O-GlcNAcylation modulates the self-aggregation ability of the fourth microtubule-binding repeat of tau

Complicated Role of Post-translational Modification and Protease-Cleaved Fragments of Tau in Alzheimer's Disease and Other Tauopathies

Tau, a microtubule-associated protein predominantly localized in neuronal axons, plays a crucial role in promoting microtubule assembly, stabilizing their structure, and participating in axonal transport. Perturbations in tau's structure and function are implicated in the pathogenesis of neurodegenerative diseases collectively known as tauopathies, the most common disorder of which is Alzheimer's disease (AD). In tauopathies, it has been found that tau has a variety of post-translational modification (PTM) abnormalities and/or tau is cleaved into a variety of fragments by some specific proteolytic enzymes; however, the precise contributions of these abnormal modifications and fragments to disease onset and progression remain incompletely understood. Herein, we provide an overview about the involvement of distinctive abnormal tau PTMs and different tau fragments in the pathogenesis of AD and other tauopathies and discuss the involvement of proteolytic enzymes such as caspases, calpains, and asparagine endopeptidase in mediating tau cleavage while also addressing the intercellular transmission role played by tau. We anticipate that further exploration into PTMs and fragmented forms of tau will yield valuable insights for diagnostic approaches and therapeutic interventions targeting AD and other related disorders.

14-3-3ζ Participates in the Phase Separation of Phosphorylated and Glycated Tau and Modulates the Physiological and Pathological Functions of Tau

Tau plays a major role in Alzheimer's disease (AD) and several other neurodegenerative diseases. Tau undergoing liquid-liquid phase separation (LLPS) performs specific physiological functions, induces pathological processes, and contributes to neurodegeneration. Regulating Tau phase separation helps maintain physiological functions of Tau and inhibits pathological aggregation. Here, we show that the 14-3-3 zeta isoform (14-3-3ζ) participates in Tau LLPS. 14-3-3ζ can undergo co-phase separation with WT Tau, participate in and stabilize Tau droplets, and inhibit Tau droplet-driven tubulin assembly. On the other hand, 14-3-3ζ disrupts the LLPS of phosphorylated and glycated Tau, thereby inhibiting the amyloid aggregation initiated by LLPS.

Revisiting the grammar of Tau aggregation and pathology formation: how new insights from brain pathology are shaping how we study and target Tauopathies

Converging evidence continues to point towards Tau aggregation and pathology formation as central events in the pathogenesis of Alzheimer's disease and other Tauopathies. Despite significant advances in understanding the morphological and structural properties of Tau fibrils, many fundamental questions remain about what causes Tau to aggregate in the first place. The exact roles of cofactors, Tau post-translational modifications, and Tau interactome in regulating Tau aggregation, pathology formation, and toxicity remain unknown. Recent studies have put the spotlight on the wide gap between the complexity of Tau structures, aggregation, and pathology formation in the brain and the simplicity of experimental approaches used for modeling these processes in research laboratories. Embracing and deconstructing this complexity is an essential first step to understanding the role of Tau in health and disease. To help deconstruct this complexity and understand its implication for the development of effective Tau targeting diagnostics and therapies, we firstly review how our understanding of Tau aggregation and pathology formation has evolved over the past few decades. Secondly, we present an analysis of new findings and insights from recent studies illustrating the biochemical, structural, and functional heterogeneity of Tau aggregates. Thirdly, we discuss the importance of adopting new experimental approaches that embrace the complexity of Tau aggregation and pathology as an important first step towards developing mechanism- and structure-based therapies that account for the pathological and clinical heterogeneity of Alzheimer's disease and Tauopathies. We believe that this is essential to develop effective diagnostics and therapies to treat these devastating diseases.

