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Cysteine Biosynthesis (cysteine + biosynthesis)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Sulfur assimilation and glutathione metabolism under cadmium stress in yeast, protists and plants

FEMS MICROBIOLOGY REVIEWS, Issue 4 2005
David Mendoza-Cózatl
Abstract Glutathione (,-glu-cys-gly; GSH) is usually present at high concentrations in most living cells, being the major reservoir of non-protein reduced sulfur. Because of its unique redox and nucleophilic properties, GSH serves in bio-reductive reactions as an important line of defense against reactive oxygen species, xenobiotics and heavy metals. GSH is synthesized from its constituent amino acids by two ATP-dependent reactions catalyzed by ,-glutamylcysteine synthetase and glutathione synthetase. In yeast, these enzymes are found in the cytosol, whereas in plants they are located in the cytosol and chloroplast. In protists, their location is not well established. In turn, the sulfur assimilation pathway, which leads to cysteine biosynthesis, involves high and low affinity sulfate transporters, and the enzymes ATP sulfurylase, APS kinase, PAPS reductase or APS reductase, sulfite reductase, serine acetyl transferase, O -acetylserine/O -acetylhomoserine sulfhydrylase and, in some organisms, also cystathionine ,-synthase and cystathionine ,-lyase. The biochemical and genetic regulation of these pathways is affected by oxidative stress, sulfur deficiency and heavy metal exposure. Cells cope with heavy metal stress using different mechanisms, such as complexation and compartmentation. One of these mechanisms in some yeast, plants and protists is the enhanced synthesis of the heavy metal-chelating molecules GSH and phytochelatins, which are formed from GSH by phytochelatin synthase (PCS) in a heavy metal-dependent reaction; Cd2+ is the most potent activator of PCS. In this work, we review the biochemical and genetic mechanisms involved in the regulation of sulfate assimilation-reduction and GSH metabolism when yeast, plants and protists are challenged by Cd2+. [source]

Pgt1, a glutathione transporter from the fission yeast Schizosaccharomyces pombe

FEMS YEAST RESEARCH, Issue 6 2008
Anil Thakur
Abstract The Schizosaccharomyces pombe ORF, SPAC29B12.10c, a predicted member of the oligopeptide transporter (OPT) family, was identified as a gene encoding the S. pombe glutathione transporter (Pgt1) by a genetic strategy that exploited the requirement of the cys1a, strain of S. pombe (which is defective in cysteine biosynthesis) for either cysteine or glutathione, for growth. Disruption of the ORF in the cys1a, strain led to an inability to grow on glutathione as a source of cysteine. Cloning and subsequent biochemical characterization of the ORF revealed that a high-affinity transporter for glutathione (Km=63 ,M) that was found to be localized to the plasma membrane. The transporter was specific for glutathione, as significant inhibition in glutathione uptake could be observed only by either reduced or oxidized glutathione, or glutathione conjugates, but not by dipeptides or tripeptides. Furthermore, although glu,cys,gly, an analogue of glutathione (,-glu,cys,gly), could be utilized as a sulphur source, the growth was not Pgt1 dependent. This further underlined the specificity of this transporter for glutathione. The strong repression of pgt1+ expression by cysteine suggested a role in scavenging glutathione from the extracellular environment for the maintenance of sulphur homeostasis in this yeast. [source]

Increased cysteine availability is essential for cadmium tolerance and accumulation in Arabidopsis thaliana

PLANT BIOTECHNOLOGY JOURNAL, Issue 6 2004
José R. Domínguez-Solís
Summary Employing genetic transformation using an Atcys-3A cDNA construct expressing the cytosolic O -acetylserine(thiol)lyase (OASTL), we obtained two Arabidopsis lines with different capabilities for supplying cysteine under metal stress conditions. Lines 1-2 and 10-10, grown under standard conditions, showed similar levels of cysteine and glutathione (GSH) to those of the wild-type. However, in the presence of cadmium, line 10-10 showed significantly higher levels. The increased thiol content allowed line 10-10 to survive under severe heavy metal stress conditions (up to 400 µm of cadmium in the growth medium), and resulted in an accumulation of cadmium in the leaves to a level similar to that of metal hyperaccumulator plants. Investigation of the epidermal leaf surface clearly showed that most of the cadmium had accumulated in the trichomes. Furthermore, line 10-10 was able to accumulate more cadmium in its trichomes than the wild-type, whereas line 1-2 showed a reduced capacity for cadmium accumulation. Our results suggest that an increased rate of cysteine biosynthesis is responsible for the enhanced cadmium tolerance and accumulation in trichome leaves. Thus, molecular engineering of the cysteine biosynthesis pathway, together with modification of the number of leaf trichomes, may have considerable potential in increasing heavy metal accumulation for phytoremediation purposes. [source]

Crystallization and preliminary crystallographic analysis of cysteine synthase from Entamoeba histolytica

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2007
Chinthalapudi Krishna
Entamoeba histolytica, the causative agent of human amoebiasis, is essentially anaerobic, requiring a small amount of oxygen for growth. It cannot tolerate the higher concentration of oxygen present in human tissues or blood. However, during tissue invasion it is exposed to a higher level of oxygen, leading to oxygen stress. Cysteine, which is a vital thiol in E. histolytica, plays an essential role in its oxygen-defence mechanisms. The major route of cysteine biosynthesis in this parasite is the condensation of O -acetylserine with sulfide by the de novo cysteine-biosynthetic pathway, which involves cysteine synthase (EhCS) as a key enzyme. In this study, EhCS was cloned, expressed in Escherichia coli and purified by affinity and size-exclusion chromatography. The purified protein was crystallized in space group P41 with two molecules per asymmetric unit and a complete data set was collected to a resolution of 1.86,Å. A molecular-replacement solution was obtained using the Salmonella typhimuriumO -acetylserine sulfhydrylase structure as a probe and had a correlation coefficient of 37.7% and an R factor of 48.8%. [source]