Kinetics of Methionine Transport and Metabolism by Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense

Goldberg, Burt; Rattendi, Donna; Lloyd, David; Yarlett, Nigel; Bacchi, Cyrus J.

doi:10.1006/abbi.2000.1740

Cited by 17 publications

(14 citation statements)

References 32 publications

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“…Altogether, these data have extended the previous findings suggesting the presence of the transsulfuration pathway in trypanosomes (45,46). The presence of an intact transsulfuration pathway in T. cruzi is further bolstered by our finding that another important enzyme in transsulfuration pathway, cystathionine ␥-lyase, which forms cysteine, ammonia, and 2-oxobutyric acid from cystathionine, was eluted at fractions 39 -40 on DEAE anion exchange chromatography (data not shown, Fig.…”

Section: Resultssupporting

confidence: 87%

“…In contrast to the down-regulation of CBS activity in the mammalian forms of T. cruzi, CBS and other activities involved in transsulfuration pathway were detected in the mammalian forms (bloodstream trypomastigotes) of T. brucei (45,46). This indicates that substantial differences in metabolism of sulfurcontaining amino acids exist between T. cruzi and T. brucei.…”

Section: Functional Rescue Of the Yeast Cbs-deficient Mutant Strain Wmentioning

confidence: 83%

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Characterization of Transsulfuration and Cysteine Biosynthetic Pathways in the Protozoan Hemoflagellate, Trypanosoma cruzi

Nozaki

Shigeta

Saito‐Nakano

et al. 2001

Journal of Biological Chemistry

102

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Sulfur-containing amino acids play an important role in a variety of cellular functions such as protein synthesis, methylation, and polyamine and glutathione synthesis. We cloned and characterized cDNA encoding cystathionine ␤-synthase (CBS), which is a key enzyme of transsulfuration pathway, from a hemoflagellate protozoan parasite Trypanosoma cruzi. T. cruzi CBS, unlike mammalian CBS, lacks the regulatory carboxyl terminus, does not contain heme, and is not activated by S-adenosylmethionine. T. cruzi CBS mRNA is expressed as at least six independent isotypes with sequence microheterogeneity from tandemly linked multicopy genes. The enzyme forms a homotetramer and, in addition to CBS activity, the enzyme has serine sulfhydrylase and cysteine synthase (CS) activities in vitro. Expression of the T. cruzi CBS in Saccharomyces cerevisiae and Escherichia coli demonstrates that the CBS and CS activities are functional in vivo. Enzymatic studies on T. cruzi extracts indicate that there is an additional CS enzyme and stage-specific control of CBS and CS expression. We also cloned and characterized cDNA encoding serine acetyltransferase (SAT), a key enzyme in the sulfate assimilatory cysteine biosynthetic pathway. Dissimilar to bacterial and plant SAT, a recombinant T. cruzi SAT showed allosteric inhibition by L-cysteine, L-cystine, and, to a lesser extent, glutathione. Together, these studies demonstrate the T. cruzi is a unique protist in possessing both transsulfuration and sulfur assimilatory pathways.Various sulfur compounds, especially cysteine, methionine, and S-adenosylmethionine, are essential for the growth and activities of all cells (1, 2). Methionine initiates the synthesis of proteins, whereas cysteine plays a critical role in the structure, stability, and catalytic function of many proteins. S-Adenosylmethionine plays a crucial role in methyl group transfer and in polyamine biosynthesis. Cysteine is also involved in the synthesis of the major antioxidant glutathione.In the filamentous fungi, Aspergillus nidulans and Neurospora crassa, the major route for the synthesis of cysteine is the condensation of O-acetylserine (OAS) 1 with sulfide, catalyzed by cysteine synthase (CS, OAS sulfhydrase) (3, 4). This pathway has been shown to be present in prokaryotes, plants, and enteric protozoan Entamoebae, and is generally called assimilatory cysteine biosynthetic pathway since this process involves reduction and fixation of inorganic sulfate to organic amino acids. Cysteine can also be synthesized by an alternative pathway: the sulfurylation of O-acetylhomoserine to give homocysteine, which then can be converted to cysteine via cystathionine by the transsulfuration pathway. In vertebrates, cysteine is synthesized from methionine via cystathionine by the transsulfuration pathway. This pathway is believed to be the sole route for cysteine synthesis in vertebrates with cystathionine ␤-synthase (CBS) acting as the flux-controlling enzyme (1). In mammals, this pathway also functions as catabolic pathway of methionine a...

