Glyceraldehyde-3-phosphate dehydrogenase: Aggregation mechanisms and impact on amyloid neurodegenerative diseases

Glyceraldehyde-3-phosphate dehydrogenase is involved in the pathogenesis of Alzheimer's disease

One of important characteristics of Alzheimer's disease is a persistent oxidative/nitrosative stress caused by pro-oxidant properties of amyloid-beta peptide (Aβ) and chronic inflammation in the brain. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is easily oxidized under oxidative stress. Numerous data indicate that oxidative modifications of GAPDH in vitro and in cell cultures stimulate GAPDH denaturation and aggregation, and the catalytic cysteine residue Cys152 is important for these processes. Both intracellular and extracellular GAPDH aggregates are toxic for the cells. Interaction of denatured GAPDH with soluble Aβ results in mixed insoluble aggregates with increased toxicity. The above-described properties of GAPDH (sensitivity to oxidation and propensity to form aggregates, including mixed aggregates with Aβ) determine its role in the pathogenesis of Alzheimer's disease.

The Relationship Between GAPDH Gene Polymorphism and Risk of Acute Coronary Syndrome in South Indians with Type 2 Diabetes Mellitus

As glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is one of the regulators of carbonyl stress, a pathogenic mechanism for diabetic complications like acute coronary syndrome (ACS), the study aimed to investigate the relationship between GAPDH gene polymorphism, GAPDH activity in red blood cell (RBC), methylglyoxal (MG) levels in plasma and ACS risk in South Indians with type 2 diabetes mellitus (T2DM). This study comprised 150 T2DM with ACS as cases and 150 T2DM without ACS as controls. The GAPDH rs1136666, rs1060620 and rs1060619 gene polymorphisms were identified by TaqMan probe assays. The RBC GAPDH activity and plasma MG levels were estimated. Cases had significantly higher plasma MG levels and lower RBC GAPDH activity than controls (P < 0.001). The distribution of rs1060620 or rs1060619 alleles and genotypes significantly differed between groups. The rs1060620 AG (OR 0.55; 95% CI 0.33-0.92; P = 0.022) or rs1060619 CT (OR 0.51; 95% CI 0.31-0.83; P = 0.007) genotype was associated with reduced ACS risk, confirmed in the over-dominant genetic model. Haplotype analyses revealed that the GAT and CGC haplotypes were associated with increased (OR 28.37; 95% CI 3.82-210.49; P = 8.51 × 10-7) and decreased (OR 0.45; 95% CI 0.24-0.86; P = 0.014) ACS risk in T2DM patients, respectively. Lower GAPDH activity was observed in the TT and CT genotypes compared to the CC genotype of rs1060619 (P < 0.001). This work established that the GAPDH rs1060620 or rs1060619 gene polymorphisms are associated with ACS risk in South Indians with T2DM.

Proteomic Comparisons of Caprine Milk Whole Cream Buttermilk Whey and Cheese Whey Cream Buttermilk

Buttermilk, a potential material used to produce milk fat globule membrane (MFGM), is obtained as a byproduct of butter making from milk whole cream and cheese whey cream. This study investigated the effects of rennet and acid coagulation on the protein profiles of buttermilk rennet-coagulated whey (BRW) and buttermilk acid-coagulated whey (BAW). They were compared to those of whey cream buttermilk (WCB). Rennet coagulation was more efficient in removing casein, while retaining more IgG and lactoferrin than acid coagulation. BRW had more MFGM than BAW. Butyrophilin, xanthine dehydrogenase, and mucin1 were significantly higher (P < 0.05) in BRW, while fatty acid-binding protein 3 was enriched in BAW. KEGG analysis showed that complement and coagulation cascades had the greatest differences, and the abundance of proteins involved in this signaling pathway in BRW and BAW was higher, suggesting their potential anticoagulant and anti-inflammatory activity. BAW had higher apolipoprotein A4 and transcobalamin 2, which are essential carriers for transporting long-chain fatty acids and vitamin B12 from the intestine to the blood. Therefore, BAW intake might improve lipids and vitamin B12 absorption. This study can help deepen the understanding of protein composition of MFGM-enriched whey and facilitate the production of MFGM proteins for infants and old-aged populations.

