Post-translational Modifications Of Α-synuclein Research Articles

Posttranslational Modifications of α-Synuclein, Their Therapeutic Potential, and Crosstalk in Health and Neurodegenerative Diseases.

α-Synuclein (α-Syn) aggregation in Lewy bodies and Lewy neurites has emerged as a key pathogenetic feature in Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Various factors, including posttranslational modifications (PTMs), can influence the propensity of α-Syn to misfold and aggregate. PTMs are biochemical modifications of a protein that occur during or after translation and are typically mediated by enzymes. PTMs modulate several characteristics of proteins including their structure, activity, localization, and stability. α-Syn undergoes various posttranslational modifications, including phosphorylation, ubiquitination, SUMOylation, acetylation, glycation, O-GlcNAcylation, nitration, oxidation, polyamination, arginylation, and truncation. Different PTMs of a protein can physically interact with one another or work together to influence a particular physiological or pathological feature in a process known as PTMs crosstalk. The development of detection techniques for the cooccurrence of PTMs in recent years has uncovered previously unappreciated mechanisms of their crosstalk. This has led to the emergence of evidence supporting an association between α-Syn PTMs crosstalk and synucleinopathies. In this review, we provide a comprehensive evaluation of α-Syn PTMs, their impact on misfolding and pathogenicity, the pharmacological means of targeting them, and their potential as biomarkers of disease. We also highlight the importance of the crosstalk between these PTMs in α-Syn function and aggregation. Insight into these PTMS and the complexities of their crosstalk can improve our understanding of the pathogenesis of synucleinopathies and identify novel targets of therapeutic potential. SIGNIFICANCE STATEMENT: α-Synuclein is a key pathogenic protein in Parkinson's disease and other synucleinopathies, making it a leading therapeutic target for disease modification. Multiple posttranslational modifications occur at various sites in α-Synuclein and alter its biophysical and pathological properties, some interacting with one another to add to the complexity of the pathogenicity of this protein. This review details these modifications, their implications in disease, and potential therapeutic opportunities.

An Examination of Post-translational Modifications of α-synuclein and its Effects on Parkinson's disease

Parkinson’s disease (PD) is the second most common degenerative disease of the central nervous system. PD affects millions of people worldwide, so it is critical to research and understand Parkinson’s disease to better help those affected. The exact cause and pathogenesis of PD is unknown, but the aggregation of α-Synuclein into Lewy bodies has been associated with PD. a-Synuclein often goes through post-translational modifications (PTMs). PTMs can affect the shape, localization, function, and activity of proteins like a-Synuclein. PTMs of a-Synuclein can also affect how the protein aggregates. PTMs of α-Synuclein can play a big role in the pathogenesis of PD, and understanding how PTMs affect α-Synuclein is critical in helping forward research that focuses on PD. This paper discusses the effects of various PTMs on α-Synuclein and how they affect the pathogenesis of Parkinson’s Disease.

Truncation or proteolysis of α-synuclein in Parkinsonism.

Posttranslational modifications of α-synuclein, such as truncation or abnormal proteolysis, are implicated in Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). A key focus of this article includes the proteases responsible for inducing truncation, the specific sites susceptible to truncation, and the resultant influence of these truncated species on the seeding and aggregation of endogenous α-synuclein. We also shed light on the unique structural attributes of these truncated species, and how these modifications can lead to distinctive forms of synucleinopathies. In addition, we explore the comparative toxic potentials of various α-synuclein species. An extensive analysis of available evidence of truncated α-synuclein species in human-synucleinopathy brains is also provided. Lastly, we delve into the detrimental impact of truncated species on key cellular structures such as the mitochondria and endoplasmic reticulum. Our article discusses enzymes involved in α-synuclein truncation, including 20S proteasome, cathepsins, asparagine endopeptidase, caspase-1, calpain-1, neurosin/kallikrein-6, matrix metalloproteinase-1/-3, and plasmin. Truncation patterns impact α-synuclein aggregation - C-terminal truncation accelerates aggregation with larger truncations correlated with shortened aggregation lag times. N-terminal truncation affects aggregation differently based on the truncation location. C-terminally truncated α-synuclein forms compact, shorter fibrils compared to the full-length (FL) protein. N-terminally truncated monomers form fibrils similar in length to FL α-synuclein. Truncated forms show distinct fibril morphologies, increased β-sheet structures, and greater protease resistance. Misfolded α-synuclein can adopt various conformations, leading to unique aggregates and distinct synucleinopathies. Fibrils, with prion-like transmission, are potentially more toxic than oligomers, though this is still debated. Different α-synuclein variants with N- and C-terminal truncations, namely 5-140, 39-140, 65-140, 66-140, 68-140, 71-140, 1-139, 1-135, 1-133, 1-122, 1-119, 1-115, 1-110, and 1-103 have been found in PD, DLB, and MSA patients' brains. In Parkinsonism, excess misfolded α-synuclein overwhelms the proteasome degradation system, resulting in truncated protein production and accumulation in the mitochondria and endoplasmic reticulum.

