Protein Glycation in Plants-An Under-Researched Field with Much Still to Discover

Preparation of Green Tea Polyphenol-Loaded Diacylglycerol Nanostructured Lipid Carrier Hydrogels and Their Activities Related to Skin Protection

Diacylglycerol (DAG) is a functional oil but is rarely used in the cosmetic industry because low solubility, susceptibility to leakage and low viscosity to skin are still the main hurdles. A novel diacylglycerol nanostructured lipid carrier hydrogel (GTP-DAG-NLC-GEL) loaded with green tea polyphenol (GTP) was designed and successfully prepared to broaden DAG's application in cosmetics, which significantly improved GTP stability and skin stickiness of DAG. The results showed that DAG-NLC-GEL had good viscosity, which was 980 Pa·s when the shear rate was 5 rpm, and its viscosity decreased quickly with the increase in shear rate, making it easily expand on skin. Meanwhile, the encapsulation rate and drug loading of GTP in GDP-DAG-NLC-GEL reached 86.7% and 2.6%, respectively, and the DPPH free radicals scavenging rate and inhibition rate of the advanced glycation end-products (AGEs) were 85.46% and 89.72%, respectively, which indicate that GTP-DAG-NLC-GEL has significant skin sunscreen, antioxidant and anti-glycation activities. The GTP-loaded nanostructured lipid carrier hydrogel can be deemed to have great prospects for skin protection in cosmetics.

Unveiling the Role of β-Glucosidase Genes in Bletilla striata's Secondary Metabolism: A Genome-Wide Analysis

β-glucosidases (BGLUs) are abundant enzymes in plants that play pivotal roles in cell wall modification, hormone signal transduction, secondary metabolism, defense against herbivores, and volatile compound release. Bletilla striata, a perennial herb revered for its therapeutic properties, lacks a comprehensive analysis of its BGLU gene family despite the critical role these genes play in plant secondary metabolism. This study aims to perform a genome-wide analysis of the BGLU gene family in B. striata (BsBGLU) to elucidate their functions and regulatory mechanisms in secondary metabolite biosynthesis. We conducted a genome-wide screening to identify BsBGLU, followed by phylogenetic analysis to classify these genes into groups. Sequence characteristics were analyzed to predict functional roles. Simple sequence repeat (SSR) markers were examined to assess conservation and polymorphism among different landraces. Expression profiles of BsBGLUs were evaluated under sodium acetate and salicylic acid elicitor treatments and across different tissues. The accumulation of phylogenetic metabolites in different treatments and tissues was also analyzed by HPLC and LCMS detection to explore the correlation between gene expression and metabolite accumulation. A total of 23 BsBGLU genes were identified and classified into eight distinct groups. Sequence analysis suggested diverse functions related to hormone responses, secondary metabolism, and stress resistance. BsBGLUs with SSR sequences were conserved yet showed polymorphism among different B. striata landraces. Under elicitor treatments, expression profiling revealed that BsBGLUs significantly modulate the synthesis of secondary metabolites such as dactylorhin A and militarine. Tissue-specific expression analysis indicated that BsBGLU15 and BsBGLU28 were highly expressed in tubers compared to other tissues, suggesting their central role and a potential negative regulatory effect in metabolite accumulation. The elicitor NaAc can regulate metabolite synthesis by modulating the expression of BsBGLUs. The BsBGLU gene family in B. striata is integral to the modulation of secondary metabolite biosynthesis and accumulation and can respond to elicitors to promote the synthesis of militarine. These findings provide a theoretical foundation for the further exploration of BsBGLU gene functions and their regulatory mechanisms, advancing the production of medicinally active compounds in B. striata.

Crosstalk of methylglyoxal and calcium signaling in maize (Zea mays L.) thermotolerance through methylglyoxal-scavenging system