Regulation of Intersubunit Interactions in Homotetramer of Glyceraldehyde-3-Phosphate Dehydrogenases upon Its Immobilization in Protein-Kappa-Carrageenan Gels

Polysaccharides, being biocompatible and biodegradable polymers, are highly attractive as materials for protein delivery systems. However, protein-polysaccharide interactions may lead to protein structural transformation. In the current study, we analyze the structural adjustment of a homotetrameric protein, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), upon its interactions with both flexible coil chain and the rigid helix of κ-carrageenan. FTIR spectroscopy was used to probe the secondary structures of both protein and polysaccharide. Electrostatically driven protein-polysaccharide interactions in dilute solutions resulted in an insoluble complex formation with a constant κ-carrageenan/GAPDH ratio of 0.2, which amounts to 75 disaccharide units per mole of protein tetramer. Upon interactions with both coiled and helical polysaccharides, a weakening of the intersubunit interactions was revealed and attributed to a partial GAPDH tetramer dissociation. In turn, protein distorted the helical conformation of κ-carrageenan when co-gelled. Molecular modeling showed the energy favorable interactions between κ-carrageenan and GAPDH at different levels of oligomerization. κ-Carrageenan binds in the region of the NAD-binding groove and the S-loop in OR contact, which may stabilize the OP dimers. The obtained results highlight the mutual conformational adjustment of oligomeric GAPDH and κ-carrageenan upon interaction and the stabilization of GAPDH's dissociated forms upon immobilization in polysaccharide gels.

Exploring the Role of Glycolytic Enzymes PFKFB3 and GAPDH in the Modulation of Aβ and Neurodegeneration and Their Potential of Therapeutic Targets in Alzheimer's Disease

Alzheimer's disease (AD) is presently the 6th major cause of mortality across the globe. However, it is expected to rise rapidly, following cancer and heart disease, as a leading cause of death among the elderly peoples. AD is largely characterized by metabolic changes linked to glucose metabolism and age-induced mitochondrial failure. Recent research suggests that the glycolytic pathway is required for a range of neuronal functions in the brain including synaptic transmission, energy production, and redox balance; however, alteration in glycolytic pathways may play a significant role in the development of AD. Moreover, it is hypothesized that targeting the key enzymes involved in glucose metabolism may help to prevent or reduce the risk of neurodegenerative disorders. One of the major pro-glycolytic enzyme is 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3); it is normally absent in neurons but abundant in astrocytes. Similarly, another key of glycolysis is glyceraldehyde-3-phosphate dehydrogenase (GAPDH) which catalyzes the conversion of aldolase and glyceraldehyde 3 phosphates to 1,3 bisphosphoglycerate. GAPDH has been reported to interact with various neurodegenerative disease-associated proteins, including the amyloid-β protein precursor (AβPP). These findings indicate PFKFB3 and GAPDH as a promising therapeutic target to AD. Current review highlight the contributions of PFKFB3 and GAPDH in the modulation of Aβand AD pathogenesis and further explore the potential of PFKFB3 and GAPDH as therapeutic targets in AD.

3-Bromo-Isoxazoline Derivatives Inhibit GAPDH Enzyme in PDAC Cells Triggering Autophagy and Apoptotic Cell Death

A growing interest in the study of aerobic glycolysis as a key pathway for cancer-cell energetic metabolism, favouring tumour progression and invasion, has led to consider GAPDH as an effective drug target to specifically hit cancer cells. In this study, we have investigated a panel of 3-bromo-isoxazoline derivatives based on previously identified inhibitors of Plasmodium falciparum GAPDH (PfGAPDH). The compounds are active, to a different extent, as inhibitors of human-recombinant GAPDH. They showed an antiproliferative effect on pancreatic ductal-adenocarcinoma cells (PDAC) and pancreatic-cancer stem cells (CSCs), and among them two promising compounds were selected to be tested in vivo. Interestingly, these compounds were not effective in fibroblasts. The AXP-3019 derivative was able to block PDAC-cell growth in mice xenograft without apparent toxicity. The overall results support the assumption that selective inhibition of the glycolytic pathway, by targeting GAPDH, is an effective therapy for pancreatic cancer and that 3-bromo-isoxazoline derivatives represent a new class of anti-cancer compounds targeting glycolysis.

Arsenic alters nitric oxide signaling similar to autism spectrum disorder and Alzheimer's disease-associated mutations

Epidemiological studies have proven that exposure to Arsenic (AS) leads to the development of many neurological disorders. However, few studies have investigated its molecular mechanisms in the brain. Our previous work has revealed nitric oxide (NO)-mediated apoptosis and SNO reprogramming in the cortex following arsenic treatment, yet the role of NO and S-nitrosylation (SNO) in AS-mediated neurotoxicity has not been investigated. Therefore, we have conducted a multidisciplinary in-vivo study in mice with two different doses of Sodium Arsenite (SA) (0.1 ppm and 1 ppm) in drinking water. We used the novel SNOTRAP-based mass spectrometry method followed by the bioinformatics analysis, Western blot validation, and five different behavioral tests. Bioinformatics analysis of SA-treated mice showed significant SNO-enrichment of processes involved in mitochondrial respiratory function, endogenous antioxidant systems, transcriptional regulation, cytoskeleton maintenance, and regulation of apoptosis. Western blotting showed increased levels of cleaved PARP-1 and cleaved caspase-3 in SA-treated mice consistent with SA-induced apoptosis. Behavioral studies showed significant cognitive dysfunctions similar to those of Autism spectrum disorder (ASD) and Alzheimer's disease (AD). A comparative analysis of the SNO-proteome of SA-treated mice with two transgenic mouse strains, models of ASD and AD, showed molecular convergence of SA environmental neurotoxicity and the genetic mutations causing ASD and AD. This is the first study to show the effects of AS on SNO-signaling in the striatum and hippocampus and its effects on behavioral characteristics. Finally, further investigation of the NO-dependent mechanisms of AS-mediated neurotoxicity may reveal new drug targets for its prevention.