Regulation of liquid-liquid phase separation with focus on post-translational modifications

Liquid-liquid phase separation (LLPS), a type of phase transition that is important in organisms, is a unique means of forming biomolecular condensates. LLPS plays a significant role in transcription, genome organisation, immune response and cell signaling, and its dysregulation may cause neurodegenerative diseases and cancers. Exploring the regulatory mechanism of LLPS contributes to the understanding of the pathogenic mechanism of abnormal phase transition and enables potential therapeutic targets to be proposed. Many factors have been found to regulate LLPS, of which post-translational modification (PTM) is among the most important. PTMs can change the structure, charge, hydrophobicity and other properties of the proteins involved in phase separation and thereby affect the phase transition behaviour. In this review, we discuss LLPS and the regulatory effects of PTMs, RNA and molecular chaperones in a phase separation system. We introduce several common PTMs (including phosphorylation, arginine methylation, arginine citrullination, acetylation, ubiquitination and poly(ADP-ribosyl)ation), highlight recent advances regarding their roles in LLPS and describe the regulatory mechanisms behind these features. This review provides a detailed overview of the field that will help further the understanding of and interventions in LLPS.

Tau Protein Interaction Partners and Their Roles in Alzheimer's Disease and Other Tauopathies

Tau protein plays a critical role in the assembly, stabilization, and modulation of microtubules, which are important for the normal function of neurons and the brain. In diseased conditions, several pathological modifications of tau protein manifest. These changes lead to tau protein aggregation and the formation of paired helical filaments (PHF) and neurofibrillary tangles (NFT), which are common hallmarks of Alzheimer's disease and other tauopathies. The accumulation of PHFs and NFTs results in impairment of physiological functions, apoptosis, and neuronal loss, which is reflected as cognitive impairment, and in the late stages of the disease, leads to death. The causes of this pathological transformation of tau protein haven't been fully understood yet. In both physiological and pathological conditions, tau interacts with several proteins which maintain their proper function or can participate in their pathological modifications. Interaction partners of tau protein and associated molecular pathways can either initiate and drive the tau pathology or can act neuroprotective, by reducing pathological tau proteins or inflammation. In this review, we focus on the tau as a multifunctional protein and its known interacting partners active in regulations of different processes and the roles of these proteins in Alzheimer's disease and tauopathies.

Phosphorylation-Induced Structural Reorganization in Tau-Paired Helical Filaments

Taupathies involve the deposition of abnormal tau protein into neurofibrillary tangles (NFTs) in the human brain. The abnormally hyperphosphorylated tau dissociates from microtubules and forms insoluble aggregates known as paired helical filaments (PHFs), highlighting the importance of post-translational modifications in taupathies. The present study examines the factors responsible for the structural stability of PHFs in native as well as in phosphorylated and O-GlcNAcylated tau. We carried out molecular dynamics simulations on the R3-R4 repeat domains of the human tau protein to gain atomic insights into the key noncovalent interactions responsible for their unique dimeric C-shaped structure. The structural effects upon post-translational modification were found to be prominent for phosphorylation when compared with O-GlcNAcylation. O-GlcNAcylated tau was found to retain the "C conformation" observed in the native tau PHF, whereas upon phosphorylation, we observed a conformational transition to a more opened "H conformation". We found that this conformational transition is brought about by the loss of a key salt bridge between Lys353 and Asp358 due to the phosphorylation at Ser356 that results in the reorganization of the dimeric interface.

Capturing protein droplets: label-free visualization and detection of protein liquid-liquid phase separation with an aggregation-induced emission fluorogen

We developed a new method for protein droplet visualization by means of a droplet probe (DroProbe) based on an aggregation-induced emission (AIE) fluorogen. A simple method for viscosity comparison of the protein condensed phase based on the lifetime of the DroProbe was also developed.

