Non-native glyceraldehyde-3-phosphate dehydrogenase can be an intrinsic component of amyloid structures

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 role of sperm-specific glyceraldehyde-3-phosphate dehydrogenase in the development of pathologies-from asthenozoospermia to carcinogenesis

The review considers various aspects of the influence of the glycolytic enzyme, sperm-specific glyceraldehyde-3-phosphate dehydrogenase (GAPDS) on the energy metabolism of spermatozoa and on the occurrence of several pathologies both in spermatozoa and in other cells. GAPDS is a unique enzyme normally found only in mammalian spermatozoa. GAPDS provides movement of the sperm flagellum through the ATP formation in glycolytic reactions. Oxidation of cysteine residues in GAPDS results in inactivation of the enzyme and decreases sperm motility. In particular, reduced sperm motility in diabetes can be associated with GAPDS oxidation by superoxide anion produced during glycation reactions. Mutations in GAPDS gene lead in the loss of motility, and in some cases, disrupts the formation of the structural elements of the sperm flagellum, in which the enzyme incorporates during spermiogenesis. GAPDS activation can be used to increase the spermatozoa fertility, and inhibitors of this enzyme are being tried as contraceptives. A truncated GAPDS lacking the N-terminal fragment of 72 amino acids that attaches the enzyme to the sperm flagellum was found in melanoma cell lines and then in specimens of melanoma and other tumors. Simultaneous production of the somatic form of GAPDH and sperm-specific GAPDS in cancer cells leads to a reorganization of their energy metabolism, which is accompanied by a change in the efficiency of metastasis of certain forms of cancer. Issues related to the use of GAPDS for the diagnosis of cancer, as well as the possibility of regulating the activity of this enzyme to prevent metastasis, are discussed.

Moonlighting enzymes: when cellular context defines specificity

It is not often realized that the absolute protein specificity is an exception rather than a rule. Two major kinds of protein multi-specificities are promiscuity and moonlighting. This review discusses the idea of enzyme specificity and then focusses on moonlighting. Some important examples of protein moonlighting, such as crystallins, ceruloplasmin, metallothioniens, macrophage migration inhibitory factor, and enzymes of carbohydrate metabolism are discussed. How protein plasticity and intrinsic disorder enable the removing the distinction between enzymes and other biologically active proteins are outlined. Finally, information on important roles of moonlighting in human diseases is updated.

Protein Interactome of Amyloid-β as a Therapeutic Target

The amyloid concept of Alzheimer's disease (AD) assumes the β-amyloid peptide (Aβ) as the main pathogenic factor, which injures neural and other brain cells, causing their malfunction and death. Although Aβ has been documented to exert its cytotoxic effect in a solitary manner, there is much evidence to claim that its toxicity can be modulated by other proteins. The list of such Aβ co-factors or interactors includes tau, APOE, transthyretin, and others. These molecules interact with the peptide and affect the ability of Aβ to form oligomers or aggregates, modulating its toxicity. Thus, the list of potential substances able to reduce the harmful effects of the peptide should include ones that can prevent the pathogenic interactions by specifically binding Aβ and/or its partners. In the present review, we discuss the data on Aβ-based complexes in AD pathogenesis and on the compounds directly targeting Aβ or the destructors of its complexes with other polypeptides.

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.

Combination of a Chaperone Synthesis Inducer and an Inhibitor of GAPDH Aggregation for Rehabilitation after Traumatic Brain Injury: A Pilot Study

The recovery period after traumatic brain injury (TBI) is often complicated by secondary damage that may last for days or even months after trauma. Two proteins, Hsp70 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), were recently described as modulating post-traumatic processes, and in this study, we test them as targets for combination therapy using an inhibitor of GAPDH aggregation (derivative of hydrocortisone RX624) and an inducer of Hsp70 synthesis (the pyrrolylazine derivative PQ-29). The protective effect of the combination on C6 rat glioblastoma cells treated with the cerebrospinal fluid of traumatized animals resulted in an increase in the cell index and in a reduced level of apoptosis. Using a rat weight drop model of TBI, we found that the combined use of both drugs prevented memory impairment and motor deficits, as well as a reduction of neurons and accumulation of GAPDH aggregates in brain tissue. In conclusion, we developed and tested a new approach to the treatment of TBI based on influencing distinct molecular mechanisms in brain cells.

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 GAPDH Promotes Alzheimer Disease Progression by Enhancing Amyloid-β Aggregation and Cytotoxicity

Neuronal cell death at late stages of Alzheimer's disease (AD) causes the release of cytosolic proteins. One of the most abundant such proteins, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), forms stable aggregates with extracellular amyloid-β (Aβ). We detect these aggregates in cerebrospinal fluid (CSF) from AD patients at levels directly proportional to the progressive stages of AD. We found that GAPDH forms a covalent bond with Q15 of Aβ that is mediated by transglutaminase (tTG). The Q15A substitution weakens the interaction between Aβ and GAPDH and reduces Aβ-GAPDH cytotoxicity. Lentivirus-driven GAPDH overexpression in two AD animal models increased the level of apoptosis of hippocampal cells, neural degeneration, and cognitive dysfunction. In contrast, in vivo knockdown of GAPDH reversed these pathogenic abnormalities suggesting a pivotal role of GAPDH in Aβ-stimulated neurodegeneration. CSF from animals with enhanced GAPDH expression demonstrates increased cytotoxicity in vitro. Furthermore, RX-624, a specific GAPDH small molecular ligand reduced accumulation of Aβ aggregates and reversed memory deficit in AD transgenic mice. These findings argue that extracellular GAPDH compromises Aβ clearance and accelerates neurodegeneration, and, thus, is a promising pharmacological target for AD.