Glycomic and Glycoproteomic Techniques in Neurodegenerative Disorders and Neurotrauma: Towards Personalized Markers

The proteome represents all the proteins expressed by a genome, a cell, a tissue, or an organism at any given time under defined physiological or pathological circumstances. Proteomic analysis has provided unparalleled opportunities for the discovery of expression patterns of proteins in a biological system, yielding precise and inclusive data about the system. Advances in the proteomics field opened the door to wider knowledge of the mechanisms underlying various post-translational modifications (PTMs) of proteins, including glycosylation. As of yet, the role of most of these PTMs remains unidentified. In this state-of-the-art review, we present a synopsis of glycosylation processes and the pathophysiological conditions that might ensue secondary to glycosylation shortcomings. The dynamics of protein glycosylation, a crucial mechanism that allows gene and pathway regulation, is described. We also explain how-at a biomolecular level-mutations in glycosylation-related genes may lead to neuropsychiatric manifestations and neurodegenerative disorders. We then analyze the shortcomings of glycoproteomic studies, putting into perspective their downfalls and the different advanced enrichment techniques that emanated to overcome some of these challenges. Furthermore, we summarize studies tackling the association between glycosylation and neuropsychiatric disorders and explore glycoproteomic changes in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington disease, multiple sclerosis, and amyotrophic lateral sclerosis. We finally conclude with the role of glycomics in the area of traumatic brain injury (TBI) and provide perspectives on the clinical application of glycoproteomics as potential diagnostic tools and their application in personalized medicine.

Modification of Glyceraldehyde-3-Phosphate Dehydrogenase with Nitric Oxide: Role in Signal Transduction and Development of Apoptosis

This review focuses on the consequences of GAPDH S-nitrosylation at the catalytic cysteine residue. The widespread hypothesis according to which S-nitrosylation causes a change in GAPDH structure and its subsequent binding to the Siah1 protein is considered in detail. It is assumed that the GAPDH complex with Siah1 is transported to the nucleus by carrier proteins, interacts with nuclear proteins, and induces apoptosis. However, there are several conflicting and unproven elements in this hypothesis. In particular, there is no direct confirmation of the interaction between the tetrameric GAPDH and Siah1 caused by S-nitrosylation of GAPDH. The question remains as to whether the translocation of GAPDH into the nucleus is caused by S-nitrosylation or by some other modification of the catalytic cysteine residue. The hypothesis of the induction of apoptosis by oxidation of GAPDH is considered. This oxidation leads to a release of the coenzyme NAD+ from the active center of GAPDH, followed by the dissociation of the tetramer into subunits, which move to the nucleus due to passive transport and induce apoptosis. In conclusion, the main tasks are summarized, the solutions to which will make it possible to more definitively establish the role of nitric oxide in the induction of apoptosis.

Extracellular Vesicles under Oxidative Stress Conditions: Biological Properties and Physiological Roles

Under physio-pathological conditions, cells release membrane-surrounded structures named Extracellular Vesicles (EVs), which convey their molecular cargo to neighboring or distant cells influencing their metabolism. Besides their involvement in the intercellular communication, EVs might represent a tool used by cells to eliminate unnecessary/toxic material. Here, we revised the literature exploring the link between EVs and redox biology. The first proof of this link derives from evidence demonstrating that EVs from healthy cells protect target cells from oxidative insults through the transfer of antioxidants. Oxidative stress conditions influence the release and the molecular cargo of EVs that, in turn, modulate the redox status of target cells. Oxidative stress-related EVs exert both beneficial or harmful effects, as they can carry antioxidants or ROS-generating enzymes and oxidized molecules. As mediators of cell-to-cell communication, EVs are also implicated in the pathophysiology of oxidative stress-related diseases. The review found evidence that numerous studies speculated on the role of EVs in redox signaling and oxidative stress-related pathologies, but few of them unraveled molecular mechanisms behind this complex link. Thus, the purpose of this review is to report and discuss this evidence, highlighting that the analysis of the molecular content of oxidative stress-released EVs (reminiscent of the redox status of originating cells), is a starting point for the use of EVs as diagnostic and therapeutic tools in oxidative stress-related diseases.