Methylglyoxal (MG) and calcium ion (Ca2+) can increase multiple-stress tolerance including plant thermotolerance. However, whether crosstalk of MG and Ca2+ exists in the formation of maize thermotolerance and underlying mechanism still remain elusive. In this paper, maize seedlings were irrigated with MG and calcium chloride alone or in combination, and then exposed to heat stress (HS). The results manifested that, compared with the survival percentage (SP, 45.3%) of the control seedlings, the SP of MG and Ca2+ alone or in combination was increased to 72.4%, 74.2%, and 83.4% under HS conditions, indicating that Ca2+ and MG alone or in combination could upraise seedling thermotolerance. Also, the MG-upraised SP was separately weakened to 42.2%, 40.3%, 52.1%, and 39.4% by Ca2+ chelator (ethylene glycol tetraacetic acid, EGTA), plasma membrane Ca2+ channel blocker (lanthanum chloride, LaCl3), intracellular Ca2+ channel blocker (neomycin, NEC), and calmodulin (CaM) antagonist (trifluoperazine, TFP). However, significant effect of MG scavengers N-acetylcysteine (NAC) and aminoguanidine (AG) on Ca2+-induced thermotolerance was not observed. Similarly, an endogenous Ca2+ level in seedlings was increased by exogenous MG under non-HS and HS conditions, while exogenous Ca2+ had no significant effect on endogenous MG. These data implied that Ca2+ signaling, at least partly, mediated MG-upraised thermotolerance in maize seedlings. Moreover, the activity and gene expression of glyoxalase system (glyoxalase I, glyoxalase II, and glyoxalase III) and non-glyoxalase system (MG reductase, aldehyde reductase, aldo-keto reductase, and lactate dehydrogenase) were up-regulated to a certain extent by Ca2+ and MG alone in seedlings under non-HS and HS conditions. The up-regulated MG-scavenging system by MG was enhanced by Ca2+, while impaired by EGTA, LaCl3, NEC, or TFP. These data suggest that the crosstalk of MG and Ca2+ signaling in maize thermotolerance through MG-scavenging system. These findings provided a theoretical basis for breeding climate-resilient maize crop and developing smart agriculture.

Reactive Byproducts of Plant Redox Metabolism and Protein Functions

Living organisms exhibit an impressive ability to expand the basic information encoded in their genome, specifically regarding the structure and function of protein. Two basic strategies are employed to increase protein diversity and functionality: alternative mRNA splicing and post-translational protein modifications (PTMs). Enzymatic regulation is responsible for the majority of the chemical reactions occurring within living cells. However, plants redox metabolism perpetually generates reactive byproducts that spontaneously interact with and modify biomolecules, including proteins. Reactive carbonyls resulted from the oxidative metabolism of carbohydrates and lipids carbonylate proteins, leading to the latter inactivation and deposition in the form of glycation and lipoxidation end products. The protein nitrosylation caused by reactive nitrogen species plays a crucial role in plant morphogenesis and stress reactions. The redox state of protein thiol groups modified by reactive oxygen species is regulated through the interplay of thioredoxins and glutaredoxins, thereby influencing processes such as protein folding, enzyme activity, and calcium and hormone signaling. This review provides a summary of the PTMs caused by chemically active metabolites and explores their functional consequences in plant proteins.

Research progress on plant-based protein Pickering particles: Stabilization mechanisms, preparation methods, and application prospects in the food industry

At present, there have been many research articles reporting that plant-based protein Pickering particles from different sources are used to stabilize Pickering emulsions, but the reports of corresponding review articles are still far from sufficient. This study focuses on the research hotspots and related progress on plant-based protein Pickering particles in the past five years. First, the article describes the mechanism by which Pickering emulsions are stabilized by different types of plant-based protein Pickering particles. Then, the extraction, preparation, and modification methods of various plant-based protein Pickering particles are highlighted to provide a reference for the development of greener and more efficient plant-based protein Pickering particles. The article also introduces some of the most promising applications of Pickering emulsions stabilized by plant-based protein Pickering particles in the food field. Finally, the paper also discusses the potential applications and challenges of plant-based protein Pickering particles in the food industry.

Role of methylglyoxal and glyoxalase in the regulation of plant response to heavy metal stress

KEY MESSAGE

Methylglyoxal and glyoxalase function a significant role in plant response to heavy metal stress. We update and discuss the most recent developments of methylglyoxal and glyoxalase in regulating plant response to heavy metal stress. Methylglyoxal (MG), a by-product of several metabolic processes, is created by both enzymatic and non-enzymatic mechanisms. It plays an important role in plant growth and development, signal transduction, and response to heavy metal stress (HMS). Changes in MG content and glyoxalase (GLY) activity under HMS imply that they may be potential biomarkers of plant stress resistance. In this review, we summarize recent advances in research on the mechanisms of MG and GLY in the regulation of plant responses to HMS. It has been discovered that appropriate concentrations of MG assist plants in maintaining a balance between growth and development and survival defense, therefore shielding them from heavy metal harm. MG and GLY regulate plant physiological processes by remodeling cellular redox homeostasis, regulating stomatal movement, and crosstalking with other signaling molecules (including abscisic acid, gibberellic acid, jasmonic acid, cytokinin, salicylic acid, melatonin, ethylene, hydrogen sulfide, and nitric oxide). We also discuss the involvement of MG and GLY in the regulation of plant responses to HMS at the transcriptional, translational, and metabolic levels. Lastly, considering the current state of research, we present a perspective on the future direction of MG research to elucidate the MG anti-stress mechanism and offer a theoretical foundation and useful advice for the remediation of heavy metal-contaminated environments in the future.