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.

An investigation of the correlation between the S-glutathionylated GAPDH levels in blood and Alzheimer's disease progression

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by two aggregates, namely, amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs) of hyperphosphorylated tau protein (tau-p), which are released into the blood in a very small amount and cannot be easily detected. An increasing number of recent studies have suggested that S-glutathionylated glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is highly correlated with Aβ in patients with AD and that S-glutathionylated GAPDH plays a role as a proapoptotic factor in AD. We found that S-glutathionylated GAPDH is abundant in the blood of AD patients, which is unusual because S-glutathionylated GAPDH cannot exist in the blood under normal conditions. The aim of this study was to further explore the correlation between the S-glutathionylated GAPDH levels in blood plasma and AD progression. As controls, we recruited 191 people without AD, which included 111 healthy individuals and 37 patients with depression and insomnia, in the psychosomatic clinic. Moreover, 47 patients with AD (aged 40–89 years) were recruited at the neurology clinic. The blood S-glutathionylated GAPDH levels in the AD patients were significantly (p < 0.001) higher (752.7 ± 301.7 ng/dL) than those in the controls (59.92 ± 122.4 ng/dL), irrespective of gender and age. For AD diagnosis, the criterion blood S-glutathionylated GAPDH level > 251.62 ng/dL exhibited 95.74% sensitivity and 92.67% specificity. In fact, the individuals aged 70–89 years, namely, 37 patients from the psychosomatic clinic and 42 healthy individuals, showed significant blood S-glutathionylated GAPDH levels (230.5 ± 79.3 and 8.05 ± 20.51 ng/dL, respectively). This finding might indicate neurodegenerative AD progression in psychosomatic patients and suggests that the degree of neuronal apoptosis during AD progression might be sensitively evaluated based on the level of S-glutathionylated GAPDH in blood.

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.

The amyloid precursor protein affects glyceraldehyde 3-phosphate dehydrogenase levels, organelle localisation and thermal stability

Glyceraldehyde 3-phosphate dehydrogenase's (GAPDH) proapoptotic response to cellular oxidative stress has suspected implication for Alzheimer's disease (AD). Interestingly, the overexpression of the amyloid precursor protein (APP) can initiate oxidative stress responses within mammalian cell lines. Here, APP695 and APP770 overexpression significantly increased the level of GAPDH, while no effect was observed when the APP homologues APLP1 or APLP2 were used. Heterologous expression of APP695 was shown to increase the level of GAPDH within the cytoplasm by over 100% and within the mitochondria by approximately 50%. Moreover, a shift in organelle distribution from cytoplasm > nucleus > mitochondria in control cell lines to cytoplasm > mitochondria > nucleus in the APP695 overexpressing cell line was also observed. Further, the overexpression of APP695 increased GAPDH aggregation temperature by 3.09 ± 0.46 °C, indicative of greater thermal stability. These results demonstrate a clear correlation between APP overexpression and GAPDH levels, organelle distribution and thermal stability.

Comparison of protective properties of resveratrol and melatonin in the radiation inactivation and destruction of glyceraldehyde-3-phosphate dehydrogenase and lactate dehydrogenase

Purpose: This work investigates the effect of resveratrol and melatonin on structural and functional changes of two enzymes, lactate dehydrogenase (LDH) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), exposed to radiation-induced reactive oxygen species.Materials and methods: Solutions of dehydrogenases with or without antioxidants (resveratrol or melatonin) were irradiated with X-rays under the atmosphere of air and at room temperature (21 ± 2 °C). In order to determine the protective effect of melatonin and resveratrol in radiation-induced damage to GAPDH and LDH spectroscopy and HPLC methods were used. Furthermore, plausible binding sites of melatonin or resveratrol to the GAPDH or LDH molecule were analysed.Results and conclusions: Resveratrol shows better protective properties in the inactivation of GAPDH when compared to melatonin. LDH does not contain ‒SH groups in its active site, and is not inactivated by water radiolysis products other than hydroxyl radicals or the secondary radicals of the studied low-molecular-weight compounds. Resveratrol and melatonin protected the structure of LDH to a greater extent than GAPDH. This difference can be attributed to the fact that LDH potentially binds more resveratrol or melatonin molecules (27 binding sites for resveratrol and 40 for melatonin) than GAPDH (10 binding sites for resveratrol and 18 for melatonin).