The Multifaceted Roles of Zinc in Neuronal Mitochondrial Dysfunction

Zinc is a highly abundant cation in the brain, essential for cellular functions, including transcription, enzymatic activity, and cell signaling. However, zinc can also trigger injurious cascades in neurons, contributing to the pathology of neurodegenerative diseases. Mitochondria, critical for meeting the high energy demands of the central nervous system (CNS), are a principal target of the deleterious actions of zinc. An increasing body of work suggests that intracellular zinc can, under certain circumstances, contribute to neuronal damage by inhibiting mitochondrial energy processes, including dissipation of the mitochondrial membrane potential (MMP), leading to ATP depletion. Additional consequences of zinc-mediated mitochondrial damage include reactive oxygen species (ROS) generation, mitochondrial permeability transition, and excitotoxic calcium deregulation. Zinc can also induce mitochondrial fission, resulting in mitochondrial fragmentation, as well as inhibition of mitochondrial motility. Here, we review the known mechanisms responsible for the deleterious actions of zinc on the organelle, within the context of neuronal injury associated with neurodegenerative processes. Elucidating the critical contributions of zinc-induced mitochondrial defects to neurotoxicity and neurodegeneration may provide insight into novel therapeutic targets in the clinical setting.

Formation of protein cross-links by singlet oxygen-mediated disulfide oxidation

Cross-links formed within and between proteins are a major cause of protein dysfunction, and are postulated to drive the accumulation of protein aggregates in some human pathologies. Cross-links can be formed from multiple residues and can be reversible (usually sulfur-sulfur bonds) or irreversible (typically carbon-carbon or carbon-heteroatom bonds). Disulfides formed from oxidation of two Cys residues are widespread, with these formed both deliberately, via enzymatic reactions, or as a result of unintended oxidation reactions. We have recently demonstrated that new protein-glutathione mixed disulfides can be formed through oxidation of a protein disulfide to a thiosulfinate, and subsequent reaction of this species with glutathione. Here we investigate whether similar reactions occur between an oxidized protein disulfide, and a Cys residues on a second protein, to give novel protein cross-links. Singlet oxygen (¹O₂)-mediated oxidation of multiple proteins (α-lactalbumin, lysozyme, beta-2-microglobulin, C-reactive protein), and subsequent incubation with the Cys-containing protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH), generates inter-protein cross-links as detected by SDS-PAGE, immunoblotting and mass spectrometry (MS). The cross-link yield is dependent on the ¹O₂ concentration, the presence of the original protein disulfide bond, and the free Cys on GAPDH. MS with ¹⁸O-labeling has allowed identification of the residues involved in some cases (e.g. Cys25 from the Cys25-Cys80 disulfide in beta-2-microglobulin, with Cys149 or Cys244 of GAPDH). The formation of these cross-links results in a loss of GAPDH enzymatic activity. These data provide 'proof-of-concept' for a novel mechanism of protein cross-link formation which may help rationalize the accumulation of cross-linked proteins in multiple human pathologies.

Glycation of glyceraldehyde-3-phosphate dehydrogenase inhibits the binding with α-synuclein and RNA

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) shows great diversity of functions, interaction partners and post-translational modifications. GAPDH undergoes glycation of positively charged residues in diabetic patient's tissues and therefore may change interaction with partners. The influence of GAPDH glycation on interaction with two important partners, α-synuclein and RNA, has been investigated in silico using molecular dynamics simulations and in vitro using surface plasmon resonance measurements. Since positively charged groove including substrate- and NAD⁺-binding sites is proposed as potential binding site for α-synuclein and RNA, GAPDH was glycated on residues in grooves and randomly distributed over the whole surface. Lysine residues were replaced with negatively charged carboxymethyl lysine as a widespread advanced glycation end product. As results, GAPDH glycation suppressed the interaction with α-synuclein and RNA. Although the modified GAPDH residues participated in binding with α-synuclein, no stable binding site with both glycated forms was observed. Glycation along the whole GAPDH surface completely suppressed interaction with RNA, whereas the alternative possible RNA binding site was identified in case of groove glycation. The findings were supported by direct measurement of the binding affinity. The obtained results clarify effect of glycation on GAPDH interaction with α-synuclein and RNA and elucidate a possible mechanism of interplay between glycation occurred in diabetes and neurodegenerative diseases, which GAPDH and α-synuclein are involved in.

Influence of Oxidative Stress on Catalytic and Non-glycolytic Functions of Glyceraldehyde-3-phosphate Dehydrogenase

BACKGROUND

Glyceraldehyde-3-phosphate Dehydrogenase (GAPDH) is a unique enzyme that, besides its main function in glycolysis (catalysis of glyceraldehyde-3-phosphate oxidation), possesses a number of non-glycolytic activities. The present review summarizes information on the role of oxidative stress in the regulation of the enzymatic activity as well as non-glycolytic functions of GAPDH.