Chemical Synthesis and Biological Applications of O-GlcNAcylated Peptides and Proteins

All human cells use O-GlcNAc protein modifications (O-linked N-acetylglucosamine) to rapidly adapt to changing nutrient and stress conditions through signaling, epigenetic, and proteostasis mechanisms. A key challenge for biologists in defining precise roles for specific O-GlcNAc sites is synthetic access to homogenous isoforms of O-GlcNAc proteins, a result of the non-genetically templated, transient, and heterogeneous nature of O-GlcNAc modifications. Toward a solution, this review details the state of the art of two strategies for O-GlcNAc protein modification: advances in "bottom-up" O-GlcNAc peptide synthesis and direct "top-down" installation of O-GlcNAc on full proteins. We also describe key applications of synthetic O-GlcNAc peptide and protein tools as therapeutics, biophysical structure-function studies, biomarkers, and as disease mechanistic probes to advance translational O-GlcNAc biology.

Tau Post-translational Modifications: Dynamic Transformers of Tau Function, Degradation, and Aggregation

Post-translational modifications (PTMs) on tau have long been recognized as affecting protein function and contributing to neurodegeneration. The explosion of information on potential and observed PTMs on tau provides an opportunity to better understand these modifications in the context of tau homeostasis, which becomes perturbed with aging and disease. Prevailing views regard tau as a protein that undergoes abnormal phosphorylation prior to its accumulation into the toxic aggregates implicated in Alzheimer's disease (AD) and other tauopathies. However, the phosphorylation of tau may, in fact, represent part of the normal but interrupted function and catabolism of the protein. In addition to phosphorylation, tau undergoes another forms of post-translational modification including (but not limited to), acetylation, ubiquitination, glycation, glycosylation, SUMOylation, methylation, oxidation, and nitration. A holistic appreciation of how these PTMs regulate tau during health and are potentially hijacked in disease remains elusive. Recent studies have reinforced the idea that PTMs play a critical role in tau localization, protein-protein interactions, maintenance of levels, and modifying aggregate structure. These studies also provide tantalizing clues into the possibility that neurons actively choose how tau is post-translationally modified, in potentially competitive and combinatorial ways, to achieve broad, cellular programs commensurate with the distinctive environmental conditions found during development, aging, stress, and disease. Here, we review tau PTMs and describe what is currently known about their functional impacts. In addition, we classify these PTMs from the perspectives of protein localization, electrostatics, and stability, which all contribute to normal tau function and homeostasis. Finally, we assess the potential impact of tau PTMs on tau solubility and aggregation. Tau occupies an undoubtedly important position in the biology of neurodegenerative diseases. This review aims to provide an integrated perspective of how post-translational modifications actively, purposefully, and dynamically remodel tau function, clearance, and aggregation. In doing so, we hope to enable a more comprehensive understanding of tau PTMs that will positively impact future studies.

Late-stage peptide and protein modifications through phospha-Michael addition reaction

We developed a late-stage modification strategy by a phospha-Michael addition reaction between various functional phosphines and unprotected dehydroalanine (Dha) peptides and proteins under mild conditions. This strategy was applied to generate a staple peptide to enhance its cell membrane penetrability, and it was also able to regulate α-synuclein aggregation properties and morphological characteristics with the addition of different charges.

Prebiotic Peptides: Molecular Hubs in the Origin of Life

The fundamental roles that peptides and proteins play in today's biology makes it almost indisputable that peptides were key players in the origin of life. Insofar as it is appropriate to extrapolate back from extant biology to the prebiotic world, one must acknowledge the critical importance that interconnected molecular networks, likely with peptides as key components, would have played in life's origin. In this review, we summarize chemical processes involving peptides that could have contributed to early chemical evolution, with an emphasis on molecular interactions between peptides and other classes of organic molecules. We first summarize mechanisms by which amino acids and similar building blocks could have been produced and elaborated into proto-peptides. Next, non-covalent interactions of peptides with other peptides as well as with nucleic acids, lipids, carbohydrates, metal ions, and aromatic molecules are discussed in relation to the possible roles of such interactions in chemical evolution of structure and function. Finally, we describe research involving structural alternatives to peptides and covalent adducts between amino acids/peptides and other classes of molecules. We propose that ample future breakthroughs in origin-of-life chemistry will stem from investigations of interconnected chemical systems in which synergistic interactions between different classes of molecules emerge.