Regional hypometabolism in the 3xTg mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive age-related neurodegenerative disease. Although neurofibrillary tangles and amyloid beta are classic hallmarks of AD, the earliest deficits in AD progression may be caused by unknown factors. One suspected factor has to do with brain energy metabolism. To investigate this factor, brain metabolic activity in 3xTg-AD mice and age-matched controls were measured with FDG-PET. Significant hypometabolic changes (p < .01) in brain metabolism were detected in the cortical piriform and insular regions of AD brains relative to controls. These regions are associated with olfaction, which is a potential clinical marker for AD progression as well as neurogenesis. The activity of the terminal component of the mitochondrial respiratory chain (complex IV) and the expression of complex I-V were significantly decreased (p < .05), suggesting that impaired metabolic activity coupled with impaired oxidative phosphorylation leads to decreased mitochondrial bioenergetics and subsequent Neurodegeneration. Although there is an association between neuroinflammatory pathological markers (microglial) and hypometabolism in AD, there was no association found between neuropathological (Aβ, tau, and astrocytes) and functional changes in AD sensitive brain regions, also suggesting that brain hypometabolism occurs prior to AD pathology. Therefore, targeting metabolic mechanisms in cortical piriform and insular regions at early stages may be a promising approach for preventing, slowing, and/or blocking the onset of AD and preserving neurogenesis.

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.

A dedicated glyceraldehyde-3-phosphate dehydrogenase is involved in the biosynthesis of volatile sesquiterpenes in Trichoderma virens-evidence for the role of a fungal GAPDH in secondary metabolism

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) catalyses the sixth step of glycolysis, and is also known to perform other (moonlighting) activities in animal cells. We have earlier identified an additional GAPDH gene in Trichoderma virens genome. This gene is consistently associated with the vir cluster responsible for biosynthesis of a range of volatile sesquiterpenes in Trichoderma virens. This gene is also associated with an orthologous gene cluster in Aspergillus spp. Both glycolytic GAPDH and the vir cluster-associated GAPDH show more than 80% similarity with essentially conserved NAD⁺ cofactor- and substrate-binding sites. However, a conserved indel is consistently present only in GAPDH associated with the vir cluster, both in T. virens and Aspergillus spp. Using gene knockout, we demonstrate here that the vir cluster-associated GAPDH is involved in biosynthesis of volatile sesquiterpenes in T. virens. We thus, for the first time, elucidate the non-glycolytic role of a GAPDH in a fungal system, and also prove for the first time that a GAPDH, a primary metabolism protein, is involved in secondary metabolism.

GAPDH-targeted therapy - A new approach for secondary damage after traumatic brain injury on rats

Massive neuronal death caused by a neurodegenerative pathology or damage due to ischaemia or traumatic brain injury leads to the appearance of cytosolic proteins in the extracellular space. We found that one of the most abundant cellular polypeptides, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), appearing in the medium of dying cells or body fluids is able to form aggregates that are cytotoxic to adjacent cells. Since we previously showed that the hydrocortisone derivative RX624 can inhibit the ability of GAPDH to transport the enzyme complex with polyglutamine and reduce the cytotoxicity of the complex, we explored the effects of GAPDH on SH-SY5Y neuroblastoma cells. We found that the latter treated with particular forms of GAPDH molecules die with a high efficiency, suggesting that the exogenous enzyme does kill adjacent cells. RX624 prevented the interaction of exogenous GAPDH with the cell membrane and reduced the level of death by more than 10%. We also demonstrated the efficiency of RX624 treatment in a rat model of traumatic brain injury. The chemical blocked the formation of GAPDH aggregates in the brain, inhibited the cytotoxic effects of cerebrospinal fluid and rescued the motor function of injured rats. Importantly, RX624 treatment of rats had a similar effect as the intracranial injection of anti-GAPDH antibodies.

Lessons learned from protein aggregation: toward technological and biomedical applications

The close relationship between protein aggregation and neurodegenerative diseases has been the driving force behind the renewed interest in a field where biophysics, neurobiology and nanotechnology converge in the study of the aggregate state. On one hand, knowledge of the molecular principles that govern the processes of protein aggregation has a direct impact on the design of new drugs for high-incidence pathologies that currently can only be treated palliatively. On the other hand, exploiting the benefits of protein aggregation in the design of new nanomaterials could have a strong impact on biotechnology. Here we review the contributions of our research group on novel neuroprotective strategies developed using a purely biophysical approach. First, we examine how doxycycline, a well-known and innocuous antibiotic, can reshape α-synuclein oligomers into non-toxic high-molecular-weight species with decreased ability to destabilize biological membranes, affect cell viability and form additional toxic species. This mechanism can be exploited to diminish the toxicity of α-synuclein oligomers in Parkinson's disease. Second, we discuss a novel function in proteostasis for extracellular glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in combination with a specific glycosaminoglycan (GAG) present in the extracellular matrix. GAPDH, by changing its quaternary structure from a tetramer to protofibrillar assembly, can kidnap toxic species of α-synuclein, and thereby interfere with the spreading of the disease. Finally, we review a brighter side of protein aggregation, that of exploiting the physicochemical advantages of amyloid aggregates as nanomaterials. For this, we designed a new generation of insoluble biocatalysts based on the binding of photo-immobilized enzymes onto hybrid protein:GAG amyloid nanofibrils. These new nanomaterials can be easily functionalized by attaching different enzymes through dityrosine covalent bonds.