Probing the effects of N-terminal acetylation on α-synuclein structure, aggregation and cytotoxicity.

Parkinson's disease is associated with the aberrant aggregation of α-synuclein within brain cells. Although the causes of this process are still unclear, post-translational modifications of α-synuclein are likely to play a modulatory role. Since α-synuclein is constitutively N-terminally acetylated, we previously investigated how this protein modification affects the aggregation behavior of the protein using a variety of methods in vitro and in cell systems. This chapter describes the production of N-terminally acetylated (NTA) α-synuclein, the preparation of different seeds of NTA α-synuclein for aggregation assays and the experimental methods for the kinetic analysis of the aggregation process of NTA α-synuclein. We also detail our protocol to evaluate the effects of preformed protofibrils of NTA α-synuclein in cell-based assays. These methods can be applied to study other post-translational modifications of α-synuclein, or adapted for the study of N-acetylation of other aggregation-prone proteins.

Post-translational modification of lysine residues in erythrocyte α-synuclein.

α-Synuclein is a protein linked to various synuclein-associated diseases ('synucleinopathies'), including Parkinson's disease, dementia with Lewy Bodies and multiple system atrophy, and is highly expressed in the central nervous system and in erythrocytes. Moreover, α-synuclein-containing erythrocyte-derived extracellular vesicles may be involved in the pathogenesis of synucleinopathies and their progression across the blood-brain barrier. Several post-translational modifications of α-synuclein have been reported in brain inclusions, including S129 phosphorylation, but fewer have been found in erythrocytes. In this study, we analysed the post-translational modifications of erythrocyte α-synuclein using liquid chromatography-mass spectrometry. We found that all lysine residues in the α-synuclein protein could be modified by acetylation, glycation, ubiquitination or SUMOylation but that phosphorylation, nitration and acylation were uncommon minor post-translational modifications in erythrocytes. Since the post-translational modification of lysine residues has been implicated in both membrane association and protein clearance, our findings provide new insight into how synucleinopathies may progress and suggest possible therapeutic strategies designed to target α-synuclein.

N-Terminal Acetylation of α-Synuclein Slows down Its Aggregation Process and Alters the Morphology of the Resulting Aggregates.

Parkinson’s disease is associated with the aberrant aggregation of α-synuclein. Although the causes of this process are still unclear, post-translational modifications of α-synuclein are likely to play a modulatory role. Since α-synuclein is constitutively N-terminally acetylated, we investigated how this post-translational modification alters the aggregation behavior of this protein. By applying a three-pronged aggregation kinetics approach, we observed that N-terminal acetylation results in a reduced rate of lipid-induced aggregation and slows down both elongation and fibril-catalyzed aggregate proliferation. An analysis of the amyloid fibrils produced by the aggregation process revealed different morphologies for the acetylated and non-acetylated forms in both lipid-induced aggregation and seed-induced aggregation assays. In addition, we found that fibrils formed by acetylated α-synuclein exhibit a lower β-sheet content. These findings indicate that N-terminal acetylation of α-synuclein alters its lipid-dependent aggregation behavior, reduces its rate of in vitro aggregation, and affects the structural properties of its fibrillar aggregates.

Reduction of phosphorylated α-synuclein through downregulation of casein kinase 2α alleviates dopaminergic-neuronal function

Among the post-translational modifications of α-synuclein, phosphorylation has been reported to modulate the protein's nuclear localization, gene-expression and cytotoxicity. However, its effect on the functional performance of dopaminergic-neurons is not known. We aimed to evaluate the effect of siRNA-silencing of casein kinase (CK)2α in SH-SY5Y-cells overexpressing A53T α-synuclein, in alleviating phosphorylated α-synuclein serine129 (pSyn-129)-induced changes in intracellular Ca2+ ([Ca2+]i) response to physiological stimuli and vesicular-dopamine release. A53T transfection showed distinct increase in basal pSyn-129 expression with simultaneous nuclear localization, and CK2α siRNA decreased ROS-generation and pSyn-129 levels. A significant reduction was observed in KCl-induced ([Ca2+]i) response and vesicular-dopamine release in the A53T-transfected cells with a corresponding decrease in immunopositive-population of resting-vesicles (VMAT2). CK2α siRNA treatment showed recovery in [Ca2+]i rise with a corresponding upregulation of expression of voltage-gated Ca2+-channels (VGCC) CaV1.3 and CaV2.2 and RyR1 responsible for Ca2+ induced Ca2+ release from ER, VMAT2 expression and vesicular-dopamine release. Thus, using CK2α siRNA to reduce phosphorylation improved cellular-pathology in terms of ROS generation and pSyn-129 levels, as well as functional performance of DA-neuronal cells.

