or without oxidative stress