Assessment of GAPDH expression by quantitative real time PCR in blood of Moroccan AD cases

INTRODUCTION

Neuroproteomics studies have showed the high affinity interactions between GAPDH - β-amyloid in Alzheimer disease. The aim of our study is to complete our previous studies by assessing the mechanism responsible of decreased expression of GAPDH protein in the blood of Moroccan AD cases probably due to an alteration at the transcriptional level or at the post translational level.

METHODS

The mRNA expression of GAPDH was assessed by quantitative real time PCR in AD cases and healthy controls.

RESULTS

Our result revealed a significant difference of mRNA expression level of GAPDH in AD cases as compared to healthy controls (P<0.05).

CONCLUSION

This data is consistent with several studies by showing the direct involvement of GAPDH in amyloid aggregation by undergoing several modifications, which influence its chemical structure and its biological activity.

Sperm-Specific Glyceraldehyde-3-Phosphate Dehydrogenase - An Evolutionary Acquisition of Mammals

This review is focused on the mammalian sperm-specific glyceraldehyde-3-phosphate dehydrogenase (GAPDS). GAPDS plays the major role in the production of energy required for sperm cell movement and does not perform non-glycolytic functions that are characteristic of the somatic isoenzyme of glyceraldehyde-3-phosphate dehydrogenase. The GAPDS sequence is composed of 408 amino acid residues and includes an additional N-terminal region of 72 a.a. that binds the protein to the sperm tail cytoskeleton. GAPDS is present only in the sperm cells of mammals and lizards, possibly providing them with certain evolutionary advantages in reproduction. In this review, studies concerning the problems of GAPDS isolation, its catalytic properties, and its structural features are described in detail. GAPDS is much more stable compared to the somatic isoenzyme, perhaps due to the necessity of maintaining the enzyme function in the absence of protein expression. The site-directed mutagenesis approach revealed the two GAPDS-specific proline residues, as well as three salt bridges, which seem to be the basis of the increased stability of this protein. As distinct from the somatic isoenzyme, GAPDS exhibits positive cooperativity in binding of the coenzyme NAD+. The key role in transduction of structural changes induced by NAD+ is played by the salt bridge D311-H124. Disruption of this salt bridge cancels GAPDS cooperativity and twofold increases its enzymatic activity instead. The expression of GAPDS was detected in some melanoma cells as well. Its role in the development of certain pathologies, such as cancer and neurodegenerative diseases, is discussed.

Small molecules preventing GAPDH aggregation are therapeutically applicable in cell and rat models of oxidative stress

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is one of the most abundant targets of the oxidative stress. Oxidation of the enzyme causes its inactivation and the formation of intermolecular disulfide bonds, and leads to the accumulation of GAPDH aggregates and ultimately to cell death. The aim of this work was to reveal the ability of chemicals to break the described above pathologic linkage by inhibiting GAPDH aggregation. Using the model of oxidative stress based on SK-N-SH human neuroblastoma cells treated with hydrogen peroxide, we found that lentivirus-mediated down- or up-regulation of GAPDH content caused inhibition or enhancement of the protein aggregation and respectively reduced or increased the level of cell death. To reveal substances that are able to inhibit GAPDH aggregation, we developed a special assay based on dot ultrafiltration using the collection of small molecules of plant origin. In the first round of screening, five compounds were found to possess anti-aggregation activity as established by ultrafiltration and dynamic light scattering; some of the substances efficiently inhibited GAPDH aggregation in nanomolar concentrations. The ability of the compounds to bind GAPDH molecules was proved by the drug affinity responsive target stability assay, molecular docking and differential scanning calorimetry. Results of experiments with SK-N-SH human neuroblastoma treated with hydrogen peroxide show that two substances, RX409 and RX426, lowered the degree of GAPDH aggregation and reduced cell death by 30%. Oxidative injury was emulated in vivo by injecting of malonic acid into the rat brain, and we showed that the treatment with RX409 or RX426 inhibited GAPDH-mediated aggregation in the brain, reduced areas of the injury as proved by magnetic resonance imaging, and augmented the behavioral status of the rats as established by the "beam walking" test. In conclusion, the data show that two GAPDH binders could be therapeutically relevant in the treatment of injuries stemming from hard oxidative stress.

Glyceraldehyde 3-phosphate dehydrogenase augments the intercellular transmission and toxicity of polyglutamine aggregates in a cell model of Huntington disease

The common feature of Huntington disease is the accumulation of oligomers or aggregates of mutant huntingtin protein (mHTT), which causes the death of a subset of striatal neuronal populations. The cytotoxic species can leave neurons and migrate to other groups of cells penetrating and damaging them in a prion-like manner. We hypothesized that the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH), previously shown to elevate the aggregation of mHTT, is associated with an increased efficiency of intercellular propagation of mHTT. GAPDH, on its own or together with polyglutamine species, was shown to be released into the extracellular milieu mainly from dying cells as assessed by a novel enzyme immunoassay, western blotting, and ultrafiltration. The conditioned medium of cells with growing GAPDH-polyQ aggregates was toxic to naïve cells, whereas depletion of the aggregates from the medium lowered this cytotoxicity. The GAPDH component of the aggregates was found to increase their toxicity by two-fold in comparison with polyQ alone. Furthermore, GAPDH-polyQ complexes were shown to penetrate acceptor cells and to increase the capacity of polyQ to prionize its intracellular homolog containing a repeat of 25 glutamine residues. Finally, inhibitors of intracellular transport showed that polyQ-GAPDH complexes, as well as GAPDH itself, penetrated cells using clathrin-mediated endocytosis. This suggested a pivotal role of the enzyme in the intercellular transmission of Huntington disease pathogenicity. In conclusion, GAPDH occurring in complexes with polyglutamine strengthens the prion-like activity and toxicity of the migrating aggregates. Aggregating polygluatmine tracts were shown to release from the cells over-expressing mutant huntingtin in a complex with glyceraldehyde 3-phosphate dehydrogenase (GAPDH). The enzyme enhances the intracellular transport of aggregates to healthy cells, prionization of normal cellular proteins and finally cell death, thus demonstrating the pivotal role of GAPDH in the horizontal transmission of neurodegeneration.