Contents of ɑ-dicarbonyl compounds in commercial black tea and affected by the processing

The species and contents of ɑ-dicarbonyls in commercial black tea were examined, along with the effects of the manufacturing process and drying temperature on the formation of ɑ-dicarbonyls. Ten ɑ-dicarbonyls were quantified in commercial and in-process black tea samples by using UPLC-MS/MS and their derived quinoxalines. The ɑ-dicarbonyls content in commercial black tea decreased significantly (p < 0.05) in the following order: 3-deoxyglucosone > glucosone > 3-deoxypentosone = threosone > galactosone ≥ methylglyoxal = glyoxal ≥ 3-deoxygalactosone = 3-deoxythreosone = diacetyl. Except for 3-deoxyglucosone and 3-deoxygalactosone, a further eight ɑ-dicarbonyls were identified in all manufacturing steps of black tea. Except for the drying step, the rolling and fermenting played important roles in the formation of ɑ-dicarbonyls. The total contents of ɑ-dicarbonyls in black tea infusion ranged from 16.48 to 75.32 μg/g based on our detected ten ɑ-dicarbonyls.

The Glutathione System: A Journey from Cyanobacteria to Higher Eukaryotes

From bacteria to plants and humans, the glutathione system plays a pleiotropic role in cell defense against metabolic, oxidative and metal stresses. Glutathione (GSH), the γ-L-glutamyl-L-cysteinyl-glycine nucleophile tri-peptide, is the central player of this system that acts in redox homeostasis, detoxification and iron metabolism in most living organisms. GSH directly scavenges diverse reactive oxygen species (ROS), such as singlet oxygen, superoxide anion, hydrogen peroxide, hydroxyl radical, nitric oxide and carbon radicals. It also serves as a cofactor for various enzymes, such as glutaredoxins (Grxs), glutathione peroxidases (Gpxs), glutathione reductase (GR) and glutathione-S-transferases (GSTs), which play crucial roles in cell detoxication. This review summarizes what is known concerning the GSH-system (GSH, GSH-derived metabolites and GSH-dependent enzymes) in selected model organisms (Escherichia coli, Saccharomyces cerevisiae, Arabidopsis thaliana and human), emphasizing cyanobacteria for the following reasons. Cyanobacteria are environmentally crucial and biotechnologically important organisms that are regarded as having evolved photosynthesis and the GSH system to protect themselves against the ROS produced by their active photoautotrophic metabolism. Furthermore, cyanobacteria synthesize the GSH-derived metabolites, ergothioneine and phytochelatin, that play crucial roles in cell detoxication in humans and plants, respectively. Cyanobacteria also synthesize the thiol-less GSH homologs ophthalmate and norophthalmate that serve as biomarkers of various diseases in humans. Hence, cyanobacteria are well-suited to thoroughly analyze the role/specificity/redundancy of the players of the GSH-system using a genetic approach (deletion/overproduction) that is hardly feasible with other model organisms (E. coli and S. cerevisiae do not synthesize ergothioneine, while plants and humans acquire it from their soil and their diet, respectively).

Comparative metabolomics of root-tips reveals distinct metabolic pathways conferring drought tolerance in contrasting genotypes of rice

Background

The mechanisms underlying rice root responses to drought during the early developmental stages are yet unknown.

Results

This study aimed to determine metabolic differences in IR64, a shallow-rooting, drought-susceptible genotype, and Azucena, a drought-tolerant and deep-rooting genotype under drought stress. The morphological evaluation revealed that Azucena might evade water stress by increasing the lateral root system growth, the root surface area, and length to access water. At the same time, IR64 may rely mainly on cell wall thickening to tolerate stress. Furthermore, significant differences were observed in 49 metabolites in IR64 and 80 metabolites in Azucena, for which most metabolites were implicated in secondary metabolism, amino acid metabolism, nucleotide acid metabolism and sugar and sugar alcohol metabolism. Among these metabolites, a significant positive correlation was found between allantoin, galactaric acid, gluconic acid, glucose, and drought tolerance. These metabolites may serve as markers of drought tolerance in genotype screening programs. Based on corresponding biological pathways analysis of the differentially abundant metabolites (DAMs), biosynthesis of alkaloid-derivatives of the shikimate pathway, fatty acid biosynthesis, purine metabolism, TCA cycle and amino acid biosynthesis were the most statistically enriched biological pathway in Azucena in drought response. However, in IR64, the differentially abundant metabolites of starch and sucrose metabolism were the most statistically enriched biological pathways.

