The pentose phosphate pathway in Trypanosoma cruzi: a potential target for the chemotherapy of Chagas disease

Abstract

Trypanosoma cruzi is highly sensitive to oxidative stress caused by reactive oxygen species. Trypanothione, the parasite's major protection against oxidative stress, is kept reduced by trypanothione reductase, using NADPH; the major source of the reduced coenzyme seems to be the pentose phosphate pathway. Its seven enzymes are present in the four major stages in the parasite's biological cycle; we have cloned and expressed them in Escherichia coli as active proteins. Glucose 6-phosphate dehydrogenase, which controls glucose flux through the pathway by its response to the NADP/NADPH ratio, is encoded by a number of genes per haploid genome, and is induced up to 46-fold by hydrogen peroxide in metacyclic trypomastigotes. The genes encoding 6-phosphogluconolactonase, 6-phosphogluconate dehydrogenase, transaldolase and transketolase are present in the CL Brener clone as a single copy per haploid genome. 6-phosphogluconate dehydrogenase is very unstable, but was stabilized introducing two salt bridges by site-directed mutagenesis. Ribose-5-phosphate isomerase belongs to Type B; genes encoding Type A enzymes, present in mammals, are absent. Ribulose-5-phosphate epimerase is encoded by two genes. The enzymes of the pathway have a major cytosolic component, although several of them have a secondary glycosomal localization, and also minor localizations in other organelles.

Physiological response of Corynebacterium glutamicum to oxidative stress induced by deletion of the transcriptional repressor McbR

“…mainly a response to the oxidative stress conditions, because NADPH provides the redox power for antioxidant systems (Nogae & Johnston, 1990;Pollak et al, 2007). An enhanced supply of NADPH is found under conditions of oxidative stress in various prokaryotic and eukaryotic cells (Boada et al, 2000;Igoillo-Esteve et al, 2007;Ralser et al, 2007;Williams & Ford, 2004). Clearly, the flux rearrangement in the central metabolism leads to greater NADPH formation, but is not sufficient for recovery from the oxidative stress conditions, as indicated by the perturbed redox state and the reduced metabolic activity.…”

A new approach for potential drug target discovery through in silico metabolic pathway analysis using Trypanosoma cruzi genome information

“…The pentose phosphate shunt -The pentose phosphate shunt is the most studied pathway in T. cruzi and the participating enzymes have been well characterised both molecularly and biochemically (Igoillo-Esteve et al 2007). The enzymes of this pathway were identified as cytoplasmic, but with secondary localisation in the glycosome.…”

“…This enzyme has several copies in the T. cruzi genome, while the 6-phosphogluconolactonase, the 6-phosphogluconate dehydrogenase (6PGD) and the ribose 5-phosphate isomerase are present as only one copy. The latter enzyme is analogous to the human enzyme, which makes it an interesting therapeutic target (Igoillo-Esteve et al 2007). Recently, Stern et al (2007), using site directed mutagenesis, revealed details on the reaction mechanism of this enzyme, which acts via the formation of the 1,2-cis-enediol.…”

“…The non-oxidative branch complements the pathway and the enzymes involved are ribulose-5-phosphate epimerase, with two gene copies in T. cruzi and the transaldolase and transketolase, each with one copy per haploid genome (Igoillo-Esteve et al 2007). One of the copies of ribulose-5-phophate isomerase presents a C-terminal (PTS1) signal for glycosome targeting but the cytosol also showed activity (Maugeri & Cazzulo 2004).…”

“…A transaldolase is responsible for the transfer of the dihydroxyacetone group from fructose-6-phosphate to erythrose-4-phosphate, leading to the synthesis of sedoheptulose-7-phosphate and glyceraldeyde-3-P. The biochemical characterisation of the recombinant enzyme was reported (Igoillo-Esteve et al 2007). The transketolase of T. cruzi contains the PTS1 signal peptide, which possibly permits its distribution both in the glycosome and in the cytoplasm.…”