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

Abstract

Glutathione (gamma-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 gamma-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 beta-synthase and cystathionine gamma-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; Cd(2+) 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 Cd(2+).

Copper Uptake, Intracellular Localization, and Speciation in Marine Microalgae Measured by Synchrotron Radiation X-ray Fluorescence and Absorption Microspectroscopy

“…Glutathione (reduced and oxidised) concentration in a cell accounts for approximately 90% of non-proteinous thiols in a healthy cell. 52,53 Metal exposure alters the distribution of oxidised:reduced glutathione in microalgae, with decreases in the reduced GSH indicating high oxidative stress. 54 Previous studies have shown that dissolved Cu exposure did not significantly alter the reduced glutathione pool in P. tricornutum (58-80% of total GSH over 72 h at IC50), 11 whereas in both C. closterium and the green freshwater alga Chlamydomonas reinhardtii, dissolved Cu exposure decreased the GSH:GSSG ratio, decreasing the pool of reduced GSH within the cell (<5% total GSH over 72 h at IC50.…”

“…60,61 Once a metal ion is chelated to one or more phytochelatins, the high molecular weight complex is transported into the acidic vacuoles where it is sequestered. 52 Electron microscopy has clearly shown that Cu exposed marine microalgae (P. tricornutum, Tetraselmis sp. and Dunaliella tertiolecta) have a greater number of vacuoles per cell.…”

Carrageenan-induced NFκB activation depends on distinct pathways mediated by reactive oxygen species and Hsp27 or by Bcl10

“…Activation of glutamate cysteine ligase (glutathione synthetase), the first step in the cellular response to oxidative stress [33][34][35], and of sulfiredoxin, which functions as a high-end salvage pathway that follows periredoxin [36][37][38], suggests that the effects of CGN on oxidative stress are profound and extensive. Although oxidative stress is generally recognized in relation to exposure to oxy-and nitrosogroups, the induction of glutathione synthetase and of sulfiredoxin suggests the activation of sulfate-specific redox mechanisms following exposure to a sulfate load.…”

Differential generation of hydrogen peroxide upon exposure to zinc and cadmium in the hyperaccumulating plant specie (Sedum alfredii Hance)

“…The detoxification of heavy metals in plant cell through antioxidant system has been investigated, and GSH has been approved to play an important role in detoxifying heavy metals like nickel (Ni) and Cd (Howden et al, 1995;Mendoza-Cozatl et al, 2005). Sun et al(2005; reported that GSH concentration in shoots of S. alfredii H. increased with increasing of Zn, Pb and Cd supply levels.…”

“…It has been approved to act as a new signal molecule and played important roles in many physiological process such as cell expansion, development, stomatal closure and programmed cell death (Bienert et al, 2006;Cheng and Song, 2006;Laloi et al, 2004). GSH could eliminate toxicity of heavy metals in the cells by chelating with itself -SH in addition to clean up substance of active oxygen (Freeman et al, 2004;Jumarie et al, 2001;Mendoza-Cozatl et al, 2005). It is also the main antioxidation matter which could clean H 2 O 2 under the action of GSH peroxidase in cells (Aravind and Prasad, 2005;Elia et al, 2003).…”