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Section: Resultssupporting

confidence: 87%

Section: Functional Rescue Of the Yeast Cbs-deficient Mutant Strain Wmentioning

confidence: 83%

Characterization of Transsulfuration and Cysteine Biosynthetic Pathways in the Protozoan Hemoflagellate, Trypanosoma cruzi

Nozaki

Shigeta

Saito‐Nakano

et al. 2001

Journal of Biological Chemistry

102

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“…Parasitic T. cruzi and Leishmania species lack the enzyme of Met synthase, which catalyses the Met production from homocysteine; however, debate remains as to whether homocysteine can be converted to Met in T. brucei [30]. Goldberg et al [31] also suggested that, even though homocysteine remethylation may exist in T. brucei , as most trans-sulfuration metabolites are secreted from trypanosomes, any homocysteine recycled to Met will not be significant. AdoHcy, which is toxic if accumulated in cells [28], was also observed to remain unchanged under perturbed conditions in T. brucei , i.e.…”

Section: Methodsmentioning

confidence: 99%

Mathematical Modelling of Polyamine Metabolism in Bloodstream-Form Trypanosoma brucei: An Application to Drug Target Identification

Reid

Higham

et al. 2013

PLoS ONE

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We present the first computational kinetic model of polyamine metabolism in bloodstream-form Trypanosoma brucei, the causative agent of human African trypanosomiasis. We systematically extracted the polyamine pathway from the complete metabolic network while still maintaining the predictive capability of the pathway. The kinetic model is constructed on the basis of information gleaned from the experimental biology literature and defined as a set of ordinary differential equations. We applied Michaelis-Menten kinetics featuring regulatory factors to describe enzymatic activities that are well defined. Uncharacterised enzyme kinetics were approximated and justified with available physiological properties of the system. Optimisation-based dynamic simulations were performed to train the model with experimental data and inconsistent predictions prompted an iterative procedure of model refinement. Good agreement between simulation results and measured data reported in various experimental conditions shows that the model has good applicability in spite of there being gaps in the required data. With this kinetic model, the relative importance of the individual pathway enzymes was assessed. We observed that, at low-to-moderate levels of inhibition, enzymes catalysing reactions of de novo AdoMet (MAT) and ornithine production (OrnPt) have more efficient inhibitory effect on total trypanothione content in comparison to other enzymes in the pathway. In our model, prozyme and TSHSyn (the production catalyst of total trypanothione) were also found to exhibit potent control on total trypanothione content but only when they were strongly inhibited. Different chemotherapeutic strategies against T. brucei were investigated using this model and interruption of polyamine synthesis via joint inhibition of MAT or OrnPt together with other polyamine enzymes was identified as an optimal therapeutic strategy.

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“…Decarboxylated AdoMet provides the aminopropyl moiety for the synthesis of spermidine from putrescine (and of spermine from spermidine in organisms containing also this polyamine). In addition to providing the aminopropyl group for the synthesis of spermidine, AdoMet in the trypanosome parasites is utilized as the methyl donor for transmethylation reactions as well as for salvage of adenine and adenosine [7,8]. The decarboxylation of AdoMet has a pivotal role in the switching between cellular methylation and polyamine biosynthesis in the parasites [9].…”

Section: Introductionmentioning

confidence: 99%

Extremely rapid turnover of S‐adenosylmethionine decarboxylase in Crithidia fasciculata

Nasizadeh

Persson

2003

FEBS Letters

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The activity of S-adenosylmethionine decarboxylase (AdoMetDC) in Crithidia fasciculata was shown to be correlated to the growth of the parasite. An increase in activity was observed during exponential growth. Inhibition of protein synthesis induced an extremely rapid decay of AdoMetDC activity. The half-life of the enzyme was estimated to be about 3 min, which is the shortest half-life ever recorded for an eukaryotic AdoMetDC. The reduction in AdoMetDC activity was correlated with a decrease in AdoMetDC protein content, demonstrating a rapid turnover of the enzyme. No polyamine-mediated feedback regulation of AdoMetDC was observed in the parasite.

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Kinetics of Methionine Transport and Metabolism by Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense

Cited by 17 publications

References 32 publications

Characterization of Transsulfuration and Cysteine Biosynthetic Pathways in the Protozoan Hemoflagellate, Trypanosoma cruzi

Characterization of Transsulfuration and Cysteine Biosynthetic Pathways in the Protozoan Hemoflagellate, Trypanosoma cruzi

Mathematical Modelling of Polyamine Metabolism in Bloodstream-Form Trypanosoma brucei: An Application to Drug Target Identification

Extremely rapid turnover of S‐adenosylmethionine decarboxylase in Crithidia fasciculata

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