Tryptophan–glucosamine conjugates modulate tau-derived PHF6 aggregation at low concentrations

Tryptophan–glucosamine conjugates efficiently inhibit tau-derived PHF6-peptide fibrillization and disrupt its preformed fibrils at very low concentrations.

It's all about tau

Tau is a protein that is highly enriched in neurons and was originally defined by its ability to bind and stabilize microtubules. However, it is now becoming evident that the functions of tau extend beyond its ability to modulate microtubule dynamics. Tau plays a role in mediating axonal transport, synaptic structure and function, and neuronal signaling pathways. Although tau plays important physiological roles in neurons, its involvement in neurodegenerative diseases, and most prominently in the pathogenesis of Alzheimer disease (AD), has directed the majority of tau studies. However, a thorough knowledge of the physiological functions of tau and its post-translational modifications under normal conditions are necessary to provide the foundation for understanding its role in pathological settings. In this review, we will focus on human tau, summarizing tau structure and organization, as well as its posttranslational modifications associated with physiological processes. We will highlight possible mechanisms involved in mediating the turnover of tau and finally discuss newly elucidated tau functions in a physiological context.

Implications of PI3K/AKT/PTEN Signaling on Superoxide Dismutases Expression and in the Pathogenesis of Alzheimer's Disease

Alzheimer’s disease is a neurodegenerative sickness, where the speed of personal disease progression differs prominently due to genetic and environmental factors such as life style. Alzheimer’s disease is described by the construction of neuronal plaques and neurofibrillary tangles composed of phosphorylated tau protein. Mitochondrial dysfunction may be a noticeable feature of Alzheimer’s disease and increased production of reactive oxygen species has long been described. Superoxide dismutases (SODs) protect from excess reactive oxygen species to form less reactive hydrogen peroxide. It is suggested that SODs can play a protective role in neurodegeneration. In addition, PI3K/AKT pathway has been shown to play a critical role on the neuroprotection and inhibiting apoptosis via the enhancing expression of the SODs. This pathway appears to be crucial in Alzheimer’s disease because it is related to the tau protein hyper-phosphorylation. Dietary supplementation of several ordinary compounds may provide a novel therapeutic approach to brain disorders by modulating the function of the PI3K/AKT pathway. Understanding these systems may offer a better efficacy of new therapeutic approaches. In this review, we summarize recent progresses on the involvement of the SODs and PI3K/AKT pathway in neuroprotective signaling against Alzheimer’s disease.

Amyloidogenesis of Tau protein

The role of microtubule-associated protein Tau in neurodegeneration has been extensively investigated since the discovery of Tau amyloid aggregates in the brains of patients with Alzheimer's disease (AD). The process of formation of amyloid fibrils is known as amyloidogenesis and attracts much attention as a potential target in the prevention and treatment of neurodegenerative conditions linked to protein aggregation. Cerebral deposition of amyloid aggregates of Tau is observed not only in AD but also in numerous other tauopathies and prion diseases. Amyloidogenesis of intrinsically unstructured monomers of Tau can be triggered by mutations in the Tau gene, post-translational modifications, or interactions with polyanionic molecules and aggregation-prone proteins/peptides. The self-assembly of amyloid fibrils of Tau shares a number of characteristic features with amyloidogenesis of other proteins involved in neurodegenerative diseases. For example, in vitro experiments have demonstrated that the nucleation phase, which is the rate-limiting stage of Tau amyloidogenesis, is shortened in the presence of fragmented preformed Tau fibrils acting as aggregation templates ("seeds"). Accordingly, Tau aggregates released by tauopathy-affected neurons can spread the neurodegenerative process in the brain through a prion-like mechanism, originally described for the pathogenic form of prion protein. Moreover, Tau has been shown to form amyloid strains-structurally diverse self-propagating aggregates of potentially various pathological effects, resembling in this respect prion strains. Here, we review the current literature on Tau aggregation and discuss mechanisms of propagation of Tau amyloid in the light of the prion-like paradigm.

