Episomal expression of human glutathione reductase (HuGR) in Leishmania sheds light on evolutionary pressure for unique redox metabolism pathway: Impaired stress tolerance ability of Leishmania donovani.

Trypanothione based redox metabolism is unique to the Trypanosomatida family. Despite extensive studies on redox metabolism of Leishmania parasites, a prominent question of why Leishmania adopt this unique redox pathway remains elusive. We have episomally expressed human glutathione reductase (HuGR) in Leishmania donovani (LdGR) and investigated its effect. LdGR strain has slower growth compared to the wild type (Ld) indicating decreased survival ability of the strain. Further, LdGR strain showed enhanced accumulation of intracellular reactive oxygen species (ROS) and more sensitivity to the anti-leishmanial drug, Miltefosine, inferring increased stress level. In contrast, the expression analyses of genes specific to redox metabolism were increased significantly in LdGR strain compared to wild type. Lower infectivity index of the LdGR strain substantiated the above findings and indicated that the expression of HuGR reduces the stress tolerance ability of the parasite. From molecular docking studies with HuGR, it was observed that oxidized trypanothione (TS2) binds much better than oxidized glutathione (GS2). These results also give us hints that the parasite is losing infectivity potential due to an overall increase in intracellular stress caused with the expression of HuGR, showcasing a possible role of evolutionary pressure on the Leishmania parasites posed by HuGR.