Physiological thiols as promoters of glutathione oxidation and modifying agents in protein S-thiolation.

Glutathione is one of the most relevant antioxidants present in cells. It exerts its scavenging action through the involvement of efficient and ubiquitous enzymes. GSH on the other hand, because of its chemical features, can scavenge reactive oxygen species without the involvement of enzymatic systems. The study deals with the mobilization of GSH pool in a nonenzymatic antioxidant system by other physiological thiols (i.e., cysteine and cysteinyl-glycine), which are far more sensitive than GSH to oxidative conditions. These thiol compounds, in the presence of iron/EDTA, can promote oxygen activation through their oxidation to disulfides. GSH, through trans-thiolation reactions, can regenerate Cys and CysGly, which can then recycle, thus inducing a massive GSH oxidation. In these conditions, making use of bovine lens aldose reductase as a protein model, evidence is given that Cys and CysGly promote specific protein S-thiolation reactions. The possibility that GSH may be recruited in controlling cellular oxygen tension is considered.     

The actin cytoskeleton response to oxidants: from small heat shock protein phosphorylation to changes in the redox state of actin itself

Actin is the major constituent of the cytoskeleton of almost all the eukaryotic cells. In vitro experiments have indicated that oxidant-stressed nonmuscle mammalian cells undergo remarkable changes in their morphology and in the structure of the actin cytoskeleton, often resulting in plasma membrane blebbing. Although the microfilament network is one of the earliest targets of oxidative stress, the mechanism by which oxidants change both the structure and the spatial organization of actin filaments is still a matter of debate and far from being fully elucidated. Starting from the 2-fold role of oxidants as injurious by-products of cellular metabolism and essential participants in cell signaling and regulation, this review attempts to gather the most relevant information related to (i) the activation of mitogen-activated protein (MAP) kinase stress-activated protein kinase-2/p38 (SAPK2/p38) which, via MAP kinase-activated protein (MAPKAP) kinase 2/3, leads to the phosphorylation of the actin polymerization (F-actin) modulator 25/27 kDa heat shock protein (HSP25/27), whose phosphorylation is causally related to the regulation of microfilament dynamics following oxidative stress; (ii) the alteration of the redox state of actin or some actin regulatory proteins. The actin cytoskeleton response to oxidants is discussed on the basis of the growing body of evidence indicating the actin system as the most sensitive constituent of the cytoskeleton to the oxidant attack.     

Stress-related RNase PR-10c is post-translationally modified by glutathione in birch

The PR‐10c (previously termed as Bet v 1‐Sc3) protein of birch belongs to the family of intracellular pathogenesis‐related proteins. The high‐performance liquid chromatography electrospray ionization ion trap mass spectrometry (HPLC‐ESI‐MS) analysis of PR‐10c‐His fusion protein, produced in Escherichia coli, revealed three major peaks and masses. Enzymatic digestions and HPLC‐ESI‐MS and matrix assisted laser desorption/ionization – time of flight mass spectrometry (MALDI‐TOF‐MS) analyses of each fraction indicated that PR‐10c‐His protein is post‐translationally modified by carbamylation and S‐glutathiolation. Carbamylation was localized into the N‐terminal end of PR‐10c‐His and does not represent a biologically significant modification. The possible nuclease activity of PR‐10c was analysed with S‐glutathiolated and reduced fractions of PR‐10c‐His fusion protein. Both forms of PR‐10c‐His as well as the dimeric form of the protein possess RNase activity which is capable of digesting different RNA substrates. None of the fractions showed activity against single‐ or double‐stranded DNA. The MALDI‐TOF‐MS analysis of PR‐10c polypeptide extracted from zinc‐exposed birch roots showed that the protein is post‐translationally modified by glutathione (γ‐Glu‐Cys‐Gly) also in vivo. The S‐glutathiolated cysteine residue of PR‐10c is not conserved among Bet v 1 homologous proteins and is also unique in the PR‐10 family. As far as we know this is the first observation of S‐glutathiolation in plants, or any post‐translational modification in the PR‐10 family of proteins.     

Redox proteomics: identification and functional role of glutathionylated proteins

Although radical oxygen and nitrogen species are harmful molecules that destroy cell functions, many operate as mediators of important cell signaling pathways when not in excess. Oxidants can modify protein function through the covalent, reversible addition of glutathione to cysteine. This review addresses different proteomic methods of identifying glutathionylation targets and emphasizes ways of defining their pattern of modification in response to oxidative stimuli in cells. Finally, the literature on nonproteomic studies that investigate the functional changes induced by glutathionylation are reviewed and future studies are commented on.