Roles of O-GlcNAc in chronic diseases of aging

O-GlcNAcylation, a dynamic nutrient and stress sensitive post-translational modification, occurs on myriad proteins in the cell nucleus, cytoplasm and mitochondria. O-GlcNAcylation serves as a nutrient sensor to regulate signaling, transcription, translation, cell division, metabolism, and stress sensitivity in all cells. Aberrant protein O-GlcNAcylation plays a critical role both in the development, as well as in the progression of a variety of age related diseases. O-GlcNAcylation underlies the etiology of diabetes, and changes in specific protein O-GlcNAc levels and sites are responsible for insulin expression and sensitivity and glucose toxicity. Abnormal O-GlcNAcylation contributes directly to diabetes related dysfunction of the heart, kidney and eyes and affects progression of cardiomyopathy, nephropathy and retinopathy. O-GlcNAcylation is a critical modification in the brain and plays a role in both plaque and tangle formation, thus making its study important in neurodegenerative disorders. O-GlcNAcylation also affects cellular growth and metabolism during the development and metastasis of cancer. Finally, alterations in O-GlcNAcylation of transcription factors in macrophages and lymphocytes affect inflammation and cytokine production. Thus, O-GlcNAcylation plays key roles in many of the major diseases associated with aging. Elucidation of its specific functions in both normal and diseased tissues is likely to uncover totally novel avenues for therapeutic intervention.

O-GlcNAcylation: A regulator of tau pathology and neurodegeneration

O-GlcNAcylation is the posttranslational modification of intracellular proteins by O-linked β-N-acetylglucosamine (O-GlcNAc). The discovery of O-GlcNAc modification of tau and its impact on tau phosphorylation has attracted recent research interest in O-GlcNAc studies in the Alzheimer's disease (AD) field. Modification of proteins by O-GlcNAc occurs extensively in the brain. The expressions and activities of the enzymes catalyzing O-GlcNAc cycling are several-fold higher in the brain than in the peripheral tissues. The O-GlcNAcylation levels of brain proteins including tau are decreased in AD brain, probably due to decreased brain glucose metabolism. The reduction of brain O-GlcNAcylation appears to mediate the molecular mechanism by which decreased brain glucose metabolism contributes to neurodegeneration. Studies on mouse models of tauopathies suggest a neuroprotective role of pharmacological elevation of brain O-GlcNAc, which could potentially be a promising approach for treating AD and other neurodegenerative diseases.

Invited review: Drug development for tauopathies

Many different approaches to treating tauopathies are currently being explored, with a few compounds already in clinical development (including small molecules such as anti-aggregation compound LMTX and active vaccines AADvac1 and ACI-35). This review aims to summarize the status of the clinical candidates and to highlight the emerging areas of research that hold promise for drug development. Tau is post-translationally modified in several different ways (phosphorylated, acetylated, glycosylated and truncated). The extent of these modifications can be manipulated to influence tau aggregation state and pathogenesis and the enzymes involved provide tractable targets for drug intervention. In addition, modulation of tau expression levels is an attractive therapeutic approach. Finally, the recently described prion-like spreading of tau between cells opens up novel avenues from the tau drug development perspective. The review compares the merits of small-molecule and antibody-based therapies and emphasizes the need for amenable clinical biomarkers for drug development, particularly PET imaging.

Cellular factors modulating the mechanism of tau protein aggregation

Pathological accumulation of the microtubule-associated protein tau, in the form of neurofibrillary tangles, is a major hallmark of Alzheimer's disease, the most prevalent neurodegenerative condition worldwide. In addition to Alzheimer's disease, a number of neurodegenerative diseases, called tauopathies, are characterized by the accumulation of aggregated tau in a variety of brain regions. While tau normally plays an important role in stabilizing the microtubule network of the cytoskeleton, its dissociation from microtubules and eventual aggregation into pathological deposits is an area of intense focus for therapeutic development. Here we discuss the known cellular factors that affect tau aggregation, from post-translational modifications to molecular chaperones.