METHODS

Based on the analysis of literature data and the results obtained in our research group, mechanisms of the regulation of GAPDH functions through the oxidation of the sulfhydryl groups in the active site of the enzyme have been suggested.

RESULTS

Mechanism of GAPDH oxidation includes consecutive oxidation of the catalytic Cysteine (Cys150) into sulfenic, sulfinic, and sulfonic acid derivatives, resulting in the complete inactivation of the enzyme. The cysteine sulfenic acid reacts with reduced glutathione (GSH) to form a mixed disulfide (S-glutathionylated GAPDH) that further reacts with Cys154 yielding the disulfide bond in the active site of the enzyme. In contrast to the sulfinic and sulfonic acids, the mixed disulfide and the intramolecular disulfide bond are reversible oxidation products that can be reduced in the presence of GSH or thioredoxin.

CONCLUSION

Oxidation of sulfhydryl groups in the active site of GAPDH is unavoidable due to the enhanced reactivity of Cys150. The irreversible oxidation of Cys150 is prevented by Sglutathionylation and disulfide bonding with Cys154. The oxidation/reduction of the sulfhydryl groups in the active site of GAPDH can be used for regulation of glycolysis and numerous side activities of this enzyme including the induction of apoptosis.

Identification of Functional Interactome of Gastric Cancer Cells with Helicobacter pylori Outer Membrane Protein HpaA by HPLC-MS/MS

HpaA as an outer membrane protein of Helicobacter pylori (H. pylori) plays a significant role in the adhesion to the human stomach, but the functional relation between HpaA and gastric epithelial cells is still not clear. To screen the interaction between HpaA and cellular proteins in gastric epithelial cells, the HpaA protein from H. pylori 26695 fused with a tag (6× His) was expressed and purified successfully, the secondary structure was estimated by the Circular Dichroism (CD) spectrum, and the purified recombinant protein was used to perform the pull-down assays with gastric cancer cell lines (AGS and SGC-7901) lysates, respectively. The pull-down proteins were identified by high-performance liquid chromatography tandem mass spectrometry system (HPLC-MS/MS). A total of 9 and 13 proteins related were analyzed from AGS and SGC-7901 cell lysates, respectively. ANXA2 was considered as putative HpaA functional partner discovered from lysates of both cell lines with high score and coverage. It is hypothesized that HpaA may be involved in the biological process of regulation of transcription and nucleic acid metabolism during the adhesion of H. pylori to human gastric epithelial cells, and HpaA-binding proteins also be used as targets for the development of antiadhesion drugs against H. pylori.

Glyceraldehyde-3-phosphate Dehydrogenase is a Multifaceted Therapeutic Target

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a glycolytic enzyme whose role in cell metabolism and homeostasis is well defined, while its function in pathologic processes needs further elucidation. Depending on the cell context, GAPDH may bind a number of physiologically important proteins, control their function and correspondingly affect the cell’s fate. These interprotein interactions and post-translational modifications of GAPDH mediate its cytotoxic or cytoprotective functions in the manner of a Janus-like molecule. In this review, we discuss the functional features of the enzyme in cellular physiology and its possible involvement in human pathologies. In the last part of the article, we describe drugs that can be employed to modulate this enzyme’s function in some pathologic states.

Global Proteomic Analysis of Lysine Malonylation in Toxoplasma gondii

Lysine malonylation (Kmal) is a new post-translational modification (PTM), which has been reported in several prokaryotic and eukaryotic species. Although Kmal can regulate many and diverse biological processes in various organisms, knowledge about this important PTM in the apicomplexan parasite Toxoplasma gondii is limited. In this study, we performed the first global profiling of malonylated proteins in T. gondii tachyzoites using affinity enrichment and Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Three experiments performed in tandem revealed 294, 345, 352 Kmal sites on 203, 236, 230 malonylated proteins, respectively. Computational analysis showed the identified malonylated proteins to be localized in various subcellular compartments and involved in many cellular functions, particularly mitochondrial function. Additionally, one conserved Kmal motif with a strong bias for cysteine was detected. Taken together, these findings provide the first report of Kmal profile in T. gondii and should be an important resource for studying the physiological roles of Kmal in this parasite.