Analysis of Potential Binding Sites of 3,5,4'-Trihydroxystilbene (Resveratrol) and trans-3,3',5,5'-Tetrahydroxy-4'-methoxystilbene (THMS) to the GAPDH Molecule Using a Computational Ligand-Docking Method: Structural and Functional Changes in GAPDH Induced by the Examined Polyphenols

The presented study analyzed potential binding sites of 3,5,4'-trihydroxystilbene (resveratrol, RSV) and its derivative, trans-3,3',5,5'-tetrahydroxy-4'-methoxystilbene (THMS) to glyceraldehyde 3-phosphate dehydrogenase (GAPDH). The effects of stilbene analogs on the structure of GAPDH were determined by fluorescence spectroscopy and ζ potential measurements. To what extent the studied compounds affect the activity of the enzyme was also assessed. A computational ligand-docking study showed that there are 11 potential binding sites of RSV and 8 such sites of THMS in the GAPDH molecule. While resveratrol does not significantly affect the activity of the dehydrogenase upon binding to it, THMS leads to approximately 10% inactivation of this enzyme. THMS has no effect on GAPDH inactivation induced by the superoxide anion radical, in contrast to resveratrol, which increases dehydrogenase inactivation.

Structural basis for regulation of stability and activity in glyceraldehyde-3-phosphate dehydrogenases. Differential scanning calorimetry and molecular dynamics

Tissue specific isoforms of human glyceraldehyde-3-phosphate dehydrogenase, somatic (GAPD) and sperm-specific (GAPDS), have been reported to display different levels of both stability and catalytic activity. Here we apply MD simulations to investigate molecular basis of this phenomenon. The protein is a tetramer where each subunit consists of two domains - catalytic and NAD-binding one. We demonstrated key residues responsible for intersubunit and interdomain interactions. Effect of several residues was studied by point mutations. Overall we considered three mutations (Glu96Gln, Glu244Gln and Asp311Asn) disrupting GAPDS-specific salt bridges. Comparison of calculated interaction energies with calorimetric enthalpies confirmed that intersubunit interactions were responsible for enhanced thermostability of GAPDS whereas interdomain interactions had indirect influence on intersubunit contacts. Mutation Asp311Asn was around 10Å far from the active center and corresponded to the closest natural substitution in the isoenzymes. MD simulations revealed that this residue had slight interaction with catalytic residues but influenced the hydrogen bond net and dynamics in active site. These effects can be responsible for a strong influence of this residue on catalytic activity. Overall, our results provide new insight into glyceraldehyde-3-phosphate dehydrogenase structure-function relationships and can be used for the engineering of mutant proteins with modified properties and for development of new inhibitors with indirect influence on the catalytic site.

The effects of endogenous non-peptide molecule isatin and hydrogen peroxide on proteomic profiling of rat brain amyloid-β binding proteins: relevance to Alzheimer's disease?

The amyloid-β peptide is considered as a key player in the development and progression of Alzheimer’s disease (AD). Although good evidence exists that amyloid-β accumulates inside cells, intracellular brain amyloid-binding proteins remain poorly characterized. Proteomic profiling of rat brain homogenates, performed in this study, resulted in identification of 89 individual intracellular amyloid-binding proteins, and approximately 25% of them were proteins that we had previously identified as specifically binding to isatin, an endogenous neuroprotector molecule. A significant proportion of the amyloid-binding proteins (more than 30%) are differentially expressed or altered/oxidatively modified in AD patients. Incubation of brain homogenates with 70 µM hydrogen peroxide significantly influenced the profile of amyloid-β binding proteins and 0.1 mM isatin decreased the number of identified amyloid-β binding proteins both in control and hydrogen peroxide treated brain homogenates. The effects of hydrogen peroxide and isatin have been confirmed in optical biosensor experiments with purified glyceraldehyde-3-phosphate dehydrogenase, one of the known crucial amyloid-β binding proteins (also identified in this study). Data obtained suggest that isatin protects crucial intracellular protein targets against amyloid binding, and possibly favors intracellular degradation of this protein via preventing formation of amyloid-β oligomers described in the literature for some isatin derivatives.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and Alzheimer's disease

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a ubiquitous enzyme that catalyzes the sixth step of glycolysis and thus, serves to break down glucose for energy production. Beyond the traditional aerobic metabolism of glucose, recent studies have highlighted additional roles played by GAPDH in non-metabolic processes, such as control of gene expression and redox post-translational modifications. Neuroproteomics have revealed high affinity interactions between GAPDH and Alzheimer's disease-associated proteins, including the β-amyloid, β-amyloid precursor protein and tau. This neuronal protein interaction may lead to impairment of the GAPDH glycolytic function in Alzheimer's disease and may be a forerunner of its participation in apoptosis. The present review examines the crucial implication of GAPDH in neurodegenerative processes and clarifies its role in apoptotic cell death.