Alzheimer disease therapeutics: focus on the disease and not just plaques and tangles

The bulk of AD research during the last 25 years has been Aβ-centric based on a strong faith in the Amyloid Cascade Hypothesis which is not supported by the data on humans. To date, Aβ-based therapeutic clinical trials on sporadic cases of AD have been negative. Although most likely the major reason for the failure is that Aβ is not an effective therapeutic target for sporadic AD, initiation of the treatment at mild to moderate stages of the disease is blamed as too late to be effective. Clinical trials on presymptomatic familial AD cases have been initiated with the logic that Aβ is a trigger of the disease and hence initiation of the Aβ immunotherapies several years before any clinical symptoms would be effective. There is an urgent need to explore targets other than Aβ. There is now increasing interest in inhibiting tau pathology, which does have a far more compelling rationale than Aβ. AD is multifactorial and over 99% of the cases are the sporadic form of the disease. Understanding of the various etiopathogenic mechanisms of sporadic AD and generation of the disease-relevant animal models are required to develop rational therapeutic targets and therapies. Treatment of AD will require both inhibition of neurodegeneration and regeneration of the brain.

Increasing brain protein O-GlcNAc-ylation mitigates breathing defects and mortality of Tau.P301L mice

The microtubule associated protein tau causes primary and secondary tauopathies by unknown molecular mechanisms. Post-translational O-GlcNAc-ylation of brain proteins was demonstrated here to be beneficial for Tau.P301L mice by pharmacological inhibition of O-GlcNAc-ase. Chronic treatment of ageing Tau.P301L mice mitigated their loss in body-weight and improved their motor deficits, while the survival was 3-fold higher at the pre-fixed study endpoint at age 9.5 months. Moreover, O-GlcNAc-ase inhibition significantly improved the breathing parameters of Tau.P301L mice, which underpinned pharmacologically the close correlation of mortality and upper-airway defects. O-GlcNAc-ylation of brain proteins increased rapidly and stably by systemic inhibition of O-GlcNAc-ase. Conversely, biochemical evidence for protein Tau.P301L to become O-GlcNAc-ylated was not obtained, nor was its phosphorylation consistently or markedly affected. We conclude that increasing O-GlcNAc-ylation of brain proteins improved the clinical condition and prolonged the survival of ageing Tau.P301L mice, but not by direct biochemical action on protein tau. The pharmacological effect is proposed to be located downstream in the pathological cascade initiated by protein Tau.P301L, opening novel venues for our understanding, and eventually treating the neurodegeneration mediated by protein tau.

Increased O-GlcNAcylation reduces pathological tau without affecting its normal phosphorylation in a mouse model of tauopathy

Neurofibrillary tangles (NFT), mainly consisting of fibrillar aggregates of hyperphosphorylated tau, are a defining pathological feature of Alzheimer's Disease and other tauopathies. Progressive accumulation of tau into NFT is considered to be a toxic cellular event causing neurodegeneration. Tau is subject to O-linked N-acetylglucosamine (O-GlcNAc) modification and O-GlcNAcylation of tau has been suggested to regulate tau phosphorylation. We tested if an increase in tau O-GlcNAcylation affected tau phosphorylation and aggregation in the rTg4510 tau transgenic mouse model. Acute treatment of rTg4510 mice with an O-GlcNAcase inhibitor transiently reduced tau phosphorylation at epitopes implicated in tau pathology. More importantly, long-term inhibitor treatment strongly increased tau O-GlcNAcylation, reduced the number of dystrophic neurons, and protected against the formation of pathological tau species without altering the phosphorylation of non-pathological tau. This indicates that O-GlcNAcylation prevents the aggregation of tau in a manner that does not affect its normal phosphorylation state. Collectively, our results support O-GlcNAcase inhibition as a potential therapeutic strategy for the treatment of Alzheimer's Disease and other tauopathies.