Conclusion

Metabolic marker candidates for drought tolerance were identified in both genotypes. Thus, these markers that were experimentally determined in distinct metabolic pathways can be used for the development or selection of drought-tolerant rice genotypes.

More Than a Diamine Oxidase Inhibitor: L-Aminoguanidine Modulates Polyamine-Related Abiotic Stress Responses of Plants

L-aminoguanidine (AG) is an inhibitor frequently used for investigating plant abiotic stress responses; however, its exact mode of action is not well understood. Many studies used this compound as a specific diamine oxidase inhibitor, whereas other studies used it for reducing nitric oxide (NO) production. Recent studies suggest its antiglycation effect; however, this remains elusive in plants. This review summarises our current knowledge about different targets of AG in plants. Our recommendation is to use AG as a modulator of polyamine-related mechanisms rather than a specific inhibitor. In the future overall investigation is needed to decipher the exact mechanisms of AG. More careful application of AG could give more insight into plant abiotic stress responses.

Role of Nitric Oxide-Derived Metabolites in Reactions of Methylglyoxal with Lysine and Lysine-Rich Protein Leghemoglobin

Carbonyl stress occurs when reactive carbonyl compounds (RCC), such as reducing sugars, dicarbonyls etc., accumulate in the organism. The interaction of RCC carbonyl groups with amino groups of molecules is called the Maillard reaction. One of the most active RCCs is α-dicarbonyl methylglyoxal (MG) that modifies biomolecules forming non-enzymatic glycation products. Organic free radicals are formed in the reaction between MG and lysine or Nα-acetyllysine. S-nitrosothiols and nitric oxide (^•NO) donor PAPA NONOate increased the yield of organic free radical intermediates, while other ^•NO-derived metabolites, namely, nitroxyl anion and dinitrosyl iron complexes (DNICs) decreased it. At the late stages of the Maillard reaction, S-nitrosoglutathione (GSNO) also inhibited the formation of glycation end products (AGEs). The formation of a new type of DNICs, bound with Maillard reaction products, was found. The results obtained were used to explain the glycation features of legume hemoglobin-leghemoglobin (Lb), which is a lysine-rich protein. In Lb, lysine residues can form fluorescent cross-linked AGEs, and ^•NO-derived metabolites slow down their formation. The knowledge of these processes can be used to increase the stability of Lb. It can help in better understanding the impact of stress factors on legume plants and contribute to the production of recombinant Lb for biotechnology.

Glyoxalase I activity affects Arabidopsis sensitivity to ammonium nutrition

Elevated methylglyoxal levels contribute to ammonium-induced growth disorders in Arabidopsis thaliana. Methylglyoxal detoxification pathway limitation, mainly the glyoxalase I activity, leads to enhanced sensitivity of plants to ammonium nutrition. Ammonium applied to plants as the exclusive source of nitrogen often triggers multiple phenotypic effects, with severe growth inhibition being the most prominent symptom. Glycolytic flux increase, leading to overproduction of its toxic by-product methylglyoxal (MG), is one of the major metabolic consequences of long-term ammonium nutrition. This study aimed to evaluate the influence of MG metabolism on ammonium-dependent growth restriction in Arabidopsis thaliana plants. As the level of MG in plant cells is maintained by the glyoxalase (GLX) system, we analyzed MG-related metabolism in plants with a dysfunctional glyoxalase pathway. We report that MG detoxification, based on glutathione-dependent glyoxalases, is crucial for plants exposed to ammonium nutrition, and its essential role in ammonium sensitivity relays on glyoxalase I (GLXI) activity. Our results indicated that the accumulation of MG-derived advanced glycation end products significantly contributes to the incidence of ammonium toxicity symptoms. Using A. thaliana frostbite1 as a model plant that overcomes growth repression on ammonium, we have shown that its resistance to enhanced MG levels is based on increased GLXI activity and tolerance to elevated MG-derived advanced glycation end-product (MAGE) levels. Furthermore, our results show that glyoxalase pathway activity strongly affects cellular antioxidative systems. Under stress conditions, the disruption of the MG detoxification pathway limits the functioning of antioxidant defense. However, under optimal growth conditions, a defect in the MG detoxification route results in the activation of antioxidative systems.