A proteomic approach for the involvement of the GAPDH in Alzheimer disease in the blood of Moroccan FAD cases

Several articles have highlighted the potential involvement of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in neurodegeneration by showing a non-glycolytic activity of GAPDH specifically in the brains of subjects with Alzheimer's disease (AD). The novel aim of this study was to elucidate the critical role of GAPDH and its interaction with β-amyloid in the blood of Moroccan patients with familial AD (FAD) carrying presenilin mutations and in sporadic late onset AD (LOAD). Our results show a significant decrease in the activity of GAPDH in blood samples from patients with FAD as compared to sporadic cases and healthy controls. The expression level of GAPDH in brain specimens from mutant tau transgenic mice and patients with FAD was unchanged as compared to healthy controls. In contrast, the expression level of GAPDH in blood samples from mutant tau transgenic mice and patients with FAD was decreased as compared to sporadic cases and healthy controls. Moreover, there is an accumulation of β-amyloid aggregates in the blood samples of patients with FAD and an increase in amyloid fibrils in both the blood and brain samples of these patients. Our study adds new insight to previous ones by showing the involvement of GAPDH in AD, which may influence the pathogenesis of this neurodegenerative disease.

Differential expression of proteins in brain regions of Alzheimer's disease patients

Alzheimer's disease (AD), a progressive neurodegenerative disorder and the most common form of dementia and cognitive impairment is usually characterized by neuritic amyloid plaques, cerebrovascular amyloidosis and neurofibrillary tangles. In order to find out the pathological protein expression, a quantitative proteome analysis of AD hippocampus, substantia nigra and cortex was performed and the extent of protein expression variation not only in contrast to age-matched controls but also among the understudied regions was analyzed. Expression alterations of 48 proteins were observed in each region along with significant co/contra regulation of malate dehydrogenase, lactate dehydrogenase B chain, aconitate hydratase, protein NipSnap homolog 2, actin cytoplasmic 1, creatine kinase U-type and glyceraldehyde-3-phosphate dehydrogenase. These differentially expressed proteins are mainly involved in energy metabolism, cytoskeleton integration, apoptosis and several other potent cellular/molecular processes. Interaction association network analysis further confirms the close interacting relationship between the co/contra regulated differentially expressed proteins among all the three regions. Elucidation of co/contra regulation of differentially expressed proteins will be helpful to understand disease progression and functional alterations associated with AD.

Multiple binding partners

GAPDH interacts with a plethora of diverse cellular proteins. The network of interacting partners, or interactome, is presented for GAPDH with the interacting molecules grouped into specific functional and structural categories. By organizing the binding partners in this way, certain common structural features are beginning to surface, such as acidic dipeptide sequences that are found in several of these binding proteins. Additionally, the consensus sequences for target polynucleotides are being brought to light. The categories, which are presented according to function, offer an opportunity for research into the corresponding structural correlates to these interactions. Recent discoveries of interacting proteins have revealed novel relationships that are generating emerging mechanisms. Proteins that are associated with age-related neurodegenerative diseases appear to be particularly prone to binding GAPDH, suggesting that GAPDH may be playing a role in these diseases. Neurodegenerative diseases that are discussed are the conformational diseases of aging, suggesting that GAPDH may be a global sensor for cellular conformational stress. In addition to GAPDH's oxidoreductase activity, several other enzymatic functions have been discovered, including peroxidase, nitrosylase, mono-ADP-ribosylase and kinase activities.

Mitochondrial dysfunction and cellular metabolic deficiency in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder. The pathology of AD includes amyloid-β (Aβ) deposits in neuritic plaques and neurofibrillary tangles composed of hyperphosphorylated tau, as well as neuronal loss in specific brain regions. Increasing epidemiological and functional neuroimaging evidence indicates that global and regional disruptions in brain metabolism are involved in the pathogenesis of this disease. Aβ precursor protein is cleaved to produce both extracellular and intracellular Aβ, accumulation of which might interfere with the homeostasis of cellular metabolism. Mitochondria are highly dynamic organelles that not only supply the main energy to the cell but also regulate apoptosis. Mitochondrial dysfunction might contribute to Aβ neurotoxicity. In this review, we summarize the pathways of Aβ generation and its potential neurotoxic effects on cellular metabolism and mitochondrial dysfunction.