Inhibitors of Glyceraldehyde 3-Phosphate Dehydrogenase and Unexpected Effects of Its Reduced Activity

The review describes the use of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) inhibitors to study the enzyme and to suppress its activity in various cell types. The main problem of selective GAPDH inhibition is a highly conserved nature of the enzyme active site and, especially, Cys150 environment important for the catalytic action of cysteine sulfhydryl group. Numerous attempts to find specific inhibitors of sperm GAPDH and enzymes from Trypanosoma sp. and Mycobacterium tuberculosis that would not inhibit GAPDH of somatic mammalian cells have failed, which has pushed researchers to search for new ways to solve this problem. The sections of the review are devoted to the studies of GAPDH inactivation by reactive oxygen species, glutathione, and glycating agents. The final section discusses possible effects of GAPDH inhibition and inactivation on glycolysis and related metabolic pathways (pentose phosphate pathway, uncoupling of the glycolytic oxidation and phosphorylation, etc.).

Glutathionylation primes soluble glyceraldehyde-3-phosphate dehydrogenase for late collapse into insoluble aggregates

Protein aggregation is a complex physiological process, primarily determined by stress-related factors revealing the hidden aggregation propensity of proteins that otherwise are fully soluble. Here we report a mechanism by which glycolytic glyceraldehyde-3-phosphate dehydrogenase of Arabidopsis thaliana (AtGAPC1) is primed to form insoluble aggregates by the glutathionylation of its catalytic cysteine (Cys149). Following a lag phase, glutathionylated AtGAPC1 initiates a self-aggregation process resulting in the formation of branched chains of globular particles made of partially misfolded and totally inactive proteins. GSH molecules within AtGAPC1 active sites are suggested to provide the initial destabilizing signal. The following removal of glutathione by the formation of an intramolecular disulfide bond between Cys149 and Cys153 reinforces the aggregation process. Physiological reductases, thioredoxins and glutaredoxins, could not dissolve AtGAPC1 aggregates but could efficiently contrast their growth. Besides acting as a protective mechanism against overoxidation, S-glutathionylation of AtGAPC1 triggers an unexpected aggregation pathway with completely different and still unexplored physiological implications.

The formation of hybrid complexes between isoenzymes of glyceraldehyde-3-phosphate dehydrogenase regulates its aggregation state, the glycolytic activity and sphingolipid status in Saccharomyces cerevisiae

The glycolytic enzyme glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) has been traditionally considered a housekeeping protein involved in energy generation. However, evidence indicates that GAPDHs from different origins are tightly regulated and that this regulation may be on the basis of glycolysis‐related and glycolysis‐unrelated functions. In Saccharomyces cerevisiae, Tdh3 is the main GAPDH, although two other isoenzymes encoded by TDH1 and TDH2 have been identified. Like other GAPDHs, Tdh3 exists predominantly as a tetramer, although dimeric and monomeric forms have also been isolated. Mechanisms of Tdh3 regulation may thus imply changes in its oligomeric state or be based in its ability to interact with Tdh1 and/or Tdh2 to form hybrid complexes. However, no direct evidence of the existence of these interactions has been provided and the exact function of Tdh1,2 is unknown. Here, we show that Tdh1,2 immunopurified with a GFP‐tagged version of Tdh3 and that lack of this interaction stimulates the Tdh3’s aggregation. Furthermore, we found that the combined knockout of TDH1 and TDH2 promotes the loss of cell’s viability and increases the growing rate, glucose consumption and CO₂ production, suggesting a higher glycolytic flux in the mutant cells. Consistent with this, the tdh3 strain, which displays impaired in vitro GAPDH activity, exhibited the opposite phenotypes. Quite remarkably, tdh1 tdh2 mutant cells show increased sensitivity to aureobasidin A, an inhibitor of the inositolphosphoryl ceramide synthase, while cells lacking Tdh3 showed improved tolerance. The results are in agreement with a link between glycolysis and sphingolipid (SLs) metabolism. Engineering Tdh activity could be thus exploited to alter the SLs status with consequences in different aspects of yeast biotechnology.

Synthesis and metabolism of methylglyoxal, S-D-lactoylglutathione and D-lactate in cancer and Alzheimer's disease. Exploring the crossroad of eternal youth and premature aging

Both cancer and Alzheimer's disease (AD) are emerging as metabolic diseases in which aberrant/dysregulated glucose metabolism and bioenergetics occur, and play a key role in disease progression. Interestingly, an enhancement of glucose uptake, glycolysis and pentose phosphate pathway occurs in both cancer cells and amyloid-β-resistant neurons in the early phase of AD. However, this metabolic shift has its adverse effects. One of them is the increase in methylglyoxal production, a physiological cytotoxic by-product of glucose catabolism. Methylglyoxal is mainly detoxified via cytosolic glyoxalase route comprising glyoxalase 1 and glyoxalase 2 with the production of S-D-lactoylglutathione and D-lactate as intermediate and end-product, respectively. Due to the existence of mitochondrial carriers and intramitochondrial glyoxalase 2 and D-lactate dehydrogenase, the transport and metabolism of both S-D-lactoylglutathione and D-lactate in mitochondria can contribute to methylglyoxal elimination, cellular antioxidant power and energy production. In this review, it is supposed that the different ability of cancer cells and AD neurons to metabolize methylglyoxal, S-D-lactoylglutathione and D-lactate scores cell fate, therefore being at the very crossroad of the "eternal youth" of cancer and the "premature death" of AD neurons. Understanding of these processes would help to elaborate novel metabolism-based therapies for cancer and AD treatment.

