On the effect of methionine oxidation on the interplay between α-synuclein and synaptic-like vesicles

Experimental Evidence for Phosphorylation-Driven Allosteric Regulation of Alpha Synuclein Function

Phosphorylation of serine 129 (pS129) in the intrinsically disordered protein alpha synuclein has long been associated with neurodegenerative disease. In the past several years, the functional relevance of pS219 has been uncovered by electrophysiology, immunoprecipitation, and proteomics as intricately connected with neurotransmitter release and synaptic vesicle (SV) cycling. Unexpectedly, binding to SNARE complex proteins VAMP-2 and synapsin only occurs with phosphorylation-competent alpha synuclein. The VAMP-2 binding domain has been shown to be residues 96-110, which does not include the phosphorylated residue, hinting at allosteric regulation of alpha synuclein protein-protein interactions by pS129. Within this study, cross-linking, covalent labeling, and collision induced unfolding of alpha synuclein and pS129 - as well as an additional encountered form in the brain, oxidized-M1, M5, M116, M127 alpha synuclein - are studied utilizing tandem mass spectrometry. Collision induced unfolding of proteins gives a fingerprint of the structures' relative compactness and stabilities of various conformations. Covalent labeling of proteins identifies solvent accessible residues and reveals the hydrophobicity (or hydrophilicity) of their microenvironment, while cross-linking of proteins maps the proximity of residue pairs. The combination of collision induced unfolding, covalent labeling, and cross-linking show unequivocally that phosphorylated-S129 alpha synuclein results in a more stable, more compact form. Our results provide evidence of an extensively folded amphipathic region that interacts strongly with the VAMP-2 binding domain. The phosphorylation-induced folding of the amphipathic region likely tunes other protein-protein interactions and interactions with SVs and membranes.

A study of alpha-synuclein and poly(N-isopropylacrylamide) complex formation through detailed atomistic simulations

This work presents an investigation of the influence of poly(N-isopropylacrylamide) (PNIPAM) polymer on the structural dynamics of intrinsically disordered alpha-synuclein (α-syn) protein, exploring the formation and intricate features of the resulting α-syn/PNIPAM complexes. Using atomistic molecular dynamics (MD) simulations, our study analyzes the impact of initial configuration, polymer molecular weight, and protein mutations on the α-syn and the α-syn/PNIPAM complex. Atomistic simulations, of a few μs, of the protein/polymer complex reveal crucial insights into molecular interactions within the complex, emphasizing a delicate balance of forces governing its stability and structural evolution. Our findings indicate that PNIPAM polymer engages in significant non-polar interactions with the non-amyloid component (NAC) region of α-syn, which plays a crucial role in fibril formation, under various conditions such as the mutations in the protein structure and polymer chain length. Especially the PNIPAM polymer with a 40mer monomer exhibits a stabilizing effect on the structural properties of the protein, reducing intramolecular interactions that contribute to misfolding. These findings, which delve into protein/polymer interactions, hold promise as potential guidance for therapeutic strategies in various neurodegenerative disorders.

Non-enzymatic posttranslational protein modifications in protein aggregation and neurodegenerative diseases

Highly reactive metabolic intermediates and other small molecules frequently react with amino acid side chains, leading to non-enzymatic posttranslational modifications (nPTMs) of proteins. The abundance of these modifications increases under high metabolic activity or stress conditions and can dramatically impact protein structure and function. Although protein quality control mechanisms typically mitigate the effects of these impaired proteins, in long-lived and degradation-resistant proteins, nPTMs accumulate. In some cases, such as cataract development and diabetes, clear links between nPTMs, aging, and disease progression have been established. In neurodegenerative diseases such as Alzheimer's and Parkinson's disease, a key question is whether accumulation of nPTMs is a cause or consequence of protein aggregation. This review focuses on major nPTMs found on proteins with central roles in neurodegenerative diseases such as α-synuclein, β-amyloid, and tau. We summarize current knowledge on the formation of these modifications and discuss their potential impact on disease onset and progression. Additionally, we examine what is known to date about how nPTMs impair cellular detoxification, repair, and degradation systems. Finally, we critically discuss the available methodologies to systematically investigate nPTMs at the molecular level and outline suitable approaches to study their effects on protein aggregation. We aim to foster more research into the role of nPTMs in neurodegeneration by adapting methodologies that have proven successful in studying enzymatic posttranslational modifications. Specifically, we advocate for site-specific incorporation of these modifications into target proteins using advanced chemical and molecular biology techniques.