Phosphoproteome profiling of substantia nigra and cortex regions of Alzheimer's disease patients

Alzheimer's disease (AD) is the most common form of dementia and cognitive impairment usually characterized by widespread neurodegeneration throughout the association cortex, limbic system and hippocampus. Aberrant protein phosphorylation is a defining pathological hallmark of AD and implicated in the dysregulation of major cellular processes through highly dynamic and complex signaling pathways. Here in, we demonstrate 81 proteins, of 600 spots selected, unambiguously identified as phosphorylated, providing a partial phosphoproteome profile of AD substantia nigra and cortex and respective control brain regions. More importantly, abnormal phosphorylation signal intensity of nine physiologically important proteins observed can profoundly affect cell metabolism, signal transduction, cytoskeleton integration, and synaptic function and accounts for biological and morphological alterations. Our studies employed two-dimensional gel electrophoresis for protein separation, Pro-Q(®) Diamond phosphoprotein staining and electrospray ionization quadrupole time of flight tandem MS for protein identification. NetPhosk 1.0 is used for the confirmation of protein modification status as well known/putative phosphoproteins. A further insight into the links among the identified phosphoproteins and functional roles STRING 8.3, KEGG and REACTOME pathway databases were applied. The present quantitative phosphoproteomic analysis can be supportive in establishing a broad database of potential protein targets of abnormal phosphorylation in AD brain.

YajL, the prokaryotic homolog of the Parkinsonism-associated protein DJ-1, protects cells against protein sulfenylation

YajL is the closest Escherichia coli homolog of the Parkinsonism-associated protein DJ-1, a multifunctional oxidative stress response protein whose biochemical function remains unclear. We recently described the oxidative-stress-dependent aggregation of proteins in yajL mutants and the oxidative-stress-dependent formation of mixed disulfides between YajL and members of the thiol proteome. We report here that yajL mutants display increased protein sulfenic acids levels and that formation of mixed disulfides between YajL and its protein substrates in vivo is inhibited by the sulfenic acid reactant dimedone, suggesting that YajL preferentially forms disulfides with sulfenylated proteins. YajL (but not YajL(C106A)) also forms mixed disulfides in vitro with the sulfenylated form of bovine serum albumin. The YajL-serum albumin disulfides can be subsequently reduced by glutathione or dihydrolipoic acid. We also show that DJ-1 can form mixed disulfides with sulfenylated E. coli proteins and with sulfenylated serum albumin. These results suggest that YajL and possibly DJ-1 function as covalent chaperones involved in the detection of sulfenylated proteins by forming mixed disulfides with them and that these disulfides are subsequently reduced by low-molecular-weight thiols.

Housekeepers for accurate transcript expression analysis in Alzheimer's disease autopsy brain tissue

BACKGROUND

Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) is a popular technique for mRNA expression studies. Normalization to an endogenous reference transcript (housekeeper) is widely used to correct for differences in loading and RNA quality. Alzheimer's disease (AD) alters brain metabolism. The stability of housekeeper transcript expression must be carefully validated.

METHODS

qRT-PCR was used to assess eight putative housekeeper transcripts in four brain regions from 15 control, 12 AD, and 10 AD/Lewy body disease (LBD) cases.

RESULTS

RNA quality is lower in AD and AD/LBD than in controls. Frequently used housekeepers such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and β-actin had lower overall expression in AD and AD/LBD cases than in controls. RPL13 and 18S were the most stably expressed housekeepers tested. Synaptophysin and glial fibrillary acidic protein were used to evaluate normalized quantification. By using different housekeepers we confirmed that synaptophysin expression was down-regulated in AD cases, whereas glial fibrillary acidic protein expression was increased.

CONCLUSIONS

Among all candidates tested, RPL13 was the best housekeeper for qRT-PCR studies in autopsy brain tissue samples from controls and AD cases. RNA quality should be assessed and data normalized on this index as well.

Novel mechanism of Hsp70 chaperone-mediated prevention of polyglutamine aggregates in a cellular model of huntington disease

The key feature of polyglutamine aggregates accumulating in the course of Huntington disease (HD) is their resistance to protein denaturants, and to date only chaperones are proved to prevent mutant protein aggregation. It was suggested that expanded polyglutamine chains (polyQ) of mutant huntingtin are cross-linked to other proteins such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Here we clarify the roles of GAPDH and molecular chaperone Hsp70 in the formation of sodium dodecyl sulfate (SDS)-insoluble polyQ aggregates. First, the addition of pure GAPDH was found to enhance the aggregation of polyQ in a cell-free model of HD. Secondly, the immunodepletion of GAPDH dose-dependently decreased polyQ aggregation. Finally, siRNA-mediated inhibition of GAPDH protein in SK-N-SH neuroblastoma cells has also reduced the aggregation of cellular polyQ. Regulated over-expression of Hsp70 decreased the amount of GAPDH associated with SDS-insoluble polyQ aggregates. Physical association of Hsp70 and GAPDH in SK-N-SH cells was shown by reciprocal immunoprecipitation and confocal microscopy. Pure Hsp70 dose-dependently inhibited the formation of polyQ aggregates in cell-free model of HD by sequestering both GAPDH and polyQ. We demonstrated that Hsp70 binds to polyQ in adenosine triphosphate-dependent manner, which suggests that Hsp70 exerts a chaperoning activity in the course of this interaction. Binding of Hsp70 to GAPDH was nicotinamide adenine dinucleotide-dependent suggesting another type of association. Based on our findings, we conclude that Hsp70 protects cells in HD by removing/sequestering two intrinsic components of protein aggregates: the polyQ itself and GAPDH. We propose that GAPDH might be an important target for pharmacological treatment of HD and other polyglutamine expansion-related diseases.