Regulation of Autophagy by Nuclear GAPDH and Its Aggregates in Cancer and Neurodegenerative Disorders

Several studies indicate that the cytosolic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has pleiotropic functions independent of its canonical role in glycolysis. The GAPDH functional diversity is mainly due to post-translational modifications in different amino acid residues or due to protein–protein interactions altering its localization from cytosol to nucleus, mitochondria or extracellular microenvironment. Non-glycolytic functions of GAPDH include the regulation of cell death, autophagy, DNA repair and RNA export, and they are observed in physiological and pathological conditions as cancer and neurodegenerative disorders. In disease, the knowledge of the mechanisms regarding GAPDH-mediated cell death is becoming fundamental for the identification of novel therapies. Here, we elucidate the correlation between autophagy and GAPDH in cancer, describing the molecular mechanisms involved and its impact in cancer development. Since autophagy is a degradative pathway associated with the regulation of cell death, we discuss recent evidence supporting GAPDH as a therapeutic target for autophagy regulation in cancer therapy. Furthermore, we summarize the molecular mechanisms and the cellular effects of GAPDH aggregates, which are correlated with mitochondrial malfunctions and can be considered a potential therapeutic target for various diseases, including cancer and neurodegenerative disorders.

Protein Interaction with Charged Macromolecules: From Model Polymers to Unfolded Proteins and Post-Translational Modifications

Interaction of proteins with charged macromolecules is involved in many processes in cells. Firstly, there are many naturally occurred charged polymers such as DNA and RNA, polyphosphates, sulfated glycosaminoglycans, etc., as well as pronouncedly charged proteins such as histones or actin. Electrostatic interactions are also important for "generic" proteins, which are not generally considered as polyanions or polycations. Finally, protein behavior can be altered due to post-translational modifications such as phosphorylation, sulfation, and glycation, which change a local charge of the protein region. Herein we review molecular modeling for the investigation of such interactions, from model polyanions and polycations to unfolded proteins. We will show that electrostatic interactions are ubiquitous, and molecular dynamics simulations provide an outstanding opportunity to look inside binding and reveal the contribution of electrostatic interactions. Since a molecular dynamics simulation is only a model, we will comprehensively consider its relationship with the experimental data.

Expression of glyceraldehyde-3-phosphate dehydrogenase from M. tuberculosis in E. coli. Purification and characteristics of the untagged recombinant enzyme

The goal of the present work was to produce glyceraldehyde-3-phospate dehydrogenase from M. tuberculosis in E. coli cells in soluble and catalytically active form and to elaborate a method for the purification of the recombinant enzyme. The His-tagged recombinant enzyme (Mtb-GAPDH_His) was shown to be inactive and insoluble. The untagged enzyme (Mtb-GAPDH) was catalytically active and exhibited higher solubility. Mtb-GAPDH was purified from the cell extract using ammonium sulfate fractionation and ion-exchange chromatography. The presence of glycerol was necessary for isolation of Mtb-GAPDH, presumably, to facilitate folding of the recombinant enzyme. The yield of Mtb-GAPDH constituted 1.3 mg per 10 g of the cell biomass. The specific activity of the purified Mtb-GAPDH was 55 ± 5 μmol NADH/min per mg protein (pH 9.0, 22 °C) that exceeded the activity of the previously described preparation of His-tagged recombinant GAPDH from M. tuberculosis that was co-expressed with GroEL/ES chaperone by approximately 5-fold. The results suggest that the folding of the recombinant GAPDH is hindered by the His-tag, which may result in the production of insoluble protein or in isolation of the preparation with decreased specific activity.

Oxidatively modified glyceraldehyde-3-phosphate dehydrogenase in neurodegenerative processes and the role of low molecular weight compounds in counteracting its aggregation and nuclear translocation