Hyperphosphorylation-induced tau oligomers

In normal adult brain the microtubule associated protein (MAP) tau contains 2-3 phosphates per mol of the protein and at this level of phosphorylation it is a soluble cytosolic protein. The normal brain tau interacts with tubulin and promotes its assembly into microtubules and stabilizes these fibrils. In Alzheimer disease (AD) brain tau is three to fourfold hyperphosphorylated. The abnormally hyperphosphorylated tau binds to normal tau instead of the tubulin and this binding leads to the formation of tau oligomers. The tau oligomers can be sedimented at 200,000 × g whereas the normal tau under these conditions remains in the supernatant. The abnormally hyperphosphorylated tau is capable of sequestering not only normal tau but also MAP MAP1 and MAP2 and causing disruption of the microtubule network promoted by these proteins. Unlike Aβ and prion protein (PrP) oligomers, tau oligomerization in AD and related tauopathies is hyperphosphorylation-dependent; in vitro dephosphorylation of AD P-tau with protein phosphatase 2A (PP2A) inhibits and rehyperphosphorylation of the PP2A-AD P-tau with more than one combination of tau protein kinases promotes its oligomerization. In physiological assembly conditions the AD P-tau readily self-assembles into paired helical filaments. Missense tau mutations found in frontotemporal dementia apparently lead to tau oligomerization and neurofibrillary pathology by promoting its abnormal hyperphosphorylation. Dysregulation of the alternative splicing of tau that alters the 1:1 ratio of the 3-repeat: 4-repeat taus such as in Down syndrome, Pick disease, and progressive supranuclear palsy leads to the abnormal hyperphosphorylation of tau.

Cell signaling, post-translational protein modifications and NMR spectroscopy

Post-translationally modified proteins make up the majority of the proteome and establish, to a large part, the impressive level of functional diversity in higher, multi-cellular organisms. Most eukaryotic post-translational protein modifications (PTMs) denote reversible, covalent additions of small chemical entities such as phosphate-, acyl-, alkyl- and glycosyl-groups onto selected subsets of modifiable amino acids. In turn, these modifications induce highly specific changes in the chemical environments of individual protein residues, which are readily detected by high-resolution NMR spectroscopy. In the following, we provide a concise compendium of NMR characteristics of the main types of eukaryotic PTMs: serine, threonine, tyrosine and histidine phosphorylation, lysine acetylation, lysine and arginine methylation, and serine, threonine O-glycosylation. We further delineate the previously uncharacterized NMR properties of lysine propionylation, butyrylation, succinylation, malonylation and crotonylation, which, altogether, define an initial reference frame for comprehensive PTM studies by high-resolution NMR spectroscopy.

Tau oligomers and aggregation in Alzheimer's disease

We are analyzing the physiological function of Tau protein and its abnormal pathological behavior when this protein is self-assemble into pathological filaments. These aggregates of Tau protein are the main components in many diseases such as Alzheimer's disease (AD). Recent studies suggest that Tau acquires complex oligomeric conformations which may be toxic. In this review, we emphasized the possible phenomena implicated in the formation of these oligomers. Studies with chemical inductors indicates that the microtubule-binding domain is the most important region involved in Tau aggregation and showed the requirement of a pre-arrange Tau in abnormal conformation to promote self-assembly. Transgenic animal models and AD neuropathology studies showed that post-translational modifications are also implicated in Tau aggregation and neural cell death during AD development. Therefore, we analyzed some events that could be present during Tau aggregation. Finally, we included a brief discussion of the possible relation between glucose metabolism dysfunction in AD, and data of Tau aggregation by using aggregation inhibitors. In conclusion, the process Tau aggregation deserves further investigations to design possible therapeutic targets to inhibit the toxicity of these aggregates and it is possible that could be extended to other diseases with similar etiology.