Testis-specific glyceraldehyde-3-phosphate dehydrogenase: origin and evolution

Background

Glyceraldehyde-3-phosphate dehydrogenase (GAPD) catalyses one of the glycolytic reactions and is also involved in a number of non-glycolytic processes, such as endocytosis, DNA excision repair, and induction of apoptosis. Mammals are known to possess two homologous GAPD isoenzymes: GAPD-1, a well-studied protein found in all somatic cells, and GAPD-2, which is expressed solely in testis. GAPD-2 supplies energy required for the movement of spermatozoa and is tightly bound to the sperm tail cytoskeleton by the additional N-terminal proline-rich domain absent in GAPD-1. In this study we investigate the evolutionary history of GAPD and gain some insights into specialization of GAPD-2 as a testis-specific protein.

Results

A dataset of GAPD sequences was assembled from public databases and used for phylogeny reconstruction by means of the Bayesian method. Since resolution in some clades of the obtained tree was too low, syntenic analysis was carried out to define the evolutionary history of GAPD more precisely. The performed selection tests showed that selective pressure varies across lineages and isoenzymes, as well as across different regions of the same sequences.

Conclusions

The obtained results suggest that GAPD-1 and GAPD-2 emerged after duplication during the early evolution of chordates. GAPD-2 was subsequently lost by most lineages except lizards, mammals, as well as cartilaginous and bony fishes. In reptilians and mammals, GAPD-2 specialized to a testis-specific protein and acquired the novel N-terminal proline-rich domain anchoring the protein in the sperm tail cytoskeleton. This domain is likely to have originated by exonization of a microsatellite genomic region. Recognition of the proline-rich domain by cytoskeletal proteins seems to be unspecific. Besides testis, GAPD-2 of lizards was also found in some regenerating tissues, but it lacks the proline-rich domain due to tissue-specific alternative splicing.

On the functional diversity of glyceraldehyde-3-phosphate dehydrogenase: biochemical mechanisms and regulatory control

BACKGROUND

New studies provide evidence that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is not simply a classical glycolytic protein of little interest. Instead, it is a multifunctional protein with significant activity in a number of fundamental cell pathways. GAPDH is a highly conserved gene and protein, with a single mRNA transcribed from a unique gene. Control mechanisms must exist which regulate its functional diversity.

SCOPE OF REVIEW

This review focuses on new, timely studies defining not only its diverse activities but also those which define the regulatory mechanisms through which those functions may be controlled. The reader is referred to the author's prior review for the consideration of past reports which first indicated GAPDH multiple activities (Sirover, Biochim. Biophys. Acta 1432 (1999) 159-184.)

CONCLUSIONS

These investigations demonstrate fundamental roles of GAPDH in vivo, dynamic changes in its subcellular localization, and the importance of posttranslational modifications as well as protein:protein interactions as regulatory control mechanisms.

GENERAL SIGNIFICANCE

GAPDH is the prototype "moonlighting" protein which exhibits activities distinct from their classically identified functions. Their participation in diverse cell pathways is essential. Regulatory mechanisms exist which control those diverse activities as well as changes in their subcellular localization as a consequence of those new functions.

Oxidatively modified glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and Alzheimer's disease: many pathways to neurodegeneration

Recently, the oxidoreductase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), has become a subject of interest as more and more studies reveal a surfeit of diverse GAPDH functions, extending beyond traditional aerobic metabolism of glucose. As a result of multiple isoforms and cellular locales, GAPDH is able to come in contact with a variety of small molecules, proteins, membranes, etc., that play important roles in normal and pathologic cell function. Specifically, GAPDH has been shown to interact with neurodegenerative disease-associated proteins, including the amyloid-beta protein precursor (AbetaPP). Studies from our laboratory have shown significant inhibition of GAPDH dehydrogenase activity in Alzheimer's disease (AD) brain due to oxidative modification. Although oxidative stress and damage is a common phenomenon in the AD brain, it would seem that inhibition of glycolytic enzyme activity is merely one avenue in which AD pathology affects neuronal cell development and survival, as oxidative modification can also impart a toxic gain-of-function to many proteins, including GAPDH. In this review, we examine the many functions of GAPDH with respect to AD brain; in particular, the apparent role(s) of GAPDH in AD-related apoptotic cell death is emphasized.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

Glyceraldehyde-3-phosphate dehydrogenase tetramer dissociation and amyloid fibril formation induced by negatively charged membranes

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional enzyme related with Huntington's, Parkinson's and Alzheimer's diseases. The ability of negatively charged membranes to induce a rapid formation of GAPDH amyloid fibrils has been demonstrated, but the mechanisms by which GAPDH reaches the fibrillar state remains unclear. In this report, we describe the structural changes undergone by GAPDH at physiological pH and temperature conditions right from its interaction with acidic membranes until the amyloid fibril is formed. According to our results, the GAPDH-membrane binding induces a beta-structuring process along with a loss of quaternary structure in the enzyme. In this way, experimental evidences on the initial steps of GAPDH amyloid fibrils formation pathway are provided.