ChemInform Abstract: Breaking the Limits of Artificial Ubiquitination

Neurodegenerative diseases such as Parkinson, Alzheimer’s, and Huntington are proteopathic disorders characterized by the accumulation of intracellular insoluble aggregates of misfolded proteins and are one of the major medical concerns of our modern society. Particularly, Parkinson disease is a synucleinopathy caused by the cytosolic aggregation of α-Synuclein into Lewy bodies (1). Although its biological function remains obscure, numerous lines of evidence clearly point at α-Synuclein oligomers or aggregates as the causative agent of Parkinson disease (1). However, despite intense research, the detailed etiology of Parkinson disease remains elusive. Apart from missense point mutations in the α-Synuclein gene (which account for familial cases of early onset Parkinson disease), increased intracellular expression levels and posttranslational modifications of α-Synuclein have been implicated in the formation of Lewy bodies. Currently, known modifications of α-Synuclein include proteolytic truncation, oxidation, nitration, phosphorylation, and ubiquitination (1). The key to understanding proteopathic diseases such as Parkinson disease rests on elucidating the role of these modifications and how they influence the properties of the nascent α-Synuclein polypeptide. In their current research article, Haj-Yahya et al. report on an important milestone in the synthesis of selectively di- and tetra-ubiquitinated (K48) α-Synuclein, which can be used to study the biophysical and biochemical consequences of α-Synuclein ubiquitination (2). In addition to offering valuable insights into molecular biology of synucleinopathies, their findings also open up new horizons in the research on ubiquitination—a crucial posttranslational protein modification involved in quintessential aspects of cell biology (3). Ubiquitin is a small protein of 76 amino acids and is highly conserved among all eukaryotic organisms. Ubiquitin … [↵][1]1To whom correspondence should be addressed. Email: dikic{at}biochem2.uni-frankfurt.de. [1]: #xref-corresp-1-1

Breaking the limits of artificial ubiquitination

Neurodegenerative diseases such as Parkinson, Alzheimer’s, and Huntington are proteopathic disorders characterized by the accumulation of intracellular insoluble aggregates of misfolded proteins and are one of the major medical concerns of our modern society. Particularly, Parkinson disease is a synucleinopathy caused by the cytosolic aggregation of α-Synuclein into Lewy bodies (1). Although its biological function remains obscure, numerous lines of evidence clearly point at α-Synuclein oligomers or aggregates as the causative agent of Parkinson disease (1). However, despite intense research, the detailed etiology of Parkinson disease remains elusive. Apart from missense point mutations in the α-Synuclein gene (which account for familial cases of early onset Parkinson disease), increased intracellular expression levels and posttranslational modifications of α-Synuclein have been implicated in the formation of Lewy bodies. Currently, known modifications of α-Synuclein include proteolytic truncation, oxidation, nitration, phosphorylation, and ubiquitination (1). The key to understanding proteopathic diseases such as Parkinson disease rests on elucidating the role of these modifications and how they influence the properties of the nascent α-Synuclein polypeptide. In their current research article, Haj-Yahya et al. report on an important milestone in the synthesis of selectively di- and tetra-ubiquitinated (K48) α-Synuclein, which can be used to study the biophysical and biochemical consequences of α-Synuclein ubiquitination (2). In addition to offering valuable insights into molecular biology of synucleinopathies, their findings also open up new horizons in the research on ubiquitination—a crucial posttranslational protein modification involved in quintessential aspects of cell biology (3). Ubiquitin is a small protein of 76 amino acids and is highly conserved among all eukaryotic organisms. Ubiquitin … [↵][1]1To whom correspondence should be addressed. Email: dikic{at}biochem2.uni-frankfurt.de. [1]: #xref-corresp-1-1

Recent Advances in α-Synuclein Functions, Advanced Glycation, and Toxicity: Implications for Parkinson’s Disease

The toxicity of α-synuclein in the neuropathology of Parkinson's disease which includes its hallmark aggregation has been studied scrupulously in the last decade. Although little is known regarding the normal functions of α-synuclein, its association with membrane phospholipids suggests its potential role in signaling pathways. Following extensive evidences for its nuclear localization, we and others recently demonstrated DNA binding activity of α-synuclein that modulates its conformation as well as aggregation properties. Furthermore, we also underscored the similarities among various amyloidogenic proteins involved in neurodegenerative diseases including amyloid beta peptides and tau. Our more recent studies show that α-synuclein is glycated and glycosylated both in vitro and in neurons, significantly affecting its folding, oligomeric, and DNA binding properties. Glycated α-synuclein causes increased genome damage both via its direct interaction with DNA and by increased generation of reactive oxygen species as glycation byproduct. In this review, we discuss the mechanisms of glycation and other posttranslational modifications of α-synuclein, including phosphorylation and nitration, and their role in neuronal death in Parkinson's disease.