A number of independent studies have shown the contribution of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the pathogenesis of several neurodegenerative disorders. Indeed, GAPDH aggregates have been found in many post-mortem samples of brains of patients diagnosed with Alzheimer's and Parkinson disease. Currently, it is accepted that GAPDH-mediated cell death pathways in the neurodegenerative processes are associated with apoptosis caused by GAPDH nuclear translocation and excessive aggregation under oxidative stress conditions. Also the role of GAPDH in neurodegenerative diseases is linked to it directly binding to specific amyloidogenic proteins and petides such as β-amyloid precursor protein, β-amyloid peptide and tau protein in Alzheimer's disease, huntingtin in Huntington's disease and α-synuclein in Parkinson disease. One of the latest studies indicated that GAPDH aggregates significantly accelerate amyloidogenesis of the β-amyloid peptide, which implies that aggregates of GAPDH may act as a specific aggregation "seed" in vitro. Previous detailed studies revealed that the active-site cysteine (Cys152) of GAPDH plays an essential role in the oxidative stress-induced aggregation of GAPDH associated with cell death. Furthermore, oxidative modification of this cysteine residue initiates the translocation of the enzyme to the nucleus, subsequently leading to apoptosis. The crystallographic structure of GAPDH shows that the Cys152 residue is located close to the surface of the molecule in a hydrophilic environment, which means that it can react with low molecular weight compounds such as hydroxynonenal or piceatannol. Therefore, it is highly possible that GAPDH may serve as a target for small molecule compounds with the potential to slow down or prevent the progression of neurodegenerative disorders. Recently appearing new evidence has highlighted the significance of low molecular weight compounds in counteracting the oxidation of GAPDH and consequently its aggregation and other unfavourable pathological processes. Hence, this review aims to present all recent findings concerning molecules that are able to interact with GAPDH and counteract its aggregation and translocation to the nucleus.

Glyceraldehyde-3-phosphate dehydrogenase from Citrobacter sp. S-77 is post-translationally modified by CoA (protein CoAlation) under oxidative stress

Protein CoAlation (S-thiolation by coenzyme A) has recently emerged as an alternative redox-regulated post-translational modification by which protein thiols are covalently modified with coenzyme A (CoA). However, little is known about the role and mechanism of this post-translational modification. In the present study, we investigated CoAlation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from a facultative anaerobic Gram-negative bacterium Citrobacter sp. S-77 (Cb GAPDH). GAPDH is a key glycolytic enzyme whose activity relies on the thiol-based redox-regulated post-translational modifications of active-site cysteine. LC-MS/MS analysis revealed that CoAlation of Cb GAPDH occurred in vivo under sodium hypochlorite (NaOCl) stress. The purified Cb GAPDH was highly sensitive to overoxidation by H₂O₂ and NaOCl, which resulted in irreversible enzyme inactivation. By contrast, treatment with coenzyme A disulphide (CoASSCoA) or H₂O₂/NaOCl in the presence of CoA led to CoAlation and inactivation of the enzyme; activity could be recovered after incubation with dithiothreitol, glutathione and CoA. CoAlation of the enzyme in vitro was confirmed by mass spectrometry. The presence of a substrate, glyceraldehyde-3-phosphate, fully protected Cb GAPDH from inactivation by CoAlation, suggesting that the inactivation is due to the formation of mixed disulphides between CoA and the active-site cysteine Cys149. A molecular docking study also supported the formation of mixed disulphide without steric constraints. These observations suggest that CoAlation is an alternative mechanism to protect the redox-sensitive thiol (Cys149) of Cb GAPDH against irreversible oxidation, thereby regulating enzyme activity under oxidative stress.

Glutathionylation: a regulatory role of glutathione in physiological processes

Glutathione (γ-glutamyl-cysteinyl-glycine) is an intracellular thiol molecule and a potent antioxidant that participates in the toxic metabolism phase II biotransformation of xenobiotics. It can bind to a variety of proteins in a process known as glutathionylation. Protein glutathionylation is now recognised as one of important posttranslational regulatory mechanisms in cell and tissue physiology. Direct and indirect regulatory roles in physiological processes include glutathionylation of major transcriptional factors, eicosanoids, cytokines, and nitric oxide (NO). This review looks into these regulatory mechanisms through examples of glutathione regulation in apoptosis, vascularisation, metabolic processes, mitochondrial integrity, immune system, and neural physiology. The focus is on the physiological roles of glutathione beyond biotransformational metabolism.

Alpha-Synuclein Glycation and the Action of Anti-Diabetic Agents in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder with complex etiology and variable pathology. While a subset of cases is associated with single-gene mutations, the majority originates from a combination of factors we do not fully understand. Thus, understanding the underlying causes of PD is indispensable for the development of novel therapeutics. Glycation, the non-enzymatic reaction between reactive dicarbonyls and amino groups, gives rise to a variety of different reaction products known as advanced glycation end products (AGEs). AGEs accumulate over a proteins life-time, and increased levels of glycation reaction products play a role in diabetic complications. It is now also becoming evident that PD patients also display perturbed sugar metabolism and protein glycation, including that of alpha-synuclein, a key player in PD. Here, we hypothesize that anti-diabetic drugs targeting the levels of glycation precursors, or promoting the clearance of glycated proteins may also prove beneficial for PD patients.