An Introduction to the Special Issue "Protein Glycation in Food, Nutrition, Health and Disease"

On 20-24 September 2021, leading researchers in the field of glycation met online at the 14th International Symposium on the Maillard Reaction (IMARS-14), hosted by the authors of this introductory editorial, who are from Doha, Qatar [...].

Crop Proteomics under Abiotic Stress: From Data to Insights

Food security is a major challenge in the present world due to erratic weather and climatic changes. Environmental stress negatively affects plant growth and development which leads to reduced crop yields. Technological advancements have caused remarkable improvements in crop-breeding programs. Proteins have an indispensable role in developing stress resilience and tolerance in crops. Genomic and biotechnological advancements have made the process of crop improvement more accurate and targeted. Proteomic studies provide the information required for such targeted approaches. The crosstalk among cellular components is being analyzed by subcellular proteomics. Additionally, the functional diversity of proteins is being unraveled by post-translational modifications during abiotic stress. The exploration of precise cellular responses and the networking among different cellular organelles help in the prediction of signaling pathways and protein-protein interactions. High-throughput mass-spectrometry-based protein studies are now possible due to incremental advancements in mass-spectrometry techniques, sample protocols, and bioinformatic tools as well as the increasing availability of plant genome sequence information for multiple species. In this review, the key role of proteomic analysis in identifying the abiotic-stress-responsive mechanisms in various crops was summarized. The development and availability of advanced computational tools were discussed in detail. The highly variable protein responses among different crops have provided a wide avenue for molecular-marker-assisted genetic buildup studies to develop smart, high-yielding, and stress-tolerant varieties to cope with food-security challenges.

Redox post-translational modifications and their interplay in plant abiotic stress tolerance

The impact of climate change entails a progressive and inexorable modification of the Earth's climate and events such as salinity, drought, extreme temperatures, high luminous intensity and ultraviolet radiation tend to be more numerous and prolonged in time. Plants face their exposure to these abiotic stresses or their combination through multiple physiological, metabolic and molecular mechanisms, to achieve the long-awaited acclimatization to these extreme conditions, and to thereby increase their survival rate. In recent decades, the increase in the intensity and duration of these climatological events have intensified research into the mechanisms behind plant tolerance to them, with great advances in this field. Among these mechanisms, the overproduction of molecular reactive species stands out, mainly reactive oxygen, nitrogen and sulfur species. These molecules have a dual activity, as they participate in signaling processes under physiological conditions, but, under stress conditions, their production increases, interacting with each other and modifying and-or damaging the main cellular components: lipids, carbohydrates, nucleic acids and proteins. The latter have amino acids in their sequence that are susceptible to post-translational modifications, both reversible and irreversible, through the different reactive species generated by abiotic stresses (redox-based PTMs). Some research suggests that this process does not occur randomly, but that the modification of critical residues in enzymes modulates their biological activity, being able to enhance or inhibit complete metabolic pathways in the process of acclimatization and tolerance to the exposure to the different abiotic stresses. Given the importance of these PTMs-based regulation mechanisms in the acclimatization processes of plants, the present review gathers the knowledge generated in recent years on this subject, delving into the PTMs of the redox-regulated enzymes of plant metabolism, and those that participate in the main stress-related pathways, such as oxidative metabolism, primary metabolism, cell signaling events, and photosynthetic metabolism. The aim is to unify the existing information thus far obtained to shed light on possible fields of future research in the search for the resilience of plants to climate change.

Dynamics of Reactive Carbonyl Species in Pea Root Nodules in Response to Polyethylene Glycol (PEG)-Induced Osmotic Stress

Drought dramatically affects crop productivity worldwide. For legumes this effect is especially pronounced, as their symbiotic association with rhizobia is highly-sensitive to dehydration. This might be attributed to the oxidative stress, which ultimately accompanies plants' response to water deficit. Indeed, enhanced formation of reactive oxygen species in root nodules might result in up-regulation of lipid peroxidation and overproduction of reactive carbonyl compounds (RCCs), which readily modify biomolecules and disrupt cell functions. Thus, the knowledge of the nodule carbonyl metabolome dynamics is critically important for understanding the drought-related losses of nitrogen fixation efficiency and plant productivity. Therefore, here we provide, to the best of our knowledge, for the first time a comprehensive overview of the pea root nodule carbonyl metabolome and address its alterations in response to polyethylene glycol-induced osmotic stress as the first step to examine the changes of RCC patterns in drought treated plants. RCCs were extracted from the nodules and derivatized with 7-(diethylamino)coumarin-3-carbohydrazide (CHH). The relative quantification of CHH-derivatives by liquid chromatography-high resolution mass spectrometry with a post-run correction for derivative stability revealed in total 194 features with intensities above 1 × 105 counts, 19 of which were down- and three were upregulated. The upregulation of glyceraldehyde could accompany non-enzymatic conversion of glyceraldehyde-3-phosphate to methylglyoxal. The accumulation of 4,5-dioxovaleric acid could be the reason for down-regulation of porphyrin metabolism, suppression of leghemoglobin synthesis, inhibition of nitrogenase and degradation of legume-rhizobial symbiosis in response to polyethylene glycol (PEG)-induced osmotic stress effect. This effect needs to be confirmed with soil-based drought models.