Insight into the Effect of Methylglyoxal on the Conformation, Function, and Aggregation Propensity of α-Synuclein

It is well-known that people suffering from hyperglycemia have a higher propensity to develop Parkinson's disease (PD). One of the most plausible mechanisms linking these two pathologies is the glycation of neuronal proteins and the pathological consequences of it. α-Synuclein, a key component in PD, can be glycated at its fifteen lysine. In fact, the end products of this process have been detected on aggregated α-synuclein isolated from in vivo. However, the consequences of glycation are not entirely clear, which are of crucial importance to understand the mechanism underlying the connection between diabetes and PD. To better clarify this, we have here examined how methylglyoxal (the most important carbonyl compound found in the cytoplasm) affects the conformation and aggregation propensity of α-synuclein, as well as its ability to cluster and fuse synaptic-like vesicles. The obtained data prove that methylglyoxal induces the Lys-Lys crosslinking through the formation of MOLD. However, this does not have a remarkable effect on the averaged conformational ensemble of α-synuclein, although it completely depletes its native propensity to form soluble oligomers and insoluble amyloid fibrils. Moreover, methylglyoxal has a disrupting effect on the ability of α-synuclein to bind, cluster and fusion synaptic-like vesicles.

Interaction between α-Synuclein and Bioactive Lipids: Neurodegeneration, Disease Biomarkers and Emerging Therapies

The present review provides a comprehensive examination of the intricate dynamics between α-synuclein, a protein crucially involved in the pathogenesis of several neurodegenerative diseases, including Parkinson's disease and multiple system atrophy, and endogenously-produced bioactive lipids, which play a pivotal role in neuroinflammation and neurodegeneration. The interaction of α-synuclein with bioactive lipids is emerging as a critical factor in the development and progression of neurodegenerative and neuroinflammatory diseases, offering new insights into disease mechanisms and novel perspectives in the identification of potential biomarkers and therapeutic targets. We delve into the molecular pathways through which α-synuclein interacts with biological membranes and bioactive lipids, influencing the aggregation of α-synuclein and triggering neuroinflammatory responses, highlighting the potential of bioactive lipids as biomarkers for early disease detection and progression monitoring. Moreover, we explore innovative therapeutic strategies aimed at modulating the interaction between α-synuclein and bioactive lipids, including the development of small molecules and nutritional interventions. Finally, the review addresses the significance of the gut-to-brain axis in mediating the effects of bioactive lipids on α-synuclein pathology and discusses the role of altered gut lipid metabolism and microbiota composition in neuroinflammation and neurodegeneration. The present review aims to underscore the potential of targeting α-synuclein-lipid interactions as a multifaceted approach for the detection and treatment of neurodegenerative and neuroinflammatory diseases.

Oxidative stress induced conformational changes of human serum albumin

Oxidative stress, generated by reactive oxygen species (ROS), is responsible for the loss of structure and functionality of proteins and is associated with several aging-related diseases. Here, we report an in vitro study to gauge the effect of ROS on the structural rearrangement of human serum albumin (HSA), a plasma protein, through metal-catalyzed oxidation (MCO) at physiological temperature through various biophysical techniques like UV-vis absorption, circular dichroism (CD), differential scanning calorimetry (DSC), MALDI-TOF, FTIR, and Raman spectroscopy. The UV-vis spectra of oxidized HSA show an early blueshift, signifying the unfolding of the protein because of ROS followed by the broadening of the absorption peak at a longer time. The DSC data corroborate the observation, revealing an exothermic transition for the oxidized sample at a longer time, suggesting in situ aggregation. The CD and FTIR spectra indicate the associated secondary structural changes occurring with time, depicting the variation of the helical content of HSA. The amide-III analysis of Raman data also complements the structural changes, and MALDI-TOF data show the mass distribution with time. Overall, this work might help determine the effect of oxidation on the biological activity of serum albumin as it can impact the physiological properties of HSA.

Tyrosine Nitroxidation Does Not Affect the Ability of α-Synuclein to Bind Anionic Micelles, but It Diminishes Its Ability to Bind and Assemble Synaptic-like Vesicles

Parkinson's disease (PD) is characterized by dopaminergic neuron degeneration and the accumulation of neuronal inclusions known as Lewy bodies, which are formed by aggregated and post-translationally modified α-synuclein (αS). Oxidative modifications such as the formation of 3-nitrotyrosine (3-NT) or di-tyrosine are found in αS deposits, and they could be promoted by the oxidative stress typical of PD brains. Many studies have tried to elucidate the molecular mechanism correlating nitroxidation, αS aggregation, and PD. However, it is unclear how nitroxidation affects the physiological function of αS. To clarify this matter, we synthetized an αS with its Tyr residues replaced by 3-NT. Its study revealed that Tyr nitroxidation had no effect on either the affinity of αS towards anionic micelles nor the overall structure of the micelle-bound αS, which retained its α-helical folding. Nevertheless, we observed that nitroxidation of Y39 lengthened the disordered stretch bridging the two consecutive α-helices. Conversely, the affinity of αS towards synaptic-like vesicles diminished as a result of Tyr nitroxidation. Additionally, we also proved that nitroxidation precluded αS from performing its physiological function as a catalyst of the clustering and the fusion of synaptic vesicles. Our findings represent a step forward towards the completion of the puzzle that must explain the molecular mechanism behind the link between αS-nitroxidation and PD.