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Monomeric alpha-synuclein (aSyn) is a well characterised protein that importantly binds to lipids. aSyn monomers assemble into amyloid fibrils which are localised to lipids and organelles in insoluble structures found in Parkinson's disease patient's brains. Previous work to address pathological aSyn-lipid interactions has focused on using synthetic lipid membranes, which lack the complexity of physiological lipid membranes. Here, we use physiological membranes in the form of synaptic vesicles (SV) isolated from rodent brain to demonstrate that lipid-associated aSyn fibrils are more easily taken up into iPSC-derived cortical i3Neurons. Lipid-associated aSyn fibril characterisation reveals that SV lipids are an integrated part of the fibrils and while their fibril morphology differs from aSyn fibrils alone, the core fibril structure remains the same, suggesting the lipids lead to the increase in fibril uptake. Furthermore, SV enhance the aggregation rate of aSyn, yet increasing the SV:aSyn ratio causes a reduction in aggregation propensity. We finally show that aSyn fibrils disintegrate SV, whereas aSyn monomers cause clustering of SV using small angle neutron scattering and high-resolution imaging. Disease burden on neurons may be impacted by an increased uptake of lipid-associated aSyn which could enhance stress and pathology, which in turn may have fatal consequences for neurons. Interaction of alpha-synuclein (aSyn) with physiological lipid membranes leads to the disintegration of membranes, incorporation of lipids by aSyn fibrils, increased aggregation rate of aSyn fibrils, and increased uptake of lipid-associated fibrils compared to aSyn only fibrils into neurons. [ABSTRACT FROM AUTHOR]

The solvation shell is essential for the folding and function of proteins, but how it contributes to protein misfolding and aggregation has still to be elucidated. We show that the mobility of solvation shell H2O molecules influences the aggregation rate of the amyloid protein α‐synuclein (αSyn), a protein associated with Parkinson's disease. When the mobility of H2O within the solvation shell is reduced by the presence of NaCl, αSyn aggregation rate increases. Conversely, in the presence CsI the mobility of the solvation shell is increased and αSyn aggregation is reduced. Changing the solvent from H2O to D2O leads to increased aggregation rates, indicating a solvent driven effect. We show the increased aggregation rate is not directly due to a change in the structural conformations of αSyn, it is also influenced by a reduction in both the H2O mobility and αSyn mobility. We propose that reduced mobility of αSyn contributes to increased aggregation by promoting intermolecular interactions. [ABSTRACT FROM AUTHOR]

As an intrinsically disordered protein, monomeric alpha-synuclein (aSyn) occupies a large conformational space. Certain conformations lead to aggregation prone and non-aggregation prone intermediates, but identifying these within the dynamic ensemble of monomeric conformations is difficult. Herein, we used the biologically relevant calcium ion to investigate the conformation of monomeric aSyn in relation to its aggregation propensity. We observe that the more exposed the N-terminus and the beginning of the NAC region of aSyn are, the more aggregation prone monomeric aSyn conformations become. Solvent exposure of the N-terminus of aSyn occurs upon release of C-terminus interactions when calcium binds, but the level of exposure and aSyn's aggregation propensity is sequence and post translational modification dependent. Identifying aggregation prone conformations of monomeric aSyn and the environmental conditions they form under will allow us to design new therapeutics targeted to the monomeric protein. In Parkinson's disease (PD) the monomeric protein alpha-synuclein (aSyn) misfolds and aggregates into insoluble fibrils. Here the authors use NMR measurements and hydrogen–deuterium exchange mass spectrometry and find that the more solvent exposed the N-terminus of aSyn is, the more aggregation prone its conformation becomes, and further show how PD mutations and post translational modifications influence the extent of the N-terminus solvent exposure. [ABSTRACT FROM AUTHOR]

• Water and protein mobility are inextricably linked and therefore water itself plays an essential role in protein function. • IDPs have a larger solvent accessible area compared to globular proteins, making them more sensitive to changes in the surrounding environment. • Retardation of water mobility and subsequent protein mobility may lead to an increased propensity of proteins to aggregate. • Environments vary inside different cells and compartments and can directly affect water mobility and therefore protein aggregation. • Water is the rate limiting step of the 'dock and lock' mechanism of fibril elongation. The role of water in protein function and aggregation is highly important and may hold some answers to understanding initiation of misfolding diseases such as Parkinson's, Alzheimer's and Huntington's where soluble intrinsically disordered proteins (IDPs) aggregate into fibrillar structures. IDPs are highly dynamic and have larger solvent exposed areas compared to globular proteins, meaning they make and break hydrogen bonds with the surrounding water more frequently. The mobility of water can be altered by presence of ions, sugars, osmolytes, proteins and membranes which differ in different cell types, cell compartments and also as cells age. A reduction in water mobility and thus protein mobility enhances the probability that IDPs can associate to form intermolecular bonds and propagate into aggregates. This poses an interesting question as to whether localised water mobility inside cells can influence the propensity of an IDP to aggregate and furthermore whether it can influence fibril polymorphism and disease outcome. [ABSTRACT FROM AUTHOR]

The presynaptic protein α-synuclein (aSyn) is an 'intrinsically disordered protein' that is highly dynamic in conformation. Transient intramolecular interactions between its charged N and C termini, and between its hydrophobic region and the C terminus, prevent self-association. These interactions inhibit the formation of insoluble inclusions, which are the pathological hallmark of Parkinson's disease and many other synucleinopathies. This review discusses how these intramolecular interactions are influenced by the specific environment aSyn is in. We discuss how charge, pH, calcium, and salt affect the physiological structure of monomeric aSyn, and how they may favour the formation of toxic structures. The more we understand the dynamic conformations of aSyn, the better we can design desperately needed therapeutics to prevent disease progression. Highlights aSyn is a highly dynamic, intrinsically disordered protein that populates an ensemble of different conformations in its functional, monomeric form. Functional, monomeric aSyn structure is stabilised by transient electrostatic and hydrophobic tertiary long-range interactions. Post-translational modifications (PTMs), truncation, and the local cellular environment, such as pH and ion content, can influence monomeric aSyn structure. A disruption of monomeric aSyn structure can bias the protein population towards aggregation-prone conformations, leading to the formation of amyloid fibrils. The structure of monomeric aSyn can imprint into fibril morphology and lead to the formation of different aSyn strains. Different aSyn fibril strains have been shown to lead to different levels of toxicity and may influence pathophysiology. [ABSTRACT FROM AUTHOR]

Mitochondrial dysfunction has long been implicated in the neurodegenerative disorder Parkinson's disease (PD); however, it is unclear how mitochondrial impairment and a-synuclein pathology are coupled. Using specific mitochondrial inhibitors, EM analysis, and biochemical assays, we report here that intramitochondrial protein homeostasis plays a major role in a-synuclein aggregation. We found that interference with intramitochondrial proteases, such as HtrA2 and Lon protease, and mitochondrial protein import significantly aggravates a-synuclein seeding. In contrast, direct inhibition of mitochondrial complex I, an increase in intracellular calcium concentration, or formation of reactive oxygen species, all of which have been associated with mitochondrial stress, did not affect a-synuclein pathology. We further demonstrate that similar mechanisms are involved in amyloid-b 1-42 (Ab42) aggregation. Our results suggest that, in addition to other protein quality control pathways, such as the ubiq proteasome system, mitochondria per se can influence protein homeostasis of cytosolic aggregation-prone proteins. We propose that approaches that seek to maintain mitochondrial fitness, rather than target downstream mitochondrial dysfunction, may aid in the search for therapeutic strategies to manage PD and related neuropathologies. [ABSTRACT FROM AUTHOR]