BERT-Kgly: A Bidirectional Encoder Representations From Transformers (BERT)-Based Model for Predicting Lysine Glycation Site for Homo sapiens

As one of the most important posttranslational modifications (PTMs), protein lysine glycation changes the characteristics of the proteins and leads to the dysfunction of the proteins, which may cause diseases. Accurately detecting the glycation sites is of great benefit for understanding the biological function and potential mechanism of glycation in the treatment of diseases. However, experimental methods are expensive and time-consuming for lysine glycation site identification. Instead, computational methods, with their higher efficiency and lower cost, could be an important supplement to the experimental methods. In this study, we proposed a novel predictor, BERT-Kgly, for protein lysine glycation site prediction, which was developed by extracting embedding features of protein segments from pretrained Bidirectional Encoder Representations from Transformers (BERT) models. Three pretrained BERT models were explored to get the embeddings with optimal representability, and three downstream deep networks were employed to build our models. Our results showed that the model based on embeddings extracted from the BERT model pretrained on 556,603 protein sequences of UniProt outperforms other models. In addition, an independent test set was used to evaluate and compare our model with other existing methods, which indicated that our model was superior to other existing models.

Effect of transferrin glycation induced by high glucose on HK-2 cells in vitro

BACKGROUND AND OBJECTIVE

Glycation is a common post-transcriptional modification of proteins. Previous studies have shown that advanced glycation end modified transferrin (AGE-Tf) levels in diabetic rat kidney tissues were increased; however, its role in diabetic nephropathy remains unclear. In this study, differences in glycation degree and Tf sites induced by differing high glucose concentrations in vitro and the effect on total iron binding capacity (TIBC) were observed. Moreover, the effect of AGE-Tf on human renal tubular epithelial cells (HK-2) was investigated.

METHODS

In vitro Tf was incubated with increasing glucose concentrations (0 mM, 5.6 mM, 11.1 mM, 33.3 mM, 100 mM, 500 mM, and 1,000 mM) for AGE-Tf. Differences in AGE-Tf glycation degree and TIBC level were analyzed via colorimetric method. The AGE-Tf glycation sites were identified with LC-MS/MS. HK-2 cells were treated with AGE-Tf prepared with different glucose concentrations (33.3 mM and 500 mM) in vitro. The effects of AGE-Tf on HK-2 cell viability, proliferation, oxidative stress index, and Tf receptor expression levels were then observed.

RESULTS

With increasing glucose concentrations (100 mM, 500 mM, and 1,000 mM) in vitro, Tf glycation degree was significantly increased. The TIBC levels of AGE-Tf were decreased significantly with increasing glucose concentrations (33.3 mM, 100 mM, 500 mM, and 1,000 mM). Four glycated modification sites in Tf and 17 glycated modification sites were detected in AGE-Tf (500 mM) by LC-MS/MS. The structural types of AGEs were CML, G-H1, FL-1H2O, FL, and MG-H1. No significant differences were found in the survival rate of HK-2 cells among the AGE-Tf (500 mM), AGE-Tf (33.3 mM), and Tf groups (all p > 0.05). The apoptosis rate of HK-2 cells in the AGE-Tf (500 mM) group was significantly higher than that in the AGE-Tf (33.3 mM) group. Additionally, both of them were significantly higher than that in the Tf group (both p < 0.05). The MDA levels of HK-2 cells in the AGE-Tf (500 mM) and AGE-Tf (33.3 mM) groups were higher than that in the Tf group, but not significantly (both p > 0.05). The T-AOC level of HK-2 in the AGE-Tf (500 mM) group was significantly lower than that in the AGE-Tf (33.3 mM) and Tf groups (both p < 0.001). The GSH level of HK-2 cells in the AGE-Tf (500 mM) group was significantly lower than that in the Tf group (p < 0.05). The expression level of TfR in the AGE-Tf (500 mM) group was also significantly lower than that in the Tf group (p < 0.05).

CONCLUSION

The degree and sites of Tf glycation were increased in vitro secondary to high-glucose exposure; however, the binding ability of Tf to iron decreased gradually. After HK-2 was stimulated by AGE-Tf in vitro, the apoptosis of cells was increased, antioxidant capacity was decreased, and TfR expression levels were downregulated.

Plant Proteoforms Under Environmental Stress: Functional Proteins Arising From a Single Gene

Proteins are directly involved in plant phenotypic response to ever changing environmental conditions. The ability to produce multiple mature functional proteins, i.e., proteoforms, from a single gene sequence represents an efficient tool ensuring the diversification of protein biological functions underlying the diversity of plant phenotypic responses to environmental stresses. Basically, two major kinds of proteoforms can be distinguished: protein isoforms, i.e., alterations at protein sequence level arising from posttranscriptional modifications of a single pre-mRNA by alternative splicing or editing, and protein posttranslational modifications (PTMs), i.e., enzymatically catalyzed or spontaneous modifications of certain amino acid residues resulting in altered biological functions (or loss of biological functions, such as in non-functional proteins that raised as a product of spontaneous protein modification by reactive molecular species, RMS). Modulation of protein final sequences resulting in different protein isoforms as well as modulation of chemical properties of key amino acid residues by different PTMs (such as phosphorylation, N- and O-glycosylation, methylation, acylation, S-glutathionylation, ubiquitinylation, sumoylation, and modifications by RMS), thus, represents an efficient means to ensure the flexible modulation of protein biological functions in response to ever changing environmental conditions. The aim of this review is to provide a basic overview of the structural and functional diversity of proteoforms derived from a single gene in the context of plant evolutional adaptations underlying plant responses to the variability of environmental stresses, i.e., adverse cues mobilizing plant adaptive mechanisms to diminish their harmful effects.

Glutathione Metabolism in Plants under Stress: Beyond Reactive Oxygen Species Detoxification

Glutathione is an essential metabolite for plant life best known for its role in the control of reactive oxygen species (ROS). Glutathione is also involved in the detoxification of methylglyoxal (MG) which, much like ROS, is produced at low levels by aerobic metabolism under normal conditions. While several physiological processes depend on ROS and MG, a variety of stresses can dramatically increase their concentration leading to potentially deleterious effects. In this review, we examine the structure and the stress regulation of the pathways involved in glutathione synthesis and degradation. We provide a synthesis of the current knowledge on the glutathione-dependent glyoxalase pathway responsible for MG detoxification. We present recent developments on the organization of the glyoxalase pathway in which alternative splicing generate a number of isoforms targeted to various subcellular compartments. Stress regulation of enzymes involved in MG detoxification occurs at multiple levels. A growing number of studies show that oxidative stress promotes the covalent modification of proteins by glutathione. This post-translational modification is called S-glutathionylation. It affects the function of several target proteins and is relevant to stress adaptation. We address this regulatory function in an analysis of the enzymes and pathways targeted by S-glutathionylation.

Functional characterization and expression profiling of glyoxalase III genes in date palm grown under abiotic stresses

Methylglyoxal (MG), a by-product of various metabolic processes, including glycolysis, is a highly reactive cytotoxic metabolite. The level of MG in the cell is maintained at a non-toxic level via MG detoxification pathways such as the universal glyoxalase system, including glyoxalase I/II/III enzymes. Glyoxalase III (DJ-1) can breakdown MG to d-lactate in a single step without reducing glutathione (GSH). Elucidating the function of the DJ-1 gene family may provide further knowledge about its role in plants under abiotic stresses. Here, we characterize four glyoxalase III genes (PdDJ-1B1, PdDJ-1B2, PdDJ-1C, and PdDJ-1D) encoding the conserved DJ-1 domain in the genome of the date palm, a crop with high drought and salinity tolerance. The expression level of the PdDJ-1 genes increased in date palm leaves upon salinity treatment. In addition, overexpression of PdDJ-1 genes in Escherichia coli and the complementation in yeast hsp31Δ knockout mutant cells enhanced their growth rate and reduced the accumulation of reactive oxygen species (ROS) under MG and oxidative stress conditions as shown by the flow cytometry assay. Subcellular localization using confocal microscopy revealed the accumulation of PdDJ-1B1, PdDJ-1C, and PdDJ-1D in the chloroplast, whereas PdDJ-1B2 was localized to the cytosol. Remarkably, constitutive expression of the PdDJ-1C gene in Arabidopsis thaliana Columbia (Col-0) resulted in the generation of non-viable albino plants implying that PdDJ-1C plays a critical function in chloroplast development. These findings suggest that PdDJ-1 protein has an important function in MG-detoxification and maintaining the redox balance in date palm plants under abiotic stress conditions.

