Protein Oxidation and Redox Regulation of Proteolysis

Reactive oxygen species (ROS), beyond the role of toxic by-products of aerobic metabolism, contribute to cell redox homeostasis and are signalling molecules in pathogen defence and abiotic stress tolerance. The putative mechanism of cell responses to ROS is thiol modifications of cysteine residues, which cause changes in protein conformation and activity. These post-translational modifications include generation of disulphide bridges and formation of sulphenic, sulphinic, and sulphonic acids, as well as S-glutathionylation and S-nitrosylation. S-nitrosylation or reversible modification may change the activity of enzymes related to the metabolism of nitric oxide, ROS, and cellular metabolism, whereas S-glutathionylation regulates the activity of proteins that contain in their structure the active cysteine residue, regulates the oxidoreductive pathway of signal transduction, and participates in the regeneration of antioxidant enzymes. Carbonylation, an irreversible, non-enzymatic modification of proteins is the most commonly occurring oxidative protein modification. The formation of carbonyl groups can be linked to abnormal translation, altered chaperone system and responses to stress factors. Carbonylated proteins are marked for proteolysis mediated by different pathways in different cell compartments to counteract the formation of high molecular weight aggregates and accumulation of inactive proteins. However, products of proteolysis of carbonylated proteins could function as secondary ROS messengers that target the cell nucleus

Differential regulation of alanine aminotransferase homologues by abiotic stresses in wheat (Triticum aestivum L.) seedlings

Wheat (Triticum aestivum L.) seedlings contain four alanine aminotransferase (AlaAT) homologues. Two of them encode AlaAT enzymes, whereas two homologues act as glumate:glyoxylate aminotransferase (GGAT). To address the function of the distinct AlaAT homologues a comparative examination of the changes in transcript level together with the enzyme activity and alanine and glutamate content in wheat seedlings subjected to low oxygen availability, nitrogen and light deficiency has been studied. Shoots of wheat seedlings were more tolerant to hypoxia than the roots as judging on the basis of enzyme activity and transcript level. Hypoxia induced AlaAT1 earlier in roots than in shoots, while AlaAT2 and GGAT were unaffected. The increase in AlaAT activity lagged behind the increase in alanine content. Nitrogen deficiency has little effect on the activity of GGAT. In contrast, lower activity of AlaAT and the level of mRNA for AlaAT1 and AlaAT2 in wheat seedlings growing on a nitrogen-free medium seems to indicate that AlaAT is regulated by the availability of nitrogen. Both AlaAT and GGAT activities were present in etiolated wheat seedlings but their activity was half of that observed in light-grown seedlings. Exposure of etiolated seedlings to light caused an increase in enzyme activities and up-regulated GGAT1. It is proposed that hypoxia-induced AlaAT1 and light-induced peroxisomal GGAT1 appears to be crucial for the regulation of energy availability in plants grown under unfavourable environmental conditions

Multifunctional role of plant cysteine proteinases

Cysteine proteinases also referred to as thiol proteases play an essential role in plant growth and development but also in senescence and programmed cell death, in accumulation of storage proteins such as in seeds, but also in storage protein mobilization. Thus, they participate in both anabolic and catabolic processes. In addition, they are involved in signalling pathways and in the response to biotic and abiotic stresses. In this review an attempt was undertaken to illustrate these multiple roles of cysteine proteinases and the mechanisms underlying their action

Non-parametric multivariate analysis of variance in the proteomic response of potato to drought stress

<div>Spot detection is a mandatory step in all available software packages dedicated to the analysis of 2D gel images. As the majority of spots do not represent individual proteins, spot detection can obscure the results of data analysis significantly. This problem can be overcome by a pixel-level analysis of 2D images. Differences between the spot and the pixel-level approaches are demonstrated by variance analysis for real data sets (part of a larger research project initiated to investigate the molecular mechanism of the response of the potato to drought stress). As the method of choice for the analysis of data variation, the non-parametric MANOVA was chosen. NP-MANOVA is recommended as a flexible and very fast tool for the evaluation of the statistical significance of the factor(s) studied.</div