Dihydromyricetin attenuates D-galactose-induced brain aging of mice via inhibiting oxidative stress and neuroinflammation

Aging-related especially brain aging-related diseases are heavy health care burdens worldwide. Natural products with antioxidant and anti-inflammatory properties have been studied to prevent brain aging pathogenesis. In the present study we investigated the potential mechanism of dihydromyricetin (DMY), isolated from Ampelopsis grossedentata, against D-galactose (D-Gal)-triggered brain aging of mice. Mice were randomly assigned into five groups (n = 20): control group, D-gal (150 mg/kg) group, D-gal (150 mg/kg) + Puerarin group, D-gal (150 mg/kg) + DMY (168 mg/kg) and D-gal (150 mg/kg) + DMY (42 mg/kg). Morris water maze (MWM) was used to assess spatial cognition and oxidative stress and inflammation index such as advanced glycation end products (AGEs), malondialdehyde (MDA), IL-2 and IL-6 were detected by ELISA. Cellular senescence marker was detected by Western blotting analysis. We found that DMY (42 mg/kg) showed strong neuroprotective effects, evidenced by improved spatial cognition and might be attributed to the alleviated damage of hippocampal neurons. In addition, DMY also suppressed the D-Gal-induced senescence of hippocampal neurons by inhibiting the expressions of p53, p21, and p16. Furthermore, DMY restored the activity of catalase and exhibited a potent inhibitory effect on lipid peroxidation, AGEs and MDA of D-Gal-exposed mice. Moreover, DMY decreased the abundance of IL-6 but increased the abundance of IL-2 of D-Gal-exposed mice. These findings indicated that DMY might protect against brain aging caused by chronic D-Gal exposure by modulating oxidative stress and inflammation-related senescence of hippocampal neurons.

Glycation of Plant Proteins Via Maillard Reaction: Reaction Chemistry, Technofunctional Properties, and Potential Food Application

Plant proteins are being considered to become the most important protein source of the future, and to do so, they must be able to replace the animal-derived proteins currently in use as techno-functional food ingredients. This poses challenges because plant proteins are oftentimes storage proteins with a high molecular weight and low water solubility. One promising approach to overcome these limitations is the glycation of plant proteins. The covalent bonding between the proteins and different carbohydrates created via the initial stage of the Maillard reaction can improve the techno-functional characteristics of these proteins without the involvement of potentially toxic chemicals. However, compared to studies with animal-derived proteins, glycation studies on plant proteins are currently still underrepresented in literature. This review provides an overview of the existing studies on the glycation of the major groups of plant proteins with different carbohydrates using different preparation methods. Emphasis is put on the reaction conditions used for glycation as well as the modifications to physicochemical properties and techno-functionality. Different applications of these glycated plant proteins in emulsions, foams, films, and encapsulation systems are introduced. Another focus lies on the reaction chemistry of the Maillard reaction and ways to harness it for controlled glycation and to limit the formation of undesired advanced glycation products. Finally, challenges related to the controlled glycation of plant proteins to improve their properties are discussed.

Bringing New Methods to the Seed Proteomics Platform: Challenges and Perspectives

For centuries, crop plants have represented the basis of the daily human diet. Among them, cereals and legumes, accumulating oils, proteins, and carbohydrates in their seeds, distinctly dominate modern agriculture, thus play an essential role in food industry and fuel production. Therefore, seeds of crop plants are intensively studied by food chemists, biologists, biochemists, and nutritional physiologists. Accordingly, seed development and germination as well as age- and stress-related alterations in seed vigor, longevity, nutritional value, and safety can be addressed by a broad panel of analytical, biochemical, and physiological methods. Currently, functional genomics is one of the most powerful tools, giving direct access to characteristic metabolic changes accompanying plant development, senescence, and response to biotic or abiotic stress. Among individual post-genomic methodological platforms, proteomics represents one of the most effective ones, giving access to cellular metabolism at the level of proteins. During the recent decades, multiple methodological advances were introduced in different branches of life science, although only some of them were established in seed proteomics so far. Therefore, here we discuss main methodological approaches already employed in seed proteomics, as well as those still waiting for implementation in this field of plant research, with a special emphasis on sample preparation, data acquisition, processing, and post-processing. Thereby, the overall goal of this review is to bring new methodologies emerging in different areas of proteomics research (clinical, food, ecological, microbial, and plant proteomics) to the